idnits 2.17.1 draft-ietf-kitten-tls-channel-bindings-for-tls13-16.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- -- The draft header indicates that this document updates RFC7677, but the abstract doesn't seem to directly say this. It does mention RFC7677 though, so this could be OK. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year (Using the creation date from RFC5801, updated by this document, for RFC5378 checks: 2006-02-14) -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (4 May 2022) is 720 days in the past. Is this intentional? 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 informational reference (is this intentional?): RFC 5246 (Obsoleted by RFC 8446) Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Transport Layer Security S. Whited 3 Internet-Draft 4 May 2022 4 Updates: 5801, 5802, 5929, 7677 (if approved) 5 Intended status: Standards Track 6 Expires: 5 November 2022 8 Channel Bindings for TLS 1.3 9 draft-ietf-kitten-tls-channel-bindings-for-tls13-16 11 Abstract 13 This document defines a channel binding type, tls-exporter, that is 14 compatible with TLS 1.3 in accordance with RFC 5056, On Channel 15 Binding. Furthermore, it updates the default channel binding to the 16 new binding for versions of TLS greater than 1.2. This document 17 updates RFC5801, RFC5802, RFC5929, and RFC7677. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on 5 November 2022. 36 Copyright Notice 38 Copyright (c) 2022 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 43 license-info) in effect on the date of publication of this document. 44 Please review these documents carefully, as they describe your rights 45 and restrictions with respect to this document. Code Components 46 extracted from this document must include Revised BSD License text as 47 described in Section 4.e of the Trust Legal Provisions and are 48 provided without warranty as described in the Revised BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 1.1. Conventions and Terminology . . . . . . . . . . . . . . . 2 54 2. The 'tls-exporter' Channel Binding Type . . . . . . . . . . . 3 55 3. TLS 1.3 with SCRAM or GSS-API over SASL . . . . . . . . . . . 3 56 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 57 4.1. Uniqueness of Channel Bindings . . . . . . . . . . . . . 4 58 4.2. Use with Legacy TLS . . . . . . . . . . . . . . . . . . . 5 59 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 60 5.1. Registration of Channel Binding Type . . . . . . . . . . 5 61 5.2. Registration of Channel Binding TLS Exporter Label . . . 6 62 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 64 6.2. Informative References . . . . . . . . . . . . . . . . . 7 65 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 67 1. Introduction 69 The "tls-unique" channel binding type defined in [RFC5929] was found 70 to be vulnerable to the "triple handshake vulnerability" 71 [TRIPLE-HANDSHAKE] without the extended master secret extension 72 defined in [RFC7627]. While TLS 1.3 uses a complete transcript hash 73 akin to the extended master secret procedures, the safety of channel 74 bindings with TLS 1.3 was not analyzed as part of the core protocol 75 work, and so the specification of channel bindings for TLS 1.3 was 76 deferred. [RFC8446] section C.5 notes the lack of channel bindings 77 for TLS 1.3; this document defines such channel bindings, and fills 78 that gap. Furthermore, this document updates [RFC5929] by adding an 79 additional unique channel binding type, "tls-exporter", that replaces 80 some usage of "tls-unique". 82 1.1. Conventions and Terminology 84 Throughout this document the acronym "EKM" is used to refer to 85 Exported Keying Material as defined in [RFC5705]. 87 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 88 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 89 "OPTIONAL" in this document are to be interpreted as described in BCP 90 14 [RFC2119] [RFC8174] when, and only when, they appear in all 91 capitals, as shown here. 93 2. The 'tls-exporter' Channel Binding Type 95 Channel binding mechanisms are not useful until TLS implementations 96 expose the required data. To facilitate this, "tls-exporter" uses 97 exported keying material (EKM) which is already widely exposed by TLS 98 implementations. The EKM is obtained using the keying material 99 exporters for TLS as defined in [RFC5705] and [RFC8446] section 7.5 100 by supplying the following inputs: 102 Label: The ASCII string "EXPORTER-Channel-Binding" with no 103 terminating NUL. 105 Context value: Zero-length string. 107 Length: 32 bytes. 109 This channel binding mechanism is defined only when the TLS handshake 110 results in unique master secrets. This is true of TLS versions prior 111 to 1.3 when the extended master secret extension of [RFC7627] is in 112 use, and is always true for TLS 1.3 (see [RFC8446] appendix D). 114 3. TLS 1.3 with SCRAM or GSS-API over SASL 116 SCRAM ([RFC5802], and [RFC7677]) and GSS-API over SASL [RFC5801] 117 define "tls-unique" as the default channel binding to use over TLS. 118 As "tls-unique" is not defined for TLS 1.3 (and greater), this 119 document updates [RFC5801], [RFC5802], and [RFC7677] to use "tls- 120 exporter" as the default channel binding over TLS 1.3 (and greater). 121 Note that this document does not change the default channel binding 122 for SCRAM mechanisms over TLS 1.2 [RFC5246], which is still "tls- 123 unique". 125 Additionally, this document updates the aforementioned documents to 126 make "tls-exporter" the mandatory to implement channel binding if any 127 channel bindings are implemented for TLS 1.3. Implementations that 128 support channel binding over TLS 1.3 MUST implement "tls-exporter". 130 4. Security Considerations 132 The channel binding type defined in this document is constructed so 133 that disclosure of the channel binding data does not leak secret 134 information about the TLS channel and does not affect the security of 135 the TLS channel. 137 The derived data MUST NOT be used for any purpose other than channel 138 bindings as described in [RFC5056]. In particular, implementations 139 MUST NOT use channel binding as a secret key to protect privileged 140 information. 142 The Security Considerations sections of [RFC5056], [RFC5705], and 143 [RFC8446] apply to this document. 145 4.1. Uniqueness of Channel Bindings 147 The definition of channel bindings in [RFC5056] defines the concept 148 of a "unique" channel binding as being one that is unique to the 149 channel endpoints and unique over time, that is, a value that is 150 unique to a specific instance of the lower layer security protocol. 151 When TLS is the lower layer security protocol, as for the channel 152 binding type defined in this document, this concept of uniqueness 153 corresponds to uniquely identifying the specific TLS connection. 155 However, a stronger form of uniqueness is possible, which would 156 entail uniquely identifying not just the lower layer protocol but 157 also the upper layer application or authentication protocol that is 158 consuming the channel binding. The distinction is relevant only when 159 there are multiple instances of an authentication protocol, or 160 multiple distinct authentication protocols, that run atop the same 161 lower layer protocol. Such a situation is rare -- most consumers of 162 channel bindings establish an instance of the lower layer secure 163 protocol, run a single application or authentication protocol as the 164 upper layer protocol, then terminate both upper and lower layer 165 protocols. In this situation the stronger form of uniqueness is 166 trivially achieved, given that the channel binding value is unique in 167 the sense of [RFC5056]. 169 The channel binding type defined by this document provides only the 170 weaker type of uniqueness, as per [RFC5056]; it does not achieve the 171 stronger uniqueness per upper layer protocol instance described 172 above. This stronger form of uniqueness would be useful in that it 173 provides protection against cross-protocol attacks for the multiple 174 authentication protocols running over the same instance of the lower 175 layer protocol, and it provides protection against replay attacks 176 that seek to replay a message from one instance of an authentication 177 protocol in a different instance of the same authentication protocol, 178 again running over the same instance of the lower layer protocol. 179 Both of these properties are highly desirable when performing formal 180 analysis of upper layer protocols; if these properties are not 181 provided, such formal analysis is essentially impossible. In some 182 cases one or both of these properties may already be provided by 183 specific upper layer protocols, but that is dependent on the 184 mechanism(s) in question, and formal analysis requires that the 185 property is provided in a generic manner, across all potential upper 186 layer protocols that exist or might exist in the future. 188 Accordingly, applications that make use of the channel binding type 189 defined in this document MUST NOT use the channel binding for more 190 than one authentication mechanism instance on a given TLS connection. 191 Such applications MUST immediately close the TLS connection after the 192 conclusion of the upper layer protocol. 194 4.2. Use with Legacy TLS 196 While it is possible to use this channel binding mechanism with TLS 197 versions below 1.3, extra precaution must be taken to ensure that the 198 chosen cipher suites always result in unique master secrets. For 199 more information see [RFC7627] and the Security Considerations 200 section of [RFC5705] (TLS 1.3 always provides unique master secrets, 201 as discussed in Appendix D of [RFC8446].) 203 When TLS renegotiation is enabled on a connection the "tls-exporter" 204 channel binding type is not defined for that connection and 205 implementations MUST NOT support it. 207 In general, users wishing to take advantage of channel binding should 208 upgrade to TLS 1.3 or later. 210 5. IANA Considerations 212 5.1. Registration of Channel Binding Type 214 This document adds the following registration in the "Channel-Binding 215 Types" registry: 217 Subject: Registration of channel binding tls-exporter 219 Channel binding unique prefix: tls-exporter 221 Channel binding type: unique 223 Channel type: TLS [RFC8446] 225 Published specification: draft-ietf-kitten-tls-channel-bindings-for- 226 tls13-16 228 Channel binding is secret: no 230 Description: The EKM value obtained from the current TLS connection. 232 Intended usage: COMMON 234 Person and email address to contact for further information: Sam 235 Whited . 237 Owner/Change controller name and email address: IESG. 239 Expert reviewer name and contact information: IETF KITTEN or TLS WG 240 (kitten@ietf.org or tls@ietf.org, failing that, ietf@ietf.org). 242 Note: See the published specification for advice on the 243 applicability of this channel binding type. 245 5.2. Registration of Channel Binding TLS Exporter Label 247 This document adds the following registration in the "TLS Exporter 248 Labels" registry, which is part of the "Transport Layer Security 249 (TLS) Parameters" group: 251 Value: EXPORTER-Channel-Binding 253 DTLS-OK: Y 255 Recommended: Y 257 Reference: This document 259 6. References 261 6.1. Normative References 263 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 264 Requirement Levels", BCP 14, RFC 2119, 265 DOI 10.17487/RFC2119, March 1997, 266 . 268 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 269 Channels", RFC 5056, DOI 10.17487/RFC5056, November 2007, 270 . 272 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 273 Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, 274 March 2010, . 276 [RFC5801] Josefsson, S. and N. Williams, "Using Generic Security 277 Service Application Program Interface (GSS-API) Mechanisms 278 in Simple Authentication and Security Layer (SASL): The 279 GS2 Mechanism Family", RFC 5801, DOI 10.17487/RFC5801, 280 July 2010, . 282 [RFC5802] Newman, C., Menon-Sen, A., Melnikov, A., and N. Williams, 283 "Salted Challenge Response Authentication Mechanism 284 (SCRAM) SASL and GSS-API Mechanisms", RFC 5802, 285 DOI 10.17487/RFC5802, July 2010, 286 . 288 [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings 289 for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010, 290 . 292 [RFC7677] Hansen, T., "SCRAM-SHA-256 and SCRAM-SHA-256-PLUS Simple 293 Authentication and Security Layer (SASL) Mechanisms", 294 RFC 7677, DOI 10.17487/RFC7677, November 2015, 295 . 297 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 298 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 299 May 2017, . 301 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 302 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 303 . 305 6.2. Informative References 307 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 308 (TLS) Protocol Version 1.2", RFC 5246, 309 DOI 10.17487/RFC5246, August 2008, 310 . 312 [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., 313 Langley, A., and M. Ray, "Transport Layer Security (TLS) 314 Session Hash and Extended Master Secret Extension", 315 RFC 7627, DOI 10.17487/RFC7627, September 2015, 316 . 318 [TRIPLE-HANDSHAKE] 319 Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti, 320 A., and P. Strub, "Password Storage", March 2014, 321 . 323 Author's Address 325 Sam Whited 326 Atlanta, GA 327 United States of America 328 Email: sam@samwhited.com 329 URI: https://blog.samwhited.com/