Internet DRAFT - draft-schinazi-quic-version-negotiation
draft-schinazi-quic-version-negotiation
QUIC Working Group D. Schinazi
Internet-Draft Google LLC
Intended status: Informational E. Rescorla
Expires: May 7, 2020 Mozilla
November 04, 2019
Compatible Version Negotiation for QUIC
draft-schinazi-quic-version-negotiation-02
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 [1] or on the GitHub repository which
contains the draft: http://github.com/ekr/draft-schinazi-quic-
version-negotiation [2].
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 7, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 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 [3] or on the GitHub repository which
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contains the draft: http://github.com/ekr/draft-schinazi-quic-
version-negotiation [4].
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.
o 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).
o 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
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reasonably popular. This is not generally an issue in practice as
long as the the overall structure of the protocol remains similar.
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.
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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
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.
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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
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.
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
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"VERSION_NEGOTIATION_ERROR" from the QUIC Transport Error Codes
registry.
10. References
10.1. Normative References
[QUIC] Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-23 (work
in progress), September 2019.
[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>.
10.2. URIs
[1] mailto:quic@ietf.org
[2] http://github.com/ekr/draft-schinazi-quic-version-negotiation
[3] mailto:quic@ietf.org
[4] http://github.com/ekr/draft-schinazi-quic-version-negotiation
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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