< draft-ietf-ipsec-ciph-aes-ccm-03.txt		draft-ietf-ipsec-ciph-aes-ccm-04.txt >
	IPsec Working Group R. Housley		IPsec Working Group R. Housley
	Internet Draft Vigil Security		Internet Draft Vigil Security
	expires in six months May 2003		expires in six months July 2003
	Using AES CCM Mode With IPsec ESP		Using AES CCM Mode With IPsec ESP
	<draft-ietf-ipsec-ciph-aes-ccm-03.txt>		<draft-ietf-ipsec-ciph-aes-ccm-04.txt>
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is in full conformance with all		This document is an Internet-Draft and is in full conformance with all
	provisions of Section 10 of RFC2026.		provisions of Section 10 of RFC2026.
	Internet-Drafts are working documents of the Internet Engineering Task		Internet-Drafts are working documents of the Internet Engineering Task
	Force (IETF), its areas, and its working groups. Note that other		Force (IETF), its areas, and its working groups. Note that other
	groups may also distribute working documents as Internet-Drafts.		groups may also distribute working documents as Internet-Drafts.
	skipping to change at page 8, line 15 ¶		skipping to change at page 8, line 15 ¶
	7.1. Keying Material and Salt Values		7.1. Keying Material and Salt Values
	As previously described, implementations MUST use fresh keys with		As previously described, implementations MUST use fresh keys with
	AES-CCM. IKE can be used to establish fresh keys. This section		AES-CCM. IKE can be used to establish fresh keys. This section
	describes the conventions for obtaining the unpredictable salt value		describes the conventions for obtaining the unpredictable salt value
	for use in the nonce from IKE. Note that this convention provides a		for use in the nonce from IKE. Note that this convention provides a
	salt value that is secret as well as unpredictable.		salt value that is secret as well as unpredictable.
	IKE makes use of a pseudo-random function (PRF) to derive keying		IKE makes use of a pseudo-random function (PRF) to derive keying
	material. The PRF is used iteratively to derive keying material of		material. The PRF is used iteratively to derive keying material of
	arbitrary size. Keying material is extracted from the output string		arbitrary size, called KEYMAT. Keying material is extracted from the
	without regard to boundaries.		output string without regard to boundaries.
	IKE uses the PRF to generate an output stream that parsed into five
	keys: SK_d, SK_ai, SK_ar, SK_ei, and SK_er. SK_d is used to derive
	new keys for the child security associations. SK_ai and SK_ar are
	the authentication keys for the initiator and the responder,
	respectively. SK_ei and SK_er are the encryption keys for the
	initiator and the responder, respectively.
	SK_ai and SK_ei are used to protect traffic from the initiator to the
	responder. SK_ar and SK_er are used to protect traffic from the
	responder to the initiator.
	The size of SK_ei and SK_er are each three octets longer than is		The size of KEYMAT MUST be three octets longer than is needed for the
	needed by the associated AES key. The keying material is used as		associated AES key. The keying material is used as follows:
	follows:
	AES-CCM with a 128 bit key		AES-CCM with a 128 bit key
	SK_ei and SK_er are each 19 octets. The first 16 octets are		The KEYMAT requested for each AES-CCM key is 19 octets. The
	the 128-bit AES key, and the remaining three octets are used as		first 16 octets are the 128-bit AES key, and the remaining
	the salt value in the counter block.		three octets are used as the salt value in the counter block.
	AES-CCM with a 192 bit key		AES-CCM with a 192 bit key
	SK_ei and SK_er are each 27 octets. The first 24 octets are		The KEYMAT requested for each AES-CCM key is 27 octets. The
	the 192-bit AES key, and the remaining three octets are used as		first 24 octets are the 192-bit AES key, and the remaining
	the salt value in the counter block.		three octets are used as the salt value in the counter block.
	AES-CCM with a 256 bit key		AES-CCM with a 256 bit key
	SK_ei and SK_er are each 35 octets. The first 32 octets are		The KEYMAT requested for each AES-CCM key is 35 octets. The
	the 256-bit AES key, and the remaining three octets are used as		first 32 octets are the 256-bit AES key, and the remaining
	the salt value in the counter block.		three octets are used as the salt value in the counter block.
	7.2. Phase 1 Identifier		7.2. Phase 1 Identifier
	This document does not specify the conventions for using AES-CCM for		This document does not specify the conventions for using AES-CCM for
	IKE Phase 1 negotiations. For AES-CCM to be used in this manner, a		IKE Phase 1 negotiations. For AES-CCM to be used in this manner, a
	separate specification is needed, and an Encryption Algorithm		separate specification is needed, and an Encryption Algorithm
	Identifier needs to be assigned.		Identifier needs to be assigned.
	7.3. Phase 2 Identifier		7.3. Phase 2 Identifier
	skipping to change at page 9, line 16 ¶		skipping to change at page 9, line 4 ¶
	7.3. Phase 2 Identifier		7.3. Phase 2 Identifier
	For IKE Phase 2 negotiations, IANA has assigned three ESP Transform		For IKE Phase 2 negotiations, IANA has assigned three ESP Transform
	Identifiers for AES-CCM with an explicit IV:		Identifiers for AES-CCM with an explicit IV:
	<TBD1> for AES-CCM with an 8 octet ICV;		<TBD1> for AES-CCM with an 8 octet ICV;
	<TBD2> for AES-CCM with a 12 octet ICV; and		<TBD2> for AES-CCM with a 12 octet ICV; and
	<TBD3> for AES-CCM with a 16 octet ICV.		<TBD3> for AES-CCM with a 16 octet ICV.
	7.4. Key Length Attribute		7.4. Key Length Attribute
	Since the AES supports three key lengths, the Key Length attribute		Since the AES supports three key lengths, the Key Length attribute
	MUST be specified in the IKE Phase 2 exchange [DOI]. The Key Length		MUST be specified in the IKE Phase 2 exchange [DOI]. The Key Length
	attribute MUST have a value of 128, 192, or 256.		attribute MUST have a value of 128, 192, or 256.
	8. Test Vectors		8. Test Vectors
	To be supplied.		Section 8 of [CCM] provides test vectors that will assist
			implementers with AES-CCM mode.
	9. Security Considerations		9. Security Considerations
	AES-CCM employs counter (CTR) mode for confidentiality. If a counter		AES-CCM employs counter (CTR) mode for confidentiality. If a counter
	value is ever used for more that one packet with the same key, then		value is ever used for more that one packet with the same key, then
	the same key stream will be used to encrypt both packets, and the		the same key stream will be used to encrypt both packets, and the
	confidentiality guarantees are voided.		confidentiality guarantees are voided.
	What happens if the encryptor XORs the same key stream with two		What happens if the encryptor XORs the same key stream with two
	different packet plaintexts? Suppose two packets are defined by two		different packet plaintexts? Suppose two packets are defined by two
	skipping to change at page 10, line 23 ¶		skipping to change at page 10, line 11 ¶
	When IKE is used to establish fresh keys between two peer entities,		When IKE is used to establish fresh keys between two peer entities,
	separate keys are established for the two traffic flows. If a		separate keys are established for the two traffic flows. If a
	different mechanism is used to establish fresh keys, one that		different mechanism is used to establish fresh keys, one that
	establishes only a single key to encrypt packets, then there is a		establishes only a single key to encrypt packets, then there is a
	high probability that the peers will select the same IV values for		high probability that the peers will select the same IV values for
	some packets. Thus, to avoid counter block collisions, ESP		some packets. Thus, to avoid counter block collisions, ESP
	implementations that permit use of the same key for encrypting and		implementations that permit use of the same key for encrypting and
	decrypting packets with the same peer MUST ensure that the two peers		decrypting packets with the same peer MUST ensure that the two peers
	assign different salt values to the security association (SA).		assign different salt values to the security association (SA).
	AES with a 128-bit key is vulnerable to the birthday attack after		Regardless of the mode used, AES with a 128-bit key is vulnerable to
	2^64 blocks are encrypted with a single key, regardless of the mode		the birthday attack after 2^64 blocks are encrypted with a single
	used. Since ESP with Extended Sequence Numbers allows for up to 2^64		key. Since ESP with Extended Sequence Numbers allows for up to 2^64
	packets in a single security association (SA), there is real		packets in a single security association (SA), there is real
	potential for more than 2^64 blocks to be encrypted with one key.		potential for more than 2^64 blocks to be encrypted with one key.
	Implementations SHOULD generate a fresh key before 2^64 blocks are		Implementations SHOULD generate a fresh key before 2^64 blocks are
	encrypted with the same key, or implementations SHOULD make use of		encrypted with the same key, or implementations SHOULD make use of
	the longer AES key sizes. Note that ESP with 32-bit Sequence Numbers		the longer AES key sizes. Note that ESP with 32-bit Sequence Numbers
	will not exceed 2^64 blocks even if all of the packets are maximum-		will not exceed 2^64 blocks even if all of the packets are maximum-
	length Jumbograms.		length Jumbograms.
	10. Design Rationale		10. Design Rationale
	skipping to change at page 11, line 9 ¶		skipping to change at page 10, line 44 ¶
	1. Only the encryptor can ensure that the value is not used for		1. Only the encryptor can ensure that the value is not used for
	more than one packet, so there is no advantage to selecting a		more than one packet, so there is no advantage to selecting a
	mechanism that allows the decryptor to determine whether counter		mechanism that allows the decryptor to determine whether counter
	block values collide. Damage from the collision is done, whether		block values collide. Damage from the collision is done, whether
	the decryptor detects it or not.		the decryptor detects it or not.
	2. The use of explicit IVs allows adders, LFSRs, and any other		2. The use of explicit IVs allows adders, LFSRs, and any other
	technique that meets the time budget of the encryptor, so long as		technique that meets the time budget of the encryptor, so long as
	the technique results in a unique value for each packet. Adders		the technique results in a unique value for each packet. Adders
	are simple and straightforward to implement, but due to carries,		are simple and straightforward to implement, but due to carries,
	they do not execute in constant time. LSFRs offer an alternative		they do not execute in constant time. LFSRs offer an alternative
	that executes in constant time.		that executes in constant time.
	3. Complexity is in control of the implementer. Further, the		3. Complexity is in control of the implementer. Further, the
	decision made by the implementer of the encryptor does not make		decision made by the implementer of the encryptor does not make
	the decryptor more (or less) complex.		the decryptor more (or less) complex.
	4. The assignment of the per-packet counter block value needs to		4. The assignment of the per-packet counter block value needs to
	be inside the assurance boundary. Some implementations assign the		be inside the assurance boundary. Some implementations assign the
	sequence number inside the assurance boundary, but others do not.		sequence number inside the assurance boundary, but others do not.
	A sequence number collision does not have the dire consequences,		A sequence number collision does not have the dire consequences,
	skipping to change at page 12, line 19 ¶		skipping to change at page 12, line 19 ¶
	One of the most attractive aspects of CCM mode is that it is		One of the most attractive aspects of CCM mode is that it is
	unencumbered by patents. I acknowledge the companies that supported		unencumbered by patents. I acknowledge the companies that supported
	the development of an unencumbered authenticated encryption mode (in		the development of an unencumbered authenticated encryption mode (in
	alphabetical order):		alphabetical order):
	Hifn		Hifn
	Intersil		Intersil
	MacFergus		MacFergus
	RSA Security		RSA Security
			Also, I thank Tero Kivinen for his comprehensive review of this
			document.
	13. References		13. References
	This section provides normative and informative references.		This section provides normative and informative references.
	13.1. Normative References		13.1. Normative References
	[AES] NIST, FIPS PUB 197, "Advanced Encryption Standard		[AES] NIST, FIPS PUB 197, "Advanced Encryption Standard
	(AES)," November 2001.		(AES)," November 2001.
	[DOI] Piper, D., "The Internet IP Security Domain of		[DOI] Piper, D., "The Internet IP Security Domain of
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