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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 3369 (ref. '3') (Obsoleted by RFC 3852) == Outdated reference: A later version (-07) exists of draft-ietf-smime-aes-alg-06 ** Downref: Normative reference to an Informational RFC: RFC 3394 (ref. '5') -- Obsolete informational reference (is this intentional?): RFC 2246 (ref. '7') (Obsoleted by RFC 4346) == Outdated reference: A later version (-09) exists of draft-ietf-smime-rfc2633bis-03 Summary: 4 errors (**), 0 flaws (~~), 5 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 SIP WG J. Peterson 3 Internet-Draft NeuStar 4 Expires: December 27, 2003 June 28, 2003 6 S/MIME AES Requirement for SIP 7 draft-ietf-sip-smime-aes-01 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at http:// 25 www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 This Internet-Draft will expire on December 27, 2003. 32 Copyright Notice 34 Copyright (C) The Internet Society (2003). All Rights Reserved. 36 Abstract 38 RFC3261 currently specifies 3DES as the required minimum ciphersuite 39 for implementations of S/MIME in SIP. This document updates the 40 normative guidance of RFC3261 to require the Advanced Encryption 41 Standard (AES) for S/MIME. 43 Table of Contents 45 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 46 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 47 3. S/MIME Ciphersuite Requirements for SIP . . . . . . . . . . . . 4 48 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 49 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 50 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 51 Normative References . . . . . . . . . . . . . . . . . . . . . . 4 52 Informative References . . . . . . . . . . . . . . . . . . . . . 5 53 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5 54 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 6 56 1. Introduction 58 The Session Initiation Protocol (SIP) specification (RFC3261 [1]) 59 currently details optional support (a normative MAY) for the use of 60 secure MIME, or S/MIME (RFC2633 [8]). Since RFC3261 was published, 61 the S/MIME specification and the underlying Cryptographic Message 62 Syntax (CMS, RFC3369 [3]) have undergone some revision. Ongoing work 63 has identified AES as a algorithm that might be used for content 64 encryption in S/MIME. 66 The Advanced Encryption Standard (AES [6]) is widely believed to be 67 faster than Triple-DES (3DES, which has previously been mandated for 68 usage with S/MIME) and to be comparably secure. AES is also believed 69 to have comparatively low memory requirements, which make it suitable 70 for use in mobile or embedded devices, an important use-case for SIP. 72 As an additional consideration, the SIP specification has a 73 recommendation (normative SHOULD) for support of Transport Layer 74 Security (TLS, RFC2246 [7]). TLS support in SIP requires the usage 75 of AES. That means that currently, implementations that support both 76 TLS and S/MIME must support both 3DES and AES. A similar duplication 77 of effort exists with DSS in S/MIME as a digital signature algorithm 78 (the mandatory TLS ciphersuite used by SIP requires RSA). Unifying 79 the ciphersuite and signature algorithm requirements for TLS and S/ 80 MIME would simplify security implementations. 82 It is therefore desirable to bring the S/MIME requirement for SIP 83 into parity with ongoing work on the S/MIME standard, as well as to 84 unify the algorithm requirements for TLS and S/MIME. To date, S/MIME 85 has not yet seen widespread deployment in SIP user agents, and 86 therefore the minimum ciphersuite for S/MIME could be updated without 87 obsoleting any substantial deployments of S/MIME for SIP (in fact, 88 these changes will probably make support for S/MIME easier). This 89 document therefore updates the normative requirements for S/MIME in 90 RFC3261. 92 Note that work on these revisions in the S/MIME working group is 93 still in progress. This document will continue to track that work as 94 it evolves. By initiating this process in the SIP WG now, we provide 95 an early opportunity for input into the proposed changes and give 96 implementers some warning that the S/MIME requirements for SIP are 97 potentially changing. 99 2. Terminology 101 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 102 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 103 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 104 described in RFC2119 [2] and indicate requirement levels for 105 compliant SIP implementations. 107 3. S/MIME Ciphersuite Requirements for SIP 109 The following updates the text of RFC3261 Section 23.3, specifically 110 the fifth bullet point. The text currently reads: 112 o S/MIME implementations MUST at a minimum support SHA1 as a 113 digital signature algorithm, and 3DES as an encryption 114 algorithm. All other signature and encryption algorithms MAY 115 be supported. Implementations can negotiate support for these 116 algorithms with the "SMIMECapabilities" attribute. 118 This text is updated with the following: 120 S/MIME implementations MUST at a minimum support RSA as a digital 121 signature algorithm, SHA1 as a digest algorithm, and AES as an 122 encryption algorithm (as specified in [4]. For key wrap, S/MIME 123 implementations MUST support the AES Key Wrap Algorithm ([5]). S/ 124 MIME implementations of AES MUST support 128-bit AES keys, and SHOULD 125 support 192 and 256-bit keys. Note that the S/MIME specification [8] 126 mandates support for 3DES as an encryption algorithm, DH for key 127 encryption and DSS as a signature algorithm. In the SIP profile of 128 S/MIME, support for 3DES, DH and DSS is RECOMMENDED but not required. 129 All other signature and encryption algorithms MAY be supported. 130 Implementations can negotiate support for algorithms with the 131 "SMIMECapabilities" attribute. 133 Since SIP is 8-bit clean, all implementations MUST use 8-bit binary 134 Content-Transfer-Encoding for S/MIME in SIP. Implementations MAY 135 also be able to receive base-64 Content-Transfer-Encoding. 137 4. Security Considerations 139 The migration of the S/MIME requirement from Triples-DES to AES is 140 not known to introduce any new security considerations. 142 5. IANA Considerations 144 This document introduces no considerations for IANA. 146 Normative References 148 [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 149 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: 150 Session Initiation Protocol", RFC 3261, May 2002. 152 [2] Bradner, S., "Key words for use in RFCs to indicate requirement 153 levels", RFC 2119, March 1997. 155 [3] Housley, R., "Cryptographic Message Syntax", RFC 3369, August 156 2002. 158 [4] Schaad, J. and R. Housley, "Use of the AES Encryption Algorithm 159 and RSA-OAEP Key Transport in CMS", draft-ietf-smime-aes-alg-06 160 (work in progress), January 2003. 162 [5] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES) 163 Key Wrap Algorithm", RFC 3394, Sept 2002. 165 Informative References 167 [6] National Institute of Standards & Technology, "Advanced 168 Encryption Standard (AES).", FIPS 197, Nov 2001. 170 [7] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 171 2246, Jan 1999. 173 [8] Ramsdell, B., "S/MIME Version 3 Message Specification", draft- 174 ietf-smime-rfc2633bis-03 (work in progress), January 2003. 176 Author's Address 178 Jon Peterson 179 NeuStar, Inc. 180 1800 Sutter St 181 Suite 570 182 Concord, CA 94520 183 US 185 Phone: +1 925/363-8720 186 EMail: jon.peterson@neustar.biz 187 URI: http://www.neustar.biz/ 189 Appendix A. Acknowledgments 191 Thanks to Rohan Mahy, Gonzalo Camarillo and Eric Rescorla for review 192 of this document. 194 Full Copyright Statement 196 Copyright (C) The Internet Society (2003). All Rights Reserved. 198 This document and translations of it may be copied and furnished to 199 others, and derivative works that comment on or otherwise explain it 200 or assist in its implementation may be prepared, copied, published 201 and distributed, in whole or in part, without restriction of any 202 kind, provided that the above copyright notice and this paragraph are 203 included on all such copies and derivative works. However, this 204 document itself may not be modified in any way, such as by removing 205 the copyright notice or references to the Internet Society or other 206 Internet organizations, except as needed for the purpose of 207 developing Internet standards in which case the procedures for 208 copyrights defined in the Internet Standards process must be 209 followed, or as required to translate it into languages other than 210 English. 212 The limited permissions granted above are perpetual and will not be 213 revoked by the Internet Society or its successors or assigns. 215 This document and the information contained herein is provided on an 216 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 217 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 218 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 219 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 220 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 222 Acknowledgement 224 Funding for the RFC Editor function is currently provided by the 225 Internet Society.