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Versions: (draft-thomson-quic-invariants) 00

QUIC                                                          M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Standards Track                       February 28, 2018
Expires: September 1, 2018


                 Version-Independent Properties of QUIC
                     draft-ietf-quic-invariants-00

Abstract

   This document defines the properties of the QUIC transport protocol
   that are expected to remain unchanged over time as new versions of
   the protocol are developed.

Note to Readers

   Discussion of this draft takes place on the QUIC working group
   mailing list (quic@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/search/?email_list=quic [1].

   Working Group information can be found at https://github.com/quicwg
   [2]; source code and issues list for this draft can be found at
   https://github.com/quicwg/base-drafts/labels/-invariants [3].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 1, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  An Extremely Abstract Description of QUIC . . . . . . . . . .   3
   4.  QUIC Packet Headers . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Long Header . . . . . . . . . . . . . . . . . . . . . . .   3
     4.2.  Short Header  . . . . . . . . . . . . . . . . . . . . . .   4
     4.3.  Connection ID . . . . . . . . . . . . . . . . . . . . . .   5
     4.4.  Version . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Version Negotiation . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security and Privacy Considerations . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   Appendix A.  Incorrect Assumptions  . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   In addition to providing secure, multiplexed transport, QUIC
   [QUIC-TRANSPORT] includes the ability to negotiate a version.  This
   allows the protocol to change over time in response to new
   requirements.  Many characteristics of the protocol will change
   between versions.

   This document describes the subset of QUIC that is intended to remain
   stable as new versions are developed and deployed.

   The primary goal of this document is to ensure that it is possible
   deploy new versions of QUIC.  By documenting the things that can't
   change, this document aims to preserve the ability to change any
   other aspect of the protocol.  Thus, unless specifically described in
   this document, any aspect of the protocol can change between
   different versions.




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   Appendix A is a non-exhaustive list of some incorrect assumptions
   that might be made based on knowledge of QUIC version 1; these do not
   apply to every version of QUIC.

2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  An Extremely Abstract Description of QUIC

   QUIC is a connection-oriented protocol between two endpoints.  Those
   endpoints exchange UDP datagrams.  These UDP datagrams contain QUIC
   packets.  QUIC endpoints use QUIC packets to establish a QUIC
   connection, which is shared protocol state between those endpoints.

4.  QUIC Packet Headers

   A QUIC packet is the content of the UDP datagrams exchanged by QUIC
   endpoints.  This document describes the contents of those datagrams.

   QUIC defines two types of packet header: long and short.  Packets
   with long headers are identified by the most significant bit of the
   first octet being set; packets with a short header have that bit
   cleared.

   Aside from the values described here, the payload of QUIC packets is
   version-specific and of arbitrary length.

4.1.  Long Header

   Long headers take the form described in Figure 1.  Bits that have
   version-specific semantics are marked with an X.















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    0                   1                   2                   3
    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
   +-+-+-+-+-+-+-+-+
   |1|X X X X X X X|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                       Connection ID (64)                      +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Version (32)                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |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  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 1: QUIC Long Header

   A QUIC packet with a long header has the high bit of the first octet
   set to 1.

   A QUIC packet with a long header has two fixed fields immediately
   following the first octet: a 64-bit Connection ID (see Section 4.3)
   and a 32-bit Version (see Section 4.4).

4.2.  Short Header

   Short headers take the form described in Figure 2.  Bits that have
   version-specific semantics are marked with an X.

    0                   1                   2                   3
    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
   +-+-+-+-+-+-+-+-+
   |0|C|X X X X X X|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                     [Connection ID (64)]                      +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |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  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 2: QUIC Short Header

   A QUIC packet with a short header has the high bit of the first octet
   set to 0.

   A QUIC packet with a short header includes an optional connection ID
   and no version field.  The second bit of that octet (that is, 0x40)
   determines whether the connection ID is present.  If the second bit



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   is cleared, a 64-bit connection ID immediately follows the first
   octet.  If the second bit is set, the remainder of the packet has
   version-specific semantics.

4.3.  Connection ID

   A connection ID is an opaque 64-bit field.

   The primary function of a connection ID is to ensure that changes in
   addressing at lower protocol layers (UDP, IP, and below) don't cause
   packets for a QUIC connection to be delivered to the wrong endpoint.
   The connection ID is used by endpoints and the intermediaries that
   support them to ensure that each QUIC packet can be delivered to the
   correct instance of an endpoint.  At the endpoint, the connection ID
   is used to identify which QUIC connection the packet is intended for.

   The connection ID is chosen by endpoints using version-specific
   methods.  Packets for the same QUIC connection might use different
   connection ID values.

4.4.  Version

   QUIC versions are identified with a 32-bit integer, encoded in
   network byte order.  Version 0 is reserved for version negotiation
   (see Section 5).  All other version numbers are potentially valid.

5.  Version Negotiation

   A QUIC endpoint that receives a packet with a long header and a
   version it either does not understand or does not support sends a
   Version Negotiation packet in response.  Packets with a short header
   do not trigger version negotiation and are always associated with an
   existing connection.

   Consequently, until an endpoint has confirmed that its peer supports
   the QUIC version it has chosen, it can only send packets that use the
   long header.

   A Version Negotiation packet sets the high bit of the first octet,
   and thus it conforms with the format of a packet with a long header
   as defined in this document.  A Version Negotiation packet is
   identifiable as such by the Version field, which is set to
   0x00000000.








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    0                   1                   2                   3
    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
   +-+-+-+-+-+-+-+-+
   |1|X X X X X X X|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                       Connection ID (64)                      +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Version (32) = 0                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Supported Version 1 (32)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   [Supported Version 2 (32)]                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   [Supported Version N (32)]                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 3: Version Negotiation Packet

   The Version Negotiation packet contains a list of Supported Version
   fields, each identifying a version that the endpoint sending the
   packet supports.  The Supported Version fields follow the Version
   field.  A Version Negotiation packet contains no other fields.  An
   endpoint MUST ignore a packet that contains no Supported Version
   fields, or a truncated Supported Version.

   Version Negotiation packets do not use integrity or confidentiality
   protection.  A specific QUIC version might authenticate the packet as
   part of its connection establishment process.

   The Connection ID field in a Version Negotiation packet contains the
   Connection ID from the packet that was received.  This provides some
   protection against injection of Version Negotiation packets by off-
   path attackers.

   An endpoint that receives a Version Negotiation packet might change
   the version that it decides to use for subsequent packets.  The
   conditions under which an endpoint changes QUIC version will depend
   on the version of QUIC that it chooses.

   See [QUIC-TRANSPORT] for a more thorough description of how an
   endpoint that supports QUIC version 1 generates and consumes a
   Version Negotiation packet.





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6.  Security and Privacy Considerations

   It is possible that middleboxes could use traits of a specific
   version of QUIC and assume that when other versions of QUIC exhibit
   similar traits the same underlying semantic is being expressed.
   There are potentially many such traits (see Appendix A).  Some effort
   has been made to either eliminate or obscure some observable traits
   in QUIC version 1, but many of these remain.  Other QUIC versions
   might make different design decisions and so exhibit different
   traits.

   The QUIC version number does not appear in all QUIC packets, which
   means that reliably extracting information from a flow based on
   version-specific traits requires that middleboxes retain state for
   every connection ID they see.

   The Version Negotiation packet described in this document is not
   integrity-protected, it only has modest protection against insertion
   by off-path attackers.  QUIC versions MUST define a mechanism that
   authenticates the values it contains.

7.  IANA Considerations

   This document makes no request of IANA.

8.  References

8.1.  Normative References

   [QUIC-TRANSPORT]
              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport-09 (work in progress), February 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References







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   [QUIC-TLS]
              Thomson, M., Ed. and S. Turner, Ed., "Using Transport
              Layer Security (TLS) to Secure QUIC", draft-ietf-quic-
              tls-09 (work in progress), February 2018.

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
              <https://www.rfc-editor.org/info/rfc5116>.

8.3.  URIs

   [1] https://mailarchive.ietf.org/arch/search/?email_list=quic

   [2] https://github.com/quicwg

   [3] https://github.com/quicwg/base-drafts/labels/-invariants

Appendix A.  Incorrect Assumptions

   There are several traits of QUIC version 1 [QUIC-TRANSPORT] that are
   not protected from observation, but are nonetheless considered to be
   changeable when a new version is deployed.

   This section lists a sampling of incorrect assumptions that might be
   made based on knowledge of QUIC version 1.  Some of these statements
   are not even true for QUIC version 1.  This is not an exhaustive
   list, it is intended to be illustrative only.

   The following statements are NOT guaranteed to be true for every QUIC
   version:

   o  QUIC uses TLS [QUIC-TLS] and some TLS messages are visible on the
      wire

   o  QUIC long headers are only exchanged during connection
      establishment

   o  Every flow on a given 5-tuple will include a connection
      establishment phase

   o  QUIC forbids acknowledgments of packets that only contain ACK
      frames, therefore the last packet before a long period of
      quiescence might be assumed to contain an acknowledgment

   o  QUIC uses an AEAD (AEAD_AES_128_GCM [RFC5116]) to protect the
      packets it exchanges during connection establishment

   o  QUIC packet numbers appear after the Version field



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   o  QUIC packet numbers increase by one for every packet sent

   o  QUIC has a minimum size for the first handshake packet sent by a
      client

   o  QUIC stipulates that a client speaks first

   o  A QUIC Version Negotiation packet is only sent by a server

   o  A QUIC connection ID changes infrequently

   o  The same connection ID is used for packets sent by both endpoints

   o  A QUIC server chooses the connection ID

   o  QUIC endpoints change the version they speak if they are sent a
      Version Negotiation packet

   o  Only one connection at a time is established between any pair of
      QUIC endpoints

Author's Address

   Martin Thomson
   Mozilla

   Email: martin.thomson@gmail.com
























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