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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Holmberg 3 Internet-Draft Ericsson 4 Updates: 4572 (if approved) September 23, 2016 5 Intended status: Standards Track 6 Expires: March 27, 2017 8 Updates to RFC 4572 9 draft-ietf-mmusic-4572-update-06.txt 11 Abstract 13 This document updates RFC 4572 by clarifying the usage of multiple 14 SDP 'fingerprint' attributes with a single TLS connection. The 15 document also updates the preferred cipher suite with a stronger 16 cipher suite, and removes the requirement to use the same hash 17 function for calculating a certificate fingerprint that is used to 18 calculate the certificate signature. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on March 27, 2017. 37 Copyright Notice 39 Copyright (c) 2016 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 3. Update to RFC 4572 . . . . . . . . . . . . . . . . . . . . . 3 57 3.1. Update to the sixth paragraph of section 5 . . . . . . . 3 58 3.2. New paragraphs to the end of section 5 . . . . . . . . . 4 59 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 60 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 61 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 62 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 8. Normative References . . . . . . . . . . . . . . . . . . . . 7 64 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 66 1. Introduction 68 RFC 4572 [RFC4572] specifies how to establish Transport Layer 69 Security (TLS) connections using the Session Description Protocol 70 (SDP) [RFC4566]. 72 RFC 4572 defines the SDP 'fingerprint' attribute, which is used to 73 carry a secure hash value (fingerprint) associated with a 74 certificate. However, RFC 4572 is currently unclear on whether 75 multiple 'fingerprint' attributes can be associated with a single SDP 76 media description ("m= line") [RFC4566], and the associated 77 semantics. Multiple fingerprints are needed if an endpoints wants to 78 provide fingerprints associated with multiple certificates. For 79 example, with RTP-based media, an endpoint might use different 80 certificates for RTP and RTCP. 82 RFC 4572 also specifies a preferred cipher suite. However, the 83 currently preferred cipher suite is considered outdated, and the 84 preference needs to be updated. 86 RFC 4572 mandates that the hash function used to calculate the 87 fingerprint is the same hash function used to calculate the 88 certificate signature. That requirement might prevent usage of 89 newer, stronger and more collision-safe hash functions for 90 calculating certificate fingerprints. This change also requires that 91 multiple 'fingerprint' attributes can be associated with a single 92 "m=" line, so that implementations are able to provide fingerprints 93 calculated using updated hash functions alongside those that are 94 needed to interoperate with existing implementations. 96 This document updates RFC 4572 [RFC4572] by clarifying the usage of 97 multiple SDP 'fingerprint' attributes. It is clarified that multiple 98 'fingerprint' attributes can be used to carry fingerprints, 99 calculated using different hash functions, associated with a given 100 certificate, and to carry fingerprints associated with multiple 101 certificates. The fingerprint matching procedure, when multiple 102 fingerprints are provided, are also clarified. The document also 103 updates the preferred cipher suite with a stronger cipher suite, and 104 removes the requirement to use the same hash function for calculating 105 a certificate fingerprint and certificate signature. 107 NOTE: Even though this document updates the procedures in RFC 4572, 108 it does not make existing implementations non-compliant with RFC 109 4572. The updated procedures in this document have been defined in 110 order to be backward compatible with the procedures in RFC 4572. 112 2. Conventions 114 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 115 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 116 document are to be interpreted as described in [RFC2119]. 118 3. Update to RFC 4572 120 This section updates section 5 of RFC 4572. 122 3.1. Update to the sixth paragraph of section 5 123 OLD TEXT: 125 A certificate fingerprint MUST be computed using the same one-way 126 hash function as is used in the certificate's signature algorithm. 127 (This ensures that the security properties required for the 128 certificate also apply for the fingerprint. It also guarantees that 129 the fingerprint will be usable by the other endpoint, so long as the 130 certificate itself is.) Following RFC 3279 [7] as updated by RFC 131 4055 [9], therefore, the defined hash functions are 'SHA-1' [11] 132 [19], 'SHA-224' [11], 'SHA-256' [11], 'SHA-384' [11], 'SHA-512' [11] 133 , 'MD5' [12], and 'MD2' [13], with 'SHA-1' preferred. A new IANA 134 registry of Hash Function Textual Names, specified in Section 8, 135 allows for addition of future tokens, but they may only be added if 136 they are included in RFCs that update or obsolete RFC 3279 [7]. 137 Self-signed certificates (for which legacy certificates are not a 138 consideration) MUST use one of the FIPS 180 algorithms (SHA-1, 139 SHA-224, SHA-256, SHA-384, or SHA-512) as their signature algorithm, 140 and thus also MUST use it to calculate certificate fingerprints. 142 NEW TEXT: 144 Following RFC 3279 [7] as updated by RFC 4055 [9], therefore, the 145 defined hash functions are 'SHA-1' [11] [19], 'SHA-224' [11], 146 'SHA-256' [11], 'SHA-384' [11], 'SHA-512' [11], 'MD5' [12], and 147 'MD2' [13], with 'SHA-256' preferred. A new IANA registry of Hash 148 Function Textual Names, specified in Section 8, allows for addition 149 of future tokens, but they may only be added if they are included 150 in RFCs that update or obsolete RFC 3279 [7]. 152 3.2. New paragraphs to the end of section 5 153 NEW TEXT: 155 Multiple SDP fingerprint attributes can be associated with an m- 156 line. This can occur if multiple fingerprints have been calculated 157 for a certificate using different hash functions. It can also 158 occur if one or more fingerprints associated with multiple 159 certificates have been calculated. This might be needed if multiple 160 certificates will be used for media associated with an m- line 161 (e.g. if separate certificates are used for RTP and RTCP), or where 162 it is not known which certificate will be used when the 163 fingerprints are exchanged. In such cases, one or more fingerprints 164 MUST be calculated for each possible certificate. An endpoint 165 MUST, as a minimum, calculate a fingerprint using both the 'SHA-256' 166 hash function algorithm and the hash function used to generate the 167 signature on the certificate for each possible certificate. 168 Including the hash from the signature algorithm ensures 169 interoperability with strict implementations of RFC 4572. 170 Either of these fingerprints MAY be omitted if the endpoint includes 171 a hash with a stronger hash algorithm that it knows that the peer 172 supports, if it is known that the peer does not support the hash 173 algorithm, or if local policy mandates use of stronger algorithms. 175 If fingerprints associated with multiple certificates are 176 calculated, the same set of hash functions MUST be used to 177 calculate fingerprints for each certificate associated with the 178 m- line. 180 For each used certificate, an endpoint MUST be able to match at 181 least one fingerprint, calculated using the hash function that the 182 endpoint supports and considers most secure, with the used 183 certificate. If the checked fingerprint does not match the used 184 certificate, the endpoint MUST NOT establish the TLS connection. In 185 addition, the endpoint MAY also check fingerprints calculated using 186 other hash functions that it has received for a match. For each 187 hash function checked, one of the received fingerprints calculated 188 using the hash function MUST match the used certificate. 190 NOTE: The SDP fingerprint attribute does not contain a reference to 191 a specific certificate. Endpoints need to compare the fingerprint 192 with a certificate hash in order to look for a match. 194 4. Security Considerations 196 This document improves security. It updates the preferred hash 197 function cipher suite from SHA-1 to SHA-256. By clarifying the usage 198 and handling of multiple fingerprints, the document also enables hash 199 agility, and incremental deployment of newer, and more secure, cipher 200 suites. 202 5. IANA Considerations 204 IANA is requested to add a reference to this document for the att- 205 field (both session and media level) registration "fingerprint" in 206 Session Description Protocol (SDP) Parameters registry. 208 6. Acknowledgements 210 Martin Thomson, Paul Kyzivat, Jonathan Lennox and Roman Shpount 211 provided valuable comments and input on this document. 213 7. Change Log 215 [RFC EDITOR NOTE: Please remove this section when publishing] 217 Changes from draft-ietf-mmusic-4572-update-05 219 o Added a requirement to generate a fingerprint that matches the 220 signature. 222 o Added text clarifying that updates do not make existing 223 implementations non-compliant with RFC 4572. 225 o IANA Considerations text added. 227 Changes from draft-ietf-mmusic-4572-update-04 229 o Removed prevously added requirement that endpoint must calcuate at 230 least one fingerprint using a hash function that was also used by 231 the peer. 233 Changes from draft-ietf-mmusic-4572-update-03 235 o Mandatory (except in specific situations) to provide a fingerprint 236 calculated using SHA-256. 238 o When an endpoint receives fingerprints from its peer, the endpoint 239 must (except in specific situations) calculate at least one 240 fingerpint using a hash function that was also used by the peer. 242 Changes from draft-ietf-mmusic-4572-update-02 244 o Editorial fixes based on comments from Martin Thomson. 246 o Non-used references removed. 248 Changes from draft-ietf-mmusic-4572-update-01 250 o Changes based on comments from Martin Thomson. 252 o - Editorial fixes 254 o Changes in handling of multiple fingerprints. 256 o - Sender must send same set of hash functions for each offered 257 certificate. 259 o - Receiver must check the hash function it considers most secure 260 for a match. It may check other hash functions. 262 Changes from draft-ietf-mmusic-4572-update-00 264 o Changes in handling of multiple fingerprints. 266 o - Number of fingerprints calculated for each certificate does not 267 have to match. 269 o - Clarified that receiver shall check check fingerprints using 270 hash algorithms it considers safe. 272 o - Additional text added to security considerations section. 274 Changes from draft-holmberg-mmusic-4572-update-01 276 o Adopted WG document (draft-ietf-mmusic-4572-update-00) submitted. 278 o IANA considerations section added. 280 8. Normative References 282 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 283 Requirement Levels", BCP 14, RFC 2119, 284 DOI 10.17487/RFC2119, March 1997, 285 . 287 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 288 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 289 July 2006, . 291 [RFC4572] Lennox, J., "Connection-Oriented Media Transport over the 292 Transport Layer Security (TLS) Protocol in the Session 293 Description Protocol (SDP)", RFC 4572, 294 DOI 10.17487/RFC4572, July 2006, 295 . 297 Author's Address 299 Christer Holmberg 300 Ericsson 301 Hirsalantie 11 302 Jorvas 02420 303 Finland 305 Email: christer.holmberg@ericsson.com