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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 October 03, 2018 5 Expires: April 6, 2019 7 Version-Independent Properties of QUIC 8 draft-ietf-quic-invariants-03 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 April 6, 2019. 43 Copyright Notice 45 Copyright (c) 2018 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 octet 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 octet 156 set to 1. All other bits in that octet are version specific. 158 The next four octets include a 32-bit Version field (see 159 Section 4.4). 161 The next octet contains the length in octets of the two Connection 162 IDs (see Section 4.3) that follow. Each length is encoded as a 4-bit 163 unsigned integer. The length of the Destination Connection ID (DCIL) 164 occupies the high bits of the octet and the length of the Source 165 Connection ID (SCIL) occupies the low bits of the octet. An encoded 166 length of 0 indicates that the connection ID is also 0 octets in 167 length. Non-zero encoded lengths are increased by 3 to get the full 168 length of the connection ID; the final value is therefore either 0 or 169 between 4 and 18 octets in length (inclusive). For example, an octet 170 with the value 0xe0 describes a 17 octet Destination Connection ID 171 and a zero octet Source Connection ID. 173 The connection ID lengths are followed by two connection IDs. The 174 connection ID associated with the recipient of the packet (the 175 Destination Connection ID) is followed by the connection ID 176 associated with the sender of the packet (the Source Connection ID). 178 The remainder of the packet contains version-specific content. 180 4.2. Short Header 182 Short headers take the form described in Figure 2. Bits that have 183 version-specific semantics are marked with an X. 185 0 1 2 3 186 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 1 187 +-+-+-+-+-+-+-+-+ 188 |0|X X X X X X X| 189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 190 | Destination Connection ID (*) ... 191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 |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 ... 193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 195 Figure 2: QUIC Short Header 197 A QUIC packet with a short header has the high bit of the first octet 198 set to 0. 200 A QUIC packet with a short header includes a Destination Connection 201 ID. The short header does not include the Connection ID Lengths, 202 Source Connection ID, or Version fields. 204 The remainder of the packet has version-specific semantics. 206 4.3. Connection ID 208 A connection ID is an opaque field of arbitrary length. 210 The primary function of a connection ID is to ensure that changes in 211 addressing at lower protocol layers (UDP, IP, and below) don't cause 212 packets for a QUIC connection to be delivered to the wrong endpoint. 213 The connection ID is used by endpoints and the intermediaries that 214 support them to ensure that each QUIC packet can be delivered to the 215 correct instance of an endpoint. At the endpoint, the connection ID 216 is used to identify which QUIC connection the packet is intended for. 218 The connection ID is chosen by each endpoint using version-specific 219 methods. Packets for the same QUIC connection might use different 220 connection ID values. 222 4.4. Version 224 QUIC versions are identified with a 32-bit integer, encoded in 225 network byte order. Version 0 is reserved for version negotiation 226 (see Section 5). All other version numbers are potentially valid. 228 The properties described in this document apply to all versions of 229 QUIC. A protocol that does not conform to the properties described 230 in this document is not QUIC. Future documents might describe 231 additional properties which apply to a specific QUIC version, or to a 232 range of QUIC versions. 234 5. Version Negotiation 236 A QUIC endpoint that receives a packet with a long header and a 237 version it either does not understand or does not support might send 238 a Version Negotiation packet in response. Packets with a short 239 header do not trigger version negotiation. 241 A Version Negotiation packet sets the high bit of the first octet, 242 and thus it conforms with the format of a packet with a long header 243 as defined in Section 4.1. A Version Negotiation packet is 244 identifiable as such by the Version field, which is set to 245 0x00000000. 247 0 1 2 3 248 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 1 249 +-+-+-+-+-+-+-+-+ 250 |1|X X X X X X X| 251 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 252 | Version (32) = 0 | 253 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 254 |DCIL(4)|SCIL(4)| 255 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 256 | Destination Connection ID (0/32..144) ... 257 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 258 | Source Connection ID (0/32..144) ... 259 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 260 | Supported Version 1 (32) | 261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 262 | [Supported Version 2 (32)] | 263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 264 ... 265 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 266 | [Supported Version N (32)] | 267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 Figure 3: Version Negotiation Packet 271 The Version Negotiation packet contains a list of Supported Version 272 fields, each identifying a version that the endpoint sending the 273 packet supports. The Supported Version fields follow the Version 274 field. A Version Negotiation packet contains no other fields. An 275 endpoint MUST ignore a packet that contains no Supported Version 276 fields, or a truncated Supported Version. 278 Version Negotiation packets do not use integrity or confidentiality 279 protection. A specific QUIC version might authenticate the packet as 280 part of its connection establishment process. 282 An endpoint MUST include the value from the Source Connection ID 283 field of the packet it receives in the Destination Connection ID 284 field. The value for Source Connection ID MUST be copied from the 285 Destination Connection ID of the received packet, which is initially 286 randomly selected by a client. Echoing both connection IDs gives 287 clients some assurance that the server received the packet and that 288 the Version Negotiation packet was not generated by an off-path 289 attacker. 291 An endpoint that receives a Version Negotiation packet might change 292 the version that it decides to use for subsequent packets. The 293 conditions under which an endpoint changes QUIC version will depend 294 on the version of QUIC that it chooses. 296 See [QUIC-TRANSPORT] for a more thorough description of how an 297 endpoint that supports QUIC version 1 generates and consumes a 298 Version Negotiation packet. 300 6. Security and Privacy Considerations 302 It is possible that middleboxes could use traits of a specific 303 version of QUIC and assume that when other versions of QUIC exhibit 304 similar traits the same underlying semantic is being expressed. 305 There are potentially many such traits (see Appendix A). Some effort 306 has been made to either eliminate or obscure some observable traits 307 in QUIC version 1, but many of these remain. Other QUIC versions 308 might make different design decisions and so exhibit different 309 traits. 311 The QUIC version number does not appear in all QUIC packets, which 312 means that reliably extracting information from a flow based on 313 version-specific traits requires that middleboxes retain state for 314 every connection ID they see. 316 The Version Negotiation packet described in this document is not 317 integrity-protected; it only has modest protection against insertion 318 by off-path attackers. QUIC versions MUST define a mechanism that 319 authenticates the values it contains. 321 7. IANA Considerations 323 This document makes no request of IANA. 325 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-14 (work in progress), October 2018. 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-14 (work in progress), October 2018. 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 417 Martin Thomson 418 Mozilla 420 Email: martin.thomson@gmail.com