draft-ietf-ipsecme-chacha20-poly1305-07.txt   draft-ietf-ipsecme-chacha20-poly1305-08.txt 
Network Working Group Y. Nir Network Working Group Y. Nir
Internet-Draft Check Point Internet-Draft Check Point
Intended status: Standards Track May 7, 2015 Intended status: Standards Track May 14, 2015
Expires: November 8, 2015 Expires: November 15, 2015
ChaCha20, Poly1305 and their use in IKE & IPsec ChaCha20, Poly1305 and their use in IKE & IPsec
draft-ietf-ipsecme-chacha20-poly1305-07 draft-ietf-ipsecme-chacha20-poly1305-08
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
the Internet Key Exchange protocol (IKEv2) and 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
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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 November 8, 2015. This Internet-Draft will expire on November 15, 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 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 away from AES. is not feasible to re-configure IPsec installations away from AES.
[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 fast and secure ChaCha20 stream cipher as This document proposes the fast and secure ChaCha20 stream cipher as
such a standby cipher in an Authenticated Encryption with Associated such a standby cipher in an Authenticated Encryption with Associated
Data (AEAD) construction with the Poly1305 authenticator for use with Data (AEAD) construction with the Poly1305 authenticator for use with
the Encapsulated Security Protocol (ESP - [RFC4303]) and the Internet the Encapsulated Security Protocol (ESP - [RFC4303]) and the Internet
Key Exchange Protocol (IKEv2 - [RFC7296]). The algorithms are Key Exchange Protocol (IKEv2 - [RFC7296]). The algorithms are
described in a separate document ([chacha_poly]). This document only described in a separate document ([RFC7539]). This document only
describes the IPsec-specific things. describes the IPsec-specific things.
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 2.8 of construction follows the AEAD construction in section 2.8 of
[chacha_poly]: [RFC7539]:
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 invocation for a the nonce. The IV MUST be unique for each invocation for a
particular SA but does not need to be unpredictable. The use of a particular SA but does not need to be unpredictable. The use of a
counter or a linear feedback shift register (LFSR) is RECOMMENDED. counter or a linear feedback shift register (LFSR) is RECOMMENDED.
o A 32-bit Salt is prepended to the 64-bit IV to form the 96-bit o A 32-bit Salt is prepended to the 64-bit IV to form the 96-bit
nonce. The salt is fixed per SA and it is not transmitted as part nonce. The salt is fixed per SA and it is not transmitted as part
of the ESP packet. 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
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plaintext, no padding should be necessary. However, in keeping with plaintext, no padding should be necessary. However, in keeping with
the specification in RFC 4303, the plaintext always has a pad length the specification in RFC 4303, the plaintext always has a pad length
octet and a Next Header octet and may require padding bytes so as to octet and a Next Header octet and may require padding bytes so as to
align the buffer to an integral multiple of 4 octets. align the buffer to an integral multiple of 4 octets.
The same key and nonce, along with a block counter of zero are passed 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 to the ChaCha20 block function, and the top 256 bits of the result
are used as the Poly1305 key. are used as the Poly1305 key.
Finally, the Poly1305 function is run on the data to be Finally, the Poly1305 function is run on the data to be
authenticated, which is, as specified in section 2.8 of [chacha_poly] authenticated, which is, as specified in section 2.8 of [RFC7539] a
a concatenation of the following in the below order: concatenation of the following in the below order:
o The Authenticated Additional Data (AAD) - see Section 2.1. o The Authenticated Additional Data (AAD) - see Section 2.1.
o Zero-octet padding that rounds the length up to 16 bytes. This is o Zero-octet padding that rounds the length up to 16 bytes. This is
4 or 8 bytes depending on the length of the AAD. 4 or 8 bytes depending on the length of the AAD.
o The ciphertext o The ciphertext
o Zero octet padding that rounds the total length up to an integral o Zero octet padding that rounds the total length up to an integral
multiple of 16 bytes. multiple of 16 bytes.
o The length of the additional authenticated data (AAD) in octets o The length of the additional authenticated data (AAD) in octets
(as a 64-bit integer encoded in little-endian byte order). (as a 64-bit integer encoded in little-endian byte order).
o The length of the ciphertext in octets (as a 64-bit integer o The length of the ciphertext in octets (as a 64-bit integer
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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. of generating unique nonces.
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 [RFC7539].
The Salt value in used nonce construction in ESP and IKEv2 is derived The Salt value in used nonce construction in ESP and IKEv2 is derived
from the keystream, same as the encryption key. It is never from the keystream, same as the encryption key. It is never
transmitted on the wire, but the security of the algorithm does not transmitted on the wire, but the security of the algorithm does not
depend on its secrecy. Thus implementations that keep keys and other depend on its secrecy. Thus implementations that keep keys and other
secret material within some security boundary MAY export the Salt secret material within some security boundary MAY export the Salt
from the security boundary. This may be useful if the API provided from the security boundary. This may be useful if the API provided
by the library accepts the nonce as parameter rather than the IV. by the library accepts the nonce as parameter rather than the IV.
6. IANA Considerations 6. IANA Considerations
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[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.
[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] [RFC7539] Langley, A. and Y. Nir, "ChaCha20 and Poly1305 for IETF
Langley, A. and Y. Nir, "ChaCha20 and Poly1305 for IETF protocols", RFC 7539, May 2015.
protocols", draft-nir-cfrg-chacha20-poly1305-01 (work in
progress), January 2014.
8.2. 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
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