TLS Working Group D. McGrew
Internet-Draft Cisco Systems
Intended status: Informational D. Bailey
Expires: August 5, 2013 RSA/EMC
M. Campagna
R. Dugal
Certicom Corp.
February 1, 2013
AES-CCM ECC Cipher Suites for TLS
draft-mcgrew-tls-aes-ccm-ecc-06
Abstract
This memo describes the use of the Advanced Encryption Standard (AES)
in the Counter and CBC-MAC Mode (CCM) of operation within Transport
Layer Security (TLS) to provide confidentiality and data origin
authentication. The AES-CCM algorithm is amenable to compact
implementations, making it suitable for constrained environments.
The ciphersuites defined in this document use Elliptic Curve
Cryptography (ECC), and are advantageous in networks with limited
bandwidth.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 5, 2013.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions Used In This Document . . . . . . . . . . . . . 3
2. ECC based AES-CCM Cipher Suites . . . . . . . . . . . . . . . . 3
2.1. AEAD algorithms . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Required algorithms for each CipherSuite . . . . . . . . . 5
3. TLS Versions . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. History . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
6.1. Perfect Forward Secrecy . . . . . . . . . . . . . . . . . . 7
6.2. Counter Reuse . . . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
This document describes the use of Advanced Encryption Standard (AES)
[AES] in Counter with CBC-MAC Mode (CCM) [CCM] in several TLS
ciphersuites. AES-CCM provides both authentication and
confidentiality and uses as its only primitive the AES encrypt
operation (the AES decrypt operation is not needed). This makes it
amenable to compact implementations, which is advantageous in
constrained environments. Of course, adoption outside of constrained
environments is necessary to enable interoperability, such as that
between web clients and embedded servers, or between embedded clients
and web servers. The use of AES-CCM has been specified for IPsec ESP
[RFC4309] and 802.15.4 wireless networks [IEEE802154].
Authenticated encryption, in addition to providing confidentiality
for the plaintext that is encrypted, provides a way to check its
integrity and authenticity. Authenticated Encryption with Associated
Data, or AEAD [RFC5116], adds the ability to check the integrity and
authenticity of some associated data that is not encrypted. This
note utilizes the AEAD facility within TLS 1.2 [RFC5246] and the AES-
CCM-based AEAD algorithms defined in [RFC5116] and [RFC6655] . All
of these algorithms use AES-CCM; some have shorter authentication
tags, and are therefore more suitable for use across networks in
which bandwidth is constrained and message sizes may be small.
The ciphersuites defined in this document use Ephemeral Elliptic
Curve Diffie-Hellman (ECDHE) as their key establishment mechanism;
these ciphersuites can be used with DTLS [RFC6347].
1.1. Conventions Used In This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. ECC based AES-CCM Cipher Suites
The ciphersuites defined in this document are based on the AES-CCM
authenticated encryption with associated data (AEAD) algorithms
AEAD_AES_128_CCM and AEAD_AES_256_CCM described in [RFC5116]. The
following ciphersuites are defined:
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM = {TBD1,TBD1}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM = {TBD2,TBD2}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 = {TBD3,TBD3}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 = {TBD4,TBD4}
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These ciphersuites make use of the AEAD capability in TLS 1.2
[RFC5246]. Note that each of these AEAD algorithms uses AES-CCM.
Ciphersuites ending with "8" use eight-octet authentication tags; the
other ciphersuites have 16 octet authentication tags.
The HMAC truncation option described in Section 7 of [RFC6066] (which
negotiates the "truncated_hmac" TLS extension) does not have an
effect on the cipher suites defined in this note, because they do not
use HMAC to protect TLS records.
The "nonce" input to the AEAD algorithm is as defined in [RFC6655].
In DTLS, the 64-bit seq_num field is the 16-bit DTLS epoch field
concatenated with the 48-bit sequence_number field. The epoch and
sequence_number appear in the DTLS record layer.
This construction allows the internal counter to be 32-bits long,
which is a convenient size for use with CCM.
These ciphersuites make use of the default TLS 1.2 Pseudorandom
Function (PRF), which uses HMAC with the SHA-256 hash function.
The ECDHE_ECDSA key exchange is performed as defined in [RFC4492],
with the following additional stipulations:
o The curve secp256r1 MUST be supported, and the curves secp384r1
and secp521r1 MAY be supported; these curves are equivalent to the
NIST P-256, P-384, and P-521 curves. Note that all of these
curves have cofactor equal to one, which simplifies their use.
o The server's certificate MUST contain an ECDSA-capable public key,
it MUST be signed with ECDSA, and it MUST use SHA-256, SHA-384, or
SHA-512. The Signature Algorithms extension (Section 7.4.1.4.1 of
[RFC5246]) MUST be used to indicate support of those signature and
hash algorithms. If a client certificate is used, the same
conditions apply to it. The acceptable choices of hashes and
curves that can be used with each ciphersuite are detailed in
Section 2.2.
o The uncompressed point format MUST be supported. Other point
formats MAY be used.
o The client SHOULD offer the elliptic_curves extension and the
server SHOULD expect to receive it.
o The client MAY offer the ec_point_formats extension, but the
server need not expect to receive it.
o [RFC6090] MAY be used as an implementation method.
Implementations of these ciphersuites will interoperate with
[RFC4492], but can be more compact than a full implementation of that
RFC.
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Implementations that use other curves SHOULD use curves that have
cofactor equal to 1, for simplicity of implementation. Many curves,
such as the Brainpool curves [RFC5639] for example, meet this
criteria.
2.1. AEAD algorithms
The following AEAD algorithms are used:
AEAD_AES_128_CCM is used in the TLS_ECDHE_ECDSA_WITH_AES_128_CCM
ciphersuite,
AEAD_AES_256_CCM is used in the TLS_ECDHE_ECDSA_WITH_AES_256_CCM
ciphersuite,
AEAD_AES_128_CCM_8 is used in the
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 ciphersuite, and
AEAD_AES_256_CCM_8 is used in the
TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 ciphersuite.
2.2. Required algorithms for each CipherSuite
The curves and hash algorithms that must be supported are as follows:
An implementation that includes either
TLS_ECDHE_ECDSA_WITH_AES_128_CCM or
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 MUST support secp256r1 and SHA-
256.
An implementation that includes either
TLS_ECDHE_ECDSA_WITH_AES_256_CCM or
TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 MUST support secp384r1 and SHA-
384, and MAY support secp521r1 and SHA-512.
Implementations that use other curves and hash functions SHOULD
select them so that AES-128 is used with a curve and a hash function
supporting a 128-bit security level, and AES-256 is used with a curve
and a hash function supporting a 192-bit or 256-bit security level.
More detailed guidance on cryptographic parameter selection is given
in [SP800-57] (see especially Tables 2 and 3).
3. TLS Versions
These ciphersuites make use of the authenticated encryption with
additional data defined in TLS 1.2 [RFC5288]. They MUST NOT be
negotiated in older versions of TLS. Clients MUST NOT offer these
cipher suites if they do not offer TLS 1.2 or later. Servers which
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select an earlier version of TLS MUST NOT select one of these cipher
suites. Earlier versions do not have support for AEAD; for instance,
the TLSCiphertext structure does not have the "aead" option in TLS
1.1. Because TLS has no way for the client to indicate that it
supports TLS 1.2 but not earlier, a non-compliant server might
potentially negotiate TLS 1.1 or earlier and select one of the cipher
suites in this document. Clients MUST check the TLS version and
generate a fatal "illegal_parameter" alert if they detect an
incorrect version.
4. History
The 06 version replaces obsoleted references with updated ones to
RFC6606, RFC6655, RFC5246, fixes a boilerplate error, and corrects
the section reference for the truncated HMAC RFC. It also changes
the mandatory-to-implement curves and hash algorithms to be less
restrictive, so that the specification can potentially be used with
curves other than secp256r1, secp384r1, and secp521r1. A reference
to SP 800-57 was added to provide guidance on parameter selection.
The 05 version updated the IANA considerations.
The 04 version changed the intended status to "Informational", and
removed the redundant definition of the AEAD nonce and replaced it
with a reference to draft-mcgrew-tls-aes-ccm, to avoid incompatible
descriptions.
The 03 version removed materials that are redundant with
draft-mcgrew-tls-aes-ccm, and replaced them with references to that
draft. That draft has been approved for RFC and will be a suitable
stable normative reference.
The 02 version removed the AEAD_AES_128_CCM_12 and
AEAD_AES_256_CCM_12 AEAD algorithms, because they were not needed in
any ciphersuites. The AES-256 ciphersuites were retained, however,
to provide a secure cipher for use with the higher security curves
secp384r1 and secp521r1.
This section is to be removed by the RFC editor upon publication.
5. IANA Considerations
IANA is requested to assign the values for the ciphersuites defined
in Section Section 2 from the TLS and DTLS CipherSuite registries.
IANA, please note that the DTLS-OK column should be marked as "Y" for
each of these algorithms.
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6. Security Considerations
6.1. Perfect Forward Secrecy
The perfect forward secrecy properties of ephemeral Diffie-Hellman
ciphersuites are discussed in the security analysis of [RFC5246].
This analysis applies to the ECDHE ciphersuites.
6.2. Counter Reuse
AES-CCM security requires that the counter is never reused. The IV
construction in Section 2 is designed to prevent counter reuse.
7. Acknowledgements
This draft borrows heavily from [RFC5288]. Thanks are due to Robert
Cragie for his great help in making this work complete, correct, and
useful.
This draft is motivated by the considerations raised in the Zigbee
Smart Energy 2.0 working group.
8. References
8.1. Normative References
[AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard
(AES)", FIPS 197, November 2001.
[CCM] National Institute of Standards and Technology,
"Recommendation for Block Cipher Modes of Operation: The
CCM Mode for Authentication and Confidentiality", SP 800-
38C, May 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492, May 2006.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
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(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5288] Salowey, J., Choudhury, A., and D. McGrew, "AES Galois
Counter Mode (GCM) Cipher Suites for TLS", RFC 5288,
August 2008.
[RFC5639] Lochter, M. and J. Merkle, "Elliptic Curve Cryptography
(ECC) Brainpool Standard Curves and Curve Generation",
RFC 5639, March 2010.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090, February 2011.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655, July 2012.
[SP800-57]
National Institute of Standards and Technology,
"Recommendation for Key Management - Part 1: General
(Revision 3)", SP 800-57 Part 1, July 2012.
8.2. Informative References
[IEEE802154]
Institute of Electrical and Electronics Engineers,
"Wireless Personal Area Networks", IEEE Standard 802.15.4-
2006, 2006.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, December 2005.
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Authors' Addresses
David McGrew
Cisco Systems
13600 Dulles Technology Drive
Herndon, VA 20171
USA
Email: mcgrew@cisco.com
Daniel V. Bailey
RSA/EMC
174 Middlesex Tpke.
Bedford, MA 01463
USA
Email: dbailey@rsa.com
Matthew Campagna
Certicom Corp.
5520 Explorer Drive #400
Mississauga, Ontario L4W 5L1
Canada
Email: mcampagna@certicom.com
Robert Dugal
Certicom Corp.
5520 Explorer Drive #400
Mississauga, Ontario L4W 5L1
Canada
Email: rdugal@certicom.com
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