Internet DRAFT - draft-mcgrew-tls-aes-ccm-ecc
draft-mcgrew-tls-aes-ccm-ecc
TLS Working Group D. McGrew
Internet-Draft Cisco Systems
Intended status: Informational D. Bailey
Expires: August 16, 2014 RSA/EMC
M. Campagna
R. Dugal
Certicom Corp.
February 12, 2014
AES-CCM ECC Cipher Suites for TLS
draft-mcgrew-tls-aes-ccm-ecc-08
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,
while at the same time providing a high level of security. 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 16, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
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. Requirements on Curves and Hashes . . . . . . . . . . . . 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
6.3. Hardware Security Modules . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Appendix A. Recommended Curves and Algorithms . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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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
memo 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 Curves with a cofactor equal to one SHOULD be used; this
simplifies their use.
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.
o Following [RFC4492], the server's certificate MUST contain a
suitable ECC public key, and MUST be signed with a suitable ECC
public key. The elliptic curve and hash function SHOULD be
selected to ensure a uniform security level; guidance on
acceptable choices of hashes and curves that can be used with each
ciphersuite is detailed in Section 2.2. The Signature Algorithms
extension (Section 7.4.1.4.1 of [RFC5246]) SHOULD be used to
indicate support of those signature and hash algorithms. If a
client certificate is used, the same criteria SHOULD apply to it.
Implementations of these ciphersuites will interoperate with
[RFC4492], but can be more compact than a full implementation of that
RFC.
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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. Requirements on Curves and Hashes
Implementations SHOULD select elliptic curves and hash functions 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).
Appendix A describes suitable curves and hash functions that are
widely available.
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
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.
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4. History
The 08 version changed a MUST to a SHOULD to align with [RFC4492] and
tweaked text identified during IESG review. It also adds text
describing the unfortunate interaction between PKCS 11 and the TLS
AEAD ciphersuites that Mike StJohns identified.
The 07 version removed the mandatory-to-implement elliptic curves and
hash functions, and replaced them with non-normative guidance, which
is in Appendix A.
The 06 version replaced obsoleted references with updated ones to
RFC6066, 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
nonce construction in Section 2 is designed to prevent counter reuse.
6.3. Hardware Security Modules
A ciphersuite can be implemented in such a way that the secret keys
and private keys are stored inside a Hardware Security Module (HSM),
and the cryptographic operations involving those keys are performed
by the HSM on data provided by an application interacting with the
HSM through an interface such as that defined by the Cryptographic
Token Interface Standard [PKCS11]. When an AEAD ciphersuite, such as
those in this note, are implemented in this way, special handling of
the nonce is required. This is because the "salt" part of the nonce
is set to the client_write_IV or server_write_IV, which is a function
of the TLS master secret.
Another potential issue with the Cryptographic Token Interface
Standard is that the use of the DecryptUpdate function is not
possible with the CCM decrypt operation, or the decrypt operation any
other authenticated encryption method. This is because the
DecryptUpdate requires that post-decryption plaintext be returned
before the authentication check is completed.
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, and to Peter Dettman for his review. Thanks also to Mike
StJohns for pointing out the HSM issues.
This draft is motivated by the considerations raised in the Zigbee
Smart Energy 2.0 working group.
8. References
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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
(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.
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8.2. Informative References
[IEEE802154]
Institute of Electrical and Electronics Engineers,
"Wireless Personal Area Networks", IEEE Standard 802.15.4-
2006, 2006.
[PKCS11] RSA Laboratories, "PKCS #11: Cryptographic Token Interface
Standard version 2.20", Public Key Cryptography
Standards PKCS#11-v2.20, 2004.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, December 2005.
Appendix A. Recommended Curves and Algorithms
This memo does not mandate any particular elliptic curves or
cryptographic algorithms, for the sake of flexibility. However,
since the main motivation for the AES-CCM-ECC ciphersuites is their
suitability for constrained environments, it is valuable to identify
a particular suitable set of curves and algorithms.
This appendix identifies a set of elliptic curves and cryptographic
algorithms that meet the requirements of this note, which are widely
supported and believed to be secure.
The curves and hash algorithms recommended for each ciphersuite are:
An implementation that includes either
TLS_ECDHE_ECDSA_WITH_AES_128_CCM or
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 SHOULD support the secp256r1
curve and the SHA-256 hash function.
An implementation that includes either
TLS_ECDHE_ECDSA_WITH_AES_256_CCM or
TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 SHOULD support the secp384r1
curve and the SHA-384 hash function, and MAY support the secp521r1
curve and the SHA-512 hash function.
More information about the secp256r1, secp384r1, and secp521r1 curves
is available in Appendix A of [RFC4492].
It is not necessary to implement the above curves and hash functions
in order to conform to this specification. Other elliptic curves,
such as the Brainpool curves [RFC5639] for example, meet the criteria
laid out in this memo.
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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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