Internet DRAFT - draft-thomson-quic-invariants
draft-thomson-quic-invariants
QUIC M. Thomson
Internet-Draft Mozilla
Intended status: Standards Track December 01, 2017
Expires: June 4, 2018
Version-Independent Properties of QUIC
draft-thomson-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.
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This Internet-Draft will expire on June 4, 2018.
Copyright Notice
Copyright (c) 2017 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. 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. Long
packets are identified by the most significant bit of the first octet
being set; short packets 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 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 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.
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-00 (work in progress), December 2017.
[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-00 (work in progress), December 2017.
[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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