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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: October 23, 2017 D. Balfanz 6 A. Langley 7 Google Inc. 8 April 21, 2017 10 Transport Layer Security (TLS) Extension for Token Binding Protocol 11 Negotiation 12 draft-ietf-tokbind-negotiation-08 14 Abstract 16 This document specifies a Transport Layer Security (TLS) [RFC5246] 17 extension for the negotiation of Token Binding protocol 18 [I-D.ietf-tokbind-protocol] version and key 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 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 October 23, 2017. 37 Copyright Notice 39 Copyright (c) 2017 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 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 56 2. Token Binding Negotiation Client Hello Extension . . . . . . 2 57 3. Token Binding Negotiation Server Hello Extension . . . . . . 3 58 4. Negotiating Token Binding Protocol Version and Key Parameters 4 59 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . . . . . . . . 6 65 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 67 8.2. Informative References . . . . . . . . . . . . . . . . . 7 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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 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", "MAY", and "OPTIONAL" in this 86 document are to be interpreted as described in [RFC2119]. 88 2. Token Binding Negotiation Client Hello Extension 90 The client uses the "token_binding" TLS extension to indicate the 91 highest supported Token Binding protocol version and key parameters. 93 enum { 94 token_binding(24), (65535) 95 } ExtensionType; 96 The "extension_data" field of this extension contains a 97 "TokenBindingParameters" value. 99 struct { 100 uint8 major; 101 uint8 minor; 102 } ProtocolVersion; 104 enum { 105 (255) 106 } TokenBindingKeyParameters; 108 struct { 109 ProtocolVersion token_binding_version; 110 TokenBindingKeyParameters key_parameters_list<1..2^8-1> 111 } TokenBindingParameters; 113 "token_binding_version" indicates the version of the Token Binding 114 protocol the client wishes to use during this connection. This 115 SHOULD be the latest (highest valued) version supported by the 116 client. [I-D.ietf-tokbind-protocol] describes version {1, 0} of the 117 protocol. 119 RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH: Prototype 120 implementations of Token Binding drafts can indicate support of a 121 specific draft version, e.g. {0, 1} or {0, 2}. 123 "key_parameters_list" contains the list of identifiers of the Token 124 Binding key parameters supported by the client, in descending order 125 of preference. [I-D.ietf-tokbind-protocol] defines an initial set of 126 identifiers for Token Binding key parameters. 128 3. Token Binding Negotiation Server Hello Extension 130 The server uses the "token_binding" TLS extension to indicate support 131 for the Token Binding protocol and to select the protocol version and 132 key parameters. 134 The server that supports Token Binding and receives a client hello 135 message containing the "token_binding" extension will include the 136 "token_binding" extension in the server hello if all of the following 137 conditions are satisfied: 139 1. The server supports the Token Binding protocol version offered by 140 the client or a lower version. 142 2. The server finds acceptable Token Binding key parameters on the 143 client's list. 145 3. The server is also negotiating the Extended Master Secret 146 [RFC7627] and Renegotiation Indication [RFC5746] TLS extensions. 147 This requirement only applies when TLS 1.2 or an older TLS 148 version is used (see security considerations section below for 149 more details). 151 The server will ignore any key parameters that it does not recognize. 152 The "extension_data" field of the "token_binding" extension is 153 structured the same as described above for the client 154 "extension_data". 156 "token_binding_version" contains the lower of the Token Binding 157 protocol version offered by the client in the "token_binding" 158 extension and the highest version supported by the server. 160 "key_parameters_list" contains exactly one Token Binding key 161 parameters identifier selected by the server from the client's list. 163 4. Negotiating Token Binding Protocol Version and Key Parameters 165 It is expected that a server will have a list of Token Binding key 166 parameters identifiers that it supports, in preference order. The 167 server MUST only select an identifier that the client offered. The 168 server SHOULD select the most highly preferred key parameters 169 identifier it supports which is also advertised by the client. In 170 the event that the server supports none of the key parameters that 171 the client advertises, then the server MUST NOT include 172 "token_binding" extension in the server hello. 174 The client receiving the "token_binding" extension MUST terminate the 175 handshake with a fatal "unsupported_extension" alert if any of the 176 following conditions are true: 178 1. The client did not include the "token_binding" extension in the 179 client hello. 181 2. "token_binding_version" is higher than the Token Binding protocol 182 version advertised by the client. 184 3. "key_parameters_list" includes more than one Token Binding key 185 parameters identifier. 187 4. "key_parameters_list" includes an identifier that was not 188 advertised by the client. 190 5. TLS 1.2 or an older TLS version is used, but the Extended Master 191 Secret [RFC7627] and TLS Renegotiation Indication [RFC5746] 192 extensions are not negotiated (see security considerations 193 section below for more details). 195 If the "token_binding" extension is included in the server hello and 196 the client supports the Token Binding protocol version selected by 197 the server, it means that the version and key parameters have been 198 negotiated between the client and the server and SHALL be definitive 199 for the TLS connection. Please note that TLS 1.2 and earlier 200 versions support renegotiation, allowing the client and server to 201 renegotiate the Token Binding protocol version and key parameters on 202 the same connection. The client MUST use the negotiated key 203 parameters in the "provided_token_binding" as described in 204 [I-D.ietf-tokbind-protocol]. 206 If the client does not support the Token Binding protocol version 207 selected by the server, then the connection proceeds without Token 208 Binding. 210 Please note that the Token Binding protocol version and key 211 parameters are negotiated for each TLS connection, which means that 212 the client and server include their "token_binding" extensions both 213 in the full TLS handshake that establishes a new TLS session and in 214 the subsequent abbreviated TLS handshakes that resume the TLS 215 session. 217 5. IANA Considerations 219 This document updates the TLS "ExtensionType Values" registry 220 originally created in [RFC4366]. IANA has provided the following 221 temporary registration for the "token_binding" TLS extension: 223 Value: 24 225 Extension name: token_binding 227 Reference: this document 229 IANA is requested to make this registration permanent, keeping the 230 value of 24, which has been used by the prototype implementations of 231 the Token Binding protocol. 233 This document uses "Token Binding Key Parameters" registry originally 234 created in [I-D.ietf-tokbind-protocol]. This document creates no new 235 registrations in this registry. 237 6. Security Considerations 239 6.1. Downgrade Attacks 241 The Token Binding protocol version and key parameters are negotiated 242 via "token_binding" extension within the TLS handshake. TLS prevents 243 active attackers from modifying the messages of the TLS handshake, 244 therefore it is not possible for the attacker to remove or modify the 245 "token_binding" extension. The signature algorithm and key length 246 used in the Token Binding of type "provided_token_binding" MUST match 247 the parameters negotiated via "token_binding" extension. 249 6.2. Triple Handshake Vulnerability in TLS 1.2 and Older TLS Versions 251 The Token Binding protocol relies on the TLS Exporters [RFC5705] to 252 associate a TLS connection with a Token Binding. The triple 253 handshake attack [TRIPLE-HS] is a known vulnerability in TLS 1.2 and 254 older TLS versions, allowing the attacker to synchronize keying 255 material between TLS connections. The attacker can then successfully 256 replay bound tokens. For this reason, the Token Binding protocol 257 MUST NOT be negotiated with these TLS versions, unless the Extended 258 Master Secret [RFC7627] and Renegotiation Indication [RFC5746] TLS 259 extensions have also been negotiated. 261 7. Acknowledgements 263 This document incorporates comments and suggestions offered by Eric 264 Rescorla, Gabriel Montenegro, Martin Thomson, Vinod Anupam, Anthony 265 Nadalin, Michael B. Jones, Bill Cox, Nick Harper, Brian Campbell and 266 others. 268 8. References 270 8.1. Normative References 272 [I-D.ietf-tokbind-protocol] 273 Popov, A., Nystrom, M., Balfanz, D., Langley, A., and J. 274 Hodges, "The Token Binding Protocol Version 1.0", draft- 275 ietf-tokbind-protocol-13 (work in progress), February 276 2017. 278 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 279 Requirement Levels", BCP 14, RFC 2119, 280 DOI 10.17487/RFC2119, March 1997, 281 . 283 [RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., 284 and T. Wright, "Transport Layer Security (TLS) 285 Extensions", RFC 4366, DOI 10.17487/RFC4366, April 2006, 286 . 288 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 289 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 290 DOI 10.17487/RFC5226, May 2008, 291 . 293 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 294 (TLS) Protocol Version 1.2", RFC 5246, 295 DOI 10.17487/RFC5246, August 2008, 296 . 298 [RFC5705] Rescorla, E., "Keying Material Exporters for Transport 299 Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, 300 March 2010, . 302 [RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov, 303 "Transport Layer Security (TLS) Renegotiation Indication 304 Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010, 305 . 307 [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., 308 Langley, A., and M. Ray, "Transport Layer Security (TLS) 309 Session Hash and Extended Master Secret Extension", 310 RFC 7627, DOI 10.17487/RFC7627, September 2015, 311 . 313 8.2. Informative References 315 [TRIPLE-HS] 316 Bhargavan, K., Delignat-Lavaud, A., Fournet, C., Pironti, 317 A., and P. Strub, "Triple Handshakes and Cookie Cutters: 318 Breaking and Fixing Authentication over TLS. IEEE 319 Symposium on Security and Privacy", 2014. 321 Authors' Addresses 323 Andrei Popov (editor) 324 Microsoft Corp. 325 USA 327 Email: andreipo@microsoft.com 328 Magnus Nystroem 329 Microsoft Corp. 330 USA 332 Email: mnystrom@microsoft.com 334 Dirk Balfanz 335 Google Inc. 336 USA 338 Email: balfanz@google.com 340 Adam Langley 341 Google Inc. 342 USA 344 Email: agl@google.com