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Versions: (draft-schinazi-quic-version-negotiation) 00

QUIC Working Group                                           D. Schinazi
Internet-Draft                                                Google LLC
Intended status: Informational                               E. Rescorla
Expires: 29 August 2020                                          Mozilla
                                                        26 February 2020


                Compatible Version Negotiation for QUIC
                 draft-ietf-quic-version-negotiation-00

Abstract

   QUIC does not provide a complete version negotiation mechanism but
   instead only provides a way for the server to indicate that the
   version the client offered is unacceptable.  This document describes
   a version negotiation mechanism that allows a client and server to
   select a mutually supported version.  Optionally, if the original and
   negotiated version share a compatible Initial format, the negotiation
   can take place without incurring an extra round trip.

   Discussion of this work is encouraged to happen on the QUIC IETF
   mailing list quic@ietf.org (mailto:quic@ietf.org) or on the GitHub
   repository which contains the draft: https://github.com/quicwg/
   version-negotiation/ (https://github.com/quicwg/version-
   negotiation/).

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 29 August 2020.

Copyright Notice

   Copyright (c) 2020 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.  Version Negotiation Mechanism . . . . . . . . . . . . . . . .   3
   4.  Version Negotiation Transport Parameter . . . . . . . . . . .   4
   5.  Version Downgrade Prevention  . . . . . . . . . . . . . . . .   6
   6.  Supported Versions  . . . . . . . . . . . . . . . . . . . . .   7
   7.  Compatible Versions . . . . . . . . . . . . . . . . . . . . .   7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   QUIC [QUIC] does not provide a complete version negotiation (VN)
   mechanism; the VN packet only allows the server to indicate that the
   version the client offered is unacceptable, but doesn't allow the
   client to safely make use of that information to create a new
   connection with a mutually supported version.  With proper safety
   mechanisms in place, the VN packet can be part of a mechanism to
   allow two QUIC implementations to negotiate between two totally
   disjoint versions of QUIC, at the cost of an extra round trip.
   However, it is beneficial to avoid that cost whenever possible,
   especially given that most incremental versions are broadly similar
   to the the previous version.

   This specification describes a simple version negotiation mechanism
   which optionally leverages similarities between versions and can
   negotiate between the set of "compatible" versions in a single round
   trip.

   Discussion of this work is encouraged to happen on the QUIC IETF
   mailing list quic@ietf.org (mailto:quic@ietf.org) or on the GitHub
   repository which contains the draft: https://github.com/quicwg/
   version-negotiation/ (https://github.com/quicwg/version-
   negotiation/).




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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.  Version Negotiation Mechanism

   The mechanism defined in this document is straightforward: the client
   maintains a list of QUIC versions it supports, ordered by preference.
   Its Initial packet is sent using the version that the server is most
   likely to support (in the absence of other information, this will
   often be the oldest version the client supports); that Initial packet
   then lists all compatible versions (Section 7) that the client
   supports in the Compatible Version fields of its transport parameters
   (Figure 1).  Note that the client's compatible version list always
   contains its currently attempted version.

   *  If the server supports one of the client's compatible versions, it
      selects a version it supports from the client's compatible version
      list.  It then responds with that version in all of its future
      packets (except for Retry, as below).

   *  If the server does not support any of the client's compatible
      versions, it sends a Version Negotiation packet listing all the
      versions it supports.

   If the server leverages compatible versions and responds with a
   different version from the client's currently attempted version, it
   MUST NOT select a version not offered by the client.  The client MUST
   validate that the version in the server's packets is one of the
   compatible versions that it offered and that it matches the
   negotiated version in the server's transport parameters.

   If the server sends a Retry, it MUST use the same version that the
   client provided in its Initial.  Version negotiation takes place
   after the retry cycle is over.

   In order for negotiation to complete successfully, the client's
   Initial packet (and initial CRYPTO frames) MUST be interpretable by
   the server.  This implies that servers must retain the ability to
   process the Initial packet from older versions as long as they are
   reasonably popular.  This is not generally an issue in practice as
   long as the the overall structure of the protocol remains similar.





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4.  Version Negotiation Transport Parameter

   This document registers a new transport parameter,
   "version_negotiation".  The contents of this transport parameter
   depend on whether the client or server is sending it, and are shown
   below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Currently Attempted Version (32)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Previously Attempted Version (32)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Received Negotiation Version Count (i)           ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             [Received Negotiation Version 1 (32)]             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             [Received Negotiation Version 2 (32)]             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             [Received Negotiation Version N (32)]             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Compatible Version Count (i)                ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Compatible Version 1 (32)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  [Compatible Version 2 (32)]                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  [Compatible Version N (32)]                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: Client Transport Parameter Format

   The content of each field is described below:

   Currently Attempted Version:  The version that the client is using in
      this Initial.  This field MUST be equal to the value of the
      Version field in the long header that carries this transport
      parameter.

   Previously Attempted Version:  If the client is sending this Initial
      in response to a Version Negotiation packet, this field contains
      the version that the client used in the previous Initial packet
      that triggered the version negotiation packet.  If the client did



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      not receive a Version Negotiation packet, this field SHALL be all-
      zeroes.

   Received Negotiation Version Count:  A variable-length integer
      specifying the number of Received Negotiation Version fields
      following it.  If the client is sending this Initial in response
      to a Version Negotiation packet, the subsequent versions SHALL
      include all the versions from that Version Negotiation packet in
      order, even if they are not supported by the client (even if the
      versions are reserved).  If the client has not received a Version
      Negotiation packet on this connection, this field SHALL be 0.

   Compatible Version Count:  A variable-length integer specifying the
      number of Compatible Version fields following it.  The client
      lists all versions compatible with Currently Attempted Version in
      the subsequent Compatible Version fields, ordered by descending
      preference.  Note that the version in the Currently Attempted
      Version field MUST be included in the Compatible Version list to
      allow the client to communicate the currently attempted version's
      preference.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Negotiated Version (32)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 Supported Version Count (i)                 ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Supported Version 1 (32)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   [Supported Version 2 (32)]                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   [Supported Version N (32)]                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: Server Transport Parameter Format

   The content of each field is described below:

   Negotiated Version:  The version that the server chose to use for the
      connection.  This field SHALL be equal to the value of the Version
      field in the long header that carries this transport parameter.

   Supported Version Count:  A variable-length integer specifying the
      number of Supported Version fields following it.  The server
      encodes all versions it supports in the subsequent list, ordered



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      by descending preference.  Note that the version in the Negotiated
      Version field MUST be included in the Supported Version list.

   Clients MAY include versions following the pattern "0x?a?a?a?a" in
   their Compatible Version list, and the server in their Supported
   Version list.  Those versions are reserved to exercise version
   negotiation (see the Versions section of [QUIC]), and MUST be ignored
   when parsing these fields.  On the other hand, the Received
   Negotiation Version list MUST be identical to the received Version
   Negotiation packet, so clients MUST NOT add or remove reserved
   version from that list.

5.  Version Downgrade Prevention

   Clients MUST ignore any received Version Negotiation packets that
   contain the version that they initially attempted.

   Servers MUST validate that the client's "Currently Attempted Version"
   matches the version in the long header that carried the transport
   parameter.  Similarly, clients MUST validate that the server's
   "Negotiated Version" matches the long header version.  If an
   endpoint's validation fails, it MUST close the connection with an
   error of type VERSION_NEGOTIATION_ERROR.

   When a server parses the client's "version_negotiation" transport
   parameter, if the "Received Negotiation Version Count" is not zero,
   the server MUST validate that it could have sent the Version
   Negotation packet described by the client in response to an Initial
   of version "Previously Attempted Version".  In particular, the server
   MUST ensure that there are no versions that it supports that are
   absent from the Received Negotiation Versions, and that the ordering
   matches the server's preference.  If this validation fails, the
   server MUST close the connection with an error of type
   VERSION_NEGOTIATION_ERROR.  This mitigates an attacker's ability to
   forge Version Negotiation packets to force a version downgrade.

   If a server operator is progressively deploying a new QUIC version
   throughout its fleet, it MAY perform a two-step process where it
   first progressively adds support for the new version, but without
   enforcing its presence in Received Negotiation Versions.  Once all
   servers have been upgraded, the second step is to start enforcing
   that the new version is present in Received Negotiation Versions.
   This opens connections to version downgrades during the upgrade
   window, since those could be due to clients communicating with both
   upgraded and non-upgraded servers.






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6.  Supported Versions

   The server's Supported Version list allows it to communicate the full
   list of versions it supports to the client.  In the case where
   clients initially attempt connections with the oldest version they
   support, this allows them to be notified of more recent versions the
   server supports.  If the client notices that the server supports a
   version that is more preferable that the one initially attempted by
   default, the client SHOULD cache that information and attempt the
   preferred version in subsequent connections.

7.  Compatible Versions

   Two versions of QUIC A and B are said to be "compatible" if a version
   A Initial can be used to negotiate version B and vice versa.  The
   most common scenario is a sequence of versions 1, 2, 3, etc. in which
   all the Initial packets have the same basic structure but might
   include specific extensions (especially inside the crypto handshake)
   that are only meaningful in some subset of versions and are ignored
   in others.  Note that it is not possible to add new frame types in
   Initial packets because QUIC frames do not use a self-describing
   encoding, so unrecognized frame types cannot be parsed or ignored
   (see the Extension Frames section of [QUIC]).

   When a new version of QUIC is defined, it is assumed to not be
   compatible with any other version unless otherwise specified.
   Implementations MUST NOT assume compatibility between version unless
   explicitly specified.

8.  Security Considerations

   The crypto handshake is already required to guarantee agreement on
   the supported parameters, so negotiation between compatible versions
   will have the security of the weakest common version.

   The requirement that versions not be assumed compatible mitigates the
   possibility of cross-protocol attacks, but more analysis is still
   needed here.

   The presence of the Attempted Version and Negotiated Version fields
   mitigates an attacker's ability to forge packets by altering the
   version.









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9.  IANA Considerations

   If this document is approved, IANA shall assign the identifier 0x73DB
   for the "version_negotiation" transport parameter from the QUIC
   Transport Parameter Registry and the identifier 0x53F8 for
   "VERSION_NEGOTIATION_ERROR" from the QUIC Transport Error Codes
   registry.

10.  Normative References

   [QUIC]     Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", Work in Progress, Internet-Draft,
              draft-ietf-quic-transport-27, 21 February 2020,
              <http://www.ietf.org/internet-drafts/draft-ietf-quic-
              transport-27.txt>.

   [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>.

Authors' Addresses

   David Schinazi
   Google LLC
   1600 Amphitheatre Parkway
   Mountain View, California 94043,
   United States of America

   Email: dschinazi.ietf@gmail.com


   Eric Rescorla
   Mozilla

   Email: ekr@rtfm.com











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