Tech-invite3GPPspaceIETF RFCsSIP
929190898887868584838281807978777675747372717069686766656463626160595857565554535251504948474645444342414039383736353433323130292827262524232221201918171615141312111009080706050403020100
in Index   Prev   Next

RFC 5084

Using AES-CCM and AES-GCM Authenticated Encryption in the Cryptographic Message Syntax (CMS)

Pages: 11
Proposed Standard
Errata

ToP   noToC   RFC5084 - Page 1
Network Working Group                                         R. Housley
Request for Comments: 5084                                Vigil Security
Category: Standards Track                                  November 2007


           Using AES-CCM and AES-GCM Authenticated Encryption
               in the Cryptographic Message Syntax (CMS)

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

This document specifies the conventions for using the AES-CCM and the AES-GCM authenticated encryption algorithms with the Cryptographic Message Syntax (CMS) authenticated-enveloped-data content type.

1. Introduction

This document specifies the conventions for using Advanced Encryption Standard-Counter with Cipher Block Chaining-Message Authentication Code (AES-CCM) and AES-Galois/Counter Mode (GCM) authenticated encryption algorithms as the content-authenticated-encryption algorithm with the Cryptographic Message Syntax [CMS] authenticated- enveloped-data content type [AuthEnv].

1.1. Terminology

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 RFC 2119 [STDWORDS].

1.2. ASN.1

CMS values are generated using ASN.1 [X.208-88], which uses the Basic Encoding Rules (BER) [X.209-88] and the Distinguished Encoding Rules (DER) [X.509-88].

1.3. AES

Dr. Joan Daemen and Dr. Vincent Rijmen, both from Belgium, developed the Rijndael block cipher algorithm, and they submitted it for consideration as the Advanced Encryption Standard (AES). Rijndael
ToP   noToC   RFC5084 - Page 2
   was selected by the National Institute for Standards and Technology
   (NIST), and it is specified in a U.S. Federal Information Processing
   Standard (FIPS) Publication [AES].  NIST selected the Rijndael
   algorithm for AES because it offers a combination of security,
   performance, efficiency, ease of implementation, and flexibility.
   Specifically, the algorithm performs well in both hardware and
   software across a wide range of computing environments.  Also, the
   very low memory requirements of the algorithm make it very well
   suited for restricted-space environments.  The AES is widely used by
   organizations, institutions, and individuals outside of the U.S.
   Government.

   The AES specifies three key sizes: 128, 192, and 256 bits.

1.4. AES-CCM

The Counter with CBC-MAC (CCM) mode of operation is specified in [CCM]. CCM is a generic authenticated encryption block cipher mode. CCM is defined for use with any 128-bit block cipher, but in this document, CCM is used with the AES block cipher. AES-CCM has four inputs: an AES key, a nonce, a plaintext, and optional additional authenticated data (AAD). AES-CCM generates two outputs: a ciphertext and a message authentication code (also called an authentication tag). The nonce is generated by the party performing the authenticated encryption operation. Within the scope of any authenticated- encryption key, the nonce value MUST be unique. That is, the set of nonce values used with any given key MUST NOT contain any duplicate values. Using the same nonce for two different messages encrypted with the same key destroys the security properties. AAD is authenticated but not encrypted. Thus, the AAD is not included in the AES-CCM output. It can be used to authenticate plaintext packet headers. In the CMS authenticated-enveloped-data content type, authenticated attributes comprise the AAD.

1.5. AES-GCM

The Galois/Counter Mode (GCM) is specified in [GCM]. GCM is a generic authenticated encryption block cipher mode. GCM is defined for use with any 128-bit block cipher, but in this document, GCM is used with the AES block cipher. AES-GCM has four inputs: an AES key, an initialization vector (IV), a plaintext content, and optional additional authenticated data (AAD). AES-GCM generates two outputs: a ciphertext and message
ToP   noToC   RFC5084 - Page 3
   authentication code (also called an authentication tag).  To have a
   common set of terms for AES-CCM and AES-GCM, the AES-GCM IV is
   referred to as a nonce in the remainder of this document.

   The nonce is generated by the party performing the authenticated
   encryption operation.  Within the scope of any authenticated-
   encryption key, the nonce value MUST be unique.  That is, the set of
   nonce values used with any given key MUST NOT contain any duplicate
   values.  Using the same nonce for two different messages encrypted
   with the same key destroys the security properties.

   AAD is authenticated but not encrypted.  Thus, the AAD is not
   included in the AES-GCM output.  It can be used to authenticate
   plaintext packet headers.  In the CMS authenticated-enveloped-data
   content type, authenticated attributes comprise the AAD.

2. Automated Key Management

The reuse of an AES-CCM or AES-GCM nonce/key combination destroys the security guarantees. As a result, it can be extremely difficult to use AES-CCM or AES-GCM securely when using statically configured keys. For safety's sake, implementations MUST use an automated key management system [KEYMGMT]. The CMS authenticated-enveloped-data content type supports four general key management techniques: Key Transport: the content-authenticated-encryption key is encrypted in the recipient's public key; Key Agreement: the recipient's public key and the sender's private key are used to generate a pairwise symmetric key, then the content-authenticated-encryption key is encrypted in the pairwise symmetric key; Symmetric Key-Encryption Keys: the content-authenticated- encryption key is encrypted in a previously distributed symmetric key-encryption key; and Passwords: the content-authenticated-encryption key is encrypted in a key-encryption key that is derived from a password or other shared secret value. All of these key management techniques meet the automated key management system requirement as long as a fresh content- authenticated-encryption key is generated for the protection of each content. Note that some of these key management techniques use one key-encryption key to encrypt more than one content-authenticated-
ToP   noToC   RFC5084 - Page 4
   encryption key during the system life cycle.  As long as fresh
   content-authenticated-encryption key is used each time, AES-CCM and
   AES-GCM can be used safely with the CMS authenticated-enveloped-data
   content type.

   In addition to these four general key management techniques, CMS
   supports other key management techniques.  See Section 6.2.5 of
   [CMS].  Since the properties of these key management techniques are
   unknown, no statement can be made about whether these key management
   techniques meet the automated key management system requirement.
   Designers and implementers must perform their own analysis if one of
   these other key management techniques is supported.

3. Content-Authenticated Encryption Algorithms

This section specifies the conventions employed by CMS implementations that support content-authenticated encryption using AES-CCM or AES-GCM. Content-authenticated encryption algorithm identifiers are located in the AuthEnvelopedData EncryptedContentInfo contentEncryptionAlgorithm field. Content-authenticated encryption algorithms are used to encipher the content located in the AuthEnvelopedData EncryptedContentInfo encryptedContent field and to provide the message authentication code for the AuthEnvelopedData mac field. Note that the message authentication code provides integrity protection for both the AuthEnvelopedData authAttrs and the AuthEnvelopedData EncryptedContentInfo encryptedContent.

3.1. AES-CCM

The AES-CCM authenticated encryption algorithm is described in [CCM]. A brief summary of the properties of AES-CCM is provided in Section 1.4. Neither the plaintext content nor the optional AAD inputs need to be padded prior to invoking AES-CCM.
ToP   noToC   RFC5084 - Page 5
   There are three algorithm identifiers for AES-CCM, one for each AES
   key size:

      aes OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
          organization(1) gov(101) csor(3) nistAlgorithm(4) 1 }

      id-aes128-CCM OBJECT IDENTIFIER ::= { aes 7 }

      id-aes192-CCM OBJECT IDENTIFIER ::= { aes 27 }

      id-aes256-CCM OBJECT IDENTIFIER ::= { aes 47 }

   With all three AES-CCM algorithm identifiers, the AlgorithmIdentifier
   parameters field MUST be present, and the parameters field must
   contain a CCMParameter:

      CCMParameters ::= SEQUENCE {
        aes-nonce         OCTET STRING (SIZE(7..13)),
        aes-ICVlen        AES-CCM-ICVlen DEFAULT 12 }

      AES-CCM-ICVlen ::= INTEGER (4 | 6 | 8 | 10 | 12 | 14 | 16)

   The aes-nonce parameter field contains 15-L octets, where L is the
   size of the length field.  With the CMS, the normal situation is for
   the content-authenticated-encryption key to be used for a single
   content; therefore, L=8 is RECOMMENDED.  See [CCM] for a discussion
   of the trade-off between the maximum content size and the size of the
   nonce.  Within the scope of any content-authenticated-encryption key,
   the nonce value MUST be unique.  That is, the set of nonce values
   used with any given key MUST NOT contain any duplicate values.

   The aes-ICVlen parameter field tells the size of the message
   authentication code.  It MUST match the size in octets of the value
   in the AuthEnvelopedData mac field.  A length of 12 octets is
   RECOMMENDED.

3.2. AES-GCM

The AES-GCM authenticated encryption algorithm is described in [GCM]. A brief summary of the properties of AES-CCM is provided in Section 1.5. Neither the plaintext content nor the optional AAD inputs need to be padded prior to invoking AES-GCM.
ToP   noToC   RFC5084 - Page 6
   There are three algorithm identifiers for AES-GCM, one for each AES
   key size:

      aes OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840)
          organization(1) gov(101) csor(3) nistAlgorithm(4) 1 }

      id-aes128-GCM OBJECT IDENTIFIER ::= { aes 6 }

      id-aes192-GCM OBJECT IDENTIFIER ::= { aes 26 }

      id-aes256-GCM OBJECT IDENTIFIER ::= { aes 46 }

   With all three AES-GCM algorithm identifiers, the AlgorithmIdentifier
   parameters field MUST be present, and the parameters field must
   contain a GCMParameter:

      GCMParameters ::= SEQUENCE {
        aes-nonce        OCTET STRING, -- recommended size is 12 octets
        aes-ICVlen       AES-GCM-ICVlen DEFAULT 12 }

      AES-GCM-ICVlen ::= INTEGER (12 | 13 | 14 | 15 | 16)

   The aes-nonce is the AES-GCM initialization vector.  The algorithm
   specification permits the nonce to have any number of bits between 1
   and 2^64.  However, the use of OCTET STRING within GCMParameters
   requires the nonce to be a multiple of 8 bits.  Within the scope of
   any content-authenticated-encryption key, the nonce value MUST be
   unique, but need not have equal lengths.  A nonce value of 12 octets
   can be processed more efficiently, so that length is RECOMMENDED.

   The aes-ICVlen parameter field tells the size of the message
   authentication code.  It MUST match the size in octets of the value
   in the AuthEnvelopedData mac field.  A length of 12 octets is
   RECOMMENDED.

4. Security Considerations

AES-CCM and AES-GCM make use of the AES block cipher in counter mode to provide encryption. When used properly, counter mode provides strong confidentiality. Bellare, Desai, Jokipii, and Rogaway show in [BDJR] that the privacy guarantees provided by counter mode are at least as strong as those for Cipher Block Chaining (CBC) mode when using the same block cipher. Unfortunately, it is easy to misuse counter mode. If counter block values are ever used for more than one encryption operation with the same key, then the same key stream will be used to encrypt both plaintexts, and the confidentiality guarantees are voided.
ToP   noToC   RFC5084 - Page 7
   Fortunately, the CMS AuthEnvelopedData provides all the tools needed
   to avoid misuse of counter mode.  Automated key management is
   discussed in Section 2.

   There are fairly generic precomputation attacks against the use of
   any block cipher in counter mode that allow a meet-in-the-middle
   attack against the key [H][B][MF].  AES-CCM and AES-GCM both make use
   of counter mode for encryption.  These precomputation attacks require
   the creation and searching of huge tables of ciphertext associated
   with known plaintext and known keys.  Assuming that the memory and
   processor resources are available for a precomputation attack, then
   the theoretical strength of any block cipher in counter mode is
   limited to 2^(n/2) bits, where n is the number of bits in the key.
   The use of long keys is the best countermeasure to precomputation
   attacks.  Use of an unpredictable nonce value in the counter block
   significantly increases the size of the table that the attacker must
   compute to mount a successful precomputation attack.

   Implementations must randomly generate content-authenticated-
   encryption keys.  The use of inadequate pseudo-random number
   generators (PRNGs) to generate cryptographic keys can result in
   little or no security.  An attacker may find it much easier to
   reproduce the PRNG environment that produced the keys, and then
   searching the resulting small set of possibilities, rather than brute
   force searching the whole key space.  The generation of quality
   random numbers is difficult.  RFC 4086 [RANDOM] offers important
   guidance in this area.

5. References

5.1. Normative References

[AES] NIST, FIPS PUB 197, "Advanced Encryption Standard (AES)", November 2001. [CCM] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-MAC (CCM)", RFC 3610, September 2003. [CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852, July 2004. [GCM] Dworkin, M., "NIST Special Publication 800-38D: Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC." , U.S. National Institute of Standards and Technology http://csrc.nist.gov/publications/nistpubs/800-38D/SP- 800-38D.pdf
ToP   noToC   RFC5084 - Page 8
   [STDWORDS]  Bradner, S., "Key words for use in RFCs to Indicate
               Requirement Levels", BCP 14, RFC 2119, March 1997.

   [X.208-88]  CCITT.  Recommendation X.208: Specification of Abstract
               Syntax Notation One (ASN.1).  1988.

   [X.209-88]  CCITT.  Recommendation X.209: Specification of Basic
               Encoding Rules for Abstract Syntax Notation One (ASN.1).
               1988.

   [X.509-88]  CCITT.  Recommendation X.509: The Directory-
               Authentication Framework.  1988.

5.2. Informative References

[AuthEnv] Housley, R., "Cryptographic Message Syntax (CMS) Authenticated-Enveloped-Data Content Type", RFC 5083, November 2007. [B] Biham, E., "How to Forge DES-Encrypted Messages in 2^28 Steps", Technion Computer Science Department Technical Report CS0884, 1996. [BDJR] Bellare, M, Desai, A., Jokipii, E., and P. Rogaway, "A Concrete Security Treatment of Symmetric Encryption: Analysis of the DES Modes of Operation", Proceedings 38th Annual Symposium on Foundations of Computer Science, 1997. [H] Hellman, M. E., "A cryptanalytic time-memory trade-off", IEEE Transactions on Information Theory, July 1980, pp. 401-406. [KEYMGMT] Bellovin, S. and R. Housley, "Guidelines for Cryptographic Key Management", BCP 107, RFC 4107, June 2005. [MF] McGrew, D., and S. Fluhrer, "Attacks on Additive Encryption of Redundant Plaintext and Implications on Internet Security", The Proceedings of the Seventh Annual Workshop on Selected Areas in Cryptography (SAC 2000), Springer-Verlag, August, 2000. [RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005.
ToP   noToC   RFC5084 - Page 9

Appendix: ASN.1 Module

CMS-AES-CCM-and-AES-GCM { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms-aes-ccm-and-gcm(32) } DEFINITIONS IMPLICIT TAGS ::= BEGIN -- EXPORTS All -- Object Identifiers aes OBJECT IDENTIFIER ::= { joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) 1 } id-aes128-CCM OBJECT IDENTIFIER ::= { aes 7 } id-aes192-CCM OBJECT IDENTIFIER ::= { aes 27 } id-aes256-CCM OBJECT IDENTIFIER ::= { aes 47 } id-aes128-GCM OBJECT IDENTIFIER ::= { aes 6 } id-aes192-GCM OBJECT IDENTIFIER ::= { aes 26 } id-aes256-GCM OBJECT IDENTIFIER ::= { aes 46 } -- Parameters for AigorithmIdentifier CCMParameters ::= SEQUENCE { aes-nonce OCTET STRING (SIZE(7..13)), aes-ICVlen AES-CCM-ICVlen DEFAULT 12 } AES-CCM-ICVlen ::= INTEGER (4 | 6 | 8 | 10 | 12 | 14 | 16) GCMParameters ::= SEQUENCE { aes-nonce OCTET STRING, -- recommended size is 12 octets aes-ICVlen AES-GCM-ICVlen DEFAULT 12 } AES-GCM-ICVlen ::= INTEGER (12 | 13 | 14 | 15 | 16) END
ToP   noToC   RFC5084 - Page 10

Author's Address

Russell Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 USA EMail: housley@vigilsec.com
ToP   noToC   RFC5084 - Page 11
Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.