draft-ietf-quic-invariants-13.txt   rfc8999.txt 
QUIC M. Thomson Internet Engineering Task Force (IETF) M. Thomson
Internet-Draft Mozilla Request for Comments: 8999 Mozilla
Intended status: Standards Track 15 January 2021 Category: Standards Track May 2021
Expires: 19 July 2021 ISSN: 2070-1721
Version-Independent Properties of QUIC Version-Independent Properties of QUIC
draft-ietf-quic-invariants-13
Abstract Abstract
This document defines the properties of the QUIC transport protocol This document defines the properties of the QUIC transport protocol
that are common to all versions of the protocol. that are common to all versions of the protocol.
Note to Readers
Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is
archived at https://mailarchive.ietf.org/arch/
search/?email_list=quic.
Working Group information can be found at https://github.com/quicwg;
source code and issues list for this draft can be found at
https://github.com/quicwg/base-drafts/labels/-invariants.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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-
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 19 July 2021. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8999.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. An Extremely Abstract Description of QUIC . . . . . . . . . . 2 1. An Extremely Abstract Description of QUIC
2. Fixed Properties of All QUIC Versions . . . . . . . . . . . . 2 2. Fixed Properties of All QUIC Versions
3. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 3. Conventions and Definitions
4. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 4. Notational Conventions
5. QUIC Packets . . . . . . . . . . . . . . . . . . . . . . . . 4 5. QUIC Packets
5.1. Long Header . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. Long Header
5.2. Short Header . . . . . . . . . . . . . . . . . . . . . . 5 5.2. Short Header
5.3. Connection ID . . . . . . . . . . . . . . . . . . . . . . 6 5.3. Connection ID
5.4. Version . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.4. Version
6. Version Negotiation . . . . . . . . . . . . . . . . . . . . . 6 6. Version Negotiation
7. Security and Privacy Considerations . . . . . . . . . . . . . 8 7. Security and Privacy Considerations
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. References
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References
9.1. Normative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References
9.2. Informative References . . . . . . . . . . . . . . . . . 8 Appendix A. Incorrect Assumptions
Appendix A. Incorrect Assumptions . . . . . . . . . . . . . . . 9 Author's Address
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. An Extremely Abstract Description of QUIC 1. An Extremely Abstract Description of QUIC
QUIC is a connection-oriented protocol between two endpoints. Those QUIC is a connection-oriented protocol between two endpoints. Those
endpoints exchange UDP datagrams. These UDP datagrams contain QUIC endpoints exchange UDP datagrams. These UDP datagrams contain QUIC
packets. QUIC endpoints use QUIC packets to establish a QUIC packets. QUIC endpoints use QUIC packets to establish a QUIC
connection, which is shared protocol state between those endpoints. connection, which is shared protocol state between those endpoints.
2. Fixed Properties of All QUIC Versions 2. Fixed Properties of All QUIC Versions
In addition to providing secure, multiplexed transport, QUIC In addition to providing secure, multiplexed transport, QUIC
[QUIC-TRANSPORT] allows for the option to negotiate a version. This [QUIC-TRANSPORT] allows for the option to negotiate a version. This
allows the protocol to change over time in response to new allows the protocol to change over time in response to new
requirements. Many characteristics of the protocol could change requirements. Many characteristics of the protocol could change
between versions. between versions.
This document describes the subset of QUIC that is intended to remain This document describes the subset of QUIC that is intended to remain
stable as new versions are developed and deployed. All of these stable as new versions are developed and deployed. All of these
invariants are IP-version-independent. invariants are independent of the IP version.
The primary goal of this document is to ensure that it is possible to The primary goal of this document is to ensure that it is possible to
deploy new versions of QUIC. By documenting the properties that deploy new versions of QUIC. By documenting the properties that
cannot change, this document aims to preserve the ability for QUIC cannot change, this document aims to preserve the ability for QUIC
endpoints to negotiate changes to any other aspect of the protocol. endpoints to negotiate changes to any other aspect of the protocol.
As a consequence, this also guarantees a minimal amount of As a consequence, this also guarantees a minimal amount of
information that is made available to entities other than endpoints. information that is made available to entities other than endpoints.
Unless specifically prohibited in this document, any aspect of the Unless specifically prohibited in this document, any aspect of the
protocol can change between different versions. protocol can change between different versions.
Appendix A contains a non-exhaustive list of some incorrect Appendix A contains a non-exhaustive list of some incorrect
assumptions that might be made based on knowledge of QUIC version 1; assumptions that might be made based on knowledge of QUIC version 1;
these do not apply to every version of QUIC. these do not apply to every version of QUIC.
3. Conventions and Definitions 3. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in BCP
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document defines requirements on future QUIC versions, even This document defines requirements on future QUIC versions, even
where normative language is not used. where normative language is not used.
This document uses terms and notational conventions from This document uses terms and notational conventions from
[QUIC-TRANSPORT]. [QUIC-TRANSPORT].
4. Notational Conventions 4. Notational Conventions
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surrounded by a pair of matching braces. Each field in this list is surrounded by a pair of matching braces. Each field in this list is
separated by commas. separated by commas.
Individual fields include length information, plus indications about Individual fields include length information, plus indications about
fixed value, optionality, or repetitions. Individual fields use the fixed value, optionality, or repetitions. Individual fields use the
following notational conventions, with all lengths in bits: following notational conventions, with all lengths in bits:
x (A): Indicates that x is A bits long x (A): Indicates that x is A bits long
x (A..B): Indicates that x can be any length from A to B; A can be x (A..B): Indicates that x can be any length from A to B; A can be
omitted to indicate a minimum of zero bits and B can be omitted to omitted to indicate a minimum of zero bits, and B can be omitted
indicate no set upper limit; values in this format always end on to indicate no set upper limit; values in this format always end
an byte boundary on a byte boundary
x (L) = C: Indicates that x, with a length described by L, has a x (L) = C: Indicates that x has a fixed value of C; the length of x
fixed value of C is described by L, which can use any of the length forms above
x (L) ...: Indicates that x is repeated zero or more times (and that x (L) ...: Indicates that x is repeated zero or more times and that
each instance is length L) each instance has a length of L
This document uses network byte order (that is, big endian) values. This document uses network byte order (that is, big endian) values.
Fields are placed starting from the high-order bits of each byte. Fields are placed starting from the high-order bits of each byte.
Figure 1 shows an example structure: Figure 1 shows an example structure:
Example Structure { Example Structure {
One-bit Field (1), One-bit Field (1),
7-bit Field with Fixed Value (7) = 61, 7-bit Field with Fixed Value (7) = 61,
Arbitrary-Length Field (..), Arbitrary-Length Field (..),
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Figure 1: Example Format Figure 1: Example Format
5. QUIC Packets 5. QUIC Packets
QUIC endpoints exchange UDP datagrams that contain one or more QUIC QUIC endpoints exchange UDP datagrams that contain one or more QUIC
packets. This section describes the invariant characteristics of a packets. This section describes the invariant characteristics of a
QUIC packet. A version of QUIC could permit multiple QUIC packets in QUIC packet. A version of QUIC could permit multiple QUIC packets in
a single UDP datagram, but the invariant properties only describe the a single UDP datagram, but the invariant properties only describe the
first packet in a datagram. first packet in a datagram.
QUIC defines two types of packet header: long and short. Packets QUIC defines two types of packet headers: long and short. Packets
with long headers are identified by the most significant bit of the with a long header are identified by the most significant bit of the
first byte being set; packets with a short header have that bit first byte being set; packets with a short header have that bit
cleared. cleared.
QUIC packets might be integrity protected, including the header. QUIC packets might be integrity protected, including the header.
However, QUIC Version Negotiation packets are not integrity However, QUIC Version Negotiation packets are not integrity
protected; see Section 6. protected; see Section 6.
Aside from the values described here, the payload of QUIC packets is Aside from the values described here, the payload of QUIC packets is
version-specific and of arbitrary length. version specific and of arbitrary length.
5.1. Long Header 5.1. Long Header
Long headers take the form described in Figure 2. Long headers take the form described in Figure 2.
Long Header Packet { Long Header Packet {
Header Form (1) = 1, Header Form (1) = 1,
Version-Specific Bits (7), Version-Specific Bits (7),
Version (32), Version (32),
Destination Connection ID Length (8), Destination Connection ID Length (8),
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Version-Specific Data (..), Version-Specific Data (..),
} }
Figure 3: QUIC Short Header Figure 3: QUIC Short Header
A QUIC packet with a short header has the high bit of the first byte A QUIC packet with a short header has the high bit of the first byte
set to 0. set to 0.
A QUIC packet with a short header includes a Destination Connection A QUIC packet with a short header includes a Destination Connection
ID immediately following the first byte. The short header does not ID immediately following the first byte. The short header does not
include the Connection ID Lengths, Source Connection ID, or Version include the Destination Connection ID Length, Source Connection ID
fields. The length of the Destination Connection ID is not encoded Length, Source Connection ID, or Version fields. The length of the
in packets with a short header and is not constrained by this Destination Connection ID is not encoded in packets with a short
specification. header and is not constrained by this specification.
The remainder of the packet has version-specific semantics. The remainder of the packet has version-specific semantics.
5.3. Connection ID 5.3. Connection ID
A connection ID is an opaque field of arbitrary length. A connection ID is an opaque field of arbitrary length.
The primary function of a connection ID is to ensure that changes in The primary function of a connection ID is to ensure that changes in
addressing at lower protocol layers (UDP, IP, and below) do not cause addressing at lower protocol layers (UDP, IP, and below) do not cause
packets for a QUIC connection to be delivered to the wrong QUIC packets for a QUIC connection to be delivered to the wrong QUIC
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endpoint, the connection ID is used to identify the QUIC connection endpoint, the connection ID is used to identify the QUIC connection
for which the packet is intended. for which the packet is intended.
The connection ID is chosen by each endpoint using version-specific The connection ID is chosen by each endpoint using version-specific
methods. Packets for the same QUIC connection might use different methods. Packets for the same QUIC connection might use different
connection ID values. connection ID values.
5.4. Version 5.4. Version
The Version field contains a 4-byte identifier. This value can be The Version field contains a 4-byte identifier. This value can be
used by endpoints to identify a QUIC Version. A Version field with a used by endpoints to identify a QUIC version. A Version field with a
value of 0x00000000 is reserved for version negotiation; see value of 0x00000000 is reserved for version negotiation; see
Section 6. All other values are potentially valid. Section 6. All other values are potentially valid.
The properties described in this document apply to all versions of The properties described in this document apply to all versions of
QUIC. A protocol that does not conform to the properties described QUIC. A protocol that does not conform to the properties described
in this document is not QUIC. Future documents might describe in this document is not QUIC. Future documents might describe
additional properties that apply to a specific QUIC version, or to a additional properties that apply to a specific QUIC version or to a
range of QUIC versions. range of QUIC versions.
6. Version Negotiation 6. Version Negotiation
A QUIC endpoint that receives a packet with a long header and a A QUIC endpoint that receives a packet with a long header and a
version it either does not understand or does not support might send version it either does not understand or does not support might send
a Version Negotiation packet in response. Packets with a short a Version Negotiation packet in response. Packets with a short
header do not trigger version negotiation. header do not trigger version negotiation.
A Version Negotiation packet sets the high bit of the first byte, and A Version Negotiation packet sets the high bit of the first byte, and
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Destination Connection ID (0..2040), Destination Connection ID (0..2040),
Source Connection ID Length (8), Source Connection ID Length (8),
Source Connection ID (0..2040), Source Connection ID (0..2040),
Supported Version (32) ..., Supported Version (32) ...,
} }
Figure 4: Version Negotiation Packet Figure 4: Version Negotiation Packet
Only the most significant bit of the first byte of a Version Only the most significant bit of the first byte of a Version
Negotiation packet has any defined value. The remaining 7 bits, Negotiation packet has any defined value. The remaining 7 bits,
labeled Unused, can be set to any value when sending and MUST be labeled "Unused", can be set to any value when sending and MUST be
ignored on receipt. ignored on receipt.
After the Source Connection ID field, the Version Negotiation packet After the Source Connection ID field, the Version Negotiation packet
contains a list of Supported Version fields, each identifying a contains a list of Supported Version fields, each identifying a
version that the endpoint sending the packet supports. A Version version that the endpoint sending the packet supports. A Version
Negotiation packet contains no other fields. An endpoint MUST ignore Negotiation packet contains no other fields. An endpoint MUST ignore
a packet that contains no Supported Version fields, or a truncated a packet that contains no Supported Version fields or contains a
Supported Version. truncated Supported Version value.
Version Negotiation packets do not use integrity or confidentiality Version Negotiation packets do not use integrity or confidentiality
protection. Specific QUIC versions might include protocol elements protection. Specific QUIC versions might include protocol elements
that allow endpoints to detect modification or corruption in the set that allow endpoints to detect modification or corruption in the set
of supported versions. of supported versions.
An endpoint MUST include the value from the Source Connection ID An endpoint MUST include the value from the Source Connection ID
field of the packet it receives in the Destination Connection ID field of the packet it receives in the Destination Connection ID
field. The value for Source Connection ID MUST be copied from the field. The value for the Source Connection ID field MUST be copied
Destination Connection ID of the received packet, which is initially from the Destination Connection ID field of the received packet,
randomly selected by a client. Echoing both connection IDs gives which is initially randomly selected by a client. Echoing both
clients some assurance that the server received the packet and that connection IDs gives clients some assurance that the server received
the Version Negotiation packet was not generated by an attacker that the packet and that the Version Negotiation packet was not generated
is unable to observe packets. by an attacker that is unable to observe packets.
An endpoint that receives a Version Negotiation packet might change An endpoint that receives a Version Negotiation packet might change
the version that it decides to use for subsequent packets. The the version that it decides to use for subsequent packets. The
conditions under which an endpoint changes QUIC version will depend conditions under which an endpoint changes its QUIC version will
on the version of QUIC that it chooses. depend on the version of QUIC that it chooses.
See [QUIC-TRANSPORT] for a more thorough description of how an See [QUIC-TRANSPORT] for a more thorough description of how an
endpoint that supports QUIC version 1 generates and consumes a endpoint that supports QUIC version 1 generates and consumes a
Version Negotiation packet. Version Negotiation packet.
7. Security and Privacy Considerations 7. Security and Privacy Considerations
It is possible that middleboxes could observe traits of a specific It is possible that middleboxes could observe traits of a specific
version of QUIC and assume that when other versions of QUIC exhibit version of QUIC and assume that when other versions of QUIC exhibit
similar traits the same underlying semantic is being expressed. similar traits the same underlying semantic is being expressed.
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in QUIC version 1, but many of these remain. Other QUIC versions in QUIC version 1, but many of these remain. Other QUIC versions
might make different design decisions and so exhibit different might make different design decisions and so exhibit different
traits. traits.
The QUIC version number does not appear in all QUIC packets, which The QUIC version number does not appear in all QUIC packets, which
means that reliably extracting information from a flow based on means that reliably extracting information from a flow based on
version-specific traits requires that middleboxes retain state for version-specific traits requires that middleboxes retain state for
every connection ID they see. every connection ID they see.
The Version Negotiation packet described in this document is not The Version Negotiation packet described in this document is not
integrity-protected; it only has modest protection against insertion integrity protected; it only has modest protection against insertion
by attackers. An endpoint MUST authenticate the semantic content of by attackers. An endpoint MUST authenticate the semantic content of
a Version Negotiation packet if it attempts a different QUIC version a Version Negotiation packet if it attempts a different QUIC version
as a result. as a result.
8. IANA Considerations 8. References
This document makes no request of IANA.
9. References
9.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References 8.2. Informative References
[QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using Transport [QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
Layer Security (TLS) to Secure QUIC", Work in Progress, QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
Internet-Draft, draft-ietf-quic-tls-33, 15 January 2021, <https://www.rfc-editor.org/info/rfc9001>.
<https://tools.ietf.org/html/draft-ietf-quic-tls-33>.
[QUIC-TRANSPORT] [QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", Work in Progress, Multiplexed and Secure Transport", RFC 9000,
Internet-Draft, draft-ietf-quic-transport-34, 15 January DOI 10.17487/RFC9000, May 2021,
2021, <https://tools.ietf.org/html/draft-ietf-quic- <https://www.rfc-editor.org/info/rfc9000>.
transport-34>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>. <https://www.rfc-editor.org/info/rfc5116>.
Appendix A. Incorrect Assumptions Appendix A. Incorrect Assumptions
There are several traits of QUIC version 1 [QUIC-TRANSPORT] that are There are several traits of QUIC version 1 [QUIC-TRANSPORT] that are
not protected from observation, but are nonetheless considered to be not protected from observation but are nonetheless considered to be
changeable when a new version is deployed. changeable when a new version is deployed.
This section lists a sampling of incorrect assumptions that might be This section lists a sampling of incorrect assumptions that might be
made about QUIC based on knowledge of QUIC version 1. Some of these made about QUIC based on knowledge of QUIC version 1. Some of these
statements are not even true for QUIC version 1. This is not an statements are not even true for QUIC version 1. This is not an
exhaustive list; it is intended to be illustrative only. exhaustive list; it is intended to be illustrative only.
*Any and all of the following statements can be false for a given *Any and all of the following statements can be false for a given
QUIC version:* QUIC version:*
* QUIC uses TLS [QUIC-TLS] and some TLS messages are visible on the * QUIC uses TLS [QUIC-TLS], and some TLS messages are visible on the
wire wire.
* QUIC long headers are only exchanged during connection * QUIC long headers are only exchanged during connection
establishment establishment.
* Every flow on a given 5-tuple will include a connection * Every flow on a given 5-tuple will include a connection
establishment phase establishment phase.
* The first packets exchanged on a flow use the long header * The first packets exchanged on a flow use the long header.
* The last packet before a long period of quiescence might be * The last packet before a long period of quiescence might be
assumed to contain only an acknowledgment assumed to contain only an acknowledgment.
* QUIC uses an AEAD (AEAD_AES_128_GCM [RFC5116]) to protect the * QUIC uses an Authenticated Encryption with Associated Data (AEAD)
packets it exchanges during connection establishment function (AEAD_AES_128_GCM; see [RFC5116]) to protect the packets
it exchanges during connection establishment.
* QUIC packet numbers are encrypted and appear as the first * QUIC packet numbers are encrypted and appear as the first
encrypted bytes encrypted bytes.
* QUIC packet numbers increase by one for every packet sent * QUIC packet numbers increase by one for every packet sent.
* QUIC has a minimum size for the first handshake packet sent by a * QUIC has a minimum size for the first handshake packet sent by a
client client.
* QUIC stipulates that a client speaks first * QUIC stipulates that a client speak first.
* QUIC packets always have the second bit of the first byte (0x40) * QUIC packets always have the second bit of the first byte (0x40)
set set.
* A QUIC Version Negotiation packet is only sent by a server * A QUIC Version Negotiation packet is only sent by a server.
* A QUIC connection ID changes infrequently * A QUIC connection ID changes infrequently.
* QUIC endpoints change the version they speak if they are sent a * QUIC endpoints change the version they speak if they are sent a
Version Negotiation packet Version Negotiation packet.
* The Version field in a QUIC long header is the same in both * The Version field in a QUIC long header is the same in both
directions directions.
* A QUIC packet with a particular value in the Version field means * A QUIC packet with a particular value in the Version field means
that the corresponding version of QUIC is in use that the corresponding version of QUIC is in use.
* Only one connection at a time is established between any pair of * Only one connection at a time is established between any pair of
QUIC endpoints QUIC endpoints.
Author's Address Author's Address
Martin Thomson Martin Thomson
Mozilla Mozilla
Email: mt@lowentropy.net Email: mt@lowentropy.net
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