The Camellia Algorithm and Its Use wiht the Secure Real-time Transport Protocol(SRTP)
draft-avt-kanno-srtp-camellia-00

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Abstract

This document describes the use of the Camellia block cipher algorithm in the Secure Real-time Transport Protocol (SRTP) for providing confidentiality for the Real-time Transport Protocol (RTP) traffic and for the control traffic for RTP, the Real-time Transport Control Protocol (RTCP).

1.  Introduction

This document describes the use of the Camellia [RFC3713] (Matsui, M., Nakajima, J., and S. Moriai, “A Description of the Camellia Encryption Algorithm,” April 2004.) block cipher algorithm in the Secure Real-time Transport Protocol (SRTP) [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) for providing confidentiality for the Real-time Transport Protocol (RTP) [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) traffic and for the control traffic for RTP, the Real-time Transport Control Protocol (RTCP) [RFC3550] (Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, “RTP: A Transport Protocol for Real-Time Applications,” July 2003.).

1.1.  Camellia

Camellia is a symmetric cipher with a Feistel structure. Camellia was developed jointly by NTT and Mitsubishi Electric Corporation in 2000. It was designed to withstand all known cryptanalytic attacks, and it has been scrutinized by worldwide cryptographic experts. Camellia is suitable for implementation in software and hardware, offering encryption speed in software and hardware implementations that is comparable to Advanced Encryption Standard (AES) [FIPS.197.2001] (National Institute of Standards and Technology, “Advanced Encryption Standard (AES),” November 2001.).

Camellia supports 128-bit block size and 128-, 192-, and 256-bit key lengths, i.e., the same interface specifications as the AES. Therefore, it is easy to implement Camellia based algorithms by replacing the AES block of AES based algorithms with a Camellia block.

Camellia already has been adopted by the IETF and other international standardization organizations; in particular, the IETF has published specifications for the use of Camellia with IPsec [RFC4312] (Kato, A., Moriai, S., and M. Kanda, “The Camellia Cipher Algorithm and Its Use With IPsec,” December 2005.), TLS [RFC4132] (Moriai, S., Kato, A., and M. Kanda, “Addition of Camellia Cipher Suites to Transport Layer Security (TLS),” July 2005.), S/MIME [RFC3657] (Moriai, S. and A. Kato, “Use of the Camellia Encryption Algorithm in Cryptographic Message Syntax (CMS),” January 2004.) and XML Security [RFC4051] (Eastlake, D., “Additional XML Security Uniform Resource Identifiers (URIs),” April 2005.). Camellia is one of the three ISO/IEC international standard [ISO/IEC 18033‑3] (International Organization for Standardization, “Information technology - Security techniques - Encryption algorithms - Part 3: Block ciphers,” July 2005.) 128-bit block ciphers (Camellia, AES, and SEED). Camellia was selected as a recommended cryptographic primitive by the EU NESSIE (New European Schemes for Signatures, Integrity and Encryption) project [NESSIE] (, “The NESSIE project (New European Schemes for Signatures, Integrity and Encryption),” .) and was included in the list of cryptographic techniques for Japanese e-Government systems that was selected by the Japanese CRYPTREC (Cryptography Research and Evaluation Committees) [CRYPTREC] (Information-technology Promotion Agency (IPA), “Cryptography Research and Evaluation Committees,” .).

Since optimized source code is provided under several open source licenses [open source license] (, “Camellia open source software,” .), Camellia is also adopted by several open source projects (OpenSSL, GnuTLS, FreeBSD, and Linux). Camellia is also adopted by Mozilla and Camellia is ready for use with Firefox 3.0 released in June 2008.

The algorithm specification and object identifiers are described in [RFC3713] (Matsui, M., Nakajima, J., and S. Moriai, “A Description of the Camellia Encryption Algorithm,” April 2004.).

The Camellia web site [Camellia web site] (, “Camellia web site,” .) contains a wealth of information about Camellia, including detailed specification, security analysis, performance figures, reference implementation, optimized implementation, test vectors(TV), and intellectual property information.

1.2.  Terminology

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" that appear in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

2.  Camellia Algorithm Suites for SRTP

All symmetric block cipher algorithms share common characteristics and valuables, including mode, key size, weak keys, and block size. Camellia algorithm is specified as well as AES, those relations are following:

    a) Camellia-CTR comply with [RFC3711]
    b) Camellia-GCM/CCM comply with [AES-GCM/CCM]

3.  Default and mandatory-to-implement Transforms

The default transforms also are mandatory-to-implement transforms in SRTP. Of course, "mandatory-to-implement" does not imply "mandatory- to-use". Table 1 summarizes the pre-defined transforms. The default values below are valid for the pre-defined transforms.

                        man.-to-impl.  optional            default
   encryption           Camellia-CTR   Camellia-CCM, -GCM  Camellia-CTR
   message integrity    HMAC-SHA1      Camellia-CCM, -GCM  HMAC-SHA1
   key derivation (PRF) Camellia-CTR            -          Camellia-CTR

Table 1: Mandatory-to-implement, optional and default transforms in SRTP and SRTCP.

4.  Security Considerations

At the time of writing this document, there are no known weak keys for Camellia. Also, No security problem has been found on Camellia. Camellia is secure against all known attacks including Differential cryptanalysis, linear cryptanalysis, and related key attacks.

The security considerations in RFC 5289 [RFC3711] (Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, “The Secure Real-time Transport Protocol (SRTP),” March 2004.) and Draft of AES-GCM and AES-CCM for SRTP [AES‑GCM/CCM] (McGrew, D., “AES-GCM and AES-CCM Authenticated Encryption in Secure RTP (SRTP),” October 2008.) apply to this document as well.

5.  IANA Considerations

RFC 4568 [RFC4568] (Andreasen, F., Baugher, M., and D. Wing, “Session Description Protocol (SDP) Security Descriptions for Media Streams,” July 2006.) defines SRTP "crypto suites"; also, [AES‑GCM/CCM] (McGrew, D., “AES-GCM and AES-CCM Authenticated Encryption in Secure RTP (SRTP),” October 2008.) defines a crypto suite corresponds to a particular AEAD algorithm in SRTP. In order to allow SDP to signal the use of the algorithms defined in this document, IANA will register the following crypto suites into the subregistry for SRTP crypto suites under the SRTP transport of the SDP Security Descriptions:

      srtp-crypto-suite-ext = "CAMELLIA_CM_128_HMAC_SHA1_80" /
                              "CAMELLIA_CM_128_HMAC_SHA1_32" /
                              "AEAD_CAMELLIA_128_GCM"        /
                              "AEAD_CAMELLIA_256_GCM"        /
                              "AEAD_CAMELLIA_128_GCM_8"      /
                              "AEAD_CAMELLIA_256_GCM_8"      /
                              "AEAD_CAMELLIA_128_GCM_12"     /
                              "AEAD_CAMELLIA_256_GCM_12"     /
                              "AEAD_CAMELLIA_128_CCM"        /
                              "AEAD_CAMELLIA_256_CCM"        /
                              srtp-crypto-suite-ext

6.  Test Vectors

TBD.

7.  References

7.1. Normative References

7.2. Informative References

Authors' Addresses