idnits 2.17.1 draft-ietf-tokbind-negotiation-13.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 : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (May 9, 2018) is 2176 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(See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-19) exists of draft-ietf-tokbind-protocol-17 ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force A. Popov, Ed. 3 Internet-Draft M. Nystroem 4 Intended status: Standards Track Microsoft Corp. 5 Expires: November 10, 2018 D. Balfanz 6 A. Langley 7 Google Inc. 8 May 9, 2018 10 Transport Layer Security (TLS) Extension for Token Binding Protocol 11 Negotiation 12 draft-ietf-tokbind-negotiation-13 14 Abstract 16 This document specifies a Transport Layer Security (TLS) extension 17 for the negotiation of Token Binding protocol version and key 18 parameters. 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 https://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 November 10, 2018. 37 Copyright Notice 39 Copyright (c) 2018 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 (https://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 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 56 2. Token Binding Negotiation Client Hello Extension . . . . . . 2 57 3. Token Binding Negotiation Server Hello Extension . . . . . . 4 58 4. Negotiating Token Binding Protocol Version and Key Parameters 4 59 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 60 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 61 6.1. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 6 62 6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS 63 Versions . . . . . . . . . . . . . . . . . . . . . . . . 6 64 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 65 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 66 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 67 8.2. Informative References . . . . . . . . . . . . . . . . . 8 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 70 1. Introduction 72 In order to use the Token Binding protocol 73 [I-D.ietf-tokbind-protocol], the client and server need to agree on 74 the Token Binding protocol version and the parameters (signature 75 algorithm, length) of the Token Binding key. This document specifies 76 a new TLS [RFC5246] extension to accomplish this negotiation without 77 introducing additional network round-trips in TLS 1.2 and earlier 78 versions. The negotiation of the Token Binding protocol and key 79 parameters in combination with TLS 1.3 and later versions is beyond 80 the scope of this document. 82 1.1. Requirements Language 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 86 "OPTIONAL" in this document are to be interpreted as described in BCP 87 14 [RFC2119] [RFC8174] when, and only when, they appear in all 88 capitals, as shown here. 90 2. Token Binding Negotiation Client Hello Extension 92 The client uses the "token_binding" TLS extension to indicate the 93 highest supported Token Binding protocol version and key parameters. 95 enum { 96 token_binding(24), (65535) 97 } ExtensionType; 99 The "extension_data" field of this extension contains a 100 "TokenBindingParameters" value. 102 struct { 103 uint8 major; 104 uint8 minor; 105 } TB_ProtocolVersion; 107 enum { 108 rsa2048_pkcs1.5(0), rsa2048_pss(1), ecdsap256(2), (255) 109 } TokenBindingKeyParameters; 111 struct { 112 TB_ProtocolVersion token_binding_version; 113 TokenBindingKeyParameters key_parameters_list<1..2^8-1> 114 } TokenBindingParameters; 116 "token_binding_version" indicates the version of the Token Binding 117 protocol the client wishes to use during this connection. If the 118 client supports multiple Token Binding protocol versions, it SHOULD 119 indicate the latest supported version (the one with the highest 120 TB_ProtocolVersion.major and TB_ProtocolVersion.minor) in 121 TokenBindingParameters.token_binding_version. E.g. if the client 122 supports versions {1, 0} and {0, 13} of the Token Binding protocol, 123 it SHOULD indicate version {1, 0}. Please note that the server MAY 124 select any lower protocol version, see Section 3 125 "Token Binding Negotiation Server Hello Extension" for more details. 126 If the client does not support the Token Binding protocol version 127 selected by the server, then the connection proceeds without Token 128 Binding. [I-D.ietf-tokbind-protocol] describes version {1, 0} of the 129 protocol. 131 RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: Prototype 132 implementations of Token Binding drafts can indicate support of a 133 specific draft version, e.g. {0, 1} or {0, 2}. 135 "key_parameters_list" contains the list of identifiers of the Token 136 Binding key parameters supported by the client, in descending order 137 of preference. [I-D.ietf-tokbind-protocol] establishes an IANA 138 registry for Token Binding key parameter identifiers. 140 3. Token Binding Negotiation Server Hello Extension 142 The server uses the "token_binding" TLS extension to indicate support 143 for the Token Binding protocol and to select the protocol version and 144 key parameters. 146 The server that supports Token Binding and receives a client hello 147 message containing the "token_binding" extension will include the 148 "token_binding" extension in the server hello if all of the following 149 conditions are satisfied: 151 1. The server supports the Token Binding protocol version offered by 152 the client or a lower version. 154 2. The server finds acceptable Token Binding key parameters on the 155 client's list. 157 3. The server is also negotiating the Extended Master Secret 158 [RFC7627] and Renegotiation Indication [RFC5746] TLS extensions. 159 This requirement applies when TLS 1.2 or an older TLS version is 160 used (see Section 6 "Security Considerations" below for more 161 details). 163 The server will ignore any key parameters that it does not recognize. 164 The "extension_data" field of the "token_binding" extension is 165 structured the same as described above for the client 166 "extension_data". 168 "token_binding_version" contains the lower of: 170 o the Token Binding protocol version offered by the client in the 171 "token_binding" extension and 173 o the highest Token Binding protocol version supported by the 174 server. 176 "key_parameters_list" contains exactly one Token Binding key 177 parameters identifier selected by the server from the client's list. 179 4. Negotiating Token Binding Protocol Version and Key Parameters 181 It is expected that a server will have a list of Token Binding key 182 parameters identifiers that it supports, in preference order. The 183 server MUST only select an identifier that the client offered. The 184 server SHOULD select the most highly preferred key parameters 185 identifier it supports which is also advertised by the client. In 186 the event that the server supports none of the key parameters that 187 the client advertises, then the server MUST NOT include 188 "token_binding" extension in the server hello. 190 The client receiving the "token_binding" extension MUST terminate the 191 handshake with a fatal "unsupported_extension" alert if any of the 192 following conditions are true: 194 1. The client did not include the "token_binding" extension in the 195 client hello. 197 2. "token_binding_version" is higher than the Token Binding protocol 198 version advertised by the client. 200 3. "key_parameters_list" includes more than one Token Binding key 201 parameters identifier. 203 4. "key_parameters_list" includes an identifier that was not 204 advertised by the client. 206 5. TLS 1.2 or an older TLS version is used, but the Extended Master 207 Secret [RFC7627] and TLS Renegotiation Indication [RFC5746] 208 extensions are not negotiated (see Section 6 209 "Security Considerations" below for more details). 211 If the "token_binding" extension is included in the server hello and 212 the client supports the Token Binding protocol version selected by 213 the server, it means that the version and key parameters have been 214 negotiated between the client and the server and SHALL be definitive 215 for the TLS connection. TLS 1.2 and earlier versions support 216 renegotiation, allowing the client and server to renegotiate the 217 Token Binding protocol version and key parameters on the same 218 connection. The client MUST use the negotiated key parameters in the 219 "provided_token_binding" as described in [I-D.ietf-tokbind-protocol]. 221 If the client does not support the Token Binding protocol version 222 selected by the server, then the connection proceeds without Token 223 Binding. There is no requirement for the client to support any Token 224 Binding versions other than the one advertised in the client's 225 "token_binding" extension. 227 Client and server applications can choose to handle failure to 228 negotiate Token Binding in a variety of ways, e.g.: continue using 229 the connection as usual, shorten the lifetime of tokens issued during 230 this connection, require stronger authentication, terminate the 231 connection, etc. 233 The Token Binding protocol version and key parameters are negotiated 234 for each TLS connection, which means that the client and server 235 include their "token_binding" extensions both in the full TLS 236 handshake that establishes a new TLS session and in the subsequent 237 abbreviated TLS handshakes that resume the TLS session. 239 5. IANA Considerations 241 This document updates the TLS "ExtensionType Values" registry. IANA 242 has provided the following temporary registration for the 243 "token_binding" TLS extension: 245 Value: 24 247 Extension name: token_binding 249 Reference: this document 251 Recommended: Yes 253 IANA is requested to make this registration permanent, keeping the 254 value of 24, which has been used by the prototype implementations of 255 the Token Binding protocol. 257 This document uses "Token Binding Key Parameters" registry originally 258 created in [I-D.ietf-tokbind-protocol]. This document creates no new 259 registrations in this registry. 261 6. Security Considerations 263 6.1. Downgrade Attacks 265 The Token Binding protocol version and key parameters are negotiated 266 via "token_binding" extension within the TLS handshake. TLS prevents 267 active attackers from modifying the messages of the TLS handshake, 268 therefore it is not possible for the attacker to remove or modify the 269 "token_binding" extension. The signature algorithm and key length 270 used in the Token Binding of type "provided_token_binding" MUST match 271 the parameters negotiated via "token_binding" extension. 273 6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions 275 The Token Binding protocol relies on the TLS Exporters [RFC5705] to 276 associate a TLS connection with a Token Binding. The triple 277 handshake attack [TRIPLE-HS] is a known vulnerability in TLS 1.2 and 278 older TLS versions, allowing the attacker to synchronize keying 279 material between TLS connections. The attacker can then successfully 280 replay bound tokens. For this reason, the Token Binding protocol 281 MUST NOT be negotiated with these TLS versions, unless the Extended 282 Master Secret [RFC7627] and Renegotiation Indication [RFC5746] TLS 283 extensions have also been negotiated. 285 7. Acknowledgements 287 This document incorporates comments and suggestions offered by Eric 288 Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony 289 Nadalin, Michael B. Jones, Bill Cox, Nick Harper, Brian Campbell and 290 others. 292 This document was produced under the chairmanship of John Bradley and 293 Leif Johansson. The area directors included Eric Rescorla, Kathleen 294 Moriarty and Stephen Farrell. 296 8. References 298 8.1. Normative References 300 [I-D.ietf-tokbind-protocol] 301 Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J. 302 Hodges, "The Token Binding Protocol Version 1.0", draft- 303 ietf-tokbind-protocol-17 (work in progress), April 2018. 305 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 306 Requirement Levels", BCP 14, RFC 2119, 307 DOI 10.17487/RFC2119, March 1997, 308 . 310 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 311 (TLS) Protocol Version 1.2", RFC 5246, 312 DOI 10.17487/RFC5246, August 2008, 313 . 315 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 316 Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, 317 March 2010, . 319 [RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, 320 "Transport Layer Security (TLS) Renegotiation Indication 321 Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010, 322 . 324 [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., 325 Langley, A., and M. Ray, "Transport Layer Security (TLS) 326 Session Hash and Extended Master Secret Extension", 327 RFC 7627, DOI 10.17487/RFC7627, September 2015, 328 . 330 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 331 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 332 May 2017, . 334 8.2. Informative References 336 [TRIPLE-HS] 337 Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti, 338 A., and P. Strub, "Triple Handshakes and Cookie Cutters: 339 Breaking and Fixing Authentication over TLS. IEEE 340 Symposium on Security and Privacy", 2014. 342 Authors' Addresses 344 Andrei Popov (editor) 345 Microsoft Corp. 346 USA 348 Email: andreipo@microsoft.com 350 Magnus Nystroem 351 Microsoft Corp. 352 USA 354 Email: mnystrom@microsoft.com 356 Dirk Balfanz 357 Google Inc. 358 USA 360 Email: balfanz@google.com 362 Adam Langley 363 Google Inc. 364 USA 366 Email: agl@google.com