< draft-ietf-ipsecme-chacha20-poly1305-01.txt		draft-ietf-ipsecme-chacha20-poly1305-02.txt >
	Network Working Group Y. Nir		Network Working Group Y. Nir
	Internet-Draft Check Point		Internet-Draft Check Point
	Intended status: Standards Track March 31, 2015		Intended status: Standards Track April 5, 2015
	Expires: October 2, 2015		Expires: October 7, 2015
	ChaCha20, Poly1305 and their use in IKE & IPsec		ChaCha20, Poly1305 and their use in IKE & IPsec
	draft-ietf-ipsecme-chacha20-poly1305-01		draft-ietf-ipsecme-chacha20-poly1305-02
	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.		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
	skipping to change at page 1, line 32 ¶		skipping to change at page 1, line 32 ¶
	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 2, 2015.		This Internet-Draft will expire on October 7, 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
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	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. Security Considerations . . . . . . . . . . . . . . . . . . . 4		4. Negotiating in IKE . . . . . . . . . . . . . . . . . . . . . 4
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
	7.1. Normative References . . . . . . . . . . . . . . . . . . 5		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	7.2. Informative References . . . . . . . . . . . . . . . . . 5		8.1. Normative References . . . . . . . . . . . . . . . . . . 5
			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 - [FIPS-46]), which makes it not
	skipping to change at page 3, line 8 ¶		skipping to change at page 3, line 8 ¶
	1.1. Conventions Used in This Document		1.1. Conventions Used in This Document
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"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 2.7 of		construction follows the AEAD construction in section 2.8 of
	[chacha_poly]:		[chacha_poly]:
	o The IV is 64-bit, and is used as part of the nonce. TBD: do we		o The Initialization Vector (IV) is 64-bit, and is used as part of
	want to skip the IV altogether and just use the packet counter?		the nonce. The IV MUST be unique for each SA but does not need to
			be unpredictable. The use of a counter or an LFSR is RECOMMENDED.
	o A 32-bit sender ID is prepended to the 64-bit IV to form the		o A 32-bit sender ID is prepended to the 64-bit IV to form the
	96-bit nonce. For regular IPsec, this is set to all zeros. IPsec		96-bit nonce. For regular IPsec, this is set to all zeros. IPsec
	extensions that allow multiple senders, such as GDOI ([RFC6407])		extensions that allow multiple senders, such as GDOI ([RFC6407])
	or [RFC6054] may set this to different values.		or [RFC6054] may set this to different values.
	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 that is generated from a PRF. That KEYMAT is divided into
	keys for encryption, message authentication and whatever else is		keys for encryption, message authentication and whatever else is
	needed. For the ChaCha20 algorithm, 256 bits are used for the		needed. For the ChaCha20 algorithm, 256 bits are used for the
	key. TBD: do we want an extra 32 bits as salt for the nonce like		key. TBD: do we want an extra 32 bits as salt for the nonce like
	in GCM?		in GCM, or keep the salt (=SenderID) at zero?
	o The ChaCha20 encryption algorithm requires the following		o The ChaCha20 encryption algorithm requires the following
	parameters: a 256-bit key, a 96-bit nonce, and a 32-bit initial		parameters: a 256-bit key, a 96-bit nonce, and a 32-bit initial
	block counter. For ESP we set these as follows:		block counter. For ESP we set these as follows:
	* The key is set to the key mentioned above.		* The key is set to the key mentioned above.
	* The 96-bit nonce is formed from a concatenation of the 32-bit		* The 96-bit nonce is formed from a concatenation of the 32-bit
	sender ID and the 64-bit IV, as described above.		sender ID and the 64-bit IV, as described above.
	* The Initial Block Counter is set to one (1). The reason that		* The Initial Block Counter is set to one (1). The reason that
	one is used for the initial counter rather than zero is that		one is used for the initial counter rather than zero is that
	zero is reserved for generating the one-time Poly1305 key (see		zero is reserved for generating the one-time Poly1305 key (see
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	However, in keeping with the specification in RFC 4303, the ESP		However, in keeping with the specification in RFC 4303, the ESP
	does have padding, so as to align the buffer to an integral		does have padding, so as to align the buffer to an integral
	multiple of 4 octets.		multiple of 4 octets.
	o The same key and nonce, along with a block counter of zero are		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		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		result are used as the Poly1305 key. The nonce passed to the
	block function here is the same nonce that is used in ChaCha20,		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		including the 32-bit Sender ID bits, and the key passed is the
	same as the encryption key.		same as the encryption key.
	o Finally, the Poly1305 function is run on the data to be		o Finally, the Poly1305 function is run on the data to be
	authenticated, which is, as specified in section 2.7 of		authenticated, which is, as specified in section 2.8 of
	[chacha_poly] a concatenation of the following in the below order:		[chacha_poly] a concatenation of the following in the below order:
	* The Authenticated Additional Data (AAD) - see Section 2.1.		* The Authenticated Additional Data (AAD) - see Section 2.1.
	* The AAD length in bytes as a 32-bit network order quantity.
			* 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.
	* The ciphertext		* The ciphertext
	* The length of the ciphertext as a 32-bit network order		* Padding that rounds the total length up to an integral multiple
	quantity.		of 16 bytes. This padding is also all zeros.
			* The length of the additional data in octets (as a 64-bit
			little-endian integer).
			* The length of the ciphertext in octets (as a 64-bit little-
			endian integer).
	o The 128-bit output of Poly1305 is used as the tag. All 16 bytes		o The 128-bit output of Poly1305 is used as the tag. All 16 bytes
	are included in the packet.		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)
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	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, the Encrypted Payload is as described in section 3 of
	that document, the IV is 64 bits, as described in Section 2, and the		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		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)		for the IKEv2 header + 4 bytes for the encrypted payload header)
	assuming no unencrypted payloads.		assuming no unencrypted payloads.
	4. Security Considerations		4. Negotiating in IKE
			When negotiating the ChaCha20-Poly1305 algorithm for use in IKE or
			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
			with other AEAD algorithms, INTEG (type 3) transform substructures
			SHOULD NOT be specified unless at least one of the ENCR transforms is
			non-AEAD.
			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
	skipping to change at page 5, line 5 ¶		skipping to change at page 5, line 24 ¶
	of generating unique nonces, as is encrypting a counter using a		of generating unique nonces, as is encrypting a counter using a
	64-bit cipher such as DES. Note that it is not acceptable to use a		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,		truncation of a counter encrypted with a 128-bit or 256-bit cipher,
	because such a truncation may repeat after a short time.		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.
	5. 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.
	6. 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.		Yaron Sheffer for telling me to write the algorithms draft. Thanks
			also to Martin Willi for pointing out the discrepancy with the final
			version of the algorithm document.
	7. References		8. References
	7.1. 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
	skipping to change at page 5, line 47 ¶		skipping to change at page 6, line 19 ¶
	[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.
	7.2. Informative References		8.2. Informative References
	[AE] Bellare, M. and C. Namprempre, "Authenticated Encryption:		[AE] Bellare, M. and C. Namprempre, "Authenticated Encryption:
	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/
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