Internet DRAFT - draft-mcgrew-tls-aes-ccm
draft-mcgrew-tls-aes-ccm
TLS Working Group D. McGrew
Internet-Draft Cisco Systems
Intended status: Standards Track D. Bailey
Expires: November 9, 2012 RSA, the Security Division of EMC
May 8, 2012
AES-CCM Cipher Suites for TLS
draft-mcgrew-tls-aes-ccm-04
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) and Datagram TLS (DTLS) to provide
confidentiality and data origin authentication. The AES-CCM
algorithm is amenable to compact implementations, making it suitable
for constrained environments.
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 November 9, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used In This Document . . . . . . . . . . . . . . . 3
3. RSA Based AES-CCM Cipher Suites . . . . . . . . . . . . . . . . 3
4. PSK Based AES-CCM Cipher Suites . . . . . . . . . . . . . . . . 4
5. TLS Versions . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. New AEAD algorithms . . . . . . . . . . . . . . . . . . . . . . 5
6.1. AES-128-CCM with an 8-octet Integrity Check Value (ICV) . . 5
6.2. AES-256-CCM with a 8-octet Integrity Check Value (ICV) . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
8.1. Perfect Forward Secrecy . . . . . . . . . . . . . . . . . . 6
8.2. Counter Reuse . . . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . . 7
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]. Additional AEAD
algorithms are 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 RSA or Pre-Shared Key
(PSK) as their key establishment mechanism; these ciphersuites can be
used with DTLS [RFC6347]. Since the abiltiy to use AEAD ciphers was
introduced in DTLS version 1.2, the ciphersuites defined in this note
cannot be used with earlier versions of that protocol.
2. Conventions Used In This Document
he 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]
3. RSA 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 RSA-based ciphersuites are defined:
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CipherSuite TLS_RSA_WITH_AES_128_CCM = {TBD1,TBD1}
CipherSuite TLS_RSA_WITH_AES_256_CCM = {TBD2,TBD2)
CipherSuite TLS_DHE_RSA_WITH_AES_128_CCM = {TBD3,TBD3}
CipherSuite TLS_DHE_RSA_WITH_AES_256_CCM = {TBD4,TBD4}
CipherSuite TLS_RSA_WITH_AES_128_CCM_8 = {TBD5,TBD5}
CipherSuite TLS_RSA_WITH_AES_256_CCM_8 = {TBD6,TBD6)
CipherSuite TLS_DHE_RSA_WITH_AES_128_CCM_8 = {TBD7,TBD7}
CipherSuite TLS_DHE_RSA_WITH_AES_256_CCM_8 = {TBD8,TBD8}
These ciphersuites make use of the AEAD capability in TLS 1.2
[RFC5246]. Each uses AES-CCM; those that end in "_8" have an 8-octet
authentication tag, while 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 cipher suites that do not use HMAC.
The "nonce" input to the AEAD algorithm is exactly that of [RFC5288]:
the "nonce" SHALL be 12 bytes long and is 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 is the 16-bit epoch concatenated with the
48-bit seq_num.
These ciphersuites make use of the default TLS 1.2 Pseudorandom
Function (PRF), which uses HMAC with the SHA-256 hash function. The
RSA and RSA-DHE key exchange is performed as defined in [RFC5246].
4. PSK Based AES-CCM Cipher Suites
As in Section Section 3, these ciphersuites follow [RFC5116]. The
PSK and DHE_PSK key exchange is performed as in [RFC4279]. The
following ciphersuites are defined:
CipherSuite TLS_PSK_WITH_AES_128_CCM = {TBD9,TBD9}
CipherSuite TLS_PSK_WITH_AES_256_CCM = {TBD10,TBD10)
CipherSuite TLS_DHE_PSK_WITH_AES_128_CCM = {TBD11,TBD11}
CipherSuite TLS_DHE_PSK_WITH_AES_256_CCM = {TBD12,TBD12}
CipherSuite TLS_PSK_WITH_AES_128_CCM_8 = {TBD13,TBD13}
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CipherSuite TLS_PSK_WITH_AES_256_CCM_8 = {TBD14,TBD14)
CipherSuite TLS_PSK_DHE_WITH_AES_128_CCM_8 = {TBD15,TBD15}
CipherSuite TLS_PSK_DHE_WITH_AES_256_CCM_8 = {TBD16,TBD16}
The "nonce" input to the AEAD algorithm is defined as in Section
Section 3.
These ciphersuites make use of the default TLS 1.2 Pseudorandom
Function (PRF), which uses HMAC with the SHA-256 hash function. The
PSK and PSK-DHE key exchange is performed as defined in [RFC5487].
5. TLS Versions
These ciphersuites make use of the authenticated encryption with
additional data (AEAD) defined in TLS 1.2 [RFC5288]. Earlier
versions of TLS do not have support for AEAD; for instance, the
TLSCiphertext structure does not have the "aead" option in TLS 1.1.
Consequently, these ciphersuites 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.
6. New AEAD algorithms
The following AEAD algorithms are defined:
AEAD_AES_128_CCM_8 = TBD17
AEAD_AES_256_CCM_8 = TBD18
6.1. AES-128-CCM with an 8-octet Integrity Check Value (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 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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6.2. AES-256-CCM with a 8-octet Integrity Check Value (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.
7. IANA Considerations
IANA is requested to assign the values for the ciphersuites defined
in Section 3 and Section 4 from the TLS and DTLS CipherSuite
registries, and the values of the AEAD algorithms defined in
Section 6 from the AEAD algorithm registry. IANA, please note that
the DTLS-OK column should be marked as "Y" for each of these
algorithms.
8. Security Considerations
8.1. Perfect Forward Secrecy
The perfect forward secrecy properties of RSA based TLS ciphersuites
are discussed in the security analysis of [RFC5246]. It should be
noted that only the ephemeral Diffie-Hellman based ciphersuites are
capable of providing perfect forward secrecy.
8.2. Counter Reuse
AES-CCM security requires that the counter is never reused. The IV
construction in Section 3 is designed to prevent counter reuse.
9. Acknowledgements
This draft borrows heavily from [RFC5288]. Thanks are due to Stephen
Farrell and Robert Cragie for their input.
10. References
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10.1. 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.
[RFC4279] Eronen, P. and H. Tschofenig, "Pre-Shared Key Ciphersuites
for Transport Layer Security (TLS)", RFC 4279,
December 2005.
[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.
[RFC5487] Badra, M., "Pre-Shared Key Cipher Suites for TLS with SHA-
256/384 and AES Galois Counter Mode", RFC 5487,
March 2009.
[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
Extension Definitions", RFC 6066, January 2011.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
10.2. 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, the Security Division of EMC
174 Middlesex Tpke.
Bedford, MA 01463
USA
Email: dbailey@rsa.com
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