< draft-ietf-ipsecme-chacha20-poly1305-02.txt		draft-ietf-ipsecme-chacha20-poly1305-03.txt >
	Network Working Group Y. Nir		Network Working Group Y. Nir
	Internet-Draft Check Point		Internet-Draft Check Point
	Intended status: Standards Track April 5, 2015		Intended status: Standards Track April 25, 2015
	Expires: October 7, 2015		Expires: October 27, 2015
	ChaCha20, Poly1305 and their use in IKE & IPsec		ChaCha20, Poly1305 and their use in IKE & IPsec
	draft-ietf-ipsecme-chacha20-poly1305-02		draft-ietf-ipsecme-chacha20-poly1305-03
	Abstract		Abstract
	This document describes the use of the ChaCha20 stream cipher along		This document describes the use of the ChaCha20 stream cipher along
	with the Poly1305 authenticator, combined into an AEAD algorithm for		with the Poly1305 authenticator, combined into an AEAD algorithm for
	IPsec.		the Internet Key Exchange protocol (IKEv2) and for IPsec.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on October 7, 2015.		This Internet-Draft will expire on October 27, 2015.
	Copyright Notice		Copyright Notice
	Copyright (c) 2015 IETF Trust and the persons identified as the		Copyright (c) 2015 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 12 ¶		skipping to change at page 2, line 12 ¶
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Conventions Used in This Document . . . . . . . . . . . . 2		1.1. Conventions Used in This Document . . . . . . . . . . . . 2
	2. ChaCha20 & Poly1305 for ESP . . . . . . . . . . . . . . . . . 3		2. ChaCha20 & Poly1305 for ESP . . . . . . . . . . . . . . . . . 3
	2.1. AAD Construction . . . . . . . . . . . . . . . . . . . . 4		2.1. AAD Construction . . . . . . . . . . . . . . . . . . . . 4
	3. Use in IKEv2 . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Use in IKEv2 . . . . . . . . . . . . . . . . . . . . . . . . 4
	4. Negotiating in IKE . . . . . . . . . . . . . . . . . . . . . 4		4. Negotiation in IKEv2 . . . . . . . . . . . . . . . . . . . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 4		5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	8.1. Normative References . . . . . . . . . . . . . . . . . . 5		8.1. Normative References . . . . . . . . . . . . . . . . . . 5
	8.2. Informative References . . . . . . . . . . . . . . . . . 6		8.2. Informative References . . . . . . . . . . . . . . . . . 6
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
	1. Introduction		1. Introduction
	The Advanced Encryption Standard (AES - [FIPS-197]) has become the		The Advanced Encryption Standard (AES - [FIPS-197]) has become the
	gold standard in encryption. Its efficient design, wide		gold standard in encryption. Its efficient design, wide
	implementation, and hardware support allow for high performance in		implementation, and hardware support allow for high performance in
	many areas, including IPsec VPNs. On most modern platforms, AES is		many areas, including IPsec VPNs. On most modern platforms, AES is
	anywhere from 4x to 10x as fast as the previous most-used cipher,		anywhere from 4x to 10x as fast as the previous most-used cipher,
	3-key Data Encryption Standard (3DES - [FIPS-46]), which makes it not		3-key Data Encryption Standard (3DES - [SP800-67]). 3DES also has a
	only the best choice, but the only choice.		64-bit block, which means that the amount of data that can be
			encrypted before rekeying is required is not great. These reasons
			make AES not only the best choice, but the only choice.
	The problem is that if future advances in cryptanalysis reveal a		The problem is that if future advances in cryptanalysis reveal a
	weakness in AES, VPN users will be in an unenviable position. With		weakness in AES, VPN users will be in an unenviable position. With
	the only other widely supported cipher being the much slower 3DES, it		the only other widely supported cipher being the much slower 3DES, it
	is not feasible to re-configure IPsec installations to use 3DES.		is not feasible to re-configure IPsec installations to use 3DES.
	[standby-cipher] describes this issue and the need for a standby		[standby-cipher] describes this issue and the need for a standby
	cipher in greater detail.		cipher in greater detail.
	This document proposes the ChaCha20 stream cipher as such a standby		This document proposes the ChaCha20 stream cipher as such a standby
	cipher in an Authenticated Encryption with Associated Data (AEAD)		cipher in an Authenticated Encryption with Associated Data (AEAD)
	skipping to change at page 3, line 12 ¶		skipping to change at page 3, line 12 ¶
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	2. ChaCha20 & Poly1305 for ESP		2. ChaCha20 & Poly1305 for ESP
	AEAD_CHACHA20_POLY1305 is a combined mode algorithm, or AEAD. The		AEAD_CHACHA20_POLY1305 is a combined mode algorithm, or AEAD. The
	construction follows the AEAD construction in section 2.8 of		construction follows the AEAD construction in section 2.8 of
	[chacha_poly]:		[chacha_poly]:
	o The Initialization Vector (IV) is 64-bit, and is used as part of		o The Initialization Vector (IV) is 64-bit, and is used as part of
	the nonce. The IV MUST be unique for each SA but does not need to		the nonce. The IV MUST be unique for each invocation for a
	be unpredictable. The use of a counter or an LFSR is RECOMMENDED.		particular SA but does not need to be unpredictable. The use of a
	o A 32-bit sender ID is prepended to the 64-bit IV to form the		counter or a linear feedback shift register (LFSR) is RECOMMENDED.
	96-bit nonce. For regular IPsec, this is set to all zeros. IPsec		o A 32-bit Salt is prepended to the 64-bit IV to form the 96-bit
	extensions that allow multiple senders, such as GDOI ([RFC6407])		nonce. The salt is fixed per SA and it is not transmitted as part
	or [RFC6054] may set this to different values.		of the ESP packet..
	o The encryption key is 256-bit.		o The encryption key is 256-bit.
	o The Internet Key Exchange protocol generates a bitstring called		o The Internet Key Exchange protocol generates a bitstring called
	KEYMAT that is generated from a PRF. That KEYMAT is divided into		KEYMAT using a pseudo-random function (PRF). That KEYMAT is
	keys for encryption, message authentication and whatever else is		divided into keys for encryption, message authentication and
	needed. For the ChaCha20 algorithm, 256 bits are used for the		whatever else is needed. For the ChaCha20-poly1305 algorithm, 256
	key. TBD: do we want an extra 32 bits as salt for the nonce like		bits are used for the key, and a subsequent 32 bits are used for
	in GCM, or keep the salt (=SenderID) at zero?		the Salt.
	o The ChaCha20 encryption algorithm requires the following
	parameters: a 256-bit key, a 96-bit nonce, and a 32-bit initial
	block counter. For ESP we set these as follows:
	* The key is set to the key mentioned above.		The ChaCha20 encryption algorithm requires the following parameters:
	* The 96-bit nonce is formed from a concatenation of the 32-bit		a 256-bit key, a 96-bit nonce, and a 32-bit initial block counter.
	sender ID and the 64-bit IV, as described above.		For ESP we set these as follows:
	* The Initial Block Counter is set to one (1). The reason that
	one is used for the initial counter rather than zero is that
	zero is reserved for generating the one-time Poly1305 key (see
	below)
	o As ChaCha20 is not a block cipher, no padding should be necessary.
	However, in keeping with the specification in RFC 4303, the ESP
	does have padding, so as to align the buffer to an integral
	multiple of 4 octets.
	o The same key and nonce, along with a block counter of zero are
	passed to the ChaCha20 block function, and the top 256 bits of the
	result are used as the Poly1305 key. The nonce passed to the
	block function here is the same nonce that is used in ChaCha20,
	including the 32-bit Sender ID bits, and the key passed is the
	same as the encryption key.
	o Finally, the Poly1305 function is run on the data to be
	authenticated, which is, as specified in section 2.8 of
	[chacha_poly] a concatenation of the following in the below order:
	* The Authenticated Additional Data (AAD) - see Section 2.1.		o The key is set as mentioned above.
			o The 96-bit nonce is formed from a concatenation of the 32-bit Salt
			and the 64-bit IV, as described above.
			o The Initial Block Counter is set to one (1). The reason that one
			is used for the initial counter rather than zero is that zero is
			reserved for generating the one-time Poly1305 key (see below)
	* Padding that rounds the length up to 16 bytes. This is 4 or 8		As the ChaCha20 block function is not applied directly to the
	bytes depending on whether extended sequence numbers (ESN) is		plaintext, no padding should be necessary. However, in keeping with
	set for the SA. The padding is all zeros.		the specification in RFC 4303, the ESP does have padding, so as to
	* The ciphertext		align the buffer to an integral multiple of 4 octets.
	* Padding that rounds the total length up to an integral multiple
	of 16 bytes. This padding is also all zeros.		The same key and nonce, along with a block counter of zero are passed
	* The length of the additional data in octets (as a 64-bit		to the ChaCha20 block function, and the top 256 bits of the result
	little-endian integer).		are used as the Poly1305 key. The nonce passed to the block function
	* The length of the ciphertext in octets (as a 64-bit little-		here is the same nonce that is used in ChaCha20, including the 32-bit
	endian integer).		Salt, and the key passed is the same as the encryption key.
	o The 128-bit output of Poly1305 is used as the tag. All 16 bytes
	are included in the packet.		Finally, the Poly1305 function is run on the data to be
			authenticated, which is, as specified in section 2.8 of [chacha_poly]
			a concatenation of the following in the below order:
			o The Authenticated Additional Data (AAD) - see Section 2.1.
			o Padding that rounds the length up to 16 bytes. This is 4 or 8
			bytes depending on whether extended sequence numbers (ESN) is set
			for the SA. The padding is all zeros.
			o The ciphertext
			o Padding that rounds the total length up to an integral multiple of
			16 bytes. This padding is also all zeros.
			o The length of the additional authenticated data (AAD) in octets
			(as a 64-bit little-endian integer).
			o The length of the ciphertext in octets (as a 64-bit little-endian
			integer).
			The 128-bit output of Poly1305 is used as the tag. All 16 bytes are
			included in the packet.
	The encryption algorithm transform ID for negotiating this algorithm		The encryption algorithm transform ID for negotiating this algorithm
	in IKE is TBA by IANA.		in IKE is TBA by IANA.
	2.1. AAD Construction		2.1. AAD Construction
	The construction of the Additional Authenticated Data (AAD) is		The construction of the Additional Authenticated Data (AAD) is
	similar to the one in [RFC4106]. For security associations (SAs)		similar to the one in [RFC4106]. For security associations (SAs)
	with 32-bit sequence numbers the AAD is 8 bytes: 4-byte SPI followed		with 32-bit sequence numbers the AAD is 8 bytes: 4-byte SPI followed
	by 4-byte sequence number ordered exactly as it is in the packet.		by 4-byte sequence number ordered exactly as it is in the packet.
	For SAs with ESN the AAD is 12 bytes: 4-byte SPI followed by an		For SAs with ESN the AAD is 12 bytes: 4-byte SPI followed by an
	8-byte sequence number as a 64-bit network order integer.		8-byte sequence number as a 64-bit network order integer.
	3. Use in IKEv2		3. Use in IKEv2
	AEAD algorithms can be used in IKE, as described in [RFC5282]. More		AEAD algorithms can be used in IKE, as described in [RFC5282]. More
	specifically, the Encrypted Payload is as described in section 3 of		specifically:
	that document, the IV is 64 bits, as described in Section 2, and the
	AAD is as described in section 5.1 of RFC 5282, so it's 32 bytes (28
	for the IKEv2 header + 4 bytes for the encrypted payload header)
	assuming no unencrypted payloads.
	4. Negotiating in IKE		o The Encrypted Payload is as described in section 3 of that
			document.
			o The IV is 64 bits, as described in Section 2.
			o The AAD is as described in section 5.1 of RFC 5282, so it's 32
			bytes (28 for the IKEv2 header + 4 bytes for the encrypted payload
			header) assuming no unencrypted payloads.
			4. Negotiation in IKEv2
	When negotiating the ChaCha20-Poly1305 algorithm for use in IKE or		When negotiating the ChaCha20-Poly1305 algorithm for use in IKE or
	IPsec, the value xxx (TBA by IANA) should be used in the transform		IPsec, the value xxx (TBA by IANA) should be used in the transform
	substructure of the SA payload as the ENCR (type 1) transform ID. As		substructure of the SA payload as the ENCR (type 1) transform ID. As
	with other AEAD algorithms, INTEG (type 3) transform substructures		with other AEAD algorithms, INTEG (type 3) transform substructures
	SHOULD NOT be specified unless at least one of the ENCR transforms is		MUST NOT be specified or just one INTEG transform MAY be included
	non-AEAD.		with value NONE (0).
	5. Security Considerations		5. Security Considerations
	The ChaCha20 cipher is designed to provide 256-bit security.		The ChaCha20 cipher is designed to provide 256-bit security.
	The Poly1305 authenticator is designed to ensure that forged messages		The Poly1305 authenticator is designed to ensure that forged messages
	are rejected with a probability of 1-(n/(2^102)) for a 16n-byte		are rejected with a probability of 1-(n/(2^102)) for a 16n-byte
	message, even after sending 2^64 legitimate messages, so it is SUF-		message, even after sending 2^64 legitimate messages, so it is SUF-
	CMA in the terminology of [AE].		CMA in the terminology of [AE].
	The most important security consideration in implementing this draft		The most important security consideration in implementing this draft
	is the uniqueness of the nonce used in ChaCha20. The nonce should be		is the uniqueness of the nonce used in ChaCha20. The nonce should be
	selected uniquely for a particular key, but unpredictability of the		selected uniquely for a particular key, but unpredictability of the
	nonce is not required. Counters and LFSRs are both acceptable ways		nonce is not required. Counters and LFSRs are both acceptable ways
	of generating unique nonces, as is encrypting a counter using a		of generating unique nonces.
	64-bit cipher such as DES. Note that it is not acceptable to use a
	truncation of a counter encrypted with a 128-bit or 256-bit cipher,
	because such a truncation may repeat after a short time.
	Another issue with implementing these algorithms is avoiding side		Another issue with implementing these algorithms is avoiding side
	channels. This is trivial for ChaCha20, but requires some care for		channels. This is trivial for ChaCha20, but requires some care for
	Poly1305. Considerations for implementations of these algorithms are		Poly1305. Considerations for implementations of these algorithms are
	in the [chacha_poly] document.		in the [chacha_poly] document.
	6. IANA Considerations		6. IANA Considerations
	IANA is requested to assign one value from the IKEv2 "Transform Type		IANA is requested to assign one value from the IKEv2 "Transform Type
	1 - Encryption Algorithm Transform IDs" registry, with name		1 - Encryption Algorithm Transform IDs" registry, with name
	ENCR_CHACHA20_POLY1305, and this document as reference.		ENCR_CHACHA20_POLY1305, and this document as reference for both ESP
			and IKEv2.
	7. Acknowledgements		7. Acknowledgements
	All of the algorithms in this document were designed by D. J.		All of the algorithms in this document were designed by D. J.
	Bernstein. The AEAD construction was designed by Adam Langley. The		Bernstein. The AEAD construction was designed by Adam Langley. The
	author would also like to thank Adam for helpful comments, as well as		author would also like to thank Adam for helpful comments, as well as
	Yaron Sheffer for telling me to write the algorithms draft. Thanks		Yaron Sheffer for telling me to write the algorithms draft. Thanks
	also to Martin Willi for pointing out the discrepancy with the final		also to Martin Willi for pointing out the discrepancy with the final
	version of the algorithm document.		version of the algorithm document, and to Valery Smyslov and Tero
			Kivinen for helpful comments on this draft.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC		[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
	4303, December 2005.		4303, December 2005.
	[RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption		[RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption
	Algorithms with the Encrypted Payload of the Internet Key		Algorithms with the Encrypted Payload of the Internet Key
	Exchange version 2 (IKEv2) Protocol", RFC 5282, August		Exchange version 2 (IKEv2) Protocol", RFC 5282, August
	2008.		2008.
	[RFC6054] McGrew, D. and B. Weis, "Using Counter Modes with
	Encapsulating Security Payload (ESP) and Authentication
	Header (AH) to Protect Group Traffic", RFC 6054, November
	2010.
	[RFC7296] Kivinen, T., Kaufman, C., Hoffman, P., Nir, Y., and P.		[RFC7296] Kivinen, T., Kaufman, C., Hoffman, P., Nir, Y., and P.
	Eronen, "Internet Key Exchange Protocol Version 2		Eronen, "Internet Key Exchange Protocol Version 2
	(IKEv2)", RFC 7296, October 2014.		(IKEv2)", RFC 7296, October 2014.
	[chacha_poly]		[chacha_poly]
	Langley, A. and Y. Nir, "ChaCha20 and Poly1305 for IETF		Langley, A. and Y. Nir, "ChaCha20 and Poly1305 for IETF
	protocols", draft-nir-cfrg-chacha20-poly1305-01 (work in		protocols", draft-nir-cfrg-chacha20-poly1305-01 (work in
	progress), January 2014.		progress), January 2014.
	8.2. Informative References		8.2. Informative References
	skipping to change at page 6, line 32 ¶		skipping to change at page 6, line 32 ¶
	Relations among notions and analysis of the generic		Relations among notions and analysis of the generic
	composition paradigm", 2000,		composition paradigm", 2000,
	<http://cseweb.ucsd.edu/~mihir/papers/oem.html>.		<http://cseweb.ucsd.edu/~mihir/papers/oem.html>.
	[FIPS-197]		[FIPS-197]
	National Institute of Standards and Technology, "Advanced		National Institute of Standards and Technology, "Advanced
	Encryption Standard (AES)", FIPS PUB 197, November 2001,		Encryption Standard (AES)", FIPS PUB 197, November 2001,
	<http://csrc.nist.gov/publications/fips/fips197/		<http://csrc.nist.gov/publications/fips/fips197/
	fips-197.pdf>.		fips-197.pdf>.
	[FIPS-46] National Institute of Standards and Technology, "Data
	Encryption Standard", FIPS PUB 46-2, December 1993,
	<http://www.itl.nist.gov/fipspubs/fip46-2.htm>.
	[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode		[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
	(GCM) in IPsec Encapsulating Security Payload (ESP)", RFC		(GCM) in IPsec Encapsulating Security Payload (ESP)", RFC
	4106, June 2005.		4106, June 2005.
	[RFC6407] Weis, B., Rowles, S., and T. Hardjono, "The Group Domain		[SP800-67]
	of Interpretation", RFC 6407, October 2011.		National Institute of Standards and Technology,
			"Recommendation for the Triple Data Encryption Algorithm
			(TDEA) Block Cipher", FIPS SP800-67, January 2012,
			<http://csrc.nist.gov/publications/nistpubs/800-67-Rev1/
			SP-800-67-Rev1.pdf>.
	[standby-cipher]		[standby-cipher]
	McGrew, D., Grieco, A., and Y. Sheffer, "Selection of		McGrew, D., Grieco, A., and Y. Sheffer, "Selection of
	Future Cryptographic Standards", draft-mcgrew-standby-		Future Cryptographic Standards", draft-mcgrew-standby-
	cipher (work in progress), January 2013.		cipher (work in progress), January 2013.
	Author's Address		Author's Address
	Yoav Nir		Yoav Nir
	Check Point Software Technologies Ltd.		Check Point Software Technologies Ltd.
	5 Hasolelim st.		5 Hasolelim st.
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