< draft-arkko-pppext-eap-aka-15.txt		draft-arkko-pppext-eap-aka-16.txt >
	Network Working Group J. Arkko		This Internet-Draft, draft-arkko-pppext-eap-aka-15.txt, was published as an Informational RFC, RFC 4187
	Internet-Draft Ericsson		(http://www.ietf.org/rfc/rfc4187.txt), on 2006-1-16.
	Expires: June 21, 2005 H. Haverinen
	Nokia
	December 21, 2004
	Extensible Authentication Protocol Method for 3rd Generation
	Authentication and Key Agreement (EAP-AKA)
	draft-arkko-pppext-eap-aka-15.txt
	Status of this Memo
	This document is an Internet-Draft and is subject to all provisions
	of section 3 of RFC 3667. By submitting this Internet-Draft, each
	author represents that any applicable patent or other IPR claims of
	which he or she is aware have been or will be disclosed, and any of
	which he or she become aware will be disclosed, in accordance with
	RFC 3668.
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	Copyright Notice
	Copyright (C) The Internet Society (2004).
	IESG Note
	The EAP-AKA protocol was developed by 3GPP. The documentation of
	EAP-AKA is provided as information to the Internet community. While
	the EAP WG has verified that EAP-AKA is compatible with EAP as
	defined in RFC 3748, no other review has been done, including
	validation of the security claims.
	Abstract
	This document specifies an Extensible Authentication Protocol (EAP)
	mechanism for authentication and session key distribution using the
	Authentication and Key Agreement (AKA) mechanism used in the 3rd
	generation mobile networks Universal Mobile Telecommunications System
	(UMTS) and cdma2000. AKA is based on symmetric keys, and runs
	typically in a Subscriber Identity Module (UMTS Subscriber Identity
	Module USIM, or (Removable) User Identity Module (R)UIM), a smart
	card like device.
	EAP-AKA includes optional identity privacy support, optional result
	indications, and an optional fast re-authentication procedure.
	Table of Contents
	1. Introduction and Motivation . . . . . . . . . . . . . . . . . 5
	2. Terms and Conventions Used in This Document . . . . . . . . . 6
	3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10
	4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 15
	4.1 Identity Management . . . . . . . . . . . . . . . . . . . 15
	4.1.1 Format, Generation and Usage of Peer Identities . . . 16
	4.1.2 Communicating the Peer Identity to the Server . . . . 22
	4.1.3 Choice of Identity for the EAP-Response/Identity . . . 23
	4.1.4 Server Operation in the Beginning of EAP-AKA
	Exchange . . . . . . . . . . . . . . . . . . . . . . . 24
	4.1.5 Processing of EAP-Request/AKA-Identity by the Peer . . 24
	4.1.6 Attacks against Identity Privacy . . . . . . . . . . . 26
	4.1.7 Processing of AT_IDENTITY by the Server . . . . . . . 26
	4.2 Message Sequence Examples (Informative) . . . . . . . . . 27
	4.2.1 Usage of AT_ANY_ID_REQ . . . . . . . . . . . . . . . . 27
	4.2.2 Fall Back on Full Authentication . . . . . . . . . . . 28
	4.2.3 Requesting the Permanent Identity 1 . . . . . . . . . 29
	4.2.4 Requesting the Permanent Identity 2 . . . . . . . . . 30
	4.2.5 Three EAP/AKA-Identity Round Trips . . . . . . . . . . 31
	5. Fast Re-authentication . . . . . . . . . . . . . . . . . . . . 33
	5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . 33
	5.2 Comparison to AKA . . . . . . . . . . . . . . . . . . . . 34
	5.3 Fast Re-authentication Identity . . . . . . . . . . . . . 35
	5.4 Fast Re-authentication Procedure . . . . . . . . . . . . . 36
	5.5 Fast Re-authentication Procedure when Counter is Too
	Small . . . . . . . . . . . . . . . . . . . . . . . . . . 38
	6. EAP-AKA Notifications . . . . . . . . . . . . . . . . . . . . 40
	6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . 40
	6.2 Result Indications . . . . . . . . . . . . . . . . . . . . 41
	6.3 Error Cases . . . . . . . . . . . . . . . . . . . . . . . 42
	6.3.1 Peer Operation . . . . . . . . . . . . . . . . . . . . 42
	6.3.2 Server Operation . . . . . . . . . . . . . . . . . . . 43
	6.3.3 EAP-Failure . . . . . . . . . . . . . . . . . . . . . 44
	6.3.4 EAP-Success . . . . . . . . . . . . . . . . . . . . . 44
	6.4 Key Generation . . . . . . . . . . . . . . . . . . . . . . 45
	7. Message Format and Protocol Extensibility . . . . . . . . . . 47
	7.1 Message Format . . . . . . . . . . . . . . . . . . . . . . 47
	7.2 Protocol Extensibility . . . . . . . . . . . . . . . . . . 49
	8. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
	8.1 EAP-Request/AKA-Identity . . . . . . . . . . . . . . . . . 49
	8.2 EAP-Response/AKA-Identity . . . . . . . . . . . . . . . . 50
	8.3 EAP-Request/AKA-Challenge . . . . . . . . . . . . . . . . 50
	8.4 EAP-Response/AKA-Challenge . . . . . . . . . . . . . . . . 51
	8.5 EAP-Response/AKA-Authentication-Reject . . . . . . . . . . 52
	8.6 EAP-Response/AKA-Synchronization-Failure . . . . . . . . . 52
	8.7 EAP-Request/AKA-Reauthentication . . . . . . . . . . . . . 52
	8.8 EAP-Response/AKA-Reauthentication . . . . . . . . . . . . 52
	8.9 EAP-Response/AKA-Client-Error . . . . . . . . . . . . . . 53
	8.10 EAP-Request/AKA-Notification . . . . . . . . . . . . . . . 53
	8.11 EAP-Response/AKA-Notification . . . . . . . . . . . . . . 54
	9. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . 54
	9.1 Table of Attributes . . . . . . . . . . . . . . . . . . . 54
	9.2 AT_PERMANENT_ID_REQ . . . . . . . . . . . . . . . . . . . 55
	9.3 AT_ANY_ID_REQ . . . . . . . . . . . . . . . . . . . . . . 56
	9.4 AT_FULLAUTH_ID_REQ . . . . . . . . . . . . . . . . . . . . 56
	9.5 AT_IDENTITY . . . . . . . . . . . . . . . . . . . . . . . 56
	9.6 AT_RAND . . . . . . . . . . . . . . . . . . . . . . . . . 57
	9.7 AT_AUTN . . . . . . . . . . . . . . . . . . . . . . . . . 57
	9.8 AT_RES . . . . . . . . . . . . . . . . . . . . . . . . . . 58
	9.9 AT_AUTS . . . . . . . . . . . . . . . . . . . . . . . . . 58
	9.10 AT_NEXT_PSEUDONYM . . . . . . . . . . . . . . . . . . . . 58
	9.11 AT_NEXT_REAUTH_ID . . . . . . . . . . . . . . . . . . . . 59
	9.12 AT_IV, AT_ENCR_DATA and AT_PADDING . . . . . . . . . . . . 60
	9.13 AT_CHECKCODE . . . . . . . . . . . . . . . . . . . . . . . 62
	9.14 AT_RESULT_IND . . . . . . . . . . . . . . . . . . . . . . 64
	9.15 AT_MAC . . . . . . . . . . . . . . . . . . . . . . . . . . 64
	9.16 AT_COUNTER . . . . . . . . . . . . . . . . . . . . . . . . 65
	9.17 AT_COUNTER_TOO_SMALL . . . . . . . . . . . . . . . . . . . 65
	9.18 AT_NONCE_S . . . . . . . . . . . . . . . . . . . . . . . . 66
	9.19 AT_NOTIFICATION . . . . . . . . . . . . . . . . . . . . . 66
	9.20 AT_CLIENT_ERROR_CODE . . . . . . . . . . . . . . . . . . . 67
	10. IANA and Protocol Numbering Considerations . . . . . . . . . 68
	11. Security Considerations . . . . . . . . . . . . . . . . . . 70
	11.1 Identity Protection . . . . . . . . . . . . . . . . . . . 70
	11.2 Mutual Authentication . . . . . . . . . . . . . . . . . . 71
	11.3 Flooding the Authentication Centre . . . . . . . . . . . . 71
	11.4 Key Derivation . . . . . . . . . . . . . . . . . . . . . . 71
	11.5 Brute-Force and Dictionary Attacks . . . . . . . . . . . . 71
	11.6 Protection, Replay Protection and Confidentiality . . . . 72
	11.7 Negotiation Attacks . . . . . . . . . . . . . . . . . . . 73
	11.8 Protected Result Indications . . . . . . . . . . . . . . . 73
	11.9 Man-in-the-middle Attacks . . . . . . . . . . . . . . . . 74
	11.10 Generating Random Numbers . . . . . . . . . . . . . . . 74
	12. Security Claims . . . . . . . . . . . . . . . . . . . . . . 74
	13. Acknowledgements and Contributions . . . . . . . . . . . . . 75
	14. References . . . . . . . . . . . . . . . . . . . . . . . . . 75
	14.1 Normative References . . . . . . . . . . . . . . . . . . . . 75
	14.2 Informative References . . . . . . . . . . . . . . . . . . . 77
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 78
	A. Pseudo-Random Number Generator . . . . . . . . . . . . . . . . 78
	Intellectual Property and Copyright Statements . . . . . . . . 79
	1. Introduction and Motivation
	This document specifies an Extensible Authentication Protocol (EAP)
	mechanism for authentication and session key distribution using the
	3rd generation Authentication and Key Agreement mechanism, specified
	for Universal Mobile Telecommunications System (UMTS) in [TS 33.102]
	and for cdma2000 in [S.S0055-A]. UMTS and cdma2000 are global third
	generation mobile network standards that use the same AKA mechanism.
	Second generation mobile networks and third generation mobile
	networks use different authentication and key agreement mechanisms.
	The Global System for Mobile communications (GSM) is a 2nd generation
	mobile network standard, and EAP-SIM [EAP-SIM] specifies an EAP
	mechanism that is based on the GSM authentication and key agreement
	primitives.
	AKA is based on challenge-response mechanisms and symmetric
	cryptography. AKA typically runs in a UMTS Subscriber Identity
	Module (USIM) or a cdma2000 (Removable) User Identity Module
	((R)UIM). In this document, both modules are referred to as identity
	modules. Compared to the 2nd generation mechanisms such as GSM AKA,
	the 3rd generation AKA provides substantially longer key lengths and
	mutual authentication.
	The introduction of AKA inside EAP allows several new applications.
	These include the following:
	o The use of the AKA also as a secure PPP authentication method in
	devices that already contain an identity module.
	o The use of the third generation mobile network authentication
	infrastructure in the context of wireless LANs
	o Relying on AKA and the existing infrastructure in a seamless way
	with any other technology that can use EAP.
	AKA works in the following manner:
	o The identity module and the home environment have agreed on a
	secret key beforehand. (The "home environment" refers to the home
	operator's authentication network infrastructure.)
	o The actual authentication process starts by having the home
	environment produce an authentication vector, based on the secret
	key and a sequence number. The authentication vector contains a
	random part RAND, an authenticator part AUTN used for
	authenticating the network to the identity module, an expected
	result part XRES, a 128-bit session key for integrity check IK,
	and a 128-bit session key for encryption CK.
	o The RAND and the AUTN are delivered to the identity module.
	o The identity module verifies the AUTN, again based on the secret
	key and the sequence number. If this process is successful (the
	AUTN is valid and the sequence number used to generate AUTN is
	within the correct range), the identity moduleproduces an
	authentication result, RES and sends this to the home environment.
	o The home environment verifies the correct result from the identity
	module. If the result is correct, IK and CK can be used to
	protect further communications between the identity module and the
	home environment.
	When verifying AUTN, the identity module may detect that the sequence
	number the network uses is not within the correct range. In this
	case, the identity module calculates a sequence number
	synchronization parameter AUTS and sends it to the network. AKA
	authentication may then be retried with a new authentication vector
	generated using the synchronized sequence number.
	For a specification of the AKA mechanisms and how the cryptographic
	values AUTN, RES, IK, CK and AUTS are calculated, see [TS 33.102] for
	UMTS and [S.S0055-A] for cdma2000.
	In EAP-AKA, the EAP server node obtains the authentication vectors,
	compares RES and XRES, and uses CK and IK in key derivation.
	In the third generation mobile networks, AKA is used both for radio
	network authentication and IP multimedia service authentication
	purposes. Different user identities and formats are used for these;
	the radio network uses the International Mobile Subscriber Identifier
	(IMSI), whereas the IP multimedia service uses the Network Access
	Identifier (NAI) [RFC2486].
	2. Terms and Conventions Used in This Document
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].
	The terms and abbreviations "authenticator", "backend authentication
	server", "EAP server", "peer", "Silently Discard", "Master Session
	Key (MSK)", and "Extended Master Session Key (EMSK)" in this document
	are to be interpreted as described in [RFC3748].
	This document frequently uses the following terms and abbreviations.
	The AKA parameters are specified in detail in [TS 33.102] for UMTS
	and [S.S0055-A] for cdma2000.
	AAA protocol
	Authentication, Authorization and Accounting protocol
	AKA
	Authentication and Key Agreement
	AuC
	Authentication Centre. The mobile network element that can
	authenticate subscribers in the mobile networks.
	AUTN
	AKA parameter. AUTN is an authentication value generated by
	the AuC which together with the RAND authenticates the server
	to the peer, 128 bits
	AUTS
	AKA parameter. A value generated by the peer upon
	experiencing a synchronization failure, 112 bits.
	EAP
	Extensible Authentication Protocol
	[RFC3748]
	Fast re-authentication
	An EAP-AKA authentication exchange that is based on keys
	derived upon a preceding full authentication exchange. The
	3rd Generation AKA is not used in the fast re-authentication
	procedure.
	Fast Re-authentication Identity
	A fast re-authentication identity of the peer, including an
	NAI realm portion in environments where a realm is used.
	Used on re-authentication only.
	Fast Re-authentication Username
	The username portion of fast re-authentication identity,
	ie. not including any realm portions.
	Full authentication
	An EAP-AKA authentication exchange that is based on the
	3rd Generation AKA procedure.
	GSM
	Global System for Mobile communications.
	NAI
	Network Access Identifier
	[RFC2486]
	Identity module
	Identity module is used in this document to refer to the
	part of the mobile device that contains authentication and
	key agreement primitives. The identity module may be an
	integral part of the mobile device or it can be an application
	on a smart card distributed by a mobile operator. USIM and
	(R)UIM are identity modules.
	Nonce
	A value that is used at most once or that is never repeated
	within the same cryptographic context. In general, a nonce can
	be predictable (e.g. a counter) or unpredictable (e.g. a random
	value). Since some cryptographic properties may depend on the
	randomness of the nonce, attention should be paid to whether a
	nonce is required to be random or not. In this document, the
	term nonce is only used to denote random nonces, and it is not
	used to denote counters.
	Permanent Identity
	The permanent identity of the peer, including an NAI realm
	portion in environments where a realm is used. The permanent
	identity is usually based on the IMSI. Used on full
	authentication only.
	Permanent Username
	The username portion of permanent identity, ie. not including
	any realm portions.
	Pseudonym Identity
	A pseudonym identity of the peer, including an NAI realm
	portion in environments where a realm is used. Used on full
	authentication only.
	Pseudonym Username
	The username portion of pseudonym identity, ie. not including
	any realm portions.
	RAND
	An AKA parameter. Random number generated by the AuC, 128 bits
	RES
	Authentication result from the peer, which together with
	the RAND authenticates the peer to the server,
	128 bits
	(R)UIM
	cdma2000 (Removable) User Identity Module. (R)UIM is an
	application that is resident e.g. on smart cards which may
	be fixed in the terminal or distributed by cdma2000
	operators (when removable)
	SQN
	An AKA parameter. Sequence number used in the authentication
	process, 48 bits
	SIM
	Subscriber Identity Module. The SIM is traditionally a smart
	card distributed by a GSM operator.
	SRES
	The authentication result parameter in GSM, corresponds to
	the RES parameter in 3G AKA, 32 bits.
	UAK
	UIM Authentication Key, used in cdma2000 AKA. Both the identity
	module and the network can optionally generate the UAK during
	the AKA computation in cdma2000. UAK is not used in this
	version of EAP-AKA.
	UIM
	Please see (R)UIM
	USIM
	UMTS Subscriber Identity Module. USIM is an application that
	is resident e.g. on smart cards distributed by UMTS operators.
	3. Protocol Overview
	Figure 1 shows the basic successful full authentication exchange in
	EAP-AKA, when optional result indications are not used. The
	authenticator typically communicates with an EAP server that is
	located on a backend authentication server using an AAA protocol.
	The authenticator shown in the figure is often simply relaying EAP
	messages to and from the EAP server, but these back end AAA
	communications are not shown. At the minimum, EAP-AKA uses two
	roundtrips to authenticate and authorize the peer and generate
	session keys. As in other EAP schemes, an identity request/response
	message pair is usually exchanged first. On full authentication, the
	peer's identity response includes either the user's International
	Mobile Subscriber Identity (IMSI), or a temporary identity
	(pseudonym) if identity privacy is in effect, as specified in Section
	4.1. (As specified in [RFC3748], the initial identity request is not
	required, and MAY be bypassed in cases where the network can presume
	the identity, such as when using leased lines, dedicated dial-ups,
	etc. Please see also Section 4.1.2 for specification how to obtain
	the identity via EAP AKA messages.)
	After obtaining the subscriber identity, the EAP server obtains an
	authentication vector (RAND, AUTN, RES, CK, IK) for use in
	authenticating the subscriber. From the vector, the EAP server
	derives the keying material, as specified in Section 6.4. The vector
	may be obtained by contacting an Authentication Centre (AuC) on the
	mobile network; for example per UMTS specifications, several vectors
	may be obtained at a time. Vectors may be stored in the EAP server
	for use at a later time, but they may not be reused.
	In cdma2000, the vector may include a sixth value called the User
	Identity Module Authentication Key (UAK). This key is not used in
	EAP-AKA.
	Next, the EAP server starts the actual AKA protocol by sending an
	EAP-Request/AKA-Challenge message. EAP-AKA packets encapsulate
	parameters in attributes, encoded in a Type, Length, Value format.
	The packet format and the use of attributes are specified in Section
	7. The EAP-Request/AKA-Challenge message contains a RAND random
	number (AT_RAND) and a network authentication token (AT_AUTN), and a
	message authentication code AT_MAC. The EAP-Request/AKA-Challenge
	message MAY optionally contain encrypted data, which is used for
	identity privacy and fast re-authentication support, as described in
	Section 4.1. The AT_MAC attribute contains a message authentication
	code covering the EAP packet. The encrypted data is not shown in the
	figures of this section.
	The peer runs the AKA algorithm (typically using an identity module)
	and verifies the AUTN. If this is successful, the peer is talking to
	a legitimate EAP server and proceeds to send the
	EAP-Response/AKA-Challenge. This message contains a result parameter
	that allows the EAP server in turn to authenticate the peer, and the
	AT_MAC attribute to integrity protect the EAP message.
	The EAP server verifies that the RES and the MAC in the
	EAP-Response/AKA-Challenge packet are correct. Because protected
	success indications are not used in this example, the EAP server
	sends the EAP-Success packet, indicating that the authentication was
	successful. (Protected success indications are discussed in Section
	6.2.) The EAP server may also include derived keying material in the
	message it sends to the authenticator. The peer has derived the same
	keying material, so the authenticator does not forward the keying
	material to the peer along with EAP-Success.
	Peer Authenticator
	| EAP-Request/Identity |
	|<------------------------------------------------------|
	| |
	| EAP-Response/Identity |
	| (Includes user's NAI) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server runs AKA algorithms, |
	| | generates RAND and AUTN. |
	| +------------------------------+
	| EAP-Request/AKA-Challenge |
	| (AT_RAND, AT_AUTN, AT_MAC) |
	|<------------------------------------------------------|
	+-------------------------------------+ |
	| Peer runs AKA algorithms, | |
	| verifies AUTN and MAC, derives RES | |
	| and session key | |
	+-------------------------------------+ |
	| EAP-Response/AKA-Challenge |
	| (AT_RES, AT_MAC) |
	|------------------------------------------------------>|
	| +--------------------------------+
	| | Server checks the given RES, |
	| | and MAC and finds them correct.|
	| +--------------------------------+
	| EAP-Success |
	|<------------------------------------------------------|
	Figure 1: EAP-AKA full authentication procedure
	Figure 2 shows how the EAP server rejects the Peer due to a failed
	authentication.
	Peer Authenticator
	| EAP-Request/Identity |
	|<------------------------------------------------------|
	| |
	| EAP-Response/Identity |
	| (Includes user's NAI) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server runs AKA algorithms, |
	| | generates RAND and AUTN. |
	| +------------------------------+
	| EAP-Request/AKA-Challenge |
	| (AT_RAND, AT_AUTN, AT_MAC) |
	|<------------------------------------------------------|
	+-------------------------------------+ |
	| Peer runs AKA algorithms, | |
	| possibly verifies AUTN, and sends an| |
	| invalid response | |
	+-------------------------------------+ |
	| EAP-Response/AKA-Challenge |
	| (AT_RES, AT_MAC) |
	|------------------------------------------------------>|
	| +------------------------------------------+
	| | Server checks the given RES and the MAC, |
	| | and finds one of them incorrct. |
	| +------------------------------------------+
	| EAP-Request/AKA-Notification |
	|<------------------------------------------------------|
	| EAP-Response/AKA-Notification |
	|------------------------------------------------------>|
	| EAP-Failure |
	|<------------------------------------------------------|
	Figure 2: Peer authentication fails
	Figure 3 shows the peer rejecting the AUTN of the EAP server.
	The peer sends an explicit error message
	(EAP-Response/AKA-Authentication-Reject) to the EAP server, as usual
	in AKA when AUTN is incorrect. This allows the EAP server to produce
	the same error statistics as AKA in general produces in UMTS or
	cdma2000.
	Peer Authenticator
	| EAP-Request/Identity |
	|<------------------------------------------------------|
	| EAP-Response/Identity |
	| (Includes user's NAI) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server runs AKA algorithms, |
	| | generates RAND and a bad AUTN|
	| +------------------------------+
	| EAP-Request/AKA-Challenge |
	| (AT_RAND, AT_AUTN, AT_MAC) |
	|<------------------------------------------------------|
	+-------------------------------------+ |
	| Peer runs AKA algorithms | |
	| and discovers AUTN that can not be | |
	| verified | |
	+-------------------------------------+ |
	| EAP-Response/AKA-Authentication-Reject |
	|------------------------------------------------------>|
	| EAP-Failure |
	|<------------------------------------------------------|
	Figure 3: Network authentication fails
	The AKA uses shared secrets between the Peer and the Peer's home
	operator together with a sequence number to actually perform an
	authentication. In certain circumstances it is possible for the
	sequence numbers to get out of sequence. Figure 4 shows what happens
	then.
	Peer Authenticator
	| EAP-Request/Identity |
	|<------------------------------------------------------|
	| EAP-Response/Identity |
	| (Includes user's NAI) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server runs AKA algorithms, |
	| | generates RAND and AUTN. |
	| +------------------------------+
	| EAP-Request/AKA-Challenge |
	| (AT_RAND, AT_AUTN, AT_MAC) |
	|<------------------------------------------------------|
	+-------------------------------------+ |
	| Peer runs AKA algorithms | |
	| and discovers AUTN that contains an | |
	| inappropriate sequence number | |
	+-------------------------------------+ |
	| EAP-Response/AKA-Synchronization-Failure |
	| (AT_AUTS) |
	|------------------------------------------------------>|
	| +---------------------------+
	| | Perform resynchronization |
	| | Using AUTS and |
	| | the sent RAND |
	| +---------------------------+
	| |
	Figure 4: Sequence number synchronization
	After the resynchronization process has taken place in the server and
	AAA side, the process continues by the server side sending a new
	EAP-Request/AKA-Challenge message.
	In addition to the full authentication scenarios described above,
	EAP-AKA includes a fast re-authentication procedure, which is
	specified in Section 5. Fast re-authentication is based on keys
	derived on full authentication. If the peer has maintained state
	information for re-authentication and wants to use fast
	re-authentication, then the peer indicates this by using a specific
	fast re-authentication identity instead of the permanent identity or
	a pseudonym identity.
	4. Operation
	4.1 Identity Management
	4.1.1 Format, Generation and Usage of Peer Identities
	4.1.1.1 General
	In the beginning of EAP authentication, the Authenticator or the EAP
	server usually issues the EAP-Request/Identity packet to the peer.
	The peer responds with EAP-Response/Identity, which contains the
	user's identity. The formats of these packets are specified in
	[RFC3748].
	Subscribers of mobile networks are identified with the International
	Mobile Subscriber Identity (IMSI) [TS 23.003]. The IMSI is a string
	of not more than 15 digits. It is composed of a three digit Mobile
	Country Code (MCC), a two or three digit Mobile Network Code (MNC)
	and a not more than 10 digit Mobile Subscriber Identification Number
	(MSIN). MCC and MNC uniquely identify the GSM operator and help
	identify the AuC from which the authentication vectors need to be
	retrieved for this subscriber.
	Internet AAA protocols identify users with the Network Access
	Identifier (NAI) [RFC2486]. When used in a roaming environment, the
	NAI is composed of a username and a realm, separated with "@"
	(username@realm). The username portion identifies the subscriber
	within the realm.
	This section specifies the peer identity format used in EAP-AKA. In
	this document, the term identity or peer identity refers to the whole
	identity string that is used to identify the peer. The peer identity
	may include a realm portion. "Username" refers to the portion of the
	peer identity that identifies the user, i.e. the username does not
	include the realm portion.
	4.1.1.2 Identity Privacy Support
	EAP-AKA includes optional identity privacy (anonymity) support that
	can be used to hide the cleartext permanent identity and thereby to
	make the subscriber's EAP exchanges untraceable to eavesdroppers.
	Because the permanent identity never changes, revealing it would help
	observers to track the user. The permanent identity is usually based
	on the IMSI, which may further help the tracking, because the same
	identifier may be used in other contexts as well. Identity privacy
	is based on temporary identities, or pseudonyms, which are equivalent
	to but separate from the Temporary Mobile Subscriber Identities
	(TMSI) that are used on cellular networks. Please see Section 11.1
	for security considerations regarding identity privacy.
	4.1.1.3 Username Types in EAP-AKA Identities
	There are three types of usernames in EAP-AKA peer identities:
	(1) Permanent usernames. For example,
	0123456789098765@myoperator.com might be a valid permanent identity.
	In this example, 0123456789098765 is the permanent username.
	(2) Pseudonym usernames. For example, 2s7ah6n9q@myoperator.com might
	be a valid pseudonym identity. In this example, 2s7ah6n9q is the
	pseudonym username.
	(3) Fast re-authentication usernames. For example,
	43953754@myoperator.com might be a valid fast re-authentication
	identity. In this case, 43953754 is the fast re-authentication
	username. Unlike permanent usernames and pseudonym usernames, fast
	re-authentication usernames are one-time identifiers, which are not
	re-used across EAP exchanges.
	The first two types of identities are only used on full
	authentication and the last one only on fast re-authentication. When
	the optional identity privacy support is not used, the non-pseudonym
	permanent identity is used on full authentication. The fast
	re-authentication exchange is specified in Section 5.
	4.1.1.4 Username Decoration
	In some environments, the peer may need to decorate the identity by
	prepending or appending the username with a string, in order to
	indicate supplementary AAA routing information in addition to the NAI
	realm. (The usage of a NAI realm portion is not considered to be
	decoration.) Username decoration is out of the scope of this
	document. However, it should be noted that username decoration might
	prevent the server from recognizing a valid username. Hence,
	although the peer MAY use username decoration in the identities the
	peer includes in EAP-Response/Identity, and the EAP server MAY accept
	a decorated peer username in this message, the peer or the EAP server
	MUST NOT decorate any other peer identities that are used in various
	EAP-AKA attributes. Only the identity used in EAP-Response/Identity
	may be decorated.
	4.1.1.5 NAI Realm Portion
	The peer MAY include a realm portion in the peer identity, as per the
	NAI format. The use of a realm portion is not mandatory.
	If a realm is used, the realm MAY be chosen by the subscriber's home
	operator and it MAY a configurable parameter in the EAP-AKA peer
	implementation. In this case, the peer is typically configured with
	the NAI realm of the home operator. Operators MAY reserve a specific
	realm name for EAP-AKA users. This convention makes it easy to
	recognize that the NAI identifies an AKA subscriber. Such reserved
	NAI realm may be useful as a hint as to the first authentication
	method to use during method negotiation. When the peer is using a
	pseudonym username instead of the permanent username, the peer
	selects the realm name portion similarly as it select the realm
	portion when using the permanent username.
	If no configured realm name is available, the peer MAY derive the
	realm name from the MCC and MNC portions of the IMSI. A RECOMMENDED
	way to derive the realm from the IMSI using the realm 3gppnetwork.org
	will be specified in [Draft 3GPP TS 23.003].
	Some old implementations derive the realm name from the IMSI by
	concatenating "mnc", the MNC digits of IMSI, ".mcc", the MCC digits
	of IMSI and ".owlan.org". For example, if the IMSI is
	123456789098765, and the MNC is three digits long, then the derived
	realm name is "mnc456.mcc123.owlan.org". As there are no DNS servers
	running at owlan.org, these realm names can only be used with
	manually configured AAA routing. New implementations SHOULD use the
	mechanism specified in [Draft 3GPP TS 23.003] instead of owlan.org as
	soon as the 3GPP specification is finalized.
	The IMSI is a string of digits without any explicit structure, so the
	peer may not be able to determine the length of the MNC portion. If
	the peer is not able to determine whether the MNC is two or three
	digits long, the peer MAY use a 3-digit MNC. If the correct length
	of the MNC is two, then the MNC used in the realm name includes the
	first digit of MSIN. Hence, when configuring AAA networks for
	operators that have 2-digit MNC's, the network SHOULD also be
	prepared for realm names with incorrect 3-digit MNC's.
	4.1.1.6 Format of the Permanent Username
	The non-pseudonym permanent username SHOULD be derived from the IMSI.
	In this case, the permanent username MUST be of the format "0" |
	IMSI, where the character "|" denotes concatenation. In other words,
	the first character of the username is the digit zero (ASCII value 30
	hexadecimal), followed by the IMSI. The IMSI is an ASCII string that
	consists of not more than 15 decimal digits (ASCII values between 30
	and 39 hexadecimal), one character per IMSI digit, in the order as
	specified in [TS 23.003]. For example, a permanent username derived
	from the IMSI 295023820005424 would be encoded as the ASCII string
	"0295023820005424" (byte values in hexadecimal notation: 30 32 39 35
	30 32 33 38 32 30 30 30 35 34 32 34)
	The EAP server MAY use the leading "0" as a hint to try EAP-AKA as
	the first authentication method during method negotiation, rather
	than for example EAP-SIM. The EAP-AKA server MAY propose EAP-AKA
	even if the leading character was not "0".
	Alternatively, an implementation MAY choose a permanent username that
	is not based on the IMSI. In this case the selection of the
	username, its format, and its processing is out of the scope of this
	document. In this case, the peer implementation MUST NOT prepend any
	leading characters to the username.
	4.1.1.7 Generating Pseudonyms and Fast Re-authentication Identities by
	the Server
	Pseudonym usernames and fast re-authentication identities are
	generated by the EAP server. The EAP server produces pseudonym
	usernames and fast re-authentication identities in an
	implementation-dependent manner. Only the EAP server needs to be
	able to map the pseudonym username to the permanent identity, or to
	recognize a fast re-authentication identity.
	EAP-AKA includes no provisions to ensure that the same EAP server
	that generated a pseudonym username will be used on the
	authentication exchange when the pseudonym username is used. It is
	recommended that the EAP servers implement some centralized mechanism
	to allow all EAP servers of the home operator to map pseudonyms
	generated by other severs to the permanent identity. If no such
	mechanism is available, then the EAP server failing to understand a
	pseudonym issued by another server can request the peer to send the
	permanent identity.
	When issuing a fast re-authentication identity, the EAP server may
	include a realm name in the identity to make the fast
	re-authentication request be forwarded to the same EAP server.
	When generating fast re-authentication identities, the server SHOULD
	choose a fresh new fast re-authentication identity that is different
	from the previous ones used after the same full authentication
	exchange. A full authentication exchange and the associated fast
	re-authentication exchanges are referred to here as the same "full
	authentication context". The fast re-authentication identity SHOULD
	include a random component. The random component works as a full
	authentication context identifier. A context-specific fast
	re-authentication identity can help the server to detect whether its
	fast re-authentication state information matches the peer's fast
	re-authentication state information (in other words whether the state
	information is from the same full authentication exchange). The
	random component also makes the fast re-authentication identities
	unpredictable, so an attacker cannot initiate a fast
	re-authentication exchange to get the server's
	EAP-Request/AKA-Reauthentication packet.
	Transmitting pseudonyms and fast re-authentication identities from
	the server to the peer is discussed in Section 4.1.1.8. The
	pseudonym is transmitted as a username, without an NAI realm, and the
	fast re-authentication identity is transmitted as a complete NAI,
	including a realm portion if a realm is required. The realm is
	included in the fast re-authentication identity in order to allow the
	server to include a server-specific realm.
	Regardless of construction method, the pseudonym username MUST
	conform to the grammar specified for the username portion of an NAI.
	The fast re-authentication identity also MUST conform to the NAI
	grammar. The EAP servers that the subscribers of an operator can use
	MUST ensure that the pseudonym usernames and the username portions
	used in fast re-authentication identities they generate are unique.
	In any case, it is necessary that permanent usernames, pseudonym
	usernames and fast re-authentication usernames are separate and
	recognizable from each other. It is also desirable that EAP-SIM and
	EAP-AKA user names be recognizable from each other as an aid for the
	server to which method to offer.
	In general, it is the task of the EAP server and the policies of its
	administrator to ensure sufficient separation in the usernames.
	Pseudonym usernames and fast re-authentication usernames are both
	produced and used by the EAP server. The EAP server MUST compose
	pseudonym usernames and fast re-authentication usernames so that it
	can recognize if a NAI username is an EAP-AKA pseudonym username or
	an EAP-AKA fast re-authentication username. For instance, when the
	usernames have been derived from the IMSI, the server could use
	different leading characters in the pseudonym usernames and fast
	re-authentication usernames (e.g. the pseudonym could begin with a
	leading "2" character). When mapping a fast re-authentication
	identity to a permanent identity, the server SHOULD only examine the
	username portion of the fast re-authentication identity and ignore
	the realm portion of the identity.
	Because the peer may fail to save a pseudonym username sent to in an
	EAP-Request/AKA-Challenge, for example due to malfunction, the EAP
	server SHOULD maintain at least the most recently used pseudonym
	username in addition to the most recently issued pseudonym username.
	If the authentication exchange is not completed successfully, then
	the server SHOULD NOT overwrite the pseudonym username that was
	issued during the most recent successful authentication exchange.
	4.1.1.8 Transmitting Pseudonyms and Fast Re-authentication Identities
	to the Peer
	The server transmits pseudonym usernames and fast re-authentication
	identities to the peer in cipher, using the AT_ENCR_DATA attribute.
	The EAP-Request/AKA-Challenge message MAY include an encrypted
	pseudonym username and/or an encrypted fast re-authentication
	identity in the value field of the AT_ENCR_DATA attribute. Because
	identity privacy support and fast re-authentication are optional to
	implement, the peer MAY ignore the AT_ENCR_DATA attribute and always
	use the permanent identity. On fast re-authentication (discussed in
	Section 5), the server MAY include a new encrypted fast
	re-authentication identity in the EAP-Request/AKA-Reauthentication
	message.
	On receipt of the EAP-Request/AKA-Challenge, the peer MAY decrypt the
	encrypted data in AT_ENCR_DATA and if a pseudonym username is
	included, the peer may use the obtained pseudonym username on the
	next full authentication. If a fast re-authentication identity is
	included, then the peer MAY save it together with other fast
	re-authentication state information, as discussed in Section 5, for
	the next fast re-authentication.
	If the peer does not receive a new pseudonym username in the EAP-
	Request/AKA-Challenge message, the peer MAY use an old pseudonym
	username instead of the permanent username on next full
	authentication. The username portions of fast re-authentication
	identities are one-time usernames, which the peer MUST NOT re-use.
	When the peer uses a fast re-authentication identity in an EAP
	exchange, the peer MUST discard the fast re-authentication identity
	and not re-use it in another EAP authentication exchange, even if the
	authentication exchange was not completed.
	4.1.1.9 Usage of the Pseudonym by the Peer
	When the optional identity privacy support is used on full
	authentication, the peer MAY use a pseudonym username received as
	part of a previous full authentication sequence as the username
	portion of the NAI. The peer MUST NOT modify the pseudonym username
	received in AT_NEXT_PSEUDONYM. However, as discussed above, the peer
	MAY need to decorate the username in some environments by appending
	or prepending the username with a string that indicates supplementary
	AAA routing information.
	When using a pseudonym username in an environment where a realm
	portion is used, the peer concatenates the received pseudonym
	username with the "@" character and a NAI realm portion. The
	selection of the NAI realm is discussed above. The peer can select
	the realm portion similarly regardless of whether it uses the
	permanent username or a pseudonym username.
	4.1.1.10 Usage of the Fast Re-authentication Identity by the Peer
	On fast re-authentication, the peer uses the fast re-authentication
	identity, received as part of the previous authentication sequence.
	A new fast re-authentication identity may be delivered as part of
	both full authentication and fast re-authentication. The peer MUST
	NOT modify the username part of the fast re-authentication identity
	received in AT_NEXT_REAUTH_ID, except in cases when username
	decoration is required. Even in these cases, the "root" fast
	re-authentication username must not be modified, but it may be
	appended or prepended with another string.
	4.1.2 Communicating the Peer Identity to the Server
	4.1.2.1 General
	The peer identity MAY be communicated to the server with the
	EAP-Response/Identity message. This message MAY contain the
	permanent identity, a pseudonym identity, or a fast re-authentication
	identity. If the peer uses the permanent identity or a pseudonym
	identity, which the server is able to map to the permanent identity,
	then the authentication proceeds as discussed in the overview of
	Section 3. If the peer uses a fast re-authentication identity, and
	if the fast re-authentication identity matches with a valid fast
	re-authentication identity maintained by the server , then a fast
	re-authentication exchange is performed, as described in Section 5.
	The peer identity can also be transmitted from the peer to the server
	using EAP-AKA messages instead of EAP-Response/Identity. In this
	case, the server includes an identity requesting attribute
	(AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ or AT_PERMANENT_ID_REQ) in the
	EAP-Request/AKA-Identity message, and the peer includes the
	AT_IDENTITY attribute, which contains the peer's identity, in the
	EAP-Response/AKA-Identity message. The AT_ANY_ID_REQ attribute is a
	general identity requesting attribute, which the server uses if it
	does not specify which kind of an identity the peer should return in
	AT_IDENTITY. The server uses the AT_FULLAUTH_ID_REQ attribute to
	request either the permanent identity or a pseudonym identity. The
	server uses the AT_PERMANENT_ID_REQ attribute to request the peer to
	send its permanent identity. The EAP-Request/AKA-Challenge,
	EAP-Response/AKA-Challenge, or the packets used on fast
	re-authentication may optionally include the AT_CHECKCODE attribute,
	which enables the protocol peers to ensure the integrity of the
	AKA-Identity packets. AT_CHECKCODE is specified in Section 9.13.
	The identity format in the AT_IDENTITY attribute is the same as in
	the EAP-Response/Identity packet (except that identity decoration is
	not allowed). The AT_IDENTITY attribute contains a permanent
	identity, a pseudonym identity or a fast re-authentication identity.
	Please note that the EAP-AKA peer and the EAP-AKA server only process
	the AT_IDENTITY attribute and entities that only pass through EAP
	packets do not process this attribute. Hence, the authenticator and
	other intermediate AAA elements (such as possible AAA proxy servers)
	will continue to refer to the peer with the original identity from
	the EAP-Response/Identity packet unless the identity authenticated in
	the AT_IDENTITY attribute is communicated to them in another way
	within the AAA protocol.
	4.1.2.2 Relying on EAP-Response/Identity Discouraged
	The EAP-Response/Identity packet is not method specific so in many
	implementations it may be handled by an EAP Framework. This
	introduces an additional layer of processing between the EAP peer and
	EAP server. The extra layer of processing may cache identity
	responses or add decorations to the identity. A modification of the
	identity response will cause the EAP peer and EAP server to use
	different identities in the key derivation which will cause the
	protocol to fail.
	For this reason, it is RECOMMENDED that the EAP peer and server use
	the method specific identity attributes in EAP-AKA and the server is
	strongly discouraged from relying upon the EAP-Response/Identity.
	In particular, if the EAP server receives a decorated identity in
	EAP-Response/Identity, then the EAP server MUST use the
	identity-requesting attributes to request the peer to send an
	unmodified and undecorated copy of the identity in AT_IDENTITY.
	4.1.3 Choice of Identity for the EAP-Response/Identity
	If EAP-AKA peer is started upon receiving an EAP-Request/Identity
	message, then the peer performs the following steps.
	If the peer has maintained fast re-authentication state information
	and if the peer wants to use fast re-authentication, then the peer
	transmits the fast re-authentication identity in
	EAP-Response/Identity.
	Else, if the peer has a pseudonym username available, then the peer
	transmits the pseudonym identity in EAP-Response/Identity.
	In other cases, the peer transmits the permanent identity in
	EAP-Response/Identity.
	4.1.4 Server Operation in the Beginning of EAP-AKA Exchange
	If the EAP server has not received any EAP-AKA peer identity
	(permanent identity, pseudonym identity or fast re-authentication
	identity) from the peer when sending the first EAP-AKA request, or if
	the EAP server has received an EAP-Response/Identity packet but the
	contents do not appear to be a valid permanent identity, pseudonym
	identity or a re-authentication identity, then the server MUST
	request an identity from the peer using one of the methods below.
	The server sends the EAP-Request/AKA-Identity message with the
	AT_PERMANENT_ID_REQ attribute to indicate that the server wants the
	peer to include the permanent identity in the AT_IDENTITY attribute
	of the EAP-Response/AKA-Identity message. This is done in the
	following cases:
	o The server does not support fast re-authentication or identity
	privacy.
	o The server received an identity that it recognizes as a pseudonym
	identity but the server is not able to map the pseudonym identity
	to a permanent identity.
	The server issues the EAP-Request/AKA-Identity packet with the
	AT_FULLAUTH_ID_REQ attribute to indicate that the server wants the
	peer to include a full authentication identity (pseudonym identity or
	permanent identity) in the AT_IDENTITY attribute of the
	EAP-Response/AKA-Identity message. This is done in the following
	cases:
	o The server does not support fast re-authentication and the server
	supports identity privacy
	o The server received an identity that it recognizes as a
	re-authentication identity but the server is not able to map the
	re-authentication identity to a permanent identity
	The server issues the EAP-Request/AKA-Identity packet with the
	AT_ANY_ID_REQ attribute to indicate that the server wants the peer to
	include an identity in the AT_IDENTITY attribute of the
	EAP-Response/AKA-Identity message, and the server does not indicate
	any preferred type for the identity. This is done in other cases,
	such as when the server does not have any identity, or the server
	does not recognize the format of a received identity.
	4.1.5 Processing of EAP-Request/AKA-Identity by the Peer
	Upon receipt of an EAP-Request/AKA-Identity message, the peer MUST
	perform the following steps.
	If the EAP-Request/AKA-Identity includes AT_PERMANENT_ID_REQ, and if
	the peer does not have a pseudonym available, then the peer MUST
	respond with EAP-Response/AKA-Identity and include the permanent
	identity in AT_IDENTITY. If the peer has a pseudonym available, then
	the peer MAY refuse to send the permanent identity; hence in this
	case the peer MUST either respond with EAP-Response/AKA-Identity and
	include the permanent identity in AT_IDENTITY or respond with
	EAP-Response/AKA-Client-Error packet with code "unable to process
	packet".
	If the EAP-Request/AKA-Identity includes AT_FULL_AUTH_ID_REQ, and if
	the peer has a pseudonym available, then the peer SHOULD respond with
	EAP-Response/AKA-Identity and include the pseudonym identity in
	AT_IDENTITY. If the peer does not have a pseudonym when it receives
	this message, then the peer MUST respond with
	EAP-Response/AKA-Identity and include the permanent identity in
	AT_IDENTITY. The Peer MUST NOT use a fast re-authentication identity
	in the AT_IDENTITY attribute.
	If the EAP-Request/AKA-Identity includes AT_ANY_ID_REQ, and if the
	peer has maintained fast re-authentication state information and the
	peer wants to use fast re-authentication, then the peer responds with
	EAP- Response/AKA-Identity and includes the fast re-authentication
	identity in AT_IDENTITY. Else, if the peer has a pseudonym identity
	available, then the peer responds with EAP-Response/AKA-Identity and
	includes the pseudonym identity in AT_IDENTITY. Else, the peer
	responds with EAP-Response/AKA-Identity and includes the permanent
	identity in AT_IDENTITY.
	An EAP-AKA exchange may include several EAP/AKA-Identity rounds. The
	server may issue a second EAP-Request/AKA-Identity, if it was not
	able to recognize the identity the peer used in the previous
	AT_IDENTITY attribute. At most three EAP/AKA-Identity rounds can be
	used, so the peer MUST NOT respond to more than three
	EAP-Request/AKA-Identity messages within an EAP exchange. The peer
	MUST verify that the sequence of EAP-Request/AKA-Identity packets the
	peer receives comply with the sequencing rules defined in this
	document. That is, AT_ANY_ID_REQ can only be used in the first
	EAP-Request/AKA-Identity, in other words AT_ANY_ID_REQ MUST NOT be
	used in the second or third EAP-Request/AKA-Identity.
	AT_FULLAUTH_ID_REQ MUST NOT be used if the previous
	EAP-Request/AKA-Identity included AT_PERMANENT_ID_REQ. The peer
	operation in cases when it receives an unexpected attribute or an
	unexpected message is specified in Section 6.3.1.
	4.1.6 Attacks against Identity Privacy
	The section above specifies two possible ways the peer can operate
	upon receipt of AT_PERMANENT_ID_REQ. This is because a received
	AT_PERMANENT_ID_REQ does not necessarily originate from the valid
	network, but an active attacker may transmit an
	EAP-Request/AKA-Identity packet with an AT_PERMANENT_ID_REQ attribute
	to the peer, in an effort to find out the true identity of the user.
	If the peer does not want to reveal its permanent identity, then the
	peer sends the EAP-Response/AKA-Client-Error packet with the error
	code "unable to process packet", and the authentication exchange
	terminates.
	Basically, there are two different policies that the peer can employ
	with regard to AT_PERMANENT_ID_REQ. A "conservative" peer assumes
	that the network is able to maintain pseudonyms robustly. Therefore,
	if a conservative peer has a pseudonym username, the peer responds
	with EAP-Response/AKA-Client-Error to the EAP packet with
	AT_PERMANENT_ID_REQ, because the peer believes that the valid network
	is able to map the pseudonym identity to the peer's permanent
	identity. (Alternatively, the conservative peer may accept
	AT_PERMANENT_ID_REQ in certain circumstances, for example if the
	pseudonym was received a long time ago.) The benefit of this policy
	is that it protects the peer against active attacks on anonymity. On
	the other hand, a "liberal" peer always accepts the
	AT_PERMANENT_ID_REQ and responds with the permanent identity. The
	benefit of this policy is that it works even if the valid network
	sometimes loses pseudonyms and is not able to map them to the
	permanent identity.
	4.1.7 Processing of AT_IDENTITY by the Server
	When the server receives an EAP-Response/AKA-Identity message with
	the AT_IDENTITY (in response to the server's identity requesting
	attribute), the server MUST operate as follows.
	If the server used AT_PERMANENT_ID_REQ, and if the AT_IDENTITY does
	not contain a valid permanent identity, then the server sends an
	EAP-Request/AKA-Notification packet with AT_NOTIFICATION code
	"General failure" (16384) to terminate the EAP exchange. If the
	server recognizes the permanent identity and is able to continue,
	then the server proceeds with full authentication by sending
	EAP-Request/AKA-Challenge.
	If the server used AT_FULLAUTH_ID_REQ, and if AT_IDENTITY contains a
	valid permanent identity or a pseudonym identity that the server can
	map to a valid permanent identity, then the server proceeds with full
	authentication by sending EAP-Request/AKA-Challenge. If AT_IDENTITY
	contains a pseudonym identity that the server is not able to map to a
	valid permanent identity, or an identity that the server is not able
	to recognize or classify, then the server sends EAP-Request/
	AKA-Identity with AT_PERMANENT_ID_REQ.
	If the server used AT_ANY_ID_REQ, and if the AT_IDENTITY contains a
	valid permanent identity or a pseudonym identity that the server can
	map to a valid permanent identity, then the server proceeds with full
	authentication by sending EAP-Request/ AKA-Challenge.
	If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid
	fast re-authentication identity and the server agrees on using
	re-authentication, then the server proceeds with fast
	re-authentication by sending EAP-Request/AKA-Reauthentication
	(Section 5).
	If the server used AT_ANY_ID_REQ, and if the peer sent an
	EAP-Response/AKA-Identity with AT_IDENTITY that contains an identity
	that the server recognizes as a fast re-authentication identity, but
	the server is not able to map the identity to a permanent identity,
	then the server sends EAP-Request/AKA-Identity with
	AT_FULLAUTH_ID_REQ.
	If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid
	fast re-authentication identity, which the server is able to map to a
	permanent identity, and if the server does not want to use fast
	re-authentication, then the server proceeds with full authentication
	by sending EAP-Request/AKA-Challenge.
	If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an
	identity that the server recognizes as a pseudonym identity but the
	server is not able to map the pseudonym identity to a permanent
	identity, then the server sends EAP-Request/AKA-Identity with
	AT_PERMANENT_ID_REQ.
	If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an
	identity that the server is not able to recognize or classify, then
	the server sends EAP-Request/AKA-Identity with AT_FULLAUTH_ID_REQ.
	4.2 Message Sequence Examples (Informative)
	This section contains non-normative message sequence examples to
	illustrate how the peer identity can be communicated to the server.
	4.2.1 Usage of AT_ANY_ID_REQ
	Obtaining the peer identity with EAP-AKA attributes is illustrated in
	Figure 5 below.
	Peer Authenticator
	| |
	| +------------------------------+
	| | Server does not have any |
	| | Subscriber identity available|
	| | When starting EAP-AKA |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_ANY_ID_REQ) |
	|<------------------------------------------------------|
	| |
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY) |
	|------------------------------------------------------>|
	| |
	Figure 5: Usage of AT_ANY_ID_REQ
	4.2.2 Fall Back on Full Authentication
	Figure 6 illustrates the case when the server does not recognize the
	fast re-authentication identity the peer used in AT_IDENTITY.
	Peer Authenticator
	| |
	| +------------------------------+
	| | Server does not have any |
	| | Subscriber identity available|
	| | When starting EAP-AKA |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_ANY_ID_REQ) |
	|<------------------------------------------------------|
	| |
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY containing a fast re-auth. identity) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server does not recognize |
	| | The fast re-auth. |
	| | Identity |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_FULLAUTH_ID_REQ) |
	|<------------------------------------------------------|
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY with a full-auth. Identity) |
	|------------------------------------------------------>|
	| |
	Figure 6: Fall back on full authentication
	If the server recognizes the fast re-authentication identity, but
	still wants to fall back on full authentication, the server may issue
	the EAP-Request/AKA-Challenge packet. In this case, the full
	authentication procedure proceeds as usual.
	4.2.3 Requesting the Permanent Identity 1
	Figure 7 illustrates the case when the EAP server fails to decode a
	pseudonym identity included in the EAP-Response/Identity packet.
	Peer Authenticator
	| EAP-Request/Identity |
	|<------------------------------------------------------|
	| EAP-Response/Identity |
	| (Includes a pseudonym) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server fails to decode the |
	| | Pseudonym. |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_PERMANENT_ID_REQ) |
	|<------------------------------------------------------|
	| |
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY with permanent identity) |
	|------------------------------------------------------>|
	| |
	Figure 7: Requesting the permanent identity 1
	If the server recognizes the permanent identity, then the
	authentication sequence proceeds as usual with the EAP Server issuing
	the EAP-Request/AKA-Challenge message.
	4.2.4 Requesting the Permanent Identity 2
	Figure 8 illustrates the case when the EAP server fails to decode the
	pseudonym included in the AT_IDENTITY attribute.
	Peer Authenticator
	| |
	| +------------------------------+
	| | Server does not have any |
	| | Subscriber identity available|
	| | When starting EAP-AKA |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_ANY_ID_REQ) |
	|<------------------------------------------------------|
	| |
	|EAP-Response/AKA-Identity |
	|(AT_IDENTITY with a pseudonym identity) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server fails to decode the |
	| | Pseudonym in AT_IDENTITY |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_PERMANENT_ID_REQ) |
	|<------------------------------------------------------|
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY with permanent identity) |
	|------------------------------------------------------>|
	| |
	Figure 8: Requesting the permanent identity 2
	4.2.5 Three EAP/AKA-Identity Round Trips
	Figure 9 illustrates the case with three EAP/AKA-Identity round
	trips.
	Peer Authenticator
	| |
	| +------------------------------+
	| | Server does not have any |
	| | Subscriber identity available|
	| | When starting EAP-AKA |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_ANY_ID_REQ) |
	|<------------------------------------------------------|
	| |
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY with fast re-auth. identity) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server does not accept |
	| | The fast re-authentication |
	| | Identity |
	| +------------------------------+
	| |
	: :
	: :
	: :
	: :
	| EAP-Request/AKA-Identity |
	| (AT_FULLAUTH_ID_REQ) |
	|<------------------------------------------------------|
	|EAP-Response/AKA-Identity |
	|(AT_IDENTITY with a pseudonym identity) |
	|------------------------------------------------------>|
	| +------------------------------+
	| | Server fails to decode the |
	| | Pseudonym in AT_IDENTITY |
	| +------------------------------+
	| EAP-Request/AKA-Identity |
	| (AT_PERMANENT_ID_REQ) |
	|<------------------------------------------------------|
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY with permanent identity) |
	|------------------------------------------------------>|
	| |
	Figure 9: Three EAP-AKA Start rounds
	After the last EAP-Response/AKA-Identity message, the full
	authentication sequence proceeds as usual.
	5. Fast Re-authentication
	5.1 General
	In some environments, EAP authentication may be performed frequently.
	Because the EAP-AKA full authentication procedure makes use of the
	AKA algorithms, and it therefore requires fresh authentication
	vectors from the Authentication Centre, the full authentication
	procedure may result in many network operations when used very
	frequently. Therefore, EAP-AKA includes a more inexpensive fast
	re-authentication procedure that does not make use of the AKA
	algorithms and does not need new vectors from the Authentication
	Centre.
	Fast re-authentication is optional to implement for both the EAP-AKA
	server and peer. On each EAP authentication, either one of the
	entities may also fall back on full authentication if they do not
	want to use fast re-authentication.
	Fast re-authentication is based on the keys derived on the preceding
	full authentication. The same K_aut and K_encr keys as in full
	authentication are used to protect EAP-AKA packets and attributes,
	and the original Master Key from full authentication is used to
	generate a fresh Master Session Key, as specified in Section 6.4.
	The fast re-authentication exchange makes use of an unsigned 16-bit
	counter, included in the AT_COUNTER attribute. The counter has three
	goals: 1) it can be used to limit the number of successive
	reauthentication exchanges without full-authentication 2) it
	contributes to the keying material, and 3) it protects the peer and
	the server from replays. On full authentication, both the server and
	the peer initialize the counter to one. The counter value of at
	least one is used on the first fast re-authentication. On subsequent
	fast re-authentications, the counter MUST be greater than on any of
	the previous fast re-authentications. For example, on the second
	fast re-authentication, counter value is two or greater etc. The
	AT_COUNTER attribute is encrypted.
	Both the peer and the EAP server maintain a copy of the counter. The
	EAP server sends its counter value to the peer in the fast
	re-authentication request. The peer MUST verify that its counter
	value is less than or equal to the value sent by the EAP server.
	The server includes an encrypted server random nonce (AT_NONCE_S) in
	the fast re-authentication request. The AT_MAC attribute in the
	peer's response is calculated over NONCE_S to provide a
	challenge/response authentication scheme. The NONCE_S also
	contributes to the new Master Session Key.
	Both the peer and the server SHOULD have an upper limit for the
	number of subsequent fast re-authentications allowed before a full
	authentication needs to be performed. Because a 16-bit counter is
	used in fast re-authentication, the theoretical maximum number of
	re-authentications is reached when the counter value reaches FFFF
	hexadecimal. In order to use fast re-authentication, the peer and
	the EAP server need to store the following values: Master Key, latest
	counter value and the next fast re-authentication identity. K_aut,
	K_encr may either be stored or derived again from MK. The server may
	also need to store the permanent identity of the user.
	5.2 Comparison to AKA
	When analyzing the fast re-authentication exchange, it may be helpful
	to compare it with the 3rd generation Authentication and Key
	Agreement (AKA) exchange used on full authentication. The counter
	corresponds to the AKA sequence number, NONCE_S corresponds to RAND,
	and AT_MAC in EAP-Request/AKA-Reauthentication corresponds to AUTN,
	the AT_MAC in EAP-Response/AKA-Reauthentication corresponds to RES,
	AT_COUNTER_TOO_SMALL corresponds to AUTS, and encrypting the counter
	corresponds to the usage of the Anonymity Key. Also the key
	generation on fast re-authentication with regard to random or fresh
	material is similar to AKA -- the server generates the NONCE_S and
	counter values, and the peer only verifies that the counter value is
	fresh.
	It should also be noted that encrypting the AT_NONCE_S, AT_COUNTER or
	AT_COUNTER_TOO_SMALL attributes is not important to the security of
	the fast re-authentication exchange.
	5.3 Fast Re-authentication Identity
	The fast re-authentication procedure makes use of separate
	re-authentication user identities. Pseudonyms and the permanent
	identity are reserved for full authentication only. If a fast
	re-authentication identity is lost and the network does not recognize
	it, the EAP server can fall back on full authentication. If the EAP
	server supports fast re-authentication, it MAY include the skippable
	AT_NEXT_REAUTH_ID attribute in the encrypted data of EAP-
	Request/AKA-Challenge message. This attribute contains a new
	re-authentication identity for the next fast re-authentication. The
	attribute also works as a capability flag that indicates the fact
	that the server supports fast re-authentication, and that the server
	wants to continue using fast re-authentication within the current
	context. The peer MAY ignore this attribute, in which case it will
	use full authentication next time. If the peer wants to use fast
	re-authentication, it uses this fast re-authentication identity on
	next authentication. Even if the peer has a fast re-authentication
	identity, the peer MAY discard the re-authentication identity and use
	a pseudonym or the permanent identity instead, in which case full
	authentication MUST be performed. If the EAP server does not include
	the AT_NEXT_REAUTH_ID in the encrypted data of
	EAP-Request/AKA-Challenge or EAP-Request/AKA-Reauthentication, then
	the peer MUST discard its current fast re-authentication state
	information and perform a full authentication next time.
	In environments where a realm portion is needed in the peer identity,
	the fast re-authentication identity received in AT_NEXT_REAUTH_ID
	MUST contain both a username portion and a realm portion, as per the
	NAI format. The EAP Server can choose an appropriate realm part in
	order to have the AAA infrastructure route subsequent fast
	re-authentication related requests to the same AAA server. For
	example, the realm part MAY include a portion that is specific to the
	AAA server. Hence, it is sufficient to store the context required
	for fast re-authentication in the AAA server that performed the full
	authentication.
	The peer MAY use the fast re-authentication identity in the
	EAP-Response/Identity packet or, in response to server's
	AT_ANY_ID_REQ attribute, the peer MAY use the fast re-authentication
	identity in the AT_IDENTITY attribute of the
	EAP-Response/AKA-Identity packet.
	The peer MUST NOT modify the username portion of the fast
	re-authentication identity, but the peer MAY modify the realm portion
	or replace it with another realm portion. The peer might need to
	modify the realm in order to influence the AAA routing, for example
	to make sure that the correct server is reached. It should be noted
	that sharing the same fast re-authentication key among several
	servers may have security risks, so changing the realm portion of the
	NAI in order to change the EAP server is not desirable.
	Even if the peer uses a fast re-authentication identity, the server
	may want to fall back on full authentication, for example because the
	server does not recognize the fast re-authentication identity or does
	not want to use fast re-authentication. If the server was able to
	decode the fast re-authentication identity to the permanent identity,
	the server issues the EAP-Request/AKA-Challenge packet to initiate
	full authentication. If the server was not able to recover the
	peer's identity from the fast re-authentication identity, the server
	starts the full authentication procedure by issuing an
	EAP-Request/AKA-Identity packet. This packet always starts a full
	authentication sequence if it does not include the AT_ANY_ID_REQ
	attribute.
	5.4 Fast Re-authentication Procedure
	Figure 10 illustrates the fast re-authentication procedure. In this
	example, the optional protected success indication is not used.
	Encrypted attributes are denoted with '*'. The peer uses its fast
	re-authentication identity in the EAP-Response/Identity packet. As
	discussed above, an alternative way to communicate the fast
	re-authentication identity to the server is for the peer to use the
	AT_IDENTITY attribute in the EAP-Response/AKA-Identity message. This
	latter case is not illustrated in the figure below, and it is only
	possible when the server requests the peer to send its identity by
	including the AT_ANY_ID_REQ attribute in the EAP-Request/AKA-Identity
	packet.
	If the server recognizes the identity as a valid fast
	re-authentication identity, and if the server agrees on using fast
	re-authentication, then the server sends the EAP-
	Request/AKA-Reauthentication packet to the peer. This packet MUST
	include the encrypted AT_COUNTER attribute, with a fresh counter
	value, the encrypted AT_NONCE_S attribute that contains a random
	number chosen by the server, the AT_ENCR_DATA and the AT_IV
	attributes used for encryption, and the AT_MAC attribute that
	contains a message authentication code over the packet. The packet
	MAY also include an encrypted AT_NEXT_REAUTH_ID attribute that
	contains the next fast re-authentication identity.
	Fast re-authentication identities are one-time identities. If the
	peer does not receive a new fast re-authentication identity, it MUST
	use either the permanent identity or a pseudonym identity on the next
	authentication to initiate full authentication.
	The peer verifies that AT_MAC is correct and that the counter value
	is fresh (greater than any previously used value). The peer MAY save
	the next fast re-authentication identity from the encrypted
	AT_NEXT_REAUTH_ID for next time. If all checks are successful, the
	peer responds with the EAP-Response/AKA-Reauthentication packet,
	including the AT_COUNTER attribute with the same counter value and
	the AT_MAC attribute.
	The server verifies the AT_MAC attribute and also verifies that the
	counter value is the same that it used in the EAP-Request/AKA-
	Reauthentication packet. If these checks are successful, the fast
	re-authentication has succeeded and the server sends the EAP-Success
	packet to the peer.
	If protected success indications (Section 6.2) were used, the
	EAP-Success packet would be preceded by an EAP-AKA notification
	round.
	Peer Authenticator
	| |
	| EAP-Request/Identity |
	|<------------------------------------------------------|
	| |
	| EAP-Response/Identity |
	| (Includes a fast re-authentication identity) |
	|------------------------------------------------------>|
	| +--------------------------------+
	| | Server recognizes the identity |
	| | and agrees on using fast |
	| | re-authentication |
	| +--------------------------------+
	| EAP-Request/AKA-Reauthentication |
	| (AT_IV, AT_ENCR_DATA, *AT_COUNTER, |
	| *AT_NONCE_S, *AT_NEXT_REAUTH_ID, AT_MAC) |
	|<------------------------------------------------------|
	| |
	: :
	: :
	: :
	: :
	| |
	+-----------------------------------------------+ |
	| Peer verifies AT_MAC and the freshness of | |
	| the counter. Peer MAY store the new re- | |
	| authentication identity for next re-auth. | |
	+-----------------------------------------------+ |
	| |
	| EAP-Response/AKA-Reauthentication |
	| (AT_IV, AT_ENCR_DATA, *AT_COUNTER with same value, |
	| AT_MAC) |
	|------------------------------------------------------>|
	| +--------------------------------+
	| | Server verifies AT_MAC and |
	| | the counter |
	| +--------------------------------+
	| EAP-Success |
	|<------------------------------------------------------|
	| |
	Figure 10: Reauthentication
	5.5 Fast Re-authentication Procedure when Counter is Too Small
	If the peer does not accept the counter value of
	EAP-Request/AKA-Reauthentication, it indicates the counter
	synchronization problem by including the encrypted
	AT_COUNTER_TOO_SMALL in EAP-Response/AKA-Reauthentication. The
	server responds with EAP-Request/AKA-Challenge to initiate a normal
	full authentication procedure. This is illustrated in Figure 11.
	Encrypted attributes are denoted with '*'.
	Peer Authenticator
	| EAP-Request/AKA-Identity |
	| (AT_ANY_ID_REQ) |
	|<------------------------------------------------------|
	| |
	| EAP-Response/AKA-Identity |
	| (AT_IDENTITY) |
	| (Includes a fast re-authentication identity) |
	|------------------------------------------------------>|
	| |
	| EAP-Request/AKA-Reauthentication |
	| (AT_IV, AT_ENCR_DATA, *AT_COUNTER, |
	| *AT_NONCE_S, *AT_NEXT_REAUTH_ID, AT_MAC) |
	|<------------------------------------------------------|
	+-----------------------------------------------+ |
	| AT_MAC is valid but the counter is not fresh. | |
	+-----------------------------------------------+ |
	| EAP-Response/AKA-Reauthentication |
	| (AT_IV, AT_ENCR_DATA, *AT_COUNTER_TOO_SMALL, |
	| *AT_COUNTER, AT_MAC) |
	|------------------------------------------------------>|
	| +----------------------------------------------+
	| | Server verifies AT_MAC but detects |
	| | That peer has included AT_COUNTER_TOO_SMALL|
	| +----------------------------------------------+
	| EAP-Request/AKA-Challenge |
	|<------------------------------------------------------|
	+---------------------------------------------------------------+
	| Normal full authentication follows. |
	+---------------------------------------------------------------+
	| |
	Figure 11: Fast re-authentication counter too small
	In the figure above, the first three messages are similar to the
	basic fast re-authentication case. When the peer detects that the
	counter value is not fresh, it includes the AT_COUNTER_TOO_SMALL
	attribute in EAP-Response/AKA-Reauthentication. This attribute
	doesn't contain any data but it is a request for the server to
	initiate full authentication. In this case, the peer MUST ignore the
	contents of the server's AT_NEXT_REAUTH_ID attribute.
	On receipt of AT_COUNTER_TOO_SMALL, the server verifies AT_MAC and
	verifies that AT_COUNTER contains the same counter value as in the
	EAP-Request/AKA-Reauthentication packet. If not, the server
	terminates the authentication exchange by sending the
	EAP-Request/AKA-Notification packet with AT_NOTIFICATION code
	"General failure" (16384). If all checks on the packet are
	successful, the server transmits a EAP-Request/AKA-Challenge packet
	and the full authentication procedure is performed as usual. Since
	the server already knows the subscriber identity, it MUST NOT use the
	EAP-Request/AKA-Identity packet to request the identity.
	It should be noted that in this case, peer identity is only
	transmitted in the AT_IDENTITY attribute at the beginning of the
	whole EAP exchange. The fast re-authentication identity used in this
	AT_IDENTITY attribute will be used in key derivation (see Section
	Section 6.4).
	6. EAP-AKA Notifications
	6.1 General
	EAP-AKA does not prohibit the use of the EAP Notifications as
	specified in [RFC3748]. EAP Notifications can be used at any time in
	the EAP-AKA exchange. It should be noted that EAP-AKA does not
	protect EAP Notifications. EAP-AKA also specifies method specific
	EAP-AKA notifications, which are protected in some cases.
	The EAP server can use EAP-AKA notifications to convey notifications
	and result indications (Section 6.2) to the peer.
	The server MUST use notifications in cases discussed in Section
	6.3.2. When the EAP server issues an EAP-Request/AKA-Notification
	packet to the peer, the peer MUST process the notification packet.The
	peer MAY show a notification message to the user and the peer MUST
	respond to the EAP server with an EAP-Response/AKA-Notification
	packet, even if the peer did not recognize the notification code.
	An EAP-AKA full authentication exchange or a fast re-authentication
	exchange MUST NOT include more than one EAP-AKA notification round.
	The notification code is a 16-bit number. The most significant bit
	is called the Success bit (S bit). The S bit specifies whether the
	notification implies failure. The code values with the S bit set to
	zero (code values 0...32767) are used on unsuccessful cases. The
	receipt of a notification code from this range implies failed EAP
	exchange, so the peer can use the notification as a failure
	indication. After receiving the EAP-Response/AKA-Notification for
	these notification codes, the server MUST send the EAP-Failure
	packet.
	The receipt of a notification code with the S bit set to one (values
	32768...65536) does not imply failure. Notification code "Success"
	(32768) has been reserved as a general notification code to indicate
	successful authentication.
	The second most significant bit of the notification code is called
	the Phase bit (P bit). It specifies at which phase of the EAP-AKA
	exchange the notification can be used. If the P bit is set to zero,
	the notification can only be used after a successful
	EAP/AKA-Challenge round in full authentication or a successful
	EAP/AKA-Reauthentication round in reautentication. A
	re-authentication round is considered successful only if the peer has
	successfully verified AT_MAC and AT_COUNTER attributes, and does not
	include the AT_COUNTER_TOO_SMALL attribute in
	EAP-Response/AKA-Reauthentication.
	If the P bit is set to one, the notification can only by used before
	the EAP/AKA-Challenge round in full authentication or before the
	EAP/AKA-Reauthentication round in reauthentication. These
	notifications can only be used to indicate various failure cases. In
	other words, if the P bit is set to one, then the S bit MUST be set
	to zero.
	Section 8.10 and Section 8.11 specify what other attributes must be
	included in the notification packets.
	Some of the notification codes are authorization related and hence
	not usually considered as part of the responsibility of an EAP
	method. However, they are included as part of EAP-AKA because there
	are currently no other ways to convey this information to the user in
	a localizable way, and the information is potentially useful for the
	user. An EAP-AKA server implementation may decide never to send
	these EAP-AKA notifications.
	6.2 Result Indications
	As discussed in Section 6.3, the server and the peer use explicit
	error messages in all error cases. If the server detects an error
	after successful authentication, the server uses an EAP-AKA
	notification to indicate failure to the peer. In this case, the
	result indication is integrity and replay protected.
	By sending an EAP-Response/AKA-Challenge packet or an
	EAP-Response/AKA-Reauthentication packet (without
	AT_COUNTER_TOO_SMALL), the peer indicates that it has successfully
	authenticated the server and that the peer's local policy accepts the
	EAP exchange. In other words, these packets are implicit success
	indications from the peer to the server.
	EAP-AKA also supports optional protected success indications from the
	server to the peer. If the EAP server wants to use protected success
	indications, it includes the AT_RESULT_IND attribute in the
	EAP-Request/AKA-Challenge or the EAP-Request/AKA-Reauthentication
	packet. This attribute indicates, that the EAP server would like to
	use result indications in both successful and unsuccessful cases. If
	the peer also wants this, the peer includes AT_RESULT_IND in
	EAP-Response/AKA-Challenge or EAP-Response/AKA-Re-authentication.
	The peer MUST NOT include AT_RESULT_IND if it did not receive
	AT_RESULT_IND from the server. If both the peer and the server used
	AT_RESULT_IND, then the EAP exchange is not complete yet, but an
	EAP-AKA notification round will follow. The following EAP-AKA
	notification may indicate either failure or success.
	Success indications with the AT_NOTIFICATION code "Success" (32768)
	can only be used if both the server and the peer indicate they want
	to use them with AT_RESULT_IND. If the server did not include
	AT_RESULT_IND in the EAP-Request/AKA-Challenge or
	EAP-Request/AKA-Reauthentication packet, or if the peer did not
	include AT_RESULT_IND in the corresponding response packet, then the
	server MUST NOT use protected success indications.
	Because the server uses the AT_NOTIFICATION code "Success" (32768) to
	indicate that the EAP exchange has completed successfully, the EAP
	exchange cannot fail when the server processes the EAP-AKA response
	to this notification. Hence, the server MUST ignore the contents of
	the EAP-AKA response it receives to the EAP-Request/AKA-Notification
	with this code. Regardless of the contents of the EAP-AKA response,
	the server MUST send EAP-Success as the next packet.
	6.3 Error Cases
	This section specifies the operation of the peer and the server in
	error cases. The subsections below require the EAP-AKA peer and
	server to send an error packet (EAP-Response/AKA-Client-Error,
	EAP-Response/AKA-Authentication-Reject or
	EAP-Response/AKA-Synchronization-Failure from the peer and
	EAP-Request/AKA-Notification from the server) in error cases.
	However, implementations SHOULD NOT rely upon the correct error
	reporting behavior of the peer, authenticator, or the server. It is
	possible for error and other messages to be lost in transit or for a
	malicious participant to attempt to consume resources by not issuing
	error messages. Both the peer and the EAP server SHOULD have a
	mechanism to clean up state even if an error message or EAP-Success
	is not received after a timeout period.
	6.3.1 Peer Operation
	Two special error messages have been specified for error cases that
	are related to the processing of the AKA AUTN parameter, as described
	in Section 3: (1) if the peer does not accept AUTN, the peer responds
	with EAP-Response/AKA-Authentication-Reject (Section 8.5), and the
	server issues EAP-Failure, and (2) if the peer detects that the
	sequence number in AUTN is not correct, the peer responds with
	EAP-Response/AKA-Synchronization-Failure (Section 8.6), and the
	server proceeds with a new EAP-Request/AKA-Challenge.
	In other error cases, when an EAP-AKA peer detects an error in a
	received EAP-AKA packet, the EAP-AKA peer responds with the
	EAP-Response/AKA-Client-Error packet. In response to the
	EAP-Response/AKA-Client-Error, the EAP server MUST issue the
	EAP-Failure packet and the authentication exchange terminates.
	By default, the peer uses the client error code 0, "unable to process
	packet". This error code is used in the following cases:
	o EAP exchange is not acceptable according to the peer's local
	policy.
	o the peer is not able to parse the EAP request, i.e. the EAP
	request is malformed
	o the peer encountered a malformed attribute
	o wrong attribute types or duplicate attributes have been included
	in the EAP request
	o a mandatory attribute is missing
	o unrecognized non-skippable attribute
	o unrecognized or unexpected EAP-AKA Subtype in the EAP request
	o invalid AT_MAC. The peer SHOULD log this event.
	o invalid AT_CHECKCODE. The peer SHOULD log this event.
	o invalid pad bytes in AT_PADDING
	o the peer does not want to process AT_PERMANENT_ID_REQ
	6.3.2 Server Operation
	If an EAP-AKA server detects an error in a received EAP-AKA response,
	the server MUST issue the EAP-Request/AKA-Notification packet with an
	AT_NOTIFICATION code that implies failure. By default, the server
	uses one of the general failure codes ("General failure after
	authentication" (0), or "General failure" (16384)). The choice
	between these two codes depends on the phase of the EAP-AKA exchange,
	see Section 6. The errors cases when the server issues an
	EAP-Request/AKA-Notification that implies failure include the
	following:
	o the server is not able to parse the peer's EAP response
	o the server encounters a malformed attribute, a non-recognized
	non-skippable attribute, or a duplicate attribute
	o a mandatory attribute is missing or an invalid attribute was
	included
	o unrecognized or unexpected EAP-AKA Subtype in the EAP Response
	o invalid AT_MAC. The server SHOULD log this event.
	o invalid AT_CHECKCODE. The server SHOULD log this event.
	o invalid AT_COUNTER
	6.3.3 EAP-Failure
	The EAP-AKA server sends EAP-Failure in three cases:
	1) In response to an EAP-Response/AKA-Client-Error packet the server
	has received from the peer, or
	2) In response to an EAP-Response/AKA-Authentication-Reject packet
	the server has received from the peer, or
	3) Following an EAP-AKA notification round, when the AT_NOTIFICATION
	code implies failure.
	The EAP-AKA server MUST NOT send EAP-Failure in other cases than
	these three. However, it should be noted that even though the
	EAP-AKA server would not send an EAP-Failure, an authorization
	decision that happens outside EAP-AKA, such as in the AAA server or
	in an intermediate AAA proxy, may result in a failed exchange.
	The peer MUST accept the EAP-Failure packet in case 1), case 2) and
	case 3) above. The peer SHOULD silently discard the EAP-Failure
	packet in other cases.
	6.3.4 EAP-Success
	On full authentication, the server can only send EAP-Success after
	the EAP/AKA-Challenge round. The peer MUST silently discard any
	EAP-Success packets if they are received before the peer has
	successfully authenticated the server and sent the
	EAP-Response/AKA-Challenge packet.
	If the peer did not indicate that it wants to use protected success
	indications with AT_RESULT_IND (as discussed in Section 6.2) on full
	authentication, then the peer MUST accept EAP-Success after a
	successful EAP/AKA-Challenge round.
	If the peer indicated that it wants to use protected success
	indications with AT_RESULT_IND (as discussed in Section 6.2), then
	the peer MUST NOT accept EAP-Success after a successful
	EAP/AKA-Challenge round. In this case, the peer MUST only accept
	EAP-Success after receiving an EAP-AKA Notification with the
	AT_NOTIFICATION code "Success" (32768).
	On fast re-authentication, EAP-Success can only be sent after the
	EAP/AKA-Reauthentication round. The peer MUST silently discard any
	EAP-Success packets if they are received before the peer has
	successfully authenticated the server and sent the
	EAP-Response/AKA-Reauthentication packet.
	If the peer did not indicate that it wants to use protected success
	indications with AT_RESULT_IND (as discussed in Section 6.2) on fast
	re-authentication, then the peer MUST accept EAP-Success after a
	successful EAP/AKA-Reauthentication round.
	If the peer indicated that it wants to use protected success
	indications with AT_RESULT_IND (as discussed in Section 6.2), then
	the peer MUST NOT accept EAP-Success after a successful
	EAP/AKA-Reauthentication round. In this case, the peer MUST only
	accept EAP-Success after receiving an EAP-AKA Notification with the
	AT_NOTIFICATION code "Success" (32768).
	If the peer receives an EAP-AKA notification (Section 6) that
	indicates failure, then the peer MUST no longer accept the EAP-
	Success packet even if the server authentication was successfully
	completed.
	6.4 Key Generation
	This section specifies how keying material is generated.
	On EAP-AKA full authentication, a Master Key (MK) is derived from the
	underlying AKA values (CK and IK keys), and the identity as follows.
	MK = SHA1(Identity|IK|CK)
	In the formula above, the "|" character denotes concatenation.
	Identity denotes the peer identity string without any terminating
	null characters. It is the identity from the last AT_IDENTITY
	attribute sent by the peer in this exchange, or, if AT_IDENTITY was
	not used, the identity from the EAP-Response/Identity packet. The
	identity string is included as-is, without any changes. As discussed
	in Section 4.1.2.2, relying on EAP-Response/Identity for conveying
	the EAP-AKA peer identity is discouraged, and the server SHOULD use
	the EAP-AKA method specific identity attributes. The hash function
	SHA-1 is specified in [SHA-1].
	The Master Key is fed into a Pseudo-Random number Function (PRF),
	which generates separate Transient EAP Keys (TEKs) for protecting
	EAP-AKA packets, as well as a Master Session Key (MSK) for link layer
	security and an Extended Master Session Key (EMSK) for other
	purposes. On fast re-authentication, the same TEKs MUST be used for
	protecting EAP packets, but a new MSK and a new EMSK MUST be derived
	from the original MK and new values exchanged in the fast
	re-authentication.
	EAP-AKA requires two TEKs for its own purposes, the authentication
	key K_aut to be used with the AT_MAC attribute, and the encryption
	key K_encr, to be used with the AT_ENCR_DATA attribute. The same
	K_aut and K_encr keys are used in full authentication and subsequent
	fast re-authentications.
	Key derivation is based on the random number generation specified in
	NIST Federal Information Processing Standards (FIPS) Publication
	186-2 [PRF]. The pseudo-random number generator is specified in the
	change notice 1 (2001 October 5) of [PRF] (Algorithm 1). As
	specified in the change notice (page 74), when Algorithm 1 is used as
	a general-purpose pseudo-random number generator, the "mod q" term in
	step 3.3 is omitted. The function G used in the algorithm is
	constructed via Secure Hash Standard as specified in Appendix 3.3 of
	the standard. It should be noted that the function G is very similar
	to SHA-1, but the message padding is different. Please refer to
	[PRF] for full details. For convenience, the random number algorithm
	with the correct modification is cited in Annex A.
	160-bit XKEY and XVAL values are used, so b = 160. On each full
	authentication, the Master Key is used as the initial secret seed-key
	XKEY. The optional user input values (XSEED_j) in step 3.1 are set
	to zero.
	On full authentication, the resulting 320-bit random numbers x_0,
	x_1, ..., x_m-1 are concatenated and partitioned into suitable-sized
	chunks and used as keys in the following order: K_encr (128 bits),
	K_aut (128 bits), Master Session Key (64 bytes), Extended Master
	Session Key (64 bytes).
	On fast re-authentication, the same pseudo-random number generator
	can be used to generate a new Master Session Key and a new Extended
	Master Session Key. The seed value XKEY' is calculated as follows:
	XKEY' = SHA1(Identity|counter|NONCE_S| MK)
	In the formula above, the Identity denotes the fast re-authentication
	identity, without any terminating null characters, from the
	AT_IDENTITY attribute of the EAP-Response/AKA-Identity packet, or, if
	EAP-Response/AKA-Identity was not used on fast re-authentication, the
	identity string from the EAP-Response/Identity packet. The counter
	denotes the counter value from AT_COUNTER attribute used in the
	EAP-Response/AKA-Reauthentication packet. The counter is used in
	network byte order. NONCE_S denotes the 16-byte random NONCE_S value
	from the AT_NONCE_S attribute used in the
	EAP-Request/AKA-Reauthentication packet. The MK is the Master Key
	derived on the preceding full authentication.
	On fast re-authentication, the pseudo-random number generator is run
	with the new seed value XKEY', and the resulting 320-bit random
	numbers x_0, x_1, ..., x_m-1 are concatenated and partitioned into
	64-byte chunks and used as the new 64-byte Master Session Key and the
	new 64-byte Extended Master Session Key. Note that because K_encr
	and K_aut are not derived on fast re-authentication, the Master
	Session Key and the Extended Master Session key are obtained from the
	beginning of the key stream x_0, x_1, ....
	The first 32 bytes of the MSK can be used as the Pairwise Master Key
	(PMK) for IEEE 802.11i.
	When the RADIUS attributes specified in [RFC2548] are used to
	transport keying material, then the first 32 bytes of the MSK
	correspond to MS-MPPE-RECV-KEY and the second 32 bytes to
	MS-MPPE-SEND-KEY. In this case, only 64 bytes of keying material
	(the MSK) are used.
	7. Message Format and Protocol Extensibility
	7.1 Message Format
	As specified in [RFC3748], EAP packets begin with the Code,
	Identifiers, Length, and Type fields, which are followed by EAP
	method specific Type-Data. The Code field in the EAP header is set
	to 1 for EAP requests, and to 2 for EAP Responses. The usage of the
	Length and Identifier fields in the EAP header is also specified in
	[RFC3748]. In EAP-AKA, the Type field is set to 23.
	In EAP-AKA, the Type-Data begins with an EAP-AKA header that consists
	of a 1-octet Subtype field, and a 2-octet reserved field. The
	Subtype values used in EAP-AKA are defined in Section 10. The
	formats of the EAP header and the EAP-AKA header are shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Code | Identifier | Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Type | Subtype | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The rest of the Type-Data, immediately following the EAP-AKA header,
	consists of attributes that are encoded in Type, Length, Value
	format. The figure below shows the generic format of an attribute.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|Attribute Type | Length | Value...
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Attribute Type
	Indicates the particular type of attribute. The attribute type
	values are listed in
	Section 10
	.
	Length
	Indicates the length of this attribute in multiples of 4 bytes.
	The maximum length of an attribute is 1024 bytes. The length
	includes the Attribute Type and Length bytes.
	Value
	The particular data associated with this attribute. This field
	is always included and it is two or more bytes in length. The
	type and length fields determine the format and length of the
	value field.
	Attributes numbered within the range 0 through 127 are called
	non-skippable attributes. When an EAP-AKA peer encounters a
	non-skippable attribute type that the peer does not recognize, the
	peer MUST send the EAP-Response/AKA-Client-Error packet, and the
	authentication exchange terminates. If an EAP-AKA server encounters
	a non-skippable attribute that the server does not recognize, then
	the server sends EAP-Request/AKA-Notification packet with an
	AT_NOTIFICATION code that implies general failure ("General failure
	after authentication" (0), or "General failure" (16384), depending on
	the phase of the exchange), and the authentication exchange
	terminates.
	When an attribute numbered in the range 128 through 255 is
	encountered but not recognized that particular attribute is ignored,
	but the rest of the attributes and message data MUST still be
	processed. The Length field of the attribute is used to skip the
	attribute value when searching for the next attribute. These
	attributes are called skippable attributes.
	Unless otherwise specified, the order of the attributes in an EAP AKA
	message is insignificant, and an EAP-AKA implementation should not
	assume a certain order to be used.
	Attributes can be encapsulated within other attributes. In other
	words, the value field of an attribute type can be specified to
	contain other attributes.
	7.2 Protocol Extensibility
	EAP-AKA can be extended by specifying new attribute types. If
	skippable attributes are used, it is possible to extend the protocol
	without breaking old implementations. As specified in Section 9.13,
	if new attributes are specified for EAP-Request/AKA-Identity or
	EAP-Response/AKA-Identity, then the AT_CHECKCODE MUST be used to
	integrity protect the new attributes.
	When specifying new attributes, it should be noted that EAP-AKA does
	not support message fragmentation. Hence, the sizes of the new
	extensions MUST be limited so that the maximum transfer unit (MTU) of
	the underlying lower layer is not exceeded. According to [RFC3748],
	lower layers must provide an EAP MTU of 1020 bytes or greater, so any
	extensions to EAP-AKA SHOULD NOT exceed the EAP MTU of 1020 bytes.
	EAP-AKA packets do not include a version field. However, should
	there be a reason to revise this protocol in the future, new
	non-skippable or skippable attributes could be specified in order to
	implement revised EAP-AKA versions in a backward-compatible manner.
	It is possible to introduce version negotiation in the
	EAP-Request/AKA-Identity and EAP-Response/AKA-Identity messages by
	specifying new skippable attributes.
	8. Messages
	This section specifies the messages used in EAP-AKA. It specifies
	when a message may be transmitted or accepted, which attributes are
	allowed in a message, which attributes are required in a message, and
	other message specific details. Message format is specified in
	Section 7.1.
	8.1 EAP-Request/AKA-Identity
	The EAP/AKA-Identity roundtrip MAY used for obtaining the peer
	identity to the server. As discussed in Section 4.1, several
	AKA-Identity rounds may be required in order to obtain a valid peer
	identity.
	The server MUST include one of the following identity requesting
	attributes: AT_PERMANENT_ID_REQ, AT_FULLAUTH_ID_REQ, AT_ANY_ID_REQ.
	These three attributes are mutually exclusive, so the server MUST NOT
	include more than one of the attributes.
	If the server has previously issued an EAP-Request/AKA-Identity
	message with the AT_PERMANENT_ID_REQ attribute, and if the server has
	received a response from the peer, then the server MUST NOT issue a
	new EAP-Request/AKA-Identity packet.
	If the server has previously issued an EAP-Request/AKA-Identity
	message with the AT_FULLAUTH_ID_REQ attribute, and if the server has
	received a response from the peer, then the server MUST NOT issue a
	new EAP-Request/AKA-Identity packet with the AT_ANY_ID_REQ or
	AT_FULLAUTH_ID_REQ attributes.
	If the server has previously issued an EAP-Request/AKA-Identity
	message with the AT_ANY_ID_REQ attribute, and if the server has
	received a response from the peer, then the server MUST NOT issue a
	new EAP-Request/AKA-Identity packet with the AT_ANY_ID_REQ.
	This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA.
	8.2 EAP-Response/AKA-Identity
	The peer sends EAP-Response/AKA-Identity in response to a valid EAP-
	Request/AKA-Identity from the server.
	The peer MUST include the AT_IDENTITY attribute. The usage of
	AT_IDENITY is defined in Section 4.1.
	This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA.
	8.3 EAP-Request/AKA-Challenge
	The server sends the EAP-Request/AKA-Challenge on full authentication
	after successfully obtaining the subscriber identity.
	The AT_RAND attribute MUST be included.
	AT_MAC MUST be included. In EAP-Request/AKA-Challenge, there is no
	message-specific data covered by the MAC, see Section 9.15.
	The AT_RESULT_IND attribute MAY be included. The usage of this
	attribute is discussed in Section 6.2.
	The AT_CHECKCODE attribute MAY be included, and in certain cases
	specified in Section 9.13, it MUST be included.
	The EAP-Request/AKA-Challenge packet MAY include encrypted attributes
	for identity privacy and for communicating the next re-authentication
	identity. In this case, the AT_IV and AT_ENCR_DATA attributes are
	included (Section 9.12).
	The plaintext of the AT_ENCR_DATA value field consist of nested
	attributes. The nested attributes MAY include AT_PADDING (as
	specified in Section 9.12). If the server supports identity privacy
	and wants to communicate a pseudonym to the peer for the next full
	authentication, then the nested encrypted attributes include the
	AT_NEXT_PSEUDONYM attribute. If the server supports
	re-authentication and wants to communicate a fast re-authentication
	identity to the peer, then the nested encrypted attributes include
	the AT_NEXT_REAUTH_ID attribute. Later versions of this protocol MAY
	specify additional attributes to be included within the encrypted
	data.
	When processing this message, the peer MUST process AT_RAND and
	AT_AUTN before processing other attributes. Only if these attributes
	are verified to be valid, the peer derives keys and verifies AT_MAC.
	The operation in case an error occurs is specified in Section 6.3.1.
	8.4 EAP-Response/AKA-Challenge
	The peer sends EAP-Response/AKA-Challenge in response to a valid
	EAP-Request/AKA-Challenge.
	Sending this packet indicates, that the peer has successfully
	authenticated the server and that the EAP exchange will be accepted
	by the peer's local policy. Hence, if these conditions are not met,
	then the peer MUST NOT send EAP-Response/AKA-Challenge, but the peer
	MUST send EAP-Response/AKA-Client-Error.
	The AT_MAC attribute MUST be included. In
	EAP-Response/AKA-Challenge, there is no message-specific data covered
	by the MAC, see Section 9.15.
	The AT_RES attribute MUST be included.
	The AT_CHECKCODE attribute MAY be included, and in certain cases
	specified in Section 9.13, it MUST be included.
	The AT_RESULT_IND attribute MAY be included, if it was included in
	EAP-Request/AKA-Challenge. The usage of this attribute is discussed
	in Section 6.2.
	Later versions of this protocol MAY make use of the AT_ENCR_DATA and
	AT_IV attributes in this message to include encrypted (skippable)
	attributes. The EAP server MUST process EAP-Response/AKA-Challenge
	messages that include these attributes even if the server did not
	implement these optional attributes.
	8.5 EAP-Response/AKA-Authentication-Reject
	The peer sends the EAP-Response/AKA-Authentication-Reject packet if
	it does not accept the AUTN parameter. This version of the protocol
	does not specify any attributes for this message. Future versions of
	the protocol MAY specify attributes for this message.
	The AT_MAC, AT_ENCR_DATA, or AT_IV attributes MUST NOT be used in
	this message.
	8.6 EAP-Response/AKA-Synchronization-Failure
	The peer sends the EAP-Response/AKA-Synchronization-Failure, when the
	sequence number in the AUTN parameter is incorrect.
	The peer MUST include the AT_AUTS attribute. Future versions of the
	protocol MAY specify other additional attributes for this message.
	The AT_MAC, AT_ENCR_DATA, or AT_IV attributes MUST NOT be used in
	this message.
	8.7 EAP-Request/AKA-Reauthentication
	The server sends the EAP-Request/AKA-Reauthentication message if it
	wants to use fast re-authentication, and if it has received a valid
	fast re-authentication identity in EAP-Response/Identity or
	EAP-Response/AKA-Identity.
	The AT_MAC attribute MUST be included. No message-specific data is
	included in the MAC calculation, see Section 9.15.
	The AT_RESULT_IND attribute MAY be included. The usage of this
	attribute is discussed in Section 6.2.
	The AT_CHECKCODE attribute MAY be included, and in certain cases
	specified in Section 9.13, it MUST be included.
	The AT_IV and AT_ENCR_DATA attributes MUST be included. The
	plaintext consists of the following nested encrypted attributes,
	which MUST be included: AT_COUNTER and AT_NONCE_S. In addition, the
	nested encrypted attributes MAY include the following attributes:
	AT_NEXT_REAUTH_ID and AT_PADDING.
	8.8 EAP-Response/AKA-Reauthentication
	The client sends the EAP-Response/AKA-Reauthentication packet in
	response to a valid EAP-Request/AKA-Reauthentication.
	The AT_MAC attribute MUST be included. For EAP-Response/AKA-
	Reauthentication, the MAC code is calculated over the following data:
	EAP packet| NONCE_S. The EAP packet is represented as specified in
	Section 7.1. It is followed by the 16-byte NONCE_S value from the
	server's AT_NONCE_S attribute.
	The AT_CHECKCODE attribute MAY be included, and in certain cases
	specified in Section 9.13, it MUST be included.
	The AT_IV and AT_ENCR_DATA attributes MUST be included. The nested
	encrypted attributes MUST include the AT_COUNTER attribute. The
	AT_COUNTER_TOO_SMALL attribute MAY be included in the nested
	encrypted attributes, and it is included in cases specified in
	Section 5. The AT_PADDING attribute MAY be included.
	The AT_RESULT_IND attribute MAY be included, if it was included in
	EAP-Request/AKA-Reauthentication. The usage of this attribute is
	discussed in Section 6.2.
	Sending this packet without AT_COUNTER_TOO_SMALL indicates, that the
	peer has successfully authenticated the server and that the EAP
	exchange will be accepted by the peer's local policy. Hence, if
	these conditions are not met, then the peer MUST NOT send
	EAP-Response/AKA-Reauthentication, but the peer MUST send
	EAP-Response/AKA-Client-Error.
	8.9 EAP-Response/AKA-Client-Error
	The peer sends EAP-Response/AKA-Client-Error in error cases, as
	specified in Section 6.3.1.
	The AT_CLIENT_ERROR_CODE attribute MUST be included. The AT_MAC,
	AT_IV, or AT_ENCR_DATA attributes MUST NOT be used with this packet.
	8.10 EAP-Request/AKA-Notification
	The usage of this message is specified in Section 6.
	The AT_NOTIFICATION attribute MUST be included.
	The AT_MAC attribute MUST be included if the P bit of the
	AT_NOTIFICATION code is set to zero, and MUST NOT be included if the
	P bit is set to one. The P bit is discussed in in Section 6.
	No message-specific data is included in the MAC calculation. See
	Section 9.15.
	If EAP-Request/AKA-Notification is used on a fast re-authentication
	exchange, and if the P bit in AT_NOTIFICATION is set to zero, then
	AT_COUNTER is used for replay protection. In this case, the
	AT_ENCR_DATA and AT_IV attributes MUST be included, and the
	encapsulated plaintext attributes MUST include the AT_COUNTER
	attribute. The counter value included in AT_COUNTER MUST be the same
	as in the EAP-Request/AKA-Reauthentication packet on the same fast
	re-authentication exchange.
	8.11 EAP-Response/AKA-Notification
	The usage of this message is specified in Section 6. This packet is
	an acknowledgement of EAP-Request/AKA-Notification.
	The AT_MAC attribute MUST included in cases when the P bit of the
	notification code in AT_NOTIFICATION of EAP-Request/AKA-Notification
	is set to zero, and MUST NOT be included in cases when the P bit is
	set to one. The P bit is discussed in Section 6.
	If EAP-Request/AKA-Notification is used on fast a re-authentication
	exchange, and if the P bit in AT_NOTIFICATION is set to zero, then
	AT_COUNTER is used for replay protection. In this case, the
	AT_ENCR_DATA and AT_IV attributes MUST be included, and the
	encapsulated plaintext attributes MUST include the AT_COUNTER
	attribute. The counter value included in AT_COUNTER MUST be the same
	as in the EAP-Request/AKA-Reauthentication packet on the same fast
	re-authentication exchange.
	9. Attributes
	This section specifies the format of message attributes. The
	attribute type numbers are specified in Section 10.
	9.1 Table of Attributes
	The following table provides a guide to which attributes may be found
	in which kinds of messages, and in what quantity. Messages are
	denoted with numbers in parentheses as follows: (1)
	EAP-Request/AKA-Identity, (2) EAP-Response/AKA-Identity, (3)
	EAP-Request/AKA-Challenge, (4) EAP-Response/AKA-Challenge, (5)
	EAP-Request/AKA-Notification, (6) EAP-Response/AKA-Notification, (7)
	EAP- Response/AKA-Client-Error (8) EAP-Request/AKA-Reauthentication,
	(9) EAP-Response/AKA-Re-authentication, (10)
	EAP-Response/AKA-Authentication-Reject, and (11)
	EAP-Response/AKA-Synchronization-Failure. The column denoted with
	"E" indicates whether the attribute is a nested attribute that MUST
	be included within AT_ENCR_DATA.
	"0" indicates that the attribute MUST NOT be included in the message,
	"1" indicates that the attribute MUST be included in the message,
	"0-1" indicates that the attribute is sometimes included in the
	message, and "0*" indicates that the attribute is not included in the
	message in cases specified in this document, but MAY be included in
	the future versions of the protocol.
	Attribute (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)(11) E
	AT_PERMANENT_ID_REQ 0-1 0 0 0 0 0 0 0 0 0 0 N
	AT_ANY_ID_REQ 0-1 0 0 0 0 0 0 0 0 0 0 N
	AT_FULLAUTH_ID_REQ 0-1 0 0 0 0 0 0 0 0 0 0 N
	AT_IDENTITY 0 0-1 0 0 0 0 0 0 0 0 0 N
	AT_RAND 0 0 1 0 0 0 0 0 0 0 0 N
	AT_AUTN 0 0 1 0 0 0 0 0 0 0 0 N
	AT_RES 0 0 0 1 0 0 0 0 0 0 0 N
	AT_AUTS 0 0 0 0 0 0 0 0 0 0 1 N
	AT_NEXT_PSEUDONYM 0 0 0-1 0 0 0 0 0 0 0 0 Y
	AT_NEXT_REAUTH_ID 0 0 0-1 0 0 0 0 0-1 0 0 0 Y
	AT_IV 0 0 0-1 0* 0-1 0-1 0 1 1 0 0 N
	AT_ENCR_DATA 0 0 0-1 0* 0-1 0-1 0 1 1 0 0 N
	AT_PADDING 0 0 0-1 0* 0-1 0-1 0 0-1 0-1 0 0 Y
	AT_CHECKCODE 0 0 0-1 0-1 0 0 0 0-1 0-1 0 0 N
	AT_RESULT_IND 0 0 0-1 0-1 0 0 0 0-1 0-1 0 0 N
	AT_MAC 0 0 1 1 0-1 0-1 0 1 1 0 0 N
	AT_COUNTER 0 0 0 0 0-1 0-1 0 1 1 0 0 Y
	AT_COUNTER_TOO_SMALL 0 0 0 0 0 0 0 0 0-1 0 0 Y
	AT_NONCE_S 0 0 0 0 0 0 0 1 0 0 0 Y
	AT_NOTIFICATION 0 0 0 0 1 0 0 0 0 0 0 N
	AT_CLIENT_ERROR_CODE 0 0 0 0 0 0 1 0 0 0 0 N
	It should be noted that attributes AT_PERMANENT_ID_REQ, AT_ANY_ID_REQ
	and AT_FULLAUTH_ID_REQ are mutually exclusive, so that only one of
	them can be included at the same time. If one of the attributes
	AT_IV and AT_ENCR_DATA is included, then both of the attributes MUST
	be included.
	9.2 AT_PERMANENT_ID_REQ
	The format of the AT_PERMANENT_ID_REQ attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|AT_PERM..._REQ | Length = 1 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The use of the AT_PERMANENT_ID_REQ is defined in Section 4.1. The
	value field only contains two reserved bytes, which are set to zero
	on sending and ignored on reception.
	9.3 AT_ANY_ID_REQ
	The format of the AT_ANY_ID_REQ attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|AT_ANY_ID_REQ | Length = 1 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The use of the AT_ANY_ID_REQ is defined in Section 4.1. The value
	field only contains two reserved bytes, which are set to zero on
	sending and ignored on reception.
	9.4 AT_FULLAUTH_ID_REQ
	The format of the AT_FULLAUTH_ID_REQ attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|AT_FULLAUTH_...| Length = 1 | Reserved |
	+---------------+---------------+-------------------------------+
	The use of the AT_FULLAUTH_ID_REQ is defined in Section 4.1. The
	value field only contains two reserved bytes, which are set to zero
	on sending and ignored on reception.
	9.5 AT_IDENTITY
	The format of the AT_IDENTITY attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_IDENTITY | Length | Actual Identity Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	. Identity .
	. .
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The use of the AT_IDENTITY is defined in Section 4.1. The value
	field of this attribute begins with 2-byte actual identity length,
	which specifies the length of the identity in bytes. This field is
	followed by the subscriber identity of the indicated actual length.
	The identity is the permanent identity, a pseudonym identity or a
	fast re-authentication identity. The identity format is specified in
	Section 4.1.1. The same identity format is used in the AT_IDENTITY
	attribute and the EAP-Response/Identity packet, with the exception
	that the peer MUST NOT decorate the identity it includes in
	AT_IDENTITY. The identity does not include any terminating null
	characters. Because the length of the attribute must be a multiple
	of 4 bytes, the sender pads the identity with zero bytes when
	necessary.
	9.6 AT_RAND
	The format of the AT_RAND attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_RAND | Length = 5 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	| RAND |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute contains two reserved bytes
	followed by the AKA RAND parameter, 16 bytes (128 bits). The
	reserved bytes are set to zero when sending and ignored on reception.
	9.7 AT_AUTN
	The format of the AT_AUTN attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_AUTN | Length = 5 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	| AUTN |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute contains two reserved bytes
	followed by the AKA AUTN parameter, 16 bytes (128 bits). The
	reserved bytes are set to zero when sending and ignored on reception.
	9.8 AT_RES
	The format of the AT_RES attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_RES | Length | RES Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
	| |
	| RES |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute begins with the 2-byte RES Length,
	which is identifies the exact length of the RES in bits. The RES
	length is followed by the AKA RES parameter. According to [TS
	33.105] the length of the AKA RES can vary between 32 and 128 bits.
	Because the length of the AT_RES attribute must be a multiple of 4
	bytes, the sender pads the RES with zero bits where necessary.
	9.9 AT_AUTS
	The format of the AT_AUTS attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|
	| AT_AUTS | Length = 4 | |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
	| |
	| AUTS |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute contains the AKA AUTS parameter,
	112 bits (14 bytes).
	9.10 AT_NEXT_PSEUDONYM
	The format of the AT_NEXT_PSEUDONYM attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_NEXT_PSEU..| Length | Actual Pseudonym Length |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	. Next Pseudonym .
	. .
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute begins with 2-byte actual pseudonym
	length which specifies the length of the following pseudonym in
	bytes. This field is followed by a pseudonym username that the peer
	can use in the next authentication. The username MUST NOT include
	any realm portion. The username does not include any terminating
	null characters. Because the length of the attribute must be a
	multiple of 4 bytes, the sender pads the pseudonym with zero bytes
	when necessary. The username encoding MUST follow the UTF-8
	transformation format [RFC2279]. This attribute MUST always be
	encrypted by encapsulating it within the AT_ENCR_DATA attribute.
	9.11 AT_NEXT_REAUTH_ID
	The format of the AT_NEXT_REAUTH_ID attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_NEXT_REAU..| Length | Actual Re-Auth Identity Length|
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	. Next Fast Re-authentication Username .
	. .
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute begins with 2-byte actual
	re-authentication identity length which specifies the length of the
	following fast re-authentication identity in bytes. This field is
	followed by a fast re-authentication identity that the peer can use
	in the next fast re-authentication, as described in Section 5. In
	environments where a realm portion is required, the fast
	re-authentication identity includes both a username portion and a
	realm name portion. The fast re-authentication identity does not
	include any terminating null characters. Because the length of the
	attribute must be a multiple of 4 bytes, the sender pads the fast
	re-authentication identity with zero bytes when necessary. The
	identity encoding MUST follow the UTF-8 transformation format
	[RFC2279]. This attribute MUST always be encrypted by encapsulating
	it within the AT_ENCR_DATA attribute.
	9.12 AT_IV, AT_ENCR_DATA and AT_PADDING
	AT_IV and AT_ENCR_DATA attributes can be used to transmit encrypted
	information between the EAP-AKA peer and server.
	The value field of AT_IV contains two reserved bytes followed by a
	16-byte initialization vector required by the AT_ENCR_DATA attribute.
	The reserved bytes are set to zero when sending and ignored on
	reception. The AT_IV attribute MUST be included if and only if the
	AT_ENCR_DATA is included. Section 6.3 specifies the operation if a
	packet that does not meet this condition is encountered.
	The sender of the AT_IV attribute chooses the initialization vector
	by random. The sender MUST NOT reuse the initialization vector value
	from previous EAP-AKA packets. The sender SHOULD use a good source
	of randomness to generate the initialization vector. Please see
	[RFC1750] for more information about generating random numbers for
	security applications. The format of AT_IV is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_IV | Length = 5 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	| Initialization Vector |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of the AT_ENCR_DATA attribute consists of two
	reserved bytes followed by cipher text bytes encrypted using the
	Advanced Encryption Standard (AES) [AES] with a 128-bit key in the
	Cipher Block Chaining (CBC) mode of operation using the
	initialization vector from the AT_IV attribute. The reserved bytes
	are set to zero when sending and ignored on reception. Please see
	[CBC] for a description of the CBC mode. The format of the
	AT_ENCR_DATA attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_ENCR_DATA | Length | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	. Encrypted Data .
	. .
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The derivation of the encryption key (K_encr) is specified in Section
	6.4.
	The plaintext consists of nested EAP-AKA attributes.
	The encryption algorithm requires the length of the plaintext to be a
	multiple of 16 bytes. The sender may need to include the AT_PADDING
	attribute as the last attribute within AT_ENCR_DATA. The AT_PADDING
	attribute is not included if the total length of other nested
	attributes within the AT_ENCR_DATA attribute is a multiple of 16
	bytes. As usual, the Length of the Padding attribute includes the
	Attribute Type and Attribute Length fields. The length of the
	Padding attribute is 4, 8 or 12 bytes. It is chosen so that the
	length of the value field of the AT_ENCR_DATA attribute becomes a
	multiple of 16 bytes. The actual pad bytes in the value field are
	set to zero (00 hexadecimal) on sending. The recipient of the
	message MUST verify that the pad bytes are set to zero. If this
	verification fails on the peer, then it MUST send the
	EAP-Response/AKA-Client- Error packet with the error code "unable to
	process packet" to terminate the authentication exchange. If this
	verification fails on the server, then the server sends the
	EAP-Response/AKA-Notification packet with an AT_NOTIFICATION code
	that implies failure to terminate the authentication exchange. The
	format of the AT_PADDING attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_PADDING | Length | Padding... |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	9.13 AT_CHECKCODE
	The AT_MAC attribute is not used in the very first EAP-AKA messages
	during the AKA-Identity round, because keying material has not been
	derived yet. The peer and the server may exchange one or more pairs
	of EAP-AKA messages of the Subtype AKA-Identity before keys are
	derived and before the AT_MAC attribute can be applied. The
	EAP/AKA-Identity messages may also be used upon fast
	re-authentication.
	The AT_CHECKCODE attribute MAY be used to protect the
	EAP/AKA-Identity messages. In full authentication, the server MAY
	include the AT_CHECKCODE in EAP-Request/AKA-Challenge, and the peer
	MAY include AT_CHECKCODE in EAP-Response/AKA-Challenge. In fast
	re-authentication, the server MAY include AT_CHECKCODE in
	EAP-Request/AKA-Reauthentication, and the peer MAY include
	AT_CHECKCODE in EAP-Response/AKA-Reauthentication. The fact that the
	peer receives an EAP-Request with AT_CHECKCODE does not imply that
	the peer would have to include AT_CHECKCODE in the corresponding
	response. The peer MAY include AT_CHECKCODE even if the server did
	not include AT_CHECKCODE in the EAP request. Because the AT_MAC
	attribute is used in these messages, AT_CHECKCODE will be integrity
	protected with AT_MAC. The format of the AT_CHECKCODE attribute is
	shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_CHECKCODE | Length | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	| Checkcode (0 or 20 bytes) |
	| |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of AT_CHECKCODE begins with two reserved bytes, which
	may be followed by a 20-byte checkcode. If the checkcode is not
	included in AT_CHECKCODE, then the attribute indicates that no
	EAP/AKA-Identity messages were exchanged. This may occur in both
	full authentication and fast re-authentication. The reserved bytes
	are set to zero when sending and ignored on reception.
	The checkcode is a hash value, calculated with SHA1 [SHA-1], over all
	EAP-Request/AKA-Identity and EAP-Response/ AKA-Identity packets
	exchanged in this authentication exchange. The packets are included
	in the order that they were transmitted, that is, starting with the
	first EAP-Request/ AKA-Identity message, followed by the
	corresponding EAP-Response/ AKA-Identity, followed by the second
	EAP-Request/ AKA-Identity (if used) etc.
	EAP packets are included in the hash calculation "as-is", as they
	were transmitted or received. All reserved bytes, padding bytes etc.
	that are specified for various attributes are included as such, and
	the receiver must not reset them to zero. No delimiter bytes,
	padding or any other framing are included between the EAP packets
	when calculating the checkcode.
	Messages are included in request/response pairs; in other words only
	full "round trips" are included. Packets that are silently discarded
	are not included, and retransmitted packets (that have the same
	Identifier value) are only included once. (The base EAP protocol
	[RFC3748] ensures that requests and responses "match".) The EAP
	server must only include an EAP-Request/AKA-Identity in the
	calculation once it has received a corresponding response, with the
	same Identifier value.
	The peer must include the EAP-Request/AKA-Identity and the
	corresponding response in the calculation only if the peer receives a
	subsequent EAP-Request/AKA-Challenge, or a follow-up
	EAP-Request/AKA-Identity with a different Identifier value than in
	the first EAP-Request/AKA-Identity.
	The AT_CHECKCODE attribute is optional to implement. It is specified
	in order to allow protecting the EAP/AKA-Identity messages and any
	future extensions to them. The implementation of AT_CHECKCODE is
	RECOMMENDED.
	If the receiver of AT_CHECKCODE implements this attribute, then the
	receiver MUST check that the checkcode is correct. If the checkcode
	is invalid, the receiver must operate as specified in Section 6.3.
	If the EAP/AKA-Identity messages are extended with new attributes
	then AT_CHECKCODE MUST be implemented and used. More specifically,
	if the server includes any other attributes than AT_PERMANENT_ID_REQ,
	AT_FULLAUTH_ID_REQ or AT_ANY_ID_REQ in the EAP-Request/AKA-Identity
	packet, then the server MUST include AT_CHECKCODE in
	EAP-Request/AKA-Challenge or EAP-Request/AKA-Reauthentication. If
	the peer includes any other attributes than AT_IDENTITY in the
	EAP-Response/AKA-Identity message, then the peer MUST include
	AT_CHECKCODE in EAP-Response/AKA-Challenge or
	EAP-Response/AKA-Reauthentication.
	If the server implements the processing of any other attribute than
	AT_IDENTITY for the EAP-Response/AKA-Identity message, then the
	server MUST implement AT_CHECKCODE. In this case, if the server
	receives any other attribute than AT_IDENTITY in the EAP-
	Response/AKA-Identity message, then the server MUST check that
	AT_CHECKCODE is present in EAP-Response/AKA-Challenge or EAP-
	Response/AKA-Reauthentication. The operation when a mandatory
	attribute is missing is specified in Section 6.3.
	Similarly, if the peer implements the processing of any other
	attribute than AT_PERMANENT_ID_REQ, AT_FULLAUTH_ID_REQ or
	AT_ANY_ID_REQ for the EAP-Request/AKA-Identity packet, then the peer
	MUST implement AT_CHECKCODE. In this case, if the peer receives any
	other attribute than AT_PERMANENT_ID_REQ, AT_FULLAUTH_ID_REQ or
	AT_ANY_ID_REQ in the EAP-Request/AKA-Identity packet, then the peer
	MUST check that AT_CHECKCODE is present in EAP-Request/AKA-Challenge
	or EAP-Request/AKA-Reauthentication. The operation when a mandatory
	attribute is missing is specified in Section 6.3.
	9.14 AT_RESULT_IND
	The format of the AT_RESULT_IND attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_RESULT_...| Length = 1 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute consists of two reserved bytes,
	which are set to zero upon sending and ignored upon reception. This
	attribute is always sent unencrypted, so it MUST NOT be encapsulated
	within the AT_ENCR_DATA attribute.
	9.15 AT_MAC
	The AT_MAC attribute is used for EAP-AKA message authentication.
	Section 8 specifies which messages AT_MAC MUST be included.
	The value field of the AT_MAC attribute contains two reserved bytes
	followed by a keyed message authentication code (MAC). The MAC is
	calculated over the whole EAP packet, concatenated with optional
	message-specific data, with the exception that the value field of the
	MAC attribute is set to zero when calculating the MAC. The EAP
	packet includes the EAP header that begins with the Code field, the
	EAP-AKA header that begins with the Subtype field, and all the
	attributes, as specified in Section 7.1. The reserved bytes in
	AT_MAC are set to zero when sending and ignored on reception. The
	contents of the message-specific data that may be included in the MAC
	calculation are specified separately for each EAP-AKA message in
	Section 8.
	The format of the AT_MAC attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_MAC | Length = 5 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	| MAC |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The MAC algorithm is HMAC-SHA1-128 [RFC2104] keyed hash value. (The
	HMAC-SHA1-128 value is obtained from the 20-byte HMAC-SHA1 value by
	truncating the output to 16 bytes. Hence, the length of the MAC is
	16 bytes.) The derivation of the authentication key (K_aut) used in
	the calculation of the MAC is specified in Section 6.4.
	When the AT_MAC attribute is included in an EAP-AKA message, the
	recipient MUST process the AT_MAC attribute before looking at any
	other attributes, except when processing EAP-Request/AKA-Challenge.
	The processing of EAP-Request/AKA-Challenge is specified in Section
	8.3. If the message authentication code is invalid, then the
	recipient MUST ignore all other attributes in the message and operate
	as specified in Section 6.3.
	9.16 AT_COUNTER
	The format of the AT_COUNTER attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_COUNTER | Length = 1 | Counter |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of the AT_COUNTER attribute consists of a 16-bit
	unsigned integer counter value, represented in network byte order.
	This attribute MUST always be encrypted by encapsulating it within
	the AT_ENCR_DATA attribute.
	9.17 AT_COUNTER_TOO_SMALL
	The format of the AT_COUNTER_TOO_SMALL attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_COUNTER...| Length = 1 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute consists of two reserved bytes,
	which are set to zero upon sending and ignored upon reception. This
	attribute MUST always be encrypted by encapsulating it within the
	AT_ENCR_DATA attribute.
	9.18 AT_NONCE_S
	The format of the AT_NONCE_S attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| AT_NONCE_S | Length = 5 | Reserved |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| |
	| |
	| NONCE_S |
	| |
	| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of the AT_NONCE_S attribute contains two reserved
	bytes followed by a random number generated by the server (16 bytes)
	freshly for this EAP-AKA fast re-authentication. The random number
	is used as challenge for the peer and also a seed value for the new
	keying material. The reserved bytes are set to zero upon sending and
	ignored upon reception. This attribute MUST always be encrypted by
	encapsulating it within the AT_ENCR_DATA attribute.
	The server MUST NOT reuse the NONCE_S value from a previous EAP-AKA
	fast re-authentication exchange. The server SHOULD use a good source
	of randomness to generate NONCE_S. Please see [RFC1750] for more
	information about generating random numbers for security
	applications.
	9.19 AT_NOTIFICATION
	The format of the AT_NOTIFICATION attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|AT_NOTIFICATION| Length = 1 |S|P| Notification Code |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute contains a two-byte notification
	code. The first and second bit (S and P) of the notification code
	are interpreted as described in Section 6.
	The notification code values listed below have been reserved. The
	descriptions below illustrate the semantics of the notifications.
	The peer implementation MAY use different wordings when presenting
	the notifications to the user. The "requested service" depends on
	the environment where EAP-AKA is applied.
	0 - General failure after authentication. (Implies failure, used
	after successful authentication.)
	16384 - General failure. (Implies failure, used before
	authentication.)
	32768 - Success. User has been successfully authenticated. (Does
	not imply failure, used after successful authentication.) The usage
	of this code is discussed in Section 6.2.
	1026 - User has been temporarily denied access to the requested
	service. (Implies failure, used after successful authentication.)
	1031 - User has not subscribed to the requested service. (Implies
	failure, used after successful authentication.)
	9.20 AT_CLIENT_ERROR_CODE
	The format of the AT_CLIENT_ERROR_CODE attribute is shown below.
	0 1 2 3
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|AT_CLIENT_ERR..| Length = 1 | Client Error Code |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	The value field of this attribute contains a two-byte client error
	code. The following error code values have been reserved.
	0 "unable to process packet": a general error code
	10. IANA and Protocol Numbering Considerations
	IANA has assigned the EAP type number 23 for EAP-AKA authentication.
	EAP-AKA shares most of the protocol design, such as attributes and
	message Subtypes, with EAP-SIM [EAP-SIM]. EAP-AKA protocol numbers
	should be administered in the same IANA registry with EAP-SIM. This
	document establishes the registers and lists the initial protocol
	numbers for both protocols.
	EAP-AKA and EAP-SIM messages include a Subtype field. The Subtype is
	a new numbering space for which IANA administration is required. The
	Subtype is an 8-bit integer. The following Subtypes are specified in
	this document and in [EAP-SIM]:
	AKA-Challenge...................................1
	AKA-Authentication-Reject.......................2
	AKA-Synchronization-Failure.....................4
	AKA-Identity....................................5
	SIM-Start......................................10
	SIM-Challenge..................................11
	AKA-Notification and SIM-Notification..........12
	AKA-Reauthentication and SIM-Reauthentication..13
	AKA-Client-Error and SIM-Client-Error..........14
	The messages are composed of attributes, which have 8-bit attribute
	type numbers. Attributes numbered within the range 0 through 127 are
	called non-skippable attributes, and attributes within the range of
	128 through 255 are called skippable attributes. The EAP-AKA and
	EAP-SIM attribute type number is a new numbering space for which IANA
	administration is required. The following attribute types are
	specified in this document in [EAP-SIM]:
	AT_RAND.........................................1
	AT_AUTN.........................................2
	AT_RES..........................................3
	AT_AUTS.........................................4
	AT_PADDING......................................6
	AT_NONCE_MT.....................................7
	AT_PERMANENT_ID_REQ............................10
	AT_MAC.........................................11
	AT_NOTIFICATION................................12
	AT_ANY_ID_REQ..................................13
	AT_IDENTITY....................................14
	AT_VERSION_LIST................................15
	AT_SELECTED_VERSION............................16
	AT_FULLAUTH_ID_REQ.............................17
	AT_COUNTER.....................................19
	AT_COUNTER_TOO_SMALL...........................20
	AT_NONCE_S.....................................21
	AT_CLIENT_ERROR_CODE...........................22
	AT_IV.........................................129
	AT_ENCR_DATA..................................130
	AT_NEXT_PSEUDONYM.............................132
	AT_NEXT_REAUTH_ID.............................133
	AT_CHECKCODE..................................134
	AT_RESULT_IND.................................135
	The AT_NOTIFICATION attribute contains a 16-bit notification code
	value. The most significant bit of the notification code is called
	the S bit (success) and the second most significant bit is called the
	P bit (phase). If the S bit is set to zero, then the notification
	code indicates failure; notification codes with the S bit set to one
	do not indicate failure. If the P bit is set to zero, then the
	notification code can only be used before authentication has
	occurred. If the P bit is set to one, then the notification code can
	only be used after authentication. The notification code is a new
	numbering space for which IANA administration is required. The
	following values have been specified in this document and in
	[EAP-SIM].
	General failure after authentication......................0
	User has been temporarily denied access................1026
	User has not subscribed to the requested service.......1031
	General failure.......................................16384
	Success...............................................32768
	The AT_VERSION_LIST and AT_SELECTED_VERSION attributes, specified in
	[EAP-SIM], contain 16-bit EAP method version numbers. The EAP method
	version number is a new numbering space for which IANA administration
	is required. Value 1 for "EAP-SIM Version 1" has been specified in
	[EAP-SIM]. Version numbers are not currently used in EAP-AKA.
	The AT_CLIENT_ERROR_CODE attribute contains a 16-bit client error
	code. The client error code is a new numbering space for which IANA
	administration is required. Values 0, 1, 2, and 3 have been
	specified in this document and in [EAP-SIM].
	All requests for value assignment from the various number spaces
	described in this document require proper documentation, according to
	the "Specification Required" policy described in [RFC2434]. Requests
	must be specified in sufficient detail so that interoperability
	between independent implementations is possible. Possible forms of
	documentation include, but are not limited to, RFCs, the products of
	another standards body (e.g. 3GPP), or permanently and readily
	available vendor design notes.
	11. Security Considerations
	The EAP specification [RFC3748] describes the security
	vulnerabilities of EAP, which does not include its own security
	mechanisms. This section discusses the claimed security properties
	of EAP-AKA as well as vulnerabilities and security recommendations.
	11.1 Identity Protection
	EAP-AKA includes optional Identity privacy support that protects the
	privacy of the subscriber identity against passive eavesdropping.
	This document only specifies a mechanism to deliver pseudonyms from
	the server to the peer as part of an EAP-AKA exchange. Hence, a peer
	that has not yet performed any EAP-AKA exchanges does not typically
	have a pseudonym available. If the peer does not have a pseudonym
	available, then the privacy mechanism cannot be used, but the
	permanent identity will have to be sent in the clear. The terminal
	SHOULD store the pseudonym in a non-volatile memory so that it can be
	maintained across reboots. An active attacker that impersonates the
	network may use the AT_PERMANENT_ID_REQ attribute (Section 4.1.2) to
	learn the subscriber's IMSI. However, as discussed in Section 4.1.2,
	the terminal can refuse to send the cleartext IMSI if it believes
	that the network should be able to recognize the pseudonym.
	If the peer and server cannot guarantee that the pseudonym will be
	maintained reliably and Identity privacy is required then additional
	protection from an external security mechanism such as Protected
	Extensible Authentication Protocol (PEAP) [PEAP] may be used. The
	benefits and the security considerations of using an external
	security mechanism with EAP-AKA are beyond the scope of this
	document.
	11.2 Mutual Authentication
	EAP-AKA provides mutual authentication via the 3rd generation AKA
	mechanisms [TS 33.102] and [S.S0055-A].
	Note that this mutual authentication is with the EAP server. In
	general, EAP methods do not authenticate the identity or services
	provided by the EAP authenticator (if distinct from the EAP server)
	unless they provide the so-called channel bindings property. The
	vulnerabilities related to this have been discussed in [RFC3748],
	[EAP Keying], [Service Identity].
	EAP-AKA does not provide the channel bindings property, so it only
	authenticates the EAP server. However, ongoing work such as [Service
	Identity] may provide such support as an extension to popular EAP
	methods such as EAP-TLS, EAP-SIM, or EAP-AKA.
	11.3 Flooding the Authentication Centre
	The EAP-AKA server typically obtains authentication vectors from the
	Authentication Centre (AuC). EAP-AKA introduces a new usage for the
	AuC. The protocols between the EAP-AKA server and the AuC are out of
	the scope of this document. However, it should be noted that a
	malicious EAP-AKA peer may generate a lot of protocol requests to
	mount a denial of service attack. The EAP-AKA server implementation
	SHOULD take this into account and SHOULD take steps to limit the
	traffic that it generates towards the AuC, preventing the attacker
	from flooding the AuC and from extending the denial of service attack
	from EAP-AKA to other users of the AuC.
	11.4 Key Derivation
	EAP-AKA supports key derivation with 128-bit effective key strength.
	The key hierarchy is specified in Section 6.4.
	The Transient EAP Keys used to protect EAP-AKA packets (K_encr,
	K_aut), the Master Session Keys, and the Extended Master Session Keys
	are cryptographically separate. An attacker cannot derive any
	non-trivial information about any of these keys based on the other
	keys. An attacker also cannot calculate the pre-shared secret from
	AKA IK, from AKA CK, from EAP-AKA K_encr, from EAP-AKA K_aut, from
	the Master Session Key, or from the Extended Master Session Key.
	11.5 Brute-Force and Dictionary Attacks
	The effective strength of EAP-AKA values is 128 bits, and there are
	no known computationally feasible brute-force attacks. Because AKA
	is not a password protocol (the pre-shared secret is not a
	passphrase, or derived from a passphrase), EAP-AKA is not vulnerable
	to dictionary attacks.
	11.6 Protection, Replay Protection and Confidentiality
	AT_MAC, AT_IV, AT_ENCR_DATA and AT_COUNTER attributes are used to
	provide integrity, replay and confidentiality protection for EAP-AKA
	Requests and Responses. Integrity protection with AT_MAC includes
	the EAP header. Integrity protection (AT_MAC) is based on a keyed
	message authentication code. Confidentiality (AT_ENCR_DATA and
	AT_IV) is based on a block cipher.
	Because keys are not available in the beginning of the EAP methods,
	the AT_MAC attribute cannot be used for protecting EAP/AKA-Identity
	messages. However, the AT_CHECKCODE attribute can optionally be used
	to protect the integrity of the EAP/AKA-Identity roundtrip.
	Confidentiality protection is applied only to a part of the protocol
	fields. The table of attributes in Section 9.1 summarizes which
	fields are confidentiality protected. It should be noted that the
	error and notification code attributes AT_CLIENT_ERROR_CODE and
	AT_NOTIFICATION are not confidential but they are transmitted in the
	clear. Identity protection is discussed in Section 11.1.
	On full authentication, replay protection of the EAP exchange is
	provided by RAND and AUTN values from the underlying AKA scheme.
	Protection against replays of EAP-AKA messages is also based on the
	fact that messages that can include AT_MAC can only be sent once with
	a certain EAP-AKA Subtype, and on the fact that a different K_aut key
	will be used for calculating AT_MAC in each full authentication
	exchange.
	On fast re-authentication, a counter included in AT_COUNTER and a
	server random nonce is used to provide replay protection. The
	AT_COUNTER attribute is also included in EAP-AKA notifications, if
	they are used after successful authentication in order to provide
	replay protection between re-authentication exchanges.
	The contents of the user identity string are implicitly integrity
	protected by including them in key derivation.
	Because EAP-AKA is not a tunneling method, EAP-Request/Notification,
	EAP-Response/Notification, EAP-Success or EAP-Failure packets are not
	confidential, integrity protected or replay protected. On physically
	insecure networks, this may enable an attacker to mount denial of
	service attacks by spoofing these packets. As discussed in Section
	6.3, the peer will only accept EAP-Success after the peer
	successfully authenticates the server. Hence, the attacker cannot
	force the peer to believe successful mutual authentication has
	occurred before the peer successfully authenticates the server or
	after the peer failed to authenticate the server.
	The security considerations of EAP-AKA result indications are covered
	in Section 11.8
	An eavesdropper will see the EAP Notification, EAP_Success and
	EAP-Failure packets sent in the clear. With EAP-AKA, confidential
	information MUST NOT be transmitted in EAP Notification packets.
	11.7 Negotiation Attacks
	EAP-AKA does not protect the EAP-Response/Nak packet. Because
	EAP-AKA does not protect the EAP method negotiation, EAP method
	downgrading attacks may be possible, especially if the user uses the
	same identity with EAP-AKA and other EAP methods.
	As described in Section 7, EAP-AKA allows the protocol to be extended
	by defining new attribute types. When defining such attributes, it
	should be noted that any extra attributes included in
	EAP-Request/AKA-Identity or EAP-Response/AKA-Identity packets are not
	included in the MACs later on, and thus some other precautions must
	be taken to avoid modifications to them.
	EAP-AKA does not support ciphersuite negotiation or EAP-AKA protocol
	version negotiation.
	11.8 Protected Result Indications
	EAP-AKA supports optional protected success indications, and
	acknowledged failure indications. If a failure occurs after
	successful authentication, then the EAP-AKA failure indication is
	integrity and replay protected.
	Even if an EAP-Failure packet is lost when using EAP-AKA over an
	unreliable medium, then the EAP-AKA failure indications will help
	ensure that the peer and EAP server will know the other parties
	authentication decision. If protected success indications are used,
	then the loss of Success packet will also be addressed by the
	acknowledged, integrity and replay protected EAP-AKA success
	indication. If the optional success indications are not used, then
	the peer may end up believing the server succeeded authentication
	when it actually failed. Since access will not be granted in this
	case protected result indications are not needed unless the client is
	not able to realize it does not have access for an extended period of
	time.
	11.9 Man-in-the-middle Attacks
	In order to avoid man-in-the-middle attacks and session hijacking,
	user data SHOULD be integrity protected on physically insecure
	networks. The EAP-AKA Master Session Key or keys derived from it MAY
	be used as the integrity protection keys, or, if an external security
	mechanism such as PEAP is used, then the link integrity protection
	keys MAY be derived by the external security mechanism.
	There are man-in-the-middle attacks associated with the use of any
	EAP method within a tunneled protocol. For instance, an early
	version of PEAP [PEAP-02] was vulnerable to this attack. This
	specification does not address these attacks. If EAP-AKA is used
	with a tunneling protocol, there should be cryptographic binding
	provided between the protocol and EAP-AKA to prevent
	man-in-the-middle attacks through rogue authenticators being able to
	setup one-way authenticated tunnels. For example, newer versions of
	PEAP include such cryptographic binding. The EAP-AKA Master Session
	Key MAY be used to provide the cryptographic binding. However the
	mechanism how the binding is provided depends on the tunneling
	protocol and is beyond the scope of this document.
	11.10 Generating Random Numbers
	An EAP-AKA implementation SHOULD use a good source of randomness to
	generate the random numbers required in the protocol. Please see
	[RFC1750] for more information on generating random numbers for
	security applications.
	12. Security Claims
	This section provides the security claims required by [RFC3748].
	Auth. Mechanism: EAP-AKA is based on the AKA mechanism, which is an
	authentication and key agreement mechanism based on a symmetric
	128-bit pre-shared secret.
	Ciphersuite negotiation: No
	Mutual authentication: Yes (Section 11.2)
	Integrity protection: Yes (Section 11.6)
	Replay protection: Yes (Section 11.6)
	Confidentiality: Yes, except method specific success and failure
	indications (Section 11.1, Section 11.6)
	Key derivation: Yes
	Key strength: EAP-AKA supports key derivation with 128-bit effective
	key strength.
	Description of key hierarchy: Please see Section 6.4.
	Dictinary attack protection: N/A (Section 11.5)
	Fast reconnect: Yes
	Cryptographic binding: N/A
	Session independence: Yes (Section 11.4)
	Fragmentation: No
	Channel binding: No
	Indication of vulnerabilities. Vulnerabilities are discussed in
	Section 11.
	13. Acknowledgements and Contributions
	The authors wish to thank Rolf Blom of Ericsson, Bernard Aboba of
	Microsoft, Arne Norefors of Ericsson, N.Asokan of Nokia, Valtteri
	Niemi of Nokia, Kaisa Nyberg of Nokia, Jukka-Pekka Honkanen of Nokia,
	Pasi Eronen of Nokia, Olivier Paridaens of Alcatel and Ilkka Uusitalo
	of Ericsson for interesting discussions in this problem space.
	Many thanks to Yoshihiro Ohba for reviewing the document.
	This protocol has been partly developed in parallel with EAP-SIM
	[EAP-SIM], and hence this specification incorporates many ideas from
	EAP-SIM, and many contributions from the reviewer's of EAP-SIM.
	The attribute format is based on the extension format of Mobile IPv4
	[RFC3344].
	14. References
	14.1 Normative References
	[TS 33.102]
	3rd Generation Partnership Project, "3GPP Technical
	Specification 3GPP TS 33.102 V5.1.0: "Technical
	Specification Group Services and System Aspects; 3G
	Security; Security Architecture (Release 5)"", December
	2002.
	[S.S0055-A]
	3rd Generation Partnership Project 2, "3GPP2 Enhanced
	Cryptographic Algorithms", September 2003.
	[RFC2486] Aboba, B. and M. Beadles, "The Network Access Identifier",
	RFC 2486, January 1999.
	[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H.
	Levkowetz, "Extensible Authentication Protocol (EAP)", RFC
	3748, June 2004.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.
	[TS 23.003]
	3rd Generation Partnership Project, "3GPP Technical
	Specification 3GPP TS 23.003 V5.5.1: "3rd Generation
	Parnership Project; Technical Specification Group Core
	Network; Numbering, addressing and identification (Release
	5)"", January 2003.
	[RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:
	Keyed-Hashing for Message Authentication", RFC 2104,
	February 1997.
	[AES] National Institute of Standards and Technology, "Federal
	Information Processing Standards (FIPS) Publication 197,
	"Advanced Encryption Standard (AES)"", November 2001.
	http://csrc.nist.gov/publications/fips/fips197/fips-197.pd
	f
	[CBC] National Institute of Standards and Technology, "NIST
	Special Publication 800-38A, "Recommendation for Block
	Cipher Modes of Operation - Methods and Techniques"",
	December 2001.
	http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-3
	8a.pdf
	[SHA-1] National Institute of Standards and Technology, U.S.
	Department of Commerce, "Federal Information Processing
	Standard (FIPS) Publication 180-1, "Secure Hash
	Standard"", April 1995.
	[PRF] National Institute of Standards and Technology, "Federal
	Information Processing Standards (FIPS) Publication 186-2
	(with change notice); Digital Signature Standard (DSS)",
	January 2000.
	Available on-line at:
	http://csrc.nist.gov/publications/fips/fips186-2/fips186-2
	-change1.pdf
	[TS 33.105]
	3rd Generation Partnership Project, "3GPP Technical
	Specification 3GPP TS 33.105 4.1.0: "Technical
	Specification Group Services and System Aspects; 3G
	Security; Cryptographic Algorithm Requirements (Release
	4)"", June 2001.
	[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
	10646", RFC 2279, January 1998.
	[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
	IANA Considerations Section in RFCs", BCP 26, RFC 2434,
	October 1998.
	14.2 Informative References
	[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes",
	RFC 2548, March 1999.
	[PEAP] Palekar, A., Simon, D., Zorn, G., Salowey, J., Zhou, H.
	and S. Josefsson, "Protected EAP Protocol (PEAP) Version
	2", draft-josefsson-pppext-eap-tls-eap-09 (work in
	progress), October 2004.
	[PEAP-02] Anderson, H., Josefsson, S., Zorn, G., Simon, D. and A.
	Palekar, "Protected EAP Protocol (PEAP)",
	draft-josefsson-pppext-eap-tls-eap-02 (work in progress),
	February 2002.
	[EAP Keying]
	Aboba, B., Simon, D., Arkko, J., Eronen, P. and H.
	Levkowetz, "Extensible Authentication Protocol (EAP) Key
	Management Framework", draft-ietf-eap-keying-04 (work in
	progress), November 2004.
	[Service Identity]
	Arkko, J. and P. Eronen, "Authenticated Service
	Information for the Extensible Authentication Protocol
	(EAP)", draft-arkko-service-identity-auth-01 (work in
	progress), October 2004.
	[RFC1750] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
	Recommendations for Security", RFC 1750, December 1994.
	[RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344,
	August 2002.
	[EAP-SIM] Haverinen, H. and J. Salowey, "Extensible Authentication
	Protocol Method for GSM Subscriber Identity Modules
	(EAP-SIM)", draft-haverinen-pppext-eap-sim-15 (work in
	progress), November 2004.
	[Draft 3GPP TS 23.003]
	3rd Generation Partnership Project, "Draft 3GPP Technical
	Specification 3GPP TS 23.003 V 6.1.0: "3rd Generation
	Partnership Project; Technical Specification Group Core
	Network; Numbering, addressing and identification (Release
	6)", December 2003.
	work in progress
	Authors' Addresses
	Jari Arkko
	Ericsson
	FIN-02420 Jorvas
	Finland
	Phone: +358 40 5079256
	EMail: jari.Arkko@ericsson.com
	Henry Haverinen
	Nokia Enterprise Solutions
	P.O. Box 12
	FIN-40101 Jyvaskyla
	Finland
	EMail: henry.haverinen@nokia.com
	Appendix A. Pseudo-Random Number Generator
	The "|" character denotes concatenation, and "^" denotes
	exponentiation.
	Step 1: Choose a new, secret value for the seed-key, XKEY
	Step 2: In hexadecimal notation let
	t = 67452301 EFCDAB89 98BADCFE 10325476 C3D2E1F0
	This is the initial value for H0|H1|H2|H3|H4
	in the FIPS SHS [SHA-1]
	Step 3: For j = 0 to m - 1 do
	3.1 XSEED_j = 0 /* no optional user input */
	3.2 For i = 0 to 1 do
	a. XVAL = (XKEY + XSEED_j) mod 2^b
	b. w_i = G(t, XVAL)
	c. XKEY = (1 + XKEY + w_i) mod 2^b
	3.3 x_j = w_0|w_1
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