draft-ietf-quic-invariants-latest.txt   draft-ietf-quic-invariants-auth48.txt 
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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. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8. References
8.1. Normative References . . . . . . . . . . . . . . . . . . 8 8.1. Normative References
8.2. Informative References . . . . . . . . . . . . . . . . . 8 8.2. Informative References
Appendix A. Incorrect Assumptions . . . . . . . . . . . . . . . 9 Appendix A. Incorrect Assumptions
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address
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
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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 (..),
Variable-Length Field (8..24), Variable-Length Field (8..24),
Repeated Field (8) ..., Repeated Field (8) ...,
} }
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 headers: long and short. Packets QUIC defines two types of packet headers: long and short. Packets
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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),
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),
Version-Specific Data (..), Version-Specific Data (..),
} }
Figure 2: QUIC Long Header Figure 2: QUIC Long Header
A QUIC packet with a long header has the high bit of the first byte A QUIC packet with a long header has the high bit of the first byte
set to 1. All other bits in that byte are version specific. set to 1. All other bits in that byte are version specific.
The next four bytes include a 32-bit Version field. Versions are The next four bytes include a 32-bit Version field. Versions are
described in Section 5.4. described in Section 5.4.
The next byte contains the length in bytes of the Destination The next byte contains the length in bytes of the Destination
Connection ID field that follows it. This length is encoded as an Connection ID field that follows it. This length is encoded as an
8-bit unsigned integer. The Destination Connection ID field follows 8-bit unsigned integer. The Destination Connection ID field follows
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Header Form (1) = 1, Header Form (1) = 1,
Unused (7), Unused (7),
Version (32) = 0, Version (32) = 0,
Destination Connection ID Length (8), Destination Connection ID Length (8),
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
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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>.
8.2. Informative References 8.2. Informative References
[QUIC-TLS] [QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021, QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>. <https://www.rfc-editor.org/info/rfc9001>.
[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", RFC 9000, Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021, DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>. <https://www.rfc-editor.org/info/rfc9000>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
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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:*
o 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.
o QUIC long headers are only exchanged during connection * QUIC long headers are only exchanged during connection
establishment. establishment.
o 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.
o The first packets exchanged on a flow use the long header. * The first packets exchanged on a flow use the long header.
o 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.
o QUIC uses an Authenticated Encryption with Associated Data (AEAD) * QUIC uses an Authenticated Encryption with Associated Data (AEAD)
function (AEAD_AES_128_GCM; see [RFC5116]) to protect the packets function (AEAD_AES_128_GCM; see [RFC5116]) to protect the packets
it exchanges during connection establishment. it exchanges during connection establishment.
o QUIC packet numbers are encrypted and appear as the first * QUIC packet numbers are encrypted and appear as the first
encrypted bytes. encrypted bytes.
o QUIC packet numbers increase by one for every packet sent. * QUIC packet numbers increase by one for every packet sent.
o 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.
o QUIC stipulates that a client speak first. * QUIC stipulates that a client speak first.
o 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.
o A QUIC Version Negotiation packet is only sent by a server. * A QUIC Version Negotiation packet is only sent by a server.
o A QUIC connection ID changes infrequently. * A QUIC connection ID changes infrequently.
o 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.
o 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.
o 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.
o 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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