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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 December 01, 2017 5 Expires: June 4, 2018 7 Version-Independent Properties of QUIC 8 draft-thomson-quic-invariants-00 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 June 4, 2018. 43 Copyright Notice 45 Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . . . 5 69 6. Security and Privacy Considerations . . . . . . . . . . . . . 7 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 71 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 72 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 73 8.2. Informative References . . . . . . . . . . . . . . . . . 7 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. 89 The primary goal of this document is to ensure that it is possible 90 deploy new versions of QUIC. By documenting the things that can't 91 change, this document aims to preserve the ability to change any 92 other aspect of the protocol. Thus, unless specifically described in 93 this document, any aspect of the protocol can change between 94 different versions. 96 Appendix A is a non-exhaustive list of some incorrect assumptions 97 that might be made based on knowledge of QUIC version 1; these do not 98 apply to every version of QUIC. 100 2. Conventions and Definitions 102 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 103 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 104 "OPTIONAL" in this document are to be interpreted as described in BCP 105 14 [RFC2119] [RFC8174] when, and only when, they appear in all 106 capitals, as shown here. 108 3. An Extremely Abstract Description of QUIC 110 QUIC is a connection-oriented protocol between two endpoints. Those 111 endpoints exchange UDP datagrams. These UDP datagrams contain QUIC 112 packets. QUIC endpoints use QUIC packets to establish a QUIC 113 connection, which is shared protocol state between those endpoints. 115 4. QUIC Packet Headers 117 A QUIC packet is the content of the UDP datagrams exchanged by QUIC 118 endpoints. This document describes the contents of those datagrams. 120 QUIC defines two types of packet header: long and short. Long 121 packets are identified by the most significant bit of the first octet 122 being set; short packets have that bit cleared. 124 Aside from the values described here, the payload of QUIC packets is 125 version-specific and of arbitrary length. 127 4.1. Long Header 129 Long headers take the form described in Figure 1. Bits that have 130 version-specific semantics are marked with an X. 132 0 1 2 3 133 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 1 134 +-+-+-+-+-+-+-+-+ 135 |1|X X X X X X X| 136 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 137 | | 138 + Connection ID (64) + 139 | | 140 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 141 | Version (32) | 142 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 143 |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 X... 144 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 146 Figure 1: QUIC Long Header 148 A QUIC packet with a long header has the high bit of the first octet 149 set to 1. 151 A QUIC packet with a long header has two fixed fields immediately 152 following the first octet: a 64-bit Connection ID (see Section 4.3) 153 and a 32-bit Version (see Section 4.4). 155 4.2. Short Header 157 Short headers take the form described in Figure 2. Bits that have 158 version-specific semantics are marked with an X. 160 0 1 2 3 161 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 1 162 +-+-+-+-+-+-+-+-+ 163 |0|C|X X X X X X| 164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 165 | | 166 + [Connection ID (64)] + 167 | | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 |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 X... 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 172 Figure 2: QUIC Short Header 174 A QUIC packet with a short header has the high bit of the first octet 175 set to 0. 177 A QUIC packet with a short header includes an optional connection ID 178 and no version field. The second bit of that octet (that is, 0x40) 179 determines whether the connection ID is present. If the second bit 180 is cleared, a 64-bit connection ID immediately follows the first 181 octet. If the second bit is set, the remainder of the packet has 182 version-specific semantics. 184 4.3. Connection ID 186 A connection ID is an opaque 64-bit field. 188 The primary function of a connection ID is to ensure that changes in 189 addressing at lower protocol layers (UDP, IP, and below) don't cause 190 packets for a QUIC connection to be delivered to the wrong endpoint. 191 The connection ID is used by endpoints and the intermediaries that 192 support them to ensure that each QUIC packet can be delivered to the 193 correct instance of an endpoint. At the endpoint, the connection ID 194 is used to identify which QUIC connection the packet is intended for. 196 The connection ID is chosen by endpoints using version-specific 197 methods. Packets for the same QUIC connection might use different 198 connection ID values. 200 4.4. Version 202 QUIC versions are identified with a 32-bit integer, encoded in 203 network byte order. Version 0 is reserved for version negotiation 204 (see Section 5). All other version numbers are potentially valid. 206 5. Version Negotiation 208 A QUIC endpoint that receives a packet with a long header and a 209 version it either does not understand or does not support sends a 210 Version Negotiation packet in response. Packets with a short header 211 do not trigger version negotiation and are always associated with an 212 existing connection. 214 A Version Negotiation packet sets the high bit of the first octet, 215 and thus it conforms with the format of a packet with a long header 216 as defined in this document. A Version Negotiation packet is 217 identifiable as such by the Version field, which is set to 218 0x00000000. 220 0 1 2 3 221 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 1 222 +-+-+-+-+-+-+-+-+ 223 |1|X X X X X X X| 224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 225 | | 226 + Connection ID (64) + 227 | | 228 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 229 | Version (32) = 0 | 230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 231 | Supported Version 1 (32) ... 232 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 233 | [Supported Version 2 (32)] ... 234 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 235 ... 236 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 237 | [Supported Version N (32)] ... 238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 240 Figure 3: Version Negotiation Packet 242 The Version Negotiation packet contains a list of Supported Version 243 fields, each identifying a version that the endpoint sending the 244 packet supports. The Supported Version fields follow the Version 245 field. A Version Negotiation packet contains no other fields. An 246 endpoint MUST ignore a packet that contains no Supported Version 247 fields, or a truncated Supported Version. 249 Version Negotiation packets do not use integrity or confidentiality 250 protection. A specific QUIC version might authenticate the packet as 251 part of its connection establishment process. 253 The Connection ID field in a Version Negotiation packet contains the 254 Connection ID from the packet that was received. This provides some 255 protection against injection of Version Negotiation packets by off- 256 path attackers. 258 An endpoint that receives a Version Negotiation packet might change 259 the version that it decides to use for subsequent packets. The 260 conditions under which an endpoint changes QUIC version will depend 261 on the version of QUIC that it chooses. 263 See [QUIC-TRANSPORT] for a more thorough description of how an 264 endpoint that supports QUIC version 1 generates and consumes a 265 Version Negotiation packet. 267 6. Security and Privacy Considerations 269 It is possible that middleboxes could use traits of a specific 270 version of QUIC and assume that when other versions of QUIC exhibit 271 similar traits the same underlying semantic is being expressed. 272 There are potentially many such traits (see Appendix A). Some effort 273 has been made to either eliminate or obscure some observable traits 274 in QUIC version 1, but many of these remain. Other QUIC versions 275 might make different design decisions and so exhibit different 276 traits. 278 The QUIC version number does not appear in all QUIC packets, which 279 means that reliably extracting information from a flow based on 280 version-specific traits requires that middleboxes retain state for 281 every connection ID they see. 283 The Version Negotiation packet described in this document is not 284 integrity-protected, it only has modest protection against insertion 285 by off-path attackers. QUIC versions MUST define a mechanism that 286 authenticates the values it contains. 288 7. IANA Considerations 290 This document makes no request of IANA. 292 8. References 294 8.1. Normative References 296 [QUIC-TRANSPORT] 297 Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based 298 Multiplexed and Secure Transport", draft-ietf-quic- 299 transport-00 (work in progress), December 2017. 301 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 302 Requirement Levels", BCP 14, RFC 2119, 303 DOI 10.17487/RFC2119, March 1997, 304 . 306 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 307 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 308 May 2017, . 310 8.2. Informative References 312 [QUIC-TLS] 313 Thomson, M., Ed. and S. Turner, Ed., "Using Transport 314 Layer Security (TLS) to Secure QUIC", draft-ietf-quic- 315 tls-00 (work in progress), December 2017. 317 [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated 318 Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, 319 . 321 8.3. URIs 323 [1] https://mailarchive.ietf.org/arch/search/?email_list=quic 325 [2] https://github.com/quicwg 327 [3] https://github.com/quicwg/base-drafts/labels/-invariants 329 Appendix A. Incorrect Assumptions 331 There are several traits of QUIC version 1 [QUIC-TRANSPORT] that are 332 not protected from observation, but are nonetheless considered to be 333 changeable when a new version is deployed. 335 This section lists a sampling of incorrect assumptions that might be 336 made based on knowledge of QUIC version 1. Some of these statements 337 are not even true for QUIC version 1. This is not an exhaustive 338 list, it is intended to be illustrative only. 340 The following statements are NOT guaranteed to be true for every QUIC 341 version: 343 o QUIC uses TLS [QUIC-TLS] and some TLS messages are visible on the 344 wire 346 o QUIC long headers are only exchanged during connection 347 establishment 349 o Every flow on a given 5-tuple will include a connection 350 establishment phase 352 o QUIC forbids acknowledgments of packets that only contain ACK 353 frames, therefore the last packet before a long period of 354 quiescence might be assumed to contain an acknowledgment 356 o QUIC uses an AEAD (AEAD_AES_128_GCM [RFC5116]) to protect the 357 packets it exchanges during connection establishment 359 o QUIC packet numbers appear after the Version field 360 o QUIC packet numbers increase by one for every packet sent 362 o QUIC has a minimum size for the first handshake packet sent by a 363 client 365 o QUIC stipulates that a client speaks first 367 o A QUIC Version Negotiation packet is only sent by a server 369 o A QUIC connection ID changes infrequently 371 o The same connection ID is used for packets sent by both endpoints 373 o A QUIC server chooses the connection ID 375 o QUIC endpoints change the version they speak if they are sent a 376 Version Negotiation packet 378 o Only one connection at a time is established between any pair of 379 QUIC endpoints 381 Author's Address 383 Martin Thomson 384 Mozilla 386 Email: martin.thomson@gmail.com