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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 QUIC M. Thomson 3 Internet-Draft Mozilla 4 Intended status: Standards Track September 12, 2019 5 Expires: March 15, 2020 7 Version-Independent Properties of QUIC 8 draft-ietf-quic-invariants-07 10 Abstract 12 This document defines the properties of the QUIC transport protocol 13 that are expected to remain unchanged over time as new versions of 14 the protocol are developed. 16 Note to Readers 18 Discussion of this draft takes place on the QUIC working group 19 mailing list (quic@ietf.org), which is archived at 20 https://mailarchive.ietf.org/arch/search/?email_list=quic [1]. 22 Working Group information can be found at https://github.com/quicwg 23 [2]; source code and issues list for this draft can be found at 24 https://github.com/quicwg/base-drafts/labels/-invariants [3]. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on March 15, 2020. 43 Copyright Notice 45 Copyright (c) 2019 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (https://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 61 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 62 3. An Extremely Abstract Description of QUIC . . . . . . . . . . 3 63 4. QUIC Packet Headers . . . . . . . . . . . . . . . . . . . . . 3 64 4.1. Long Header . . . . . . . . . . . . . . . . . . . . . . . 3 65 4.2. Short Header . . . . . . . . . . . . . . . . . . . . . . 4 66 4.3. Connection ID . . . . . . . . . . . . . . . . . . . . . . 5 67 4.4. Version . . . . . . . . . . . . . . . . . . . . . . . . . 5 68 5. Version Negotiation . . . . . . . . . . . . . . . . . . . . . 6 69 6. Security and Privacy Considerations . . . . . . . . . . . . . 7 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 71 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 72 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 73 8.2. Informative References . . . . . . . . . . . . . . . . . 8 74 8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 8 75 Appendix A. Incorrect Assumptions . . . . . . . . . . . . . . . 8 76 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 78 1. Introduction 80 In addition to providing secure, multiplexed transport, QUIC 81 [QUIC-TRANSPORT] includes the ability to negotiate a version. This 82 allows the protocol to change over time in response to new 83 requirements. Many characteristics of the protocol will change 84 between versions. 86 This document describes the subset of QUIC that is intended to remain 87 stable as new versions are developed and deployed. All of these 88 invariants are IP-version-independent. 90 The primary goal of this document is to ensure that it is possible to 91 deploy new versions of QUIC. By documenting the properties that 92 can't change, this document aims to preserve the ability to change 93 any other aspect of the protocol. Thus, unless specifically 94 described in this document, any aspect of the protocol can change 95 between different versions. 97 Appendix A is a non-exhaustive list of some incorrect assumptions 98 that might be made based on knowledge of QUIC version 1; these do not 99 apply to every version of QUIC. 101 2. Conventions and Definitions 103 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 104 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 105 "OPTIONAL" in this document are to be interpreted as described in BCP 106 14 [RFC2119] [RFC8174] when, and only when, they appear in all 107 capitals, as shown here. 109 This document uses terms and notational conventions from 110 [QUIC-TRANSPORT]. 112 3. An Extremely Abstract Description of QUIC 114 QUIC is a connection-oriented protocol between two endpoints. Those 115 endpoints exchange UDP datagrams. These UDP datagrams contain QUIC 116 packets. QUIC endpoints use QUIC packets to establish a QUIC 117 connection, which is shared protocol state between those endpoints. 119 4. QUIC Packet Headers 121 A QUIC packet is the content of the UDP datagrams exchanged by QUIC 122 endpoints. This document describes the contents of those datagrams. 124 QUIC defines two types of packet header: long and short. Packets 125 with long headers are identified by the most significant bit of the 126 first byte being set; packets with a short header have that bit 127 cleared. 129 Aside from the values described here, the payload of QUIC packets is 130 version-specific and of arbitrary length. 132 4.1. Long Header 134 Long headers take the form described in Figure 1. Bits that have 135 version-specific semantics are marked with an X. 137 0 1 2 3 138 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 139 +-+-+-+-+-+-+-+-+ 140 |1|X X X X X X X| 141 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 142 | Version (32) | 143 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 144 | DCID Len (8) | 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 | Destination Connection ID (0..2040) ... 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | SCID Len (8) | 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 | Source Connection ID (0..2040) ... 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 152 |X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X ... 153 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 155 Figure 1: QUIC Long Header 157 A QUIC packet with a long header has the high bit of the first byte 158 set to 1. All other bits in that byte are version specific. 160 The next four bytes include a 32-bit Version field (see Section 4.4). 162 The next byte contains the length in bytes of the Destination 163 Connection ID (see Section 4.3) field that follows it. This length 164 is encoded as an 8-bit unsigned integer. The Destination Connection 165 ID field follows the DCID Len field and is between 0 and 255 bytes in 166 length. 168 The next byte contains the length in bytes of the Source Connection 169 ID field that follows it. This length is encoded as a 8-bit unsigned 170 integer. The Source Connection ID field follows the SCID Len field 171 and is between 0 and 255 bytes in length. 173 The remainder of the packet contains version-specific content. 175 4.2. Short Header 177 Short headers take the form described in Figure 2. Bits that have 178 version-specific semantics are marked with an X. 180 0 1 2 3 181 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 182 +-+-+-+-+-+-+-+-+ 183 |0|X X X X X X X| 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 | Destination Connection ID (*) ... 186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 187 |X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X ... 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 Figure 2: QUIC Short Header 192 A QUIC packet with a short header has the high bit of the first byte 193 set to 0. 195 A QUIC packet with a short header includes a Destination Connection 196 ID immediately following the first byte. The short header does not 197 include the Connection ID Lengths, Source Connection ID, or Version 198 fields. The length of the Destination Connection ID is not specified 199 in packets with a short header and is not constrained by this 200 specification. 202 The remainder of the packet has version-specific semantics. 204 4.3. Connection ID 206 A connection ID is an opaque field of arbitrary length. 208 The primary function of a connection ID is to ensure that changes in 209 addressing at lower protocol layers (UDP, IP, and below) don't cause 210 packets for a QUIC connection to be delivered to the wrong endpoint. 211 The connection ID is used by endpoints and the intermediaries that 212 support them to ensure that each QUIC packet can be delivered to the 213 correct instance of an endpoint. At the endpoint, the connection ID 214 is used to identify which QUIC connection the packet is intended for. 216 The connection ID is chosen by each endpoint using version-specific 217 methods. Packets for the same QUIC connection might use different 218 connection ID values. 220 4.4. Version 222 QUIC versions are identified with a 32-bit integer, encoded in 223 network byte order. Version 0 is reserved for version negotiation 224 (see Section 5). All other version numbers are potentially valid. 226 The properties described in this document apply to all versions of 227 QUIC. A protocol that does not conform to the properties described 228 in this document is not QUIC. Future documents might describe 229 additional properties which apply to a specific QUIC version, or to a 230 range of QUIC versions. 232 5. Version Negotiation 234 A QUIC endpoint that receives a packet with a long header and a 235 version it either does not understand or does not support might send 236 a Version Negotiation packet in response. Packets with a short 237 header do not trigger version negotiation. 239 A Version Negotiation packet sets the high bit of the first byte, and 240 thus it conforms with the format of a packet with a long header as 241 defined in Section 4.1. A Version Negotiation packet is identifiable 242 as such by the Version field, which is set to 0x00000000. 244 0 1 2 3 245 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 246 +-+-+-+-+-+-+-+-+ 247 |1|X X X X X X X| 248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 249 | Version (32) = 0 | 250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 251 | DCID Len (8) | 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | Destination Connection ID (0..2040) ... 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 | SCID Len (8) | 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 257 | Source Connection ID (0..2040) ... 258 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 259 | Supported Version 1 (32) | 260 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 261 | [Supported Version 2 (32)] | 262 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 263 ... 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 | [Supported Version N (32)] | 266 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 268 Figure 3: Version Negotiation Packet 270 The Version Negotiation packet contains a list of Supported Version 271 fields, each identifying a version that the endpoint sending the 272 packet supports. The Supported Version fields follow the Version 273 field. A Version Negotiation packet contains no other fields. An 274 endpoint MUST ignore a packet that contains no Supported Version 275 fields, or a truncated Supported Version. 277 Version Negotiation packets do not use integrity or confidentiality 278 protection. A specific QUIC version might authenticate the packet as 279 part of its connection establishment process. 281 An endpoint MUST include the value from the Source Connection ID 282 field of the packet it receives in the Destination Connection ID 283 field. The value for Source Connection ID MUST be copied from the 284 Destination Connection ID of the received packet, which is initially 285 randomly selected by a client. Echoing both connection IDs gives 286 clients some assurance that the server received the packet and that 287 the Version Negotiation packet was not generated by an off-path 288 attacker. 290 An endpoint that receives a Version Negotiation packet might change 291 the version that it decides to use for subsequent packets. The 292 conditions under which an endpoint changes QUIC version will depend 293 on the version of QUIC that it chooses. 295 See [QUIC-TRANSPORT] for a more thorough description of how an 296 endpoint that supports QUIC version 1 generates and consumes a 297 Version Negotiation packet. 299 6. Security and Privacy Considerations 301 It is possible that middleboxes could use traits of a specific 302 version of QUIC and assume that when other versions of QUIC exhibit 303 similar traits the same underlying semantic is being expressed. 304 There are potentially many such traits (see Appendix A). Some effort 305 has been made to either eliminate or obscure some observable traits 306 in QUIC version 1, but many of these remain. Other QUIC versions 307 might make different design decisions and so exhibit different 308 traits. 310 The QUIC version number does not appear in all QUIC packets, which 311 means that reliably extracting information from a flow based on 312 version-specific traits requires that middleboxes retain state for 313 every connection ID they see. 315 The Version Negotiation packet described in this document is not 316 integrity-protected; it only has modest protection against insertion 317 by off-path attackers. QUIC versions MUST define a mechanism that 318 authenticates the values it contains. 320 7. IANA Considerations 322 This document makes no request of IANA. 324 8. References 326 8.1. Normative References 328 [QUIC-TRANSPORT] 329 Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based 330 Multiplexed and Secure Transport", draft-ietf-quic- 331 transport-23 (work in progress), September 2019. 333 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 334 Requirement Levels", BCP 14, RFC 2119, 335 DOI 10.17487/RFC2119, March 1997, 336 . 338 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 339 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 340 May 2017, . 342 8.2. Informative References 344 [QUIC-TLS] 345 Thomson, M., Ed. and S. Turner, Ed., "Using Transport 346 Layer Security (TLS) to Secure QUIC", draft-ietf-quic- 347 tls-23 (work in progress), September 2019. 349 [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated 350 Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, 351 . 353 8.3. URIs 355 [1] https://mailarchive.ietf.org/arch/search/?email_list=quic 357 [2] https://github.com/quicwg 359 [3] https://github.com/quicwg/base-drafts/labels/-invariants 361 Appendix A. Incorrect Assumptions 363 There are several traits of QUIC version 1 [QUIC-TRANSPORT] that are 364 not protected from observation, but are nonetheless considered to be 365 changeable when a new version is deployed. 367 This section lists a sampling of incorrect assumptions that might be 368 made based on knowledge of QUIC version 1. Some of these statements 369 are not even true for QUIC version 1. This is not an exhaustive 370 list, it is intended to be illustrative only. 372 The following statements are NOT guaranteed to be true for every QUIC 373 version: 375 o QUIC uses TLS [QUIC-TLS] and some TLS messages are visible on the 376 wire 378 o QUIC long headers are only exchanged during connection 379 establishment 381 o Every flow on a given 5-tuple will include a connection 382 establishment phase 384 o The first packets exchanged on a flow use the long header 386 o QUIC forbids acknowledgments of packets that only contain ACK 387 frames, therefore the last packet before a long period of 388 quiescence might be assumed to contain an acknowledgment 390 o QUIC uses an AEAD (AEAD_AES_128_GCM [RFC5116]) to protect the 391 packets it exchanges during connection establishment 393 o QUIC packet numbers appear after the Version field 395 o QUIC packet numbers increase by one for every packet sent 397 o QUIC has a minimum size for the first handshake packet sent by a 398 client 400 o QUIC stipulates that a client speaks first 402 o A QUIC Version Negotiation packet is only sent by a server 404 o A QUIC connection ID changes infrequently 406 o QUIC endpoints change the version they speak if they are sent a 407 Version Negotiation packet 409 o The version field in a QUIC long header is the same in both 410 directions 412 o Only one connection at a time is established between any pair of 413 QUIC endpoints 415 Author's Address 416 Martin Thomson 417 Mozilla 419 Email: mt@lowentropy.net