TLS Working Group D. McGrew
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track D. Bailey
Expires: January 6, 2011 RSA/EMC
M. Campagna
R. Dugal
Certicom Corp.
July 5, 2010
AES-CCM ECC Cipher Suites for TLS
draft-mcgrew-tls-aes-ccm-ecc-00
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 intended for use 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
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This Internet-Draft will expire on January 6, 2011.
Copyright Notice
Copyright (c) 2010 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 . . . . . . . . . . . . . . . 4
2.1. Data Structures and Encoding . . . . . . . . . . . . . . . 5
3. TLS Versions . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. New AEAD algorithms . . . . . . . . . . . . . . . . . . . . . 8
4.1. AES-128-CCM with an 8-octet ICV . . . . . . . . . . . . . 8
4.2. AES-256-CCM with an 8-octet ICV . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. Perfect Forward Secrecy . . . . . . . . . . . . . . . . . 10
6.2. Counter Reuse . . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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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 makes it useful in
constrained environments. The use of AES-CCM has been specified for
use with 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]. Additional AEAD
algorithms are also defined, which use AES-CCM but which have shorter
authentication tags, and therefore are 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 [I-D.ietf-tls-rfc4347-bis].
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]
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2. ECC based AES-CCM Cipher Suites
The ciphersuites defined in this document are based on the 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 = {TBD3,TBD3}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM = {TBD4,TBD4}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 = {TBD5,TBD5}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 = {TBD6,TBD6)
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 = {TBD7,TBD7}
CipherSuite TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8 = {TBD8,TBD8}
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 3.5 of [RFC4366]
(which negotiates the "truncated_hmac" TLS extension) does not have
an effect on cipher suites that do not use HMAC.
The "nonce" input to the AEAD algorithm is defined as in [RFC5288].
The "nonce" SHALL be 12 bytes long and constructed as follows:
struct {
case client:
uint32 client_write_IV; // low order 32-bits
case server:
uint32 server_write_IV; // low order 32-bits
uint64 seq_num;
} CCMNonce.
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:
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The curves secp256r1, secp384r1, and secp521r1 MUST 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.
The uncompressed point format MUST be supported, and other point
formats MUST NOT be used. The use of other point formats will be
considered in later versions of this draft.
The client MUST NOT offer the elliptic_curves extension nor the
ec_point_formats extension. The server MUST NOT expect to receive
those extensions.
[I-D.mcgrew-fundamental-ecc] MAY be used as an implementation
method.
The server's certificate MUST contain an ECDSA-capable public key,
and it MUST be signed with ECDSA. If a client certificate is
used, the same conditions apply to it.
2.1. Data Structures and Encoding
The key exchange method uses the data structures and encodings
defined in this section; these are a subset of [RFC4492]. Unused
enumerated values and branches of "select" operations are not shown.
enum {
secp256r1 (23), secp384r1 (24), secp521r1 (25),
(0xFFFF)
} NamedCurve;
struct {
ECCurveType curve_type = named_curve;
NamedCurve namedcurve;
} ECParameters;
struct {
opaque point <1..2^8-1>;
} ECPoint;
struct {
ECParameters curve_params;
ECPoint public;
} ServerECDHParams;
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{
ServerECDHParams params;
Signature signed_params;
} ServerKeyExchange;
enum { ecdsa } SignatureAlgorithm;
{
digitally-signed struct {
opaque sha_hash[sha_size];
};
} Signature;
Ecdsa-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER
}
enum {
ecdsa_sign(64), (255)
} ClientCertificateType;
The TLS CertificateRequest message is extended as follows. Because
only ephemeral Diffie-Hellman is used, the PublicValueEncoding is
always "explicit".
struct {
ECPoint ecdh_Yc;
} ecdh_public;
} ClientECDiffieHellmanPublic;
struct {
{
ClientECDiffieHellmanPublic;
} exchange_keys;
} ClientKeyExchange;
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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. 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. New AEAD algorithms
The following AEAD algorithms are defined:
AEAD_AES_128_CCM_8 = TBD9
AEAD_AES_256_CCM_8 = TBD10
AEAD_AES_128_CCM_12 = TBD11
AEAD_AES_256_CCM_12 = TBD12
4.1. AES-128-CCM with an 8-octet ICV
The AEAD_AES_128_CCM_8 authenticated encryption algorithm is
identical to the AEAD_AES_128_CCM algorithm (see Section 5.3 of
[RFC5116]), except that it uses eight octets for authentication,
instead of the full sixteen octets used by AEAD_AES_128_CCM. The
AEAD_AES_128_CCM_8 ciphertext consists of the ciphertext output of
the CCM encryption operation concatenated with the 8-octet
authentication tag output of the CCM encryption operation. Test
cases are provided in [CCM]. The input and output lengths are as as
for AEAD_AES_128_CCM. An AEAD_AES_128_CCM_8 ciphertext is exactly 8
octets longer than its corresponding plaintext.
4.2. AES-256-CCM with an 8-octet ICV
The AEAD_AES_256_CCM_8 authenticated encryption algorithm is
identical to the AEAD_AES_256_CCM algorithm (see Section 5.4 of
[RFC5116]), except that it uses eight octets for authentication,
instead of the full sixteen octets used by AEAD_AES_256_CCM. The
AEAD_AES_256_CCM_8 ciphertext consists of the ciphertext output of
the CCM encryption operation concatenated with the 8-octet
authentication tag output of the CCM encryption operation. Test
cases are provided in [CCM]. The input and output lengths are as as
for AEAD_AES_128_CCM. An AEAD_AES_128_CCM_8 ciphertext is exactly 8
octets longer than its corresponding plaintext.
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5. IANA Considerations
IANA has assigned values for the Ciphersuites defined in Section 2
and the AEAD algorithms defined in Section 4 of this note.
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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 [RFC4346].
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.
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7. Acknowledgements
This draft borrows heavily from [RFC5288].
This draft is motivated by the considerations raised in the Zigbee
Smart Energy 2.0 working group.
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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.
[I-D.ietf-tls-rfc4347-bis]
Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security version 1.2", draft-ietf-tls-rfc4347-bis-03 (work
in progress), October 2009.
[I-D.mcgrew-fundamental-ecc]
McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms",
draft-mcgrew-fundamental-ecc-03 (work in progress),
May 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
[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.
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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.
[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, Inc.
170 W Tasman Drive
San Jose, CA 95134
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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