TOC 
Network Working GroupZ. Cao
Internet-DraftH. Deng
Intended status: Standards TrackChina Mobile
Expires: November 12, 2010Y. Wang
 Q. Wu
 Huawei Technologies Co., Ltd.
 G. Zorn, Ed.
 Network Zen
 May 11, 2010


EAP Re-authentication Protocol Extensions for Authenticated Anticipatory Keying (ERP/AAK)
draft-ietf-hokey-erp-aak-02

Abstract

The Extensible Authentication Protocol (EAP) is a generic framework supporting multiple types of authentication methods.

The EAP Re-authentication Protocol (ERP) specifies extensions to EAP and the EAP keying hierarchy to support an EAP method-independent protocol for efficient re-authentication between the peer and an EAP re-authentication server through any authenticator.

Authenticated Anticipatory Keying (AAK) is a method by which cryptographic keying material may be established prior to handover upon one or more candidate attachment points (CAPs), AAK uses the AAA infrastructure for key transport.

This document specifies the extensions necessary to enable AAK support in ERP.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as “work in progress.”

This Internet-Draft will expire on November 12, 2010.

Copyright Notice

Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.



Table of Contents

1.  Introduction
2.  Terminology
    2.1.  Standards Language
    2.2.  Acronyms
3.  ERP/AAK Overview
4.  ERP/AAK Key Hierarchy
5.  Packet and TLV Extension
    5.1.  EAP-Initiate/Re-auth-Start Packet Extension
    5.2.  EAP-Initiate/Re-auth Packet Extension
    5.3.  EAP-Finish/Re-auth extension
    5.4.  TV/TLV and sub-TLV Attributes
6.  Lower Layer Considerations
7.  AAA Transport Considerations
8.  Security Considerations
9.  IANA Considerations
10.  References
    10.1.  Normative References
    10.2.  Informative References




 TOC 

1.  Introduction

The Extensible Authentication Protocol (EAP) [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.) is a generic framework supporting multiple types of authentication methods. In systems where EAP is used for authentication, it is desirable to not repeat the entire EAP exchange with another authenticator. The EAP Re-authentication Protocol (ERP) [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) specifies extensions to EAP and the EAP keying hierarchy to support an EAP method-independent protocol for efficient re-authentication between the peer and an EAP re-authentication server through any authenticator. The re-authentication server may be in the home network or in the local network to which the peer is connecting.

Authenticated Anticipatory Keying (AAK) [RFC5836] (Ohba, Y., Wu, Q., and G. Zorn, “Extensible Authentication Protocol (EAP) Early Authentication Problem Statement,” April 2010.) is a method by which cryptographic keying material may be established prior to handover upon one or more candidate attachment points (CAPs). AAK utilizes the AAA infrastructure for key transport.

This document specifies the extensions necessary to enable AAK support in ERP.



 TOC 

2.  Terminology



 TOC 

2.1.  Standards Language

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 RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119]



 TOC 

2.2.  Acronyms

The following acronyms are used in this document; see the references for more details.

AAA
Authentication, Authorization and Accounting [RFC3588] (Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” September 2003.)
CAP
Candidate Attachment Point [RFC5836] (Ohba, Y., Wu, Q., and G. Zorn, “Extensible Authentication Protocol (EAP) Early Authentication Problem Statement,” April 2010.)
EA
Abbreviation for "ERP/AAK"; used in figures
MH
Mobile Host
SAP
Serving Attachment Point [RFC5836] (Ohba, Y., Wu, Q., and G. Zorn, “Extensible Authentication Protocol (EAP) Early Authentication Problem Statement,” April 2010.)



 TOC 

3.  ERP/AAK Overview

ERP/AAK is intended to allow the establishment of cryptographic keying materials on one or more Candidate Attachment Points prior to the arrival of the MH at the Candidate Access Network (CAN). The document also specifies a method by which the SAP may send the identities of neighboring attachment points to the peer in the EAP-Initiate/Re-auth-Start message.

It is assumed that the peer has previously completed full EAP authentication. Figure 1 (ERP/AAK Operation) shows the general protocol exchange by which the keying material is established on the CAP(s).


+------+    +-----+    +-----+    +-----+    +-----------+
| Peer |    | SAP |    |CAP1 |    |CAPx |    | EA Server |
+--+---+    +--+--+    +--+--+    +--+--+    +-----+-----+
   |           |          |          |             |
1. | [EAP-Initiate/       |          |             |
   | Re-auth-start        |          |             |
   | (E-flag)  |          |          |             |
   |<----------|          |          |             |
   |           |          |          |             |
2. | EAP-Initiate/        |          |             |
   | Re-auth   |          |          |             |
   | (E-flag)  |          |          |             |
   |---------->|          |          |             |
3. |           | AAA (EAP-Initiate/Re-auth(E-flag))|
   |           |---------------------------------->|
   |           |          |          |             |
   |           |          |          |   +---------+---------+
   |           |          |          |   | CA authorized &   |
4. |           |          |          |   | authenticated;    |
   |           |          |          |   | EE keying         |
   |           |          |          |   | materials derived |
   |           |          |          |   +---------+---------+
   |           |          |          |             |
5. |           |          |          | AAA(pMSKx)  |
   |           |          |AAA(pMSK1)|<----------->|
   |           |          |<---------------------->|
   |           |          |          |             |
6. |           | AAA (EAP-Finish/Re-auth(E-flag))  |
   |           |<----------------------------------|
   |           |          |          |             |
7. | EAP-Finish/          |          |             |
   | Re-auth(E-flag)      |          |             |
   |<----------|          |          |             |
   |           |          |          |             |

 Figure 1: ERP/AAK Operation 

ERP/AAK re-uses the packet format defined by ERP, but specifies a new flag to differentiate EAP early-authentication from EAP re-authentication. The peer initiates ERP/AAK itself, or does so in response to an EAP-Initiate/Re-Auth-Start message from the SAP. In this document, it is required that the SAP should support ERP/AAK. If either the peer or the SAP does not support ERP/AAK, it should fall back to full EAP authentication.

The peer sends an early-authentication request message (EAP-Initiate/Re-auth with the ‘E’ flag set) containing the keyName-NAI, the NAS-Identifier, rIK and sequence number. The realm in the keyName-NAI field is used to locate the peer’s ERP/AAK server. The NAS-Identifier is used to identify the CAP(s). The rIK is used to protect the message. The sequence number is used for replay protection. To avoid the same pre-established Master Session Key (pMSK) being derived for multiple CAPs, the sequence number MUST be unique for each CAP.

The SAP encapsulates the early-authentication message into a AAA message and sends it to the peer’s ERP/AAK server in the realm indicated in the keyName-NAI field.

Upon receiving the message, the ERP/AAK server first checks its integrity and freshness, then authenticates and authorizes the CAP(s) presented in the NAS-Identifier TLV(s). After the CAP(s) is authenticated and authorized successfully, the ERP/AAK server derives the pRK and the subsequent pMSK for each CAP.

The ERP/AAK server transports the pMSK to the authenticated and authorized CAP(s) via AAA as described in Section 7 (AAA Transport Considerations). After the keying materials are delivered, the ERP/AAK server should determine each CA whether accepts the pMSK and whether the peer could be attached to.

At last, the ERP/AAK server sends the early-authentication finish message (EAP-Finish/Re-auth with E-flag) containing the determinate CAP(s) to the peer via the SAP.



 TOC 

4.  ERP/AAK Key Hierarchy

As an optimization of ERP, ERP/AAK uses key hierarchy similar to that of ERP. The EMSK is used to derive the ERP/AAK pre-established Root Key (pRK). Similarly, the ERP/AAK pre-established Integrity Key (pIK) and the pre-established Master Session Key (pMSK) are derived from the pRK. The pMSK is established for the CAP(s) when the peer early authenticates to the network. The pIK is established for the peer to re-authenticate the network after handover. The hierarchy relationship is illustrated in Figure 2, below.


    DSRK    EMSK
     |       |
 +---+---+---+---+
 |       |       |
pRK     rRK     ...

 Figure 2 

The EMSK and DSRK both can be used to derive the pRK. In general, the pRK is derived from the EMSK in case of the peer moving in the home AAA realm and derived from the DRSK in case of the peer moving in the visited AAA realm. The DSRK is delivered from the EAP server to the ERP/AAK server as specified in [I‑D.ietf‑dime‑local‑keytran] (Zorn, G., Wu, W., and V. Cakulev, “Diameter Attribute-Value Pairs for Cryptographic Key Transport,” May 2010.). If the peer has previously authenticated by means of ERP or ERP/AAK, the DSRK SHOULD be directly re-used.

         pRK
          |
 +--------+--------+
 |        |        |
pIK     pMSK      ...

 Figure 3 

The pRK is used to derive the pIK and pMSK for the CAP(s). Different sequence numbers for each CAP MUST be used to derive the unique pMSK(s).



 TOC 

5.  Packet and TLV Extension

This section describes the packet and TLV extensions for the ERP/AAK exchange.



 TOC 

5.1.  EAP-Initiate/Re-auth-Start Packet Extension

Figure 4 shows the changed parameters contained in the EAP-Initiate/Re-auth-Start packet defined in RFC 5296 (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) [RFC5296].



 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      |E| Reserved    |     1 or more TVs or TLVs     ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 4 

Flags

‘E’ – The E flag is used to indicate early-authentication.

Reserved: MUST be set to 0.

TVs and TLVs

NAS-Identifier: As defined in [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.), it is carried in a TLV payload. It is used by the SAP to advertise the identifier(s) of CAP(s) to the peer. One or more NAS-Identifier TLVs MAY be included in the EAP-Initiate/Re-auth-Start packet if the SAP has performed CAP discovery.

If the EAP-Initiate/Re-auth-Start packet is not supported by the peer, it is discarded silently.



 TOC 

5.2.  EAP-Initiate/Re-auth Packet Extension

Figure 5 illustrates the changed parameters contained in the EAP-Initiate/Re-auth packet defined in RFC 5296 (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) [RFC5296].



 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      |R|x|L|E|Resved |             SEQ               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 1 or more TVs or TLVs                         ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptosuite  |         Authentication Tag                     ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 Figure 5 

Flags

'x' – The x flag is reserved. It MUST be set to 0.

'E’ – The E flag is used to indicate early-authentication.

The rest of the 4 bits (Resved) MUST be set to 0 and ignored on reception.

SEQ

A 16-bit sequence number is used for replay protection.

TVs and TLVs

keyName-NAI: As defined in RFC 5296 (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) [RFC5296], this is carried in a TLV payload. The Type is 1. The NAI is variable in length, not exceeding 253 octets. The username part of the NAI is the EMSKname used identify the peer. The realm part of the NAI is the peer’s home domain name or the domain to which the peer is currently attached. Exactly one keyName-NAI attribute SHALL be present in an EAP-Initiate/Re-auth packet.

NAS-Identifier: As defined in RFC 5296 (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) [RFC5296], it is carried in a TLV payload. It is used to indicate the identifier of a CAP. One or more NAS-Identifier may be included in the EAP-Initiate/Re-auth packet.

Sequence number: It is carried in a TV payload. The Type is TBD (which is lower than 128). It is used in the derivation of the pMSK for each CAP to avoid multiple CAP using the same pMSK. Each NAS-Identifier in the packet MUST be associated with a unique sequence number.

Cryptosuite

This field indicates the integrity algorithm used for ERP/AAK. Key lengths and output lengths are either indicated or are obvious from the cryptosuite name. We specify some cryptosuites below:

0
RESERVED
1
HMAC-SHA256-64
2
HMAC-SHA256-128
3
HMAC-SHA256-256

HMAC-SHA256-128 is mandatory to implement and should be enabled in the default configuration.

Authentication Tag

This field contains the integrity checksum over the ERP/AAK packet, excluding the authentication tag field itself. The length of the field is indicated by the Cryptosuite.

If the EAP-Initiate/Re-auth packet is not supported by the SAP, it is discarded silently.



 TOC 

5.3.  EAP-Finish/Re-auth extension

Figure 6 shows the changed parameters contained in the EAP-Finish/Re-auth packet defined in [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.).


 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      |R|x|L|E|Resved |             SEQ               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                 1 or more TVs or TLVs                         ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cryptosuite  |         Authentication Tag                     ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 Figure 6 

Flags

'x' – The x flag is reserved. It MUST be set to 0.

‘E’ – The E flag is used to indicate early-authentication.

The rest of the 4 bits (Resved) MUST be set to 0 and ignored on reception.

SEQ

A 16-bit sequence number is used for replay protection.

TVs and TLVs

keyName-NAI: As defined in[RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.), this is carried in a TLV payload. The Type is 1. The NAI is variable in length, not exceeding 253 octets. The realm part of the NAI is the home domain name. Exactly one keyName-NAI attribute SHALL be present in an EAP-Finish/Re-auth packet.

ERP/AAK-Key: It is carried in a TLV payload for the key container. The type is TBD. One or more than one ERP/AAK-key may be present in an EAP-Finish/Re-auth packet.

ERP/AAK-Key ::=
     { sub-TLV: NAS-Identifier }
     { sub-TLV: pMSK-lifetime }
     { sub-TLV: pRK-lifetime }
     { sub-TLV: Cryptosuites }

NAS-Identifier: It is carried in a sub-TLV payload. It is used to indicate the identifier of candidate authenticator. There exactly one instance of the NAS-Identifier TLV MUST be present in the ERP/AAK-Key TLV.

pMSK-lifetime: It is carried in a sub-TLV payload. The Type is TBD. The value field is a 32-bit field and contains the lifetime of the pMSK in seconds. If the 'L' flag is set, the pMSK Lifetime attribute SHOULD be present.

pRK-lifetime: It is carried in a sub-TLV payload. The Type is TBD. The value field is a 32-bit field and contains the lifetime of the pRK in seconds. If the 'L' flag is set, the pRK Lifetime attribute SHOULD be present.

List of Cryptosuites: This is a sub-TLV payload. The Type is TBD. The value field contains a list of cryptosuites, each 1 octet in length. The allowed cryptosuite values are as specified in Section 5.2 (EAP-Initiate/Re-auth Packet Extension), above. The server SHOULD include this attribute if the cryptosuite used in the EAP-Initiate/Re-auth message was not acceptable and the message is being rejected. The server MAY include this attribute in other cases. The server MAY use this attribute to signal to the peer about its cryptographic algorithm capabilities.

Cryptosuite

This field indicates the integrity algorithm and PRF used for ERP/AAK. Key lengths and output lengths are either indicated or are obvious from the cryptosuite name.

Authentication Tag

This field contains the integrity checksum over the ERP/AAK packet, excluding the authentication tag field itself. The length of the field is indicated by the Cryptosuite.



 TOC 

5.4.  TV/TLV and sub-TLV Attributes

The TV and TLV attributes are the same specified as section 5.3.4 of [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.). In this document, some new TLV(s) which may be present in the EAP-Initiate or EAP-Finish messages are defined as below:

Sequence number - This is a TV payload. The type is TBD.

ERP/AAK-Key - This is a TLV payload. The type is TBD.

The format of sub-TLV attributes that may be present in the EAP-Initiate or EAP-Finish messages is:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |    Length     |            Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The following types are defined in this document:

pRK Lifetime: This is a TV payload. The type of this sub-TLV is TBD.

pMSK Lifetime: This is a TV payload. The type of this sub-TLV is TBD.

List of Cryptosuites: This is a TLV payload. The type of this sub-TLV is TBD.



 TOC 

6.  Lower Layer Considerations

Similar to ERP, some lower layer specifications may need to be revised to support ERP/AAK; refer to section 6 of [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.) for additional guidance.



 TOC 

7.  AAA Transport Considerations

AAA transport of ERP/AAK messages is the same as AAA transport of the ERP message [RFC5296] (Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” August 2008.). In addition, the document requires AAA transport of the ERP/AAK keying materials delivered by the ERP/AAK server to the CAP. Hence, a new Diameter ERP/AAK application message should be specified to transport the keying materials.



 TOC 

8.  Security Considerations

TBD.



 TOC 

9.  IANA Considerations

New TLV types:

NAS-Identifier

Sequence number

ERP/AAK-Key

New sub-TLV types:

NAS-Identifier

pRK Lifetime

pMSK Lifetime

List of Cryptosuites



 TOC 

10.  References



 TOC 

10.1. Normative References

[RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).
[RFC5296] Narayanan, V. and L. Dondeti, “EAP Extensions for EAP Re-authentication Protocol (ERP),” RFC 5296, August 2008 (TXT).


 TOC 

10.2. Informative References

[I-D.ietf-dime-local-keytran] Zorn, G., Wu, W., and V. Cakulev, “Diameter Attribute-Value Pairs for Cryptographic Key Transport,” draft-ietf-dime-local-keytran-03 (work in progress), May 2010 (TXT).
[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, “Diameter Base Protocol,” RFC 3588, September 2003 (TXT).
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” RFC 3748, June 2004 (TXT).
[RFC5836] Ohba, Y., Wu, Q., and G. Zorn, “Extensible Authentication Protocol (EAP) Early Authentication Problem Statement,” RFC 5836, April 2010 (TXT).


 TOC 

Authors' Addresses

  Zhen Cao
  China Mobile
  53A Xibianmennei Ave., Xuanwu District
  Beijing, Beijing 100053
  P.R. China
EMail:  zehn.cao@gmail.com
  
  Hui Deng
  China Mobile
  53A Xibianmennei Ave., Xuanwu District
  Beijing, Beijing 100053
  P.R. China
EMail:  denghui02@gmail.com
  
  Yungui Wang
  Huawei Technologies Co., Ltd.
  Floor 10, HuiHong Mansion, No.91 BaiXia Rd.
  Nanjing, Jiangsu 210001
  P.R. China
Phone:  +86 25 84565893
EMail:  w52006@huawei.com
  
  Qin Wu
  Huawei Technologies Co., Ltd.
  Floor 12, HuiHong Mansion, No.91 BaiXia Rd.
  Nanjing, Jiangsu 210001
  P.R. China
Phone:  +86 25 84565892
EMail:  sunseawq@huawei.com
  
  Glen Zorn (editor)
  Network Zen
  1463 East Republican Street
  #358
  Seattle, Washington 98112
  USA
EMail:  gwz@net-zen.net