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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 April 12, 2019 5 Expires: October 14, 2019 7 Version-Independent Properties of QUIC 8 draft-ietf-quic-invariants-04 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 October 14, 2019. 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 . . . . . . . . . . . . . . . . . . . . . . . . . 7 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 |DCIL(4)|SCIL(4)| 145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 | Destination Connection ID (0/32..144) ... 147 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 148 | Source Connection ID (0/32..144) ... 149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 150 |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 ... 151 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 153 Figure 1: QUIC Long Header 155 A QUIC packet with a long header has the high bit of the first byte 156 set to 1. All other bits in that byte are version specific. 158 The next four bytes include a 32-bit Version field (see Section 4.4). 160 The next byte contains the length in bytes of the two Connection IDs 161 (see Section 4.3) that follow. Each length is encoded as a 4-bit 162 unsigned integer. The length of the Destination Connection ID (DCIL) 163 occupies the high bits of the byte and the length of the Source 164 Connection ID (SCIL) occupies the low bits of the byte. An encoded 165 length of 0 indicates that the connection ID is also 0 bytes in 166 length. Non-zero encoded lengths are increased by 3 to get the full 167 length of the connection ID; the final value is therefore either 0 or 168 between 4 and 18 bytes in length (inclusive). For example, an byte 169 with the value 0xe0 describes a 17 byte Destination Connection ID and 170 a zero byte Source Connection ID. 172 The connection ID lengths are followed by two connection IDs. The 173 connection ID associated with the recipient of the packet (the 174 Destination Connection ID) is followed by the connection ID 175 associated with the sender of the packet (the Source Connection ID). 177 The remainder of the packet contains version-specific content. 179 4.2. Short Header 181 Short headers take the form described in Figure 2. Bits that have 182 version-specific semantics are marked with an X. 184 0 1 2 3 185 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 1 186 +-+-+-+-+-+-+-+-+ 187 |0|X X X X X X X| 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | Destination Connection ID (*) ... 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 191 |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 ... 192 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 194 Figure 2: QUIC Short Header 196 A QUIC packet with a short header has the high bit of the first byte 197 set to 0. 199 A QUIC packet with a short header includes a Destination Connection 200 ID. The short header does not include the Connection ID Lengths, 201 Source Connection ID, or Version fields. 203 The remainder of the packet has version-specific semantics. 205 4.3. Connection ID 207 A connection ID is an opaque field of arbitrary length. 209 The primary function of a connection ID is to ensure that changes in 210 addressing at lower protocol layers (UDP, IP, and below) don't cause 211 packets for a QUIC connection to be delivered to the wrong endpoint. 212 The connection ID is used by endpoints and the intermediaries that 213 support them to ensure that each QUIC packet can be delivered to the 214 correct instance of an endpoint. At the endpoint, the connection ID 215 is used to identify which QUIC connection the packet is intended for. 217 The connection ID is chosen by each endpoint using version-specific 218 methods. Packets for the same QUIC connection might use different 219 connection ID values. 221 4.4. Version 223 QUIC versions are identified with a 32-bit integer, encoded in 224 network byte order. Version 0 is reserved for version negotiation 225 (see Section 5). All other version numbers are potentially valid. 227 The properties described in this document apply to all versions of 228 QUIC. A protocol that does not conform to the properties described 229 in this document is not QUIC. Future documents might describe 230 additional properties which apply to a specific QUIC version, or to a 231 range of QUIC versions. 233 5. Version Negotiation 235 A QUIC endpoint that receives a packet with a long header and a 236 version it either does not understand or does not support might send 237 a Version Negotiation packet in response. Packets with a short 238 header do not trigger version negotiation. 240 A Version Negotiation packet sets the high bit of the first byte, and 241 thus it conforms with the format of a packet with a long header as 242 defined in Section 4.1. A Version Negotiation packet is identifiable 243 as such by the Version field, which is set to 0x00000000. 245 0 1 2 3 246 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 1 247 +-+-+-+-+-+-+-+-+ 248 |1|X X X X X X X| 249 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 250 | Version (32) = 0 | 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 |DCIL(4)|SCIL(4)| 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 | Destination Connection ID (0/32..144) ... 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | Source Connection ID (0/32..144) ... 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | Supported Version 1 (32) | 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | [Supported Version 2 (32)] | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 ... 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 | [Supported Version N (32)] | 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 267 Figure 3: Version Negotiation Packet 269 The Version Negotiation packet contains a list of Supported Version 270 fields, each identifying a version that the endpoint sending the 271 packet supports. The Supported Version fields follow the Version 272 field. A Version Negotiation packet contains no other fields. An 273 endpoint MUST ignore a packet that contains no Supported Version 274 fields, or a truncated Supported Version. 276 Version Negotiation packets do not use integrity or confidentiality 277 protection. A specific QUIC version might authenticate the packet as 278 part of its connection establishment process. 280 An endpoint MUST include the value from the Source Connection ID 281 field of the packet it receives in the Destination Connection ID 282 field. The value for Source Connection ID MUST be copied from the 283 Destination Connection ID of the received packet, which is initially 284 randomly selected by a client. Echoing both connection IDs gives 285 clients some assurance that the server received the packet and that 286 the Version Negotiation packet was not generated by an off-path 287 attacker. 289 An endpoint that receives a Version Negotiation packet might change 290 the version that it decides to use for subsequent packets. The 291 conditions under which an endpoint changes QUIC version will depend 292 on the version of QUIC that it chooses. 294 See [QUIC-TRANSPORT] for a more thorough description of how an 295 endpoint that supports QUIC version 1 generates and consumes a 296 Version Negotiation packet. 298 6. Security and Privacy Considerations 300 It is possible that middleboxes could use traits of a specific 301 version of QUIC and assume that when other versions of QUIC exhibit 302 similar traits the same underlying semantic is being expressed. 303 There are potentially many such traits (see Appendix A). Some effort 304 has been made to either eliminate or obscure some observable traits 305 in QUIC version 1, but many of these remain. Other QUIC versions 306 might make different design decisions and so exhibit different 307 traits. 309 The QUIC version number does not appear in all QUIC packets, which 310 means that reliably extracting information from a flow based on 311 version-specific traits requires that middleboxes retain state for 312 every connection ID they see. 314 The Version Negotiation packet described in this document is not 315 integrity-protected; it only has modest protection against insertion 316 by off-path attackers. QUIC versions MUST define a mechanism that 317 authenticates the values it contains. 319 7. IANA Considerations 321 This document makes no request of IANA. 323 8. References 324 8.1. Normative References 326 [QUIC-TRANSPORT] 327 Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based 328 Multiplexed and Secure Transport", draft-ietf-quic- 329 transport-18 (work in progress), April 2019. 331 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 332 Requirement Levels", BCP 14, RFC 2119, 333 DOI 10.17487/RFC2119, March 1997, 334 . 336 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 337 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 338 May 2017, . 340 8.2. Informative References 342 [QUIC-TLS] 343 Thomson, M., Ed. and S. Turner, Ed., "Using Transport 344 Layer Security (TLS) to Secure QUIC", draft-ietf-quic- 345 tls-18 (work in progress), April 2019. 347 [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated 348 Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, 349 . 351 8.3. URIs 353 [1] https://mailarchive.ietf.org/arch/search/?email_list=quic 355 [2] https://github.com/quicwg 357 [3] https://github.com/quicwg/base-drafts/labels/-invariants 359 Appendix A. Incorrect Assumptions 361 There are several traits of QUIC version 1 [QUIC-TRANSPORT] that are 362 not protected from observation, but are nonetheless considered to be 363 changeable when a new version is deployed. 365 This section lists a sampling of incorrect assumptions that might be 366 made based on knowledge of QUIC version 1. Some of these statements 367 are not even true for QUIC version 1. This is not an exhaustive 368 list, it is intended to be illustrative only. 370 The following statements are NOT guaranteed to be true for every QUIC 371 version: 373 o QUIC uses TLS [QUIC-TLS] and some TLS messages are visible on the 374 wire 376 o QUIC long headers are only exchanged during connection 377 establishment 379 o Every flow on a given 5-tuple will include a connection 380 establishment phase 382 o The first packets exchanged on a flow use the long header 384 o QUIC forbids acknowledgments of packets that only contain ACK 385 frames, therefore the last packet before a long period of 386 quiescence might be assumed to contain an acknowledgment 388 o QUIC uses an AEAD (AEAD_AES_128_GCM [RFC5116]) to protect the 389 packets it exchanges during connection establishment 391 o QUIC packet numbers appear after the Version field 393 o QUIC packet numbers increase by one for every packet sent 395 o QUIC has a minimum size for the first handshake packet sent by a 396 client 398 o QUIC stipulates that a client speaks first 400 o A QUIC Version Negotiation packet is only sent by a server 402 o A QUIC connection ID changes infrequently 404 o QUIC endpoints change the version they speak if they are sent a 405 Version Negotiation packet 407 o The version field in a QUIC long header is the same in both 408 directions 410 o Only one connection at a time is established between any pair of 411 QUIC endpoints 413 Author's Address 415 Martin Thomson 416 Mozilla 418 Email: mt@lowentropy.net