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
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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-
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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
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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
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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
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[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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