QUIC M. Thomson, Ed.
Internet-Draft Mozilla
Intended status: Standards Track S. Turner, Ed.
Expires: September 12, 2019 sn3rd
March 11, 2019
Using TLS to Secure QUIC
draft-ietf-quic-tls-19
Abstract
This document describes how Transport Layer Security (TLS) is used to
secure QUIC.
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/-tls [3].
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 September 12, 2019.
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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4
2.1. TLS Overview . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
4. Carrying TLS Messages . . . . . . . . . . . . . . . . . . . . 7
4.1. Interface to TLS . . . . . . . . . . . . . . . . . . . . 9
4.1.1. Sending and Receiving Handshake Messages . . . . . . 9
4.1.2. Encryption Level Changes . . . . . . . . . . . . . . 11
4.1.3. TLS Interface Summary . . . . . . . . . . . . . . . . 12
4.2. TLS Version . . . . . . . . . . . . . . . . . . . . . . . 13
4.3. ClientHello Size . . . . . . . . . . . . . . . . . . . . 14
4.4. Peer Authentication . . . . . . . . . . . . . . . . . . . 14
4.5. Enabling 0-RTT . . . . . . . . . . . . . . . . . . . . . 15
4.6. Rejecting 0-RTT . . . . . . . . . . . . . . . . . . . . . 15
4.7. HelloRetryRequest . . . . . . . . . . . . . . . . . . . . 15
4.8. TLS Errors . . . . . . . . . . . . . . . . . . . . . . . 16
4.9. Discarding Unused Keys . . . . . . . . . . . . . . . . . 16
4.10. Discarding Initial Keys . . . . . . . . . . . . . . . . . 17
5. Packet Protection . . . . . . . . . . . . . . . . . . . . . . 18
5.1. Packet Protection Keys . . . . . . . . . . . . . . . . . 18
5.2. Initial Secrets . . . . . . . . . . . . . . . . . . . . . 18
5.3. AEAD Usage . . . . . . . . . . . . . . . . . . . . . . . 19
5.4. Header Protection . . . . . . . . . . . . . . . . . . . . 20
5.4.1. Header Protection Application . . . . . . . . . . . . 21
5.4.2. Header Protection Sample . . . . . . . . . . . . . . 22
5.4.3. AES-Based Header Protection . . . . . . . . . . . . . 23
5.4.4. ChaCha20-Based Header Protection . . . . . . . . . . 24
5.5. Receiving Protected Packets . . . . . . . . . . . . . . . 24
5.6. Use of 0-RTT Keys . . . . . . . . . . . . . . . . . . . . 24
5.7. Receiving Out-of-Order Protected Frames . . . . . . . . . 25
6. Key Update . . . . . . . . . . . . . . . . . . . . . . . . . 25
7. Security of Initial Messages . . . . . . . . . . . . . . . . 27
8. QUIC-Specific Additions to the TLS Handshake . . . . . . . . 28
8.1. Protocol and Version Negotiation . . . . . . . . . . . . 28
8.2. QUIC Transport Parameters Extension . . . . . . . . . . . 28
8.3. Removing the EndOfEarlyData Message . . . . . . . . . . . 29
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9. Security Considerations . . . . . . . . . . . . . . . . . . . 29
9.1. Replay Attacks with 0-RTT . . . . . . . . . . . . . . . . 29
9.2. Packet Reflection Attack Mitigation . . . . . . . . . . . 30
9.3. Peer Denial of Service . . . . . . . . . . . . . . . . . 31
9.4. Header Protection Analysis . . . . . . . . . . . . . . . 31
9.5. Key Diversity . . . . . . . . . . . . . . . . . . . . . . 32
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 33
11.1. Normative References . . . . . . . . . . . . . . . . . . 33
11.2. Informative References . . . . . . . . . . . . . . . . . 34
11.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Appendix A. Sample Initial Packet Protection . . . . . . . . . . 35
A.1. Keys . . . . . . . . . . . . . . . . . . . . . . . . . . 35
A.2. Client Initial . . . . . . . . . . . . . . . . . . . . . 36
A.3. Server Initial . . . . . . . . . . . . . . . . . . . . . 38
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 39
B.1. Since draft-ietf-quic-tls-18 . . . . . . . . . . . . . . 39
B.2. Since draft-ietf-quic-tls-17 . . . . . . . . . . . . . . 39
B.3. Since draft-ietf-quic-tls-14 . . . . . . . . . . . . . . 39
B.4. Since draft-ietf-quic-tls-13 . . . . . . . . . . . . . . 40
B.5. Since draft-ietf-quic-tls-12 . . . . . . . . . . . . . . 40
B.6. Since draft-ietf-quic-tls-11 . . . . . . . . . . . . . . 40
B.7. Since draft-ietf-quic-tls-10 . . . . . . . . . . . . . . 40
B.8. Since draft-ietf-quic-tls-09 . . . . . . . . . . . . . . 41
B.9. Since draft-ietf-quic-tls-08 . . . . . . . . . . . . . . 41
B.10. Since draft-ietf-quic-tls-07 . . . . . . . . . . . . . . 41
B.11. Since draft-ietf-quic-tls-05 . . . . . . . . . . . . . . 41
B.12. Since draft-ietf-quic-tls-04 . . . . . . . . . . . . . . 41
B.13. Since draft-ietf-quic-tls-03 . . . . . . . . . . . . . . 41
B.14. Since draft-ietf-quic-tls-02 . . . . . . . . . . . . . . 41
B.15. Since draft-ietf-quic-tls-01 . . . . . . . . . . . . . . 41
B.16. Since draft-ietf-quic-tls-00 . . . . . . . . . . . . . . 42
B.17. Since draft-thomson-quic-tls-01 . . . . . . . . . . . . . 42
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 42
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction
This document describes how QUIC [QUIC-TRANSPORT] is secured using
TLS [TLS13].
TLS 1.3 provides critical latency improvements for connection
establishment over previous versions. Absent packet loss, most new
connections can be established and secured within a single round
trip; on subsequent connections between the same client and server,
the client can often send application data immediately, that is,
using a zero round trip setup.
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This document describes how TLS acts as a security component of QUIC.
2. Notational Conventions
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.
This document uses the terminology established in [QUIC-TRANSPORT].
For brevity, the acronym TLS is used to refer to TLS 1.3, though a
newer version could be used (see Section 4.2).
2.1. TLS Overview
TLS provides two endpoints with a way to establish a means of
communication over an untrusted medium (that is, the Internet) that
ensures that messages they exchange cannot be observed, modified, or
forged.
Internally, TLS is a layered protocol, with the structure shown
below:
+--------------+--------------+--------------+
| Handshake | Alerts | Application |
| Layer | | Data |
| | | |
+--------------+--------------+--------------+
| |
| Record Layer |
| |
+--------------------------------------------+
Each upper layer (handshake, alerts, and application data) is carried
as a series of typed TLS records. Records are individually
cryptographically protected and then transmitted over a reliable
transport (typically TCP) which provides sequencing and guaranteed
delivery.
Change Cipher Spec records cannot be sent in QUIC.
The TLS authenticated key exchange occurs between two entities:
client and server. The client initiates the exchange and the server
responds. If the key exchange completes successfully, both client
and server will agree on a secret. TLS supports both pre-shared key
(PSK) and Diffie-Hellman (DH) key exchanges. PSK is the basis for
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0-RTT; the latter provides perfect forward secrecy (PFS) when the DH
keys are destroyed.
After completing the TLS handshake, the client will have learned and
authenticated an identity for the server and the server is optionally
able to learn and authenticate an identity for the client. TLS
supports X.509 [RFC5280] certificate-based authentication for both
server and client.
The TLS key exchange is resistant to tampering by attackers and it
produces shared secrets that cannot be controlled by either
participating peer.
TLS provides two basic handshake modes of interest to QUIC:
o A full 1-RTT handshake in which the client is able to send
application data after one round trip and the server immediately
responds after receiving the first handshake message from the
client.
o A 0-RTT handshake in which the client uses information it has
previously learned about the server to send application data
immediately. This application data can be replayed by an attacker
so it MUST NOT carry a self-contained trigger for any non-
idempotent action.
A simplified TLS handshake with 0-RTT application data is shown in
Figure 1. Note that this omits the EndOfEarlyData message, which is
not used in QUIC (see Section 8.3).
Client Server
ClientHello
(0-RTT Application Data) -------->
ServerHello
{EncryptedExtensions}
{Finished}
<-------- [Application Data]
{Finished} -------->
[Application Data] <-------> [Application Data]
() Indicates messages protected by early data (0-RTT) keys
{} Indicates messages protected using handshake keys
[] Indicates messages protected using application data
(1-RTT) keys
Figure 1: TLS Handshake with 0-RTT
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Data is protected using a number of encryption levels:
o Initial Keys
o Early Data (0-RTT) Keys
o Handshake Keys
o Application Data (1-RTT) Keys
Application data may appear only in the early data and application
data levels. Handshake and Alert messages may appear in any level.
The 0-RTT handshake is only possible if the client and server have
previously communicated. In the 1-RTT handshake, the client is
unable to send protected application data until it has received all
of the handshake messages sent by the server.
3. Protocol Overview
QUIC [QUIC-TRANSPORT] assumes responsibility for the confidentiality
and integrity protection of packets. For this it uses keys derived
from a TLS handshake [TLS13], but instead of carrying TLS records
over QUIC (as with TCP), TLS Handshake and Alert messages are carried
directly over the QUIC transport, which takes over the
responsibilities of the TLS record layer, as shown below.
+--------------+--------------+ +-------------+
| TLS | TLS | | QUIC |
| Handshake | Alerts | | Applications|
| | | | (h3, etc.) |
+--------------+--------------+-+-------------+
| |
| QUIC Transport |
| (streams, reliability, congestion, etc.) |
| |
+---------------------------------------------+
| |
| QUIC Packet Protection |
| |
+---------------------------------------------+
QUIC also relies on TLS for authentication and negotiation of
parameters that are critical to security and performance.
Rather than a strict layering, these two protocols are co-dependent:
QUIC uses the TLS handshake; TLS uses the reliability, ordered
delivery, and record layer provided by QUIC.
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At a high level, there are two main interactions between the TLS and
QUIC components:
o The TLS component sends and receives messages via the QUIC
component, with QUIC providing a reliable stream abstraction to
TLS.
o The TLS component provides a series of updates to the QUIC
component, including (a) new packet protection keys to install (b)
state changes such as handshake completion, the server
certificate, etc.
Figure 2 shows these interactions in more detail, with the QUIC
packet protection being called out specially.
+------------+ +------------+
| |<- Handshake Messages ->| |
| |<---- 0-RTT Keys -------| |
| |<--- Handshake Keys-----| |
| QUIC |<---- 1-RTT Keys -------| TLS |
| |<--- Handshake Done ----| |
+------------+ +------------+
| ^
| Protect | Protected
v | Packet
+------------+
| QUIC |
| Packet |
| Protection |
+------------+
Figure 2: QUIC and TLS Interactions
Unlike TLS over TCP, QUIC applications which want to send data do not
send it through TLS "application_data" records. Rather, they send it
as QUIC STREAM frames which are then carried in QUIC packets.
4. Carrying TLS Messages
QUIC carries TLS handshake data in CRYPTO frames, each of which
consists of a contiguous block of handshake data identified by an
offset and length. Those frames are packaged into QUIC packets and
encrypted under the current TLS encryption level. As with TLS over
TCP, once TLS handshake data has been delivered to QUIC, it is QUIC's
responsibility to deliver it reliably. Each chunk of data that is
produced by TLS is associated with the set of keys that TLS is
currently using. If QUIC needs to retransmit that data, it MUST use
the same keys even if TLS has already updated to newer keys.
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One important difference between TLS records (used with TCP) and QUIC
CRYPTO frames is that in QUIC multiple frames may appear in the same
QUIC packet as long as they are associated with the same encryption
level. For instance, an implementation might bundle a Handshake
message and an ACK for some Handshake data into the same packet.
Some frames are prohibited in different encryption levels, others
cannot be sent. The rules here generalize those of TLS, in that
frames associated with establishing the connection can usually appear
at any encryption level, whereas those associated with transferring
data can only appear in the 0-RTT and 1-RTT encryption levels:
o PADDING frames MAY appear in packets of any encryption level.
o CRYPTO and CONNECTION_CLOSE frames MAY appear in packets of any
encryption level except 0-RTT.
o ACK frames MAY appear in packets of any encryption level other
than 0-RTT, but can only acknowledge packets which appeared in
that packet number space.
o All other frame types MUST only be sent in the 0-RTT and 1-RTT
levels.
Note that it is not possible to send the following frames in 0-RTT
for various reasons: ACK, CRYPTO, NEW_TOKEN, PATH_RESPONSE, and
RETIRE_CONNECTION_ID.
Because packets could be reordered on the wire, QUIC uses the packet
type to indicate which level a given packet was encrypted under, as
shown in Table 1. When multiple packets of different encryption
levels need to be sent, endpoints SHOULD use coalesced packets to
send them in the same UDP datagram.
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+-----------------+------------------+-----------+
| Packet Type | Encryption Level | PN Space |
+-----------------+------------------+-----------+
| Initial | Initial secrets | Initial |
| | | |
| 0-RTT Protected | 0-RTT | 0/1-RTT |
| | | |
| Handshake | Handshake | Handshake |
| | | |
| Retry | N/A | N/A |
| | | |
| Short Header | 1-RTT | 0/1-RTT |
+-----------------+------------------+-----------+
Table 1: Encryption Levels by Packet Type
Section 17 of [QUIC-TRANSPORT] shows how packets at the various
encryption levels fit into the handshake process.
4.1. Interface to TLS
As shown in Figure 2, the interface from QUIC to TLS consists of
three primary functions:
o Sending and receiving handshake messages
o Rekeying (both transmit and receive)
o Handshake state updates
Additional functions might be needed to configure TLS.
4.1.1. Sending and Receiving Handshake Messages
In order to drive the handshake, TLS depends on being able to send
and receive handshake messages. There are two basic functions on
this interface: one where QUIC requests handshake messages and one
where QUIC provides handshake packets.
Before starting the handshake QUIC provides TLS with the transport
parameters (see Section 8.2) that it wishes to carry.
A QUIC client starts TLS by requesting TLS handshake bytes from TLS.
The client acquires handshake bytes before sending its first packet.
A QUIC server starts the process by providing TLS with the client's
handshake bytes.
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At any given time, the TLS stack at an endpoint will have a current
sending encryption level and receiving encryption level. Each
encryption level is associated with a different flow of bytes, which
is reliably transmitted to the peer in CRYPTO frames. When TLS
provides handshake bytes to be sent, they are appended to the current
flow and any packet that includes the CRYPTO frame is protected using
keys from the corresponding encryption level.
QUIC takes the unprotected content of TLS handshake records as the
content of CRYPTO frames. TLS record protection is not used by QUIC.
QUIC assembles CRYPTO frames into QUIC packets, which are protected
using QUIC packet protection.
When an endpoint receives a QUIC packet containing a CRYPTO frame
from the network, it proceeds as follows:
o If the packet was in the TLS receiving encryption level, sequence
the data into the input flow as usual. As with STREAM frames, the
offset is used to find the proper location in the data sequence.
If the result of this process is that new data is available, then
it is delivered to TLS in order.
o If the packet is from a previously installed encryption level, it
MUST not contain data which extends past the end of previously
received data in that flow. Implementations MUST treat any
violations of this requirement as a connection error of type
PROTOCOL_VIOLATION.
o If the packet is from a new encryption level, it is saved for
later processing by TLS. Once TLS moves to receiving from this
encryption level, saved data can be provided. When providing data
from any new encryption level to TLS, if there is data from a
previous encryption level that TLS has not consumed, this MUST be
treated as a connection error of type PROTOCOL_VIOLATION.
Each time that TLS is provided with new data, new handshake bytes are
requested from TLS. TLS might not provide any bytes if the handshake
messages it has received are incomplete or it has no data to send.
Once the TLS handshake is complete, this is indicated to QUIC along
with any final handshake bytes that TLS needs to send. TLS also
provides QUIC with the transport parameters that the peer advertised
during the handshake.
Once the handshake is complete, TLS becomes passive. TLS can still
receive data from its peer and respond in kind, but it will not need
to send more data unless specifically requested - either by an
application or QUIC. One reason to send data is that the server
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might wish to provide additional or updated session tickets to a
client.
When the handshake is complete, QUIC only needs to provide TLS with
any data that arrives in CRYPTO streams. In the same way that is
done during the handshake, new data is requested from TLS after
providing received data.
Important: Until the handshake is reported as complete, the
connection and key exchange are not properly authenticated at the
server. Even though 1-RTT keys are available to a server after
receiving the first handshake messages from a client, the server
cannot consider the client to be authenticated until it receives
and validates the client's Finished message.
The requirement for the server to wait for the client Finished
message creates a dependency on that message being delivered. A
client can avoid the potential for head-of-line blocking that this
implies by sending a copy of the CRYPTO frame that carries the
Finished message in multiple packets. This enables immediate
server processing for those packets.
4.1.2. Encryption Level Changes
As keys for new encryption levels become available, TLS provides QUIC
with those keys. Separately, as TLS starts using keys at a given
encryption level, TLS indicates to QUIC that it is now reading or
writing with keys at that encryption level. These events are not
asynchronous; they always occur immediately after TLS is provided
with new handshake bytes, or after TLS produces handshake bytes.
TLS provides QUIC with three items as a new encryption level becomes
available:
o A secret
o An Authenticated Encryption with Associated Data (AEAD) function
o A Key Derivation Function (KDF)
These values are based on the values that TLS negotiates and are used
by QUIC to generate packet and header protection keys (see Section 5
and Section 5.4).
If 0-RTT is possible, it is ready after the client sends a TLS
ClientHello message or the server receives that message. After
providing a QUIC client with the first handshake bytes, the TLS stack
might signal the change to 0-RTT keys. On the server, after
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receiving handshake bytes that contain a ClientHello message, a TLS
server might signal that 0-RTT keys are available.
Although TLS only uses one encryption level at a time, QUIC may use
more than one level. For instance, after sending its Finished
message (using a CRYPTO frame at the Handshake encryption level) an
endpoint can send STREAM data (in 1-RTT encryption). If the Finished
message is lost, the endpoint uses the Handshake encryption level to
retransmit the lost message. Reordering or loss of packets can mean
that QUIC will need to handle packets at multiple encryption levels.
During the handshake, this means potentially handling packets at
higher and lower encryption levels than the current encryption level
used by TLS.
In particular, server implementations need to be able to read packets
at the Handshake encryption level at the same time as the 0-RTT
encryption level. A client could interleave ACK frames that are
protected with Handshake keys with 0-RTT data and the server needs to
process those acknowledgments in order to detect lost Handshake
packets.
4.1.3. TLS Interface Summary
Figure 3 summarizes the exchange between QUIC and TLS for both client
and server. Each arrow is tagged with the encryption level used for
that transmission.
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Client Server
Get Handshake
Initial ------------->
Rekey tx to 0-RTT Keys
0-RTT --------------->
Handshake Received
Get Handshake
<------------- Initial
Rekey rx to 0-RTT keys
Handshake Received
Rekey rx to Handshake keys
Get Handshake
<----------- Handshake
Rekey tx to 1-RTT keys
<--------------- 1-RTT
Handshake Received
Rekey rx to Handshake keys
Handshake Received
Get Handshake
Handshake Complete
Handshake ----------->
Rekey tx to 1-RTT keys
1-RTT --------------->
Handshake Received
Rekey rx to 1-RTT keys
Get Handshake
Handshake Complete
<--------------- 1-RTT
Handshake Received
Figure 3: Interaction Summary between QUIC and TLS
4.2. TLS Version
This document describes how TLS 1.3 [TLS13] is used with QUIC.
In practice, the TLS handshake will negotiate a version of TLS to
use. This could result in a newer version of TLS than 1.3 being
negotiated if both endpoints support that version. This is
acceptable provided that the features of TLS 1.3 that are used by
QUIC are supported by the newer version.
A badly configured TLS implementation could negotiate TLS 1.2 or
another older version of TLS. An endpoint MUST terminate the
connection if a version of TLS older than 1.3 is negotiated.
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4.3. ClientHello Size
QUIC requires that the first Initial packet from a client contain an
entire cryptographic handshake message, which for TLS is the
ClientHello. Though a packet larger than 1200 bytes might be
supported by the path, a client improves the likelihood that a packet
is accepted if it ensures that the first ClientHello message is small
enough to stay within this limit.
QUIC packet and framing add at least 36 bytes of overhead to the
ClientHello message. That overhead increases if the client chooses a
connection ID without zero length. Overheads also do not include the
token or a connection ID longer than 8 bytes, both of which might be
required if a server sends a Retry packet.
A typical TLS ClientHello can easily fit into a 1200 byte packet.
However, in addition to the overheads added by QUIC, there are
several variables that could cause this limit to be exceeded. Large
session tickets, multiple or large key shares, and long lists of
supported ciphers, signature algorithms, versions, QUIC transport
parameters, and other negotiable parameters and extensions could
cause this message to grow.
For servers, in addition to connection IDs and tokens, the size of
TLS session tickets can have an effect on a client's ability to
connect. Minimizing the size of these values increases the
probability that they can be successfully used by a client.
A client is not required to fit the ClientHello that it sends in
response to a HelloRetryRequest message into a single UDP datagram.
The TLS implementation does not need to ensure that the ClientHello
is sufficiently large. QUIC PADDING frames are added to increase the
size of the packet as necessary.
4.4. Peer Authentication
The requirements for authentication depend on the application
protocol that is in use. TLS provides server authentication and
permits the server to request client authentication.
A client MUST authenticate the identity of the server. This
typically involves verification that the identity of the server is
included in a certificate and that the certificate is issued by a
trusted entity (see for example [RFC2818]).
A server MAY request that the client authenticate during the
handshake. A server MAY refuse a connection if the client is unable
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to authenticate when requested. The requirements for client
authentication vary based on application protocol and deployment.
A server MUST NOT use post-handshake client authentication (see
Section 4.6.2 of [TLS13]).
4.5. Enabling 0-RTT
In order to be usable for 0-RTT, TLS MUST provide a NewSessionTicket
message that contains the "early_data" extension with a
max_early_data_size of 0xffffffff; the amount of data which the
client can send in 0-RTT is controlled by the "initial_max_data"
transport parameter supplied by the server. A client MUST treat
receipt of a NewSessionTicket that contains an "early_data" extension
with any other value as a connection error of type
PROTOCOL_VIOLATION.
Early data within the TLS connection MUST NOT be used. As it is for
other TLS application data, a server MUST treat receiving early data
on the TLS connection as a connection error of type
PROTOCOL_VIOLATION.
4.6. Rejecting 0-RTT
A server rejects 0-RTT by rejecting 0-RTT at the TLS layer. This
also prevents QUIC from sending 0-RTT data. A server will always
reject 0-RTT if it sends a TLS HelloRetryRequest.
When 0-RTT is rejected, all connection characteristics that the
client assumed might be incorrect. This includes the choice of
application protocol, transport parameters, and any application
configuration. The client therefore MUST reset the state of all
streams, including application state bound to those streams.
A client MAY attempt to send 0-RTT again if it receives a Retry or
Version Negotiation packet. These packets do not signify rejection
of 0-RTT.
4.7. HelloRetryRequest
In TLS over TCP, the HelloRetryRequest feature (see Section 4.1.4 of
[TLS13]) can be used to correct a client's incorrect KeyShare
extension as well as for a stateless round-trip check. From the
perspective of QUIC, this just looks like additional messages carried
in the Initial encryption level. Although it is in principle
possible to use this feature for address verification in QUIC, QUIC
implementations SHOULD instead use the Retry feature (see Section 8.1
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of [QUIC-TRANSPORT]). HelloRetryRequest is still used to request key
shares.
4.8. TLS Errors
If TLS experiences an error, it generates an appropriate alert as
defined in Section 6 of [TLS13].
A TLS alert is turned into a QUIC connection error by converting the
one-byte alert description into a QUIC error code. The alert
description is added to 0x100 to produce a QUIC error code from the
range reserved for CRYPTO_ERROR. The resulting value is sent in a
QUIC CONNECTION_CLOSE frame.
The alert level of all TLS alerts is "fatal"; a TLS stack MUST NOT
generate alerts at the "warning" level.
4.9. Discarding Unused Keys
After QUIC moves to a new encryption level, packet protection keys
for previous encryption levels can be discarded. This occurs several
times during the handshake, as well as when keys are updated (see
Section 6). Initial packet protection keys are treated specially,
see Section 4.10.
Packet protection keys are not discarded immediately when new keys
are available. If packets from a lower encryption level contain
CRYPTO frames, frames that retransmit that data MUST be sent at the
same encryption level. Similarly, an endpoint generates
acknowledgements for packets at the same encryption level as the
packet being acknowledged. Thus, it is possible that keys for a
lower encryption level are needed for a short time after keys for a
newer encryption level are available.
An endpoint cannot discard keys for a given encryption level unless
it has both received and acknowledged all CRYPTO frames for that
encryption level and when all CRYPTO frames for that encryption level
have been acknowledged by its peer. However, this does not guarantee
that no further packets will need to be received or sent at that
encryption level because a peer might not have received all the
acknowledgements necessary to reach the same state.
After all CRYPTO frames for a given encryption level have been sent
and all expected CRYPTO frames received, and all the corresponding
acknowledgments have been received or sent, an endpoint starts a
timer. For 0-RTT keys, which do not carry CRYPTO frames, this timer
starts when the first packets protected with 1-RTT are sent or
received. To limit the effect of packet loss around a change in
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keys, endpoints MUST retain packet protection keys for that
encryption level for at least three times the current Probe Timeout
(PTO) interval as defined in [QUIC-RECOVERY]. Retaining keys for
this interval allows packets containing CRYPTO or ACK frames at that
encryption level to be sent if packets are determined to be lost or
new packets require acknowledgment.
Though an endpoint might retain older keys, new data MUST be sent at
the highest currently-available encryption level. Only ACK frames
and retransmissions of data in CRYPTO frames are sent at a previous
encryption level. These packets MAY also include PADDING frames.
Once this timer expires, an endpoint MUST NOT either accept or
generate new packets using those packet protection keys. An endpoint
can discard packet protection keys for that encryption level.
Key updates (see Section 6) can be used to update 1-RTT keys before
keys from other encryption levels are discarded. In that case,
packets protected with the newest packet protection keys and packets
sent two updates prior will appear to use the same keys. After the
handshake is complete, endpoints only need to maintain the two latest
sets of packet protection keys and MAY discard older keys. Updating
keys multiple times rapidly can cause packets to be effectively lost
if packets are significantly delayed. Because key updates can only
be performed once per round trip time, only packets that are delayed
by more than a round trip will be lost as a result of changing keys;
such packets will be marked as lost before this, as they leave a gap
in the sequence of packet numbers.
4.10. Discarding Initial Keys
Packets protected with Initial secrets (Section 5.2) are not
authenticated, meaning that an attacker could spoof packets with the
intent to disrupt a connection. To limit these attacks, Initial
packet protection keys can be discarded more aggressively than other
keys.
The successful use of Handshake packets indicates that no more
Initial packets need to be exchanged, as these keys can only be
produced after receiving all CRYPTO frames from Initial packets.
Thus, a client MUST discard Initial keys when it first sends a
Handshake packet and a server MUST discard Initial keys when it first
successfully processes a Handshake packet. Endpoints MUST NOT send
Initial packets after this point.
This results in abandoning loss recovery state for the Initial
encryption level and ignoring any outstanding Initial packets.
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5. Packet Protection
As with TLS over TCP, QUIC protects packets with keys derived from
the TLS handshake, using the AEAD algorithm negotiated by TLS.
5.1. Packet Protection Keys
QUIC derives packet protection keys in the same way that TLS derives
record protection keys.
Each encryption level has separate secret values for protection of
packets sent in each direction. These traffic secrets are derived by
TLS (see Section 7.1 of [TLS13]) and are used by QUIC for all
encryption levels except the Initial encryption level. The secrets
for the Initial encryption level are computed based on the client's
initial Destination Connection ID, as described in Section 5.2.
The keys used for packet protection are computed from the TLS secrets
using the KDF provided by TLS. In TLS 1.3, the HKDF-Expand-Label
function described in Section 7.1 of [TLS13] is used, using the hash
function from the negotiated cipher suite. Other versions of TLS
MUST provide a similar function in order to be used with QUIC.
The current encryption level secret and the label "quic key" are
input to the KDF to produce the AEAD key; the label "quic iv" is used
to derive the IV, see Section 5.3. The header protection key uses
the "quic hp" label, see Section 5.4. Using these labels provides
key separation between QUIC and TLS, see Section 9.5.
The KDF used for initial secrets is always the HKDF-Expand-Label
function from TLS 1.3 (see Section 5.2).
5.2. Initial Secrets
Initial packets are protected with a secret derived from the
Destination Connection ID field from the client's first Initial
packet of the connection. Specifically:
initial_salt = 0xef4fb0abb47470c41befcf8031334fae485e09a0
initial_secret = HKDF-Extract(initial_salt,
client_dst_connection_id)
client_initial_secret = HKDF-Expand-Label(initial_secret,
"client in", "",
Hash.length)
server_initial_secret = HKDF-Expand-Label(initial_secret,
"server in", "",
Hash.length)
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The hash function for HKDF when deriving initial secrets and keys is
SHA-256 [SHA].
The connection ID used with HKDF-Expand-Label is the Destination
Connection ID in the Initial packet sent by the client. This will be
a randomly-selected value unless the client creates the Initial
packet after receiving a Retry packet, where the Destination
Connection ID is selected by the server.
The value of initial_salt is a 20 byte sequence shown in the figure
in hexadecimal notation. Future versions of QUIC SHOULD generate a
new salt value, thus ensuring that the keys are different for each
version of QUIC. This prevents a middlebox that only recognizes one
version of QUIC from seeing or modifying the contents of packets from
future versions.
The HKDF-Expand-Label function defined in TLS 1.3 MUST be used for
Initial packets even where the TLS versions offered do not include
TLS 1.3.
Appendix A contains test vectors for the initial packet encryption.
Note: The Destination Connection ID is of arbitrary length, and it
could be zero length if the server sends a Retry packet with a
zero-length Source Connection ID field. In this case, the Initial
keys provide no assurance to the client that the server received
its packet; the client has to rely on the exchange that included
the Retry packet for that property.
5.3. AEAD Usage
The Authentication Encryption with Associated Data (AEAD) [AEAD]
function used for QUIC packet protection is the AEAD that is
negotiated for use with the TLS connection. For example, if TLS is
using the TLS_AES_128_GCM_SHA256, the AEAD_AES_128_GCM function is
used.
Packets are protected prior to applying header protection
(Section 5.4). The unprotected packet header is part of the
associated data (A). When removing packet protection, an endpoint
first removes the header protection.
All QUIC packets other than Version Negotiation and Retry packets are
protected with an AEAD algorithm [AEAD]. Prior to establishing a
shared secret, packets are protected with AEAD_AES_128_GCM and a key
derived from the Destination Connection ID in the client's first
Initial packet (see Section 5.2). This provides protection against
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off-path attackers and robustness against QUIC version unaware
middleboxes, but not against on-path attackers.
QUIC can use any of the ciphersuites defined in [TLS13] with the
exception of TLS_AES_128_CCM_8_SHA256. The AEAD for that
ciphersuite, AEAD_AES_128_CCM_8 [CCM], does not produce a large
enough authentication tag for use with the header protection designs
provided (see Section 5.4). All other ciphersuites defined in
[TLS13] have a 16-byte authentication tag and produce an output 16
bytes larger than their input.
The key and IV for the packet are computed as described in
Section 5.1. The nonce, N, is formed by combining the packet
protection IV with the packet number. The 62 bits of the
reconstructed QUIC packet number in network byte order are left-
padded with zeros to the size of the IV. The exclusive OR of the
padded packet number and the IV forms the AEAD nonce.
The associated data, A, for the AEAD is the contents of the QUIC
header, starting from the flags byte in either the short or long
header, up to and including the unprotected packet number.
The input plaintext, P, for the AEAD is the payload of the QUIC
packet, as described in [QUIC-TRANSPORT].
The output ciphertext, C, of the AEAD is transmitted in place of P.
Some AEAD functions have limits for how many packets can be encrypted
under the same key and IV (see for example [AEBounds]). This might
be lower than the packet number limit. An endpoint MUST initiate a
key update (Section 6) prior to exceeding any limit set for the AEAD
that is in use.
5.4. Header Protection
Parts of QUIC packet headers, in particular the Packet Number field,
are protected using a key that is derived separate to the packet
protection key and IV. The key derived using the "quic hp" label is
used to provide confidentiality protection for those fields that are
not exposed to on-path elements.
This protection applies to the least-significant bits of the first
byte, plus the Packet Number field. The four least-significant bits
of the first byte are protected for packets with long headers; the
five least significant bits of the first byte are protected for
packets with short headers. For both header forms, this covers the
reserved bits and the Packet Number Length field; the Key Phase bit
is also protected for packets with a short header.
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The same header protection key is used for the duration of the
connection, with the value not changing after a key update (see
Section 6). This allows header protection to be used to protect the
key phase.
This process does not apply to Retry or Version Negotiation packets,
which do not contain a protected payload or any of the fields that
are protected by this process.
5.4.1. Header Protection Application
Header protection is applied after packet protection is applied (see
Section 5.3). The ciphertext of the packet is sampled and used as
input to an encryption algorithm. The algorithm used depends on the
negotiated AEAD.
The output of this algorithm is a 5 byte mask which is applied to the
protected header fields using exclusive OR. The least significant
bits of the first byte of the packet are masked by the least
significant bits of the first mask byte, and the packet number is
masked with the remaining bytes. Any unused bytes of mask that might
result from a shorter packet number encoding are unused.
Figure 4 shows a sample algorithm for applying header protection.
Removing header protection only differs in the order in which the
packet number length (pn_length) is determined.
mask = header_protection(hp_key, sample)
pn_length = (packet[0] & 0x03) + 1
if (packet[0] & 0x80) == 0x80:
# Long header: 4 bits masked
packet[0] ^= mask[0] & 0x0f
else:
# Short header: 5 bits masked
packet[0] ^= mask[0] & 0x1f
# pn_offset is the start of the Packet Number field.
packet[pn_offset:pn_offset+pn_length] ^= mask[1:1+pn_length]
Figure 4: Header Protection Pseudocode
Figure 5 shows the protected fields of long and short headers marked
with an E. Figure 5 also shows the sampled fields.
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Long Header:
+-+-+-+-+-+-+-+-+
|1|1|T T|E E E E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version -> Length Fields ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Short Header:
+-+-+-+-+-+-+-+-+
|0|1|S|E E E E E|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Connection ID (0/32..144) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Common Fields:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E E E E E E E E E Packet Number (8/16/24/32) E E E E E E E E...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Protected Payload (8/16/24)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sampled part of Protected Payload (128) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protected Payload Remainder (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Header Protection and Ciphertext Sample
Before a TLS ciphersuite can be used with QUIC, a header protection
algorithm MUST be specified for the AEAD used with that ciphersuite.
This document defines algorithms for AEAD_AES_128_GCM,
AEAD_AES_128_CCM, AEAD_AES_256_GCM, AEAD_AES_256_CCM (all AES AEADs
are defined in [AEAD]), and AEAD_CHACHA20_POLY1305 [CHACHA]. Prior
to TLS selecting a ciphersuite, AES header protection is used
(Section 5.4.3), matching the AEAD_AES_128_GCM packet protection.
5.4.2. Header Protection Sample
The header protection algorithm uses both the header protection key
and a sample of the ciphertext from the packet Payload field.
The same number of bytes are always sampled, but an allowance needs
to be made for the endpoint removing protection, which will not know
the length of the Packet Number field. In sampling the packet
ciphertext, the Packet Number field is assumed to be 4 bytes long
(its maximum possible encoded length).
An endpoint MUST discard packets that are not long enough to contain
a complete sample.
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To ensure that sufficient data is available for sampling, packets are
padded so that the combined lengths of the encoded packet number and
protected payload is at least 4 bytes longer than the sample required
for header protection. For the AEAD functions defined in [TLS13],
which have 16-byte expansions and 16-byte header protection samples,
this results in needing at least 3 bytes of frames in the unprotected
payload if the packet number is encoded on a single byte, or 2 bytes
of frames for a 2-byte packet number encoding.
The sampled ciphertext for a packet with a short header can be
determined by the following pseudocode:
sample_offset = 1 + len(connection_id) + 4
sample = packet[sample_offset..sample_offset+sample_length]
For example, for a packet with a short header, an 8 byte connection
ID, and protected with AEAD_AES_128_GCM, the sample takes bytes 13 to
28 inclusive (using zero-based indexing).
A packet with a long header is sampled in the same way, noting that
multiple QUIC packets might be included in the same UDP datagram and
that each one is handled separately.
sample_offset = 6 + len(destination_connection_id) +
len(source_connection_id) +
len(payload_length) + 4
if packet_type == Initial:
sample_offset += len(token_length) +
len(token)
sample = packet[sample_offset..sample_offset+sample_length]
5.4.3. AES-Based Header Protection
This section defines the packet protection algorithm for
AEAD_AES_128_GCM, AEAD_AES_128_CCM, AEAD_AES_256_GCM, and
AEAD_AES_256_CCM. AEAD_AES_128_GCM and AEAD_AES_128_CCM use 128-bit
AES [AES] in electronic code-book (ECB) mode. AEAD_AES_256_GCM, and
AEAD_AES_256_CCM use 256-bit AES in ECB mode.
This algorithm samples 16 bytes from the packet ciphertext. This
value is used as the input to AES-ECB. In pseudocode:
mask = AES-ECB(hp_key, sample)
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5.4.4. ChaCha20-Based Header Protection
When AEAD_CHACHA20_POLY1305 is in use, header protection uses the raw
ChaCha20 function as defined in Section 2.4 of [CHACHA]. This uses a
256-bit key and 16 bytes sampled from the packet protection output.
The first 4 bytes of the sampled ciphertext are interpreted as a
32-bit number in little-endian order and are used as the block count.
The remaining 12 bytes are interpreted as three concatenated 32-bit
numbers in little-endian order and used as the nonce.
The encryption mask is produced by invoking ChaCha20 to protect 5
zero bytes. In pseudocode:
counter = DecodeLE(sample[0..3])
nonce = DecodeLE(sample[4..7], sample[8..11], sample[12..15])
mask = ChaCha20(hp_key, counter, nonce, {0,0,0,0,0})
5.5. Receiving Protected Packets
Once an endpoint successfully receives a packet with a given packet
number, it MUST discard all packets in the same packet number space
with higher packet numbers if they cannot be successfully unprotected
with either the same key, or - if there is a key update - the next
packet protection key (see Section 6). Similarly, a packet that
appears to trigger a key update, but cannot be unprotected
successfully MUST be discarded.
Failure to unprotect a packet does not necessarily indicate the
existence of a protocol error in a peer or an attack. The truncated
packet number encoding used in QUIC can cause packet numbers to be
decoded incorrectly if they are delayed significantly.
5.6. Use of 0-RTT Keys
If 0-RTT keys are available (see Section 4.5), the lack of replay
protection means that restrictions on their use are necessary to
avoid replay attacks on the protocol.
A client MUST only use 0-RTT keys to protect data that is idempotent.
A client MAY wish to apply additional restrictions on what data it
sends prior to the completion of the TLS handshake. A client
otherwise treats 0-RTT keys as equivalent to 1-RTT keys, except that
it MUST NOT send ACKs with 0-RTT keys.
A client that receives an indication that its 0-RTT data has been
accepted by a server can send 0-RTT data until it receives all of the
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server's handshake messages. A client SHOULD stop sending 0-RTT data
if it receives an indication that 0-RTT data has been rejected.
A server MUST NOT use 0-RTT keys to protect packets; it uses 1-RTT
keys to protect acknowledgements of 0-RTT packets. A client MUST NOT
attempt to decrypt 0-RTT packets it receives and instead MUST discard
them.
Note: 0-RTT data can be acknowledged by the server as it receives
it, but any packets containing acknowledgments of 0-RTT data
cannot have packet protection removed by the client until the TLS
handshake is complete. The 1-RTT keys necessary to remove packet
protection cannot be derived until the client receives all server
handshake messages.
5.7. Receiving Out-of-Order Protected Frames
Due to reordering and loss, protected packets might be received by an
endpoint before the final TLS handshake messages are received. A
client will be unable to decrypt 1-RTT packets from the server,
whereas a server will be able to decrypt 1-RTT packets from the
client.
However, a server MUST NOT process data from incoming 1-RTT protected
packets before verifying either the client Finished message or - in
the case that the server has chosen to use a pre-shared key - the
pre-shared key binder (see Section 4.2.11 of [TLS13]). Verifying
these values provides the server with an assurance that the
ClientHello has not been modified. Packets protected with 1-RTT keys
MAY be stored and later decrypted and used once the handshake is
complete.
A server could receive packets protected with 0-RTT keys prior to
receiving a TLS ClientHello. The server MAY retain these packets for
later decryption in anticipation of receiving a ClientHello.
6. Key Update
Once the 1-RTT keys are established and the short header is in use,
it is possible to update the keys. The KEY_PHASE bit in the short
header is used to indicate whether key updates have occurred. The
KEY_PHASE bit is initially set to 0 and then inverted with each key
update.
The KEY_PHASE bit allows a recipient to detect a change in keying
material without necessarily needing to receive the first packet that
triggered the change. An endpoint that notices a changed KEY_PHASE
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bit can update keys and decrypt the packet that contains the changed
bit.
This mechanism replaces the TLS KeyUpdate message. Endpoints MUST
NOT send a TLS KeyUpdate message. Endpoints MUST treat the receipt
of a TLS KeyUpdate message as a connection error of type 0x10a,
equivalent to a fatal TLS alert of unexpected_message (see
Section 4.8).
An endpoint MUST NOT initiate more than one key update at a time. A
new key cannot be used until the endpoint has received and
successfully decrypted a packet with a matching KEY_PHASE.
A receiving endpoint detects an update when the KEY_PHASE bit does
not match what it is expecting. It creates a new secret (see
Section 7.2 of [TLS13]) and the corresponding read key and IV using
the KDF function provided by TLS. The header protection key is not
updated.
If the packet can be decrypted and authenticated using the updated
key and IV, then the keys the endpoint uses for packet protection are
also updated. The next packet sent by the endpoint will then use the
new keys.
An endpoint does not always need to send packets when it detects that
its peer has updated keys. The next packet that it sends will simply
use the new keys. If an endpoint detects a second update before it
has sent any packets with updated keys, it indicates that its peer
has updated keys twice without awaiting a reciprocal update. An
endpoint MUST treat consecutive key updates as a fatal error and
abort the connection.
An endpoint SHOULD retain old keys for a period of no more than three
times the Probe Timeout (PTO, see [QUIC-RECOVERY]). After this
period, old keys and their corresponding secrets SHOULD be discarded.
Retaining keys allow endpoints to process packets that were sent with
old keys and delayed in the network. Packets with higher packet
numbers always use the updated keys and MUST NOT be decrypted with
old keys.
This ensures that once the handshake is complete, packets with the
same KEY_PHASE will have the same packet protection keys, unless
there are multiple key updates in a short time frame succession and
significant packet reordering.
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Initiating Peer Responding Peer
@M QUIC Frames
New Keys -> @N
@N QUIC Frames
-------->
QUIC Frames @M
New Keys -> @N
QUIC Frames @N
<--------
Figure 6: Key Update
A packet that triggers a key update could arrive after successfully
processing a packet with a higher packet number. This is only
possible if there is a key compromise and an attack, or if the peer
is incorrectly reverting to use of old keys. Because the latter
cannot be differentiated from an attack, an endpoint MUST immediately
terminate the connection if it detects this condition.
In deciding when to update keys, endpoints MUST NOT exceed the limits
for use of specific keys, as described in Section 5.5 of [TLS13].
7. Security of Initial Messages
Initial packets are not protected with a secret key, so they are
subject to potential tampering by an attacker. QUIC provides
protection against attackers that cannot read packets, but does not
attempt to provide additional protection against attacks where the
attacker can observe and inject packets. Some forms of tampering -
such as modifying the TLS messages themselves - are detectable, but
some - such as modifying ACKs - are not.
For example, an attacker could inject a packet containing an ACK
frame that makes it appear that a packet had not been received or to
create a false impression of the state of the connection (e.g., by
modifying the ACK Delay). Note that such a packet could cause a
legitimate packet to be dropped as a duplicate. Implementations
SHOULD use caution in relying on any data which is contained in
Initial packets that is not otherwise authenticated.
It is also possible for the attacker to tamper with data that is
carried in Handshake packets, but because that tampering requires
modifying TLS handshake messages, that tampering will cause the TLS
handshake to fail.
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8. QUIC-Specific Additions to the TLS Handshake
QUIC uses the TLS handshake for more than just negotiation of
cryptographic parameters. The TLS handshake validates protocol
version selection, provides preliminary values for QUIC transport
parameters, and allows a server to perform return routeability checks
on clients.
8.1. Protocol and Version Negotiation
The QUIC version negotiation mechanism is used to negotiate the
version of QUIC that is used prior to the completion of the
handshake. However, this packet is not authenticated, enabling an
active attacker to force a version downgrade.
To ensure that a QUIC version downgrade is not forced by an attacker,
version information is copied into the TLS handshake, which provides
integrity protection for the QUIC negotiation. This does not prevent
version downgrade prior to the completion of the handshake, though it
means that a downgrade causes a handshake failure.
QUIC requires that the cryptographic handshake provide authenticated
protocol negotiation. TLS uses Application Layer Protocol
Negotiation (ALPN) [RFC7301] to select an application protocol.
Unless another mechanism is used for agreeing on an application
protocol, endpoints MUST use ALPN for this purpose. When using ALPN,
endpoints MUST abort a connection if an application protocol is not
negotiated.
An application-layer protocol MAY restrict the QUIC versions that it
can operate over. Servers MUST select an application protocol
compatible with the QUIC version that the client has selected. If
the server cannot select a compatible combination of application
protocol and QUIC version, it MUST abort the connection. A client
MUST abort a connection if the server picks an incompatible
combination of QUIC version and ALPN identifier.
8.2. QUIC Transport Parameters Extension
QUIC transport parameters are carried in a TLS extension. Different
versions of QUIC might define a different format for this struct.
Including transport parameters in the TLS handshake provides
integrity protection for these values.
enum {
quic_transport_parameters(0xffa5), (65535)
} ExtensionType;
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The "extension_data" field of the quic_transport_parameters extension
contains a value that is defined by the version of QUIC that is in
use. The quic_transport_parameters extension carries a
TransportParameters struct when the version of QUIC defined in
[QUIC-TRANSPORT] is used.
The quic_transport_parameters extension is carried in the ClientHello
and the EncryptedExtensions messages during the handshake.
While the transport parameters are technically available prior to the
completion of the handshake, they cannot be fully trusted until the
handshake completes, and reliance on them should be minimized.
However, any tampering with the parameters will cause the handshake
to fail.
Endpoints MUST NOT send this extension in a TLS connection that does
not use QUIC (such as the use of TLS with TCP defined in [TLS13]). A
fatal unsupported_extension alert MUST be sent if this extension is
received when the transport is not QUIC.
8.3. Removing the EndOfEarlyData Message
The TLS EndOfEarlyData message is not used with QUIC. QUIC does not
rely on this message to mark the end of 0-RTT data or to signal the
change to Handshake keys.
Clients MUST NOT send the EndOfEarlyData message. A server MUST
treat receipt of a CRYPTO frame in a 0-RTT packet as a connection
error of type PROTOCOL_VIOLATION.
As a result, EndOfEarlyData does not appear in the TLS handshake
transcript.
9. Security Considerations
There are likely to be some real clangers here eventually, but the
current set of issues is well captured in the relevant sections of
the main text.
Never assume that because it isn't in the security considerations
section it doesn't affect security. Most of this document does.
9.1. Replay Attacks with 0-RTT
As described in Section 8 of [TLS13], use of TLS early data comes
with an exposure to replay attack. The use of 0-RTT in QUIC is
similarly vulnerable to replay attack.
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Endpoints MUST implement and use the replay protections described in
[TLS13], however it is recognized that these protections are
imperfect. Therefore, additional consideration of the risk of replay
is needed.
QUIC is not vulnerable to replay attack, except via the application
protocol information it might carry. The management of QUIC protocol
state based on the frame types defined in [QUIC-TRANSPORT] is not
vulnerable to replay. Processing of QUIC frames is idempotent and
cannot result in invalid connection states if frames are replayed,
reordered or lost. QUIC connections do not produce effects that last
beyond the lifetime of the connection, except for those produced by
the application protocol that QUIC serves.
Note: TLS session tickets and address validation tokens are used to
carry QUIC configuration information between connections. These
MUST NOT be used to carry application semantics. The potential
for reuse of these tokens means that they require stronger
protections against replay.
A server that accepts 0-RTT on a connection incurs a higher cost than
accepting a connection without 0-RTT. This includes higher
processing and computation costs. Servers need to consider the
probability of replay and all associated costs when accepting 0-RTT.
Ultimately, the responsibility for managing the risks of replay
attacks with 0-RTT lies with an application protocol. An application
protocol that uses QUIC MUST describe how the protocol uses 0-RTT and
the measures that are employed to protect against replay attack. An
analysis of replay risk needs to consider all QUIC protocol features
that carry application semantics.
Disabling 0-RTT entirely is the most effective defense against replay
attack.
QUIC extensions MUST describe how replay attacks affects their
operation, or prohibit their use in 0-RTT. Application protocols
MUST either prohibit the use of extensions that carry application
semantics in 0-RTT or provide replay mitigation strategies.
9.2. Packet Reflection Attack Mitigation
A small ClientHello that results in a large block of handshake
messages from a server can be used in packet reflection attacks to
amplify the traffic generated by an attacker.
QUIC includes three defenses against this attack. First, the packet
containing a ClientHello MUST be padded to a minimum size. Second,
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if responding to an unverified source address, the server is
forbidden to send more than three UDP datagrams in its first flight
(see Section 8.1 of [QUIC-TRANSPORT]). Finally, because
acknowledgements of Handshake packets are authenticated, a blind
attacker cannot forge them. Put together, these defenses limit the
level of amplification.
9.3. Peer Denial of Service
QUIC, TLS, and HTTP/2 all contain messages that have legitimate uses
in some contexts, but that can be abused to cause a peer to expend
processing resources without having any observable impact on the
state of the connection. If processing is disproportionately large
in comparison to the observable effects on bandwidth or state, then
this could allow a malicious peer to exhaust processing capacity
without consequence.
QUIC prohibits the sending of empty "STREAM" frames unless they are
marked with the FIN bit. This prevents "STREAM" frames from being
sent that only waste effort.
While there are legitimate uses for some redundant packets,
implementations SHOULD track redundant packets and treat excessive
volumes of any non-productive packets as indicative of an attack.
9.4. Header Protection Analysis
Header protection relies on the packet protection AEAD being a
pseudorandom function (PRF), which is not a property that AEAD
algorithms guarantee. Therefore, no strong assurances about the
general security of this mechanism can be shown in the general case.
The AEAD algorithms described in this document are assumed to be
PRFs.
The header protection algorithms defined in this document take the
form:
protected_field = field XOR PRF(hp_key, sample)
This construction is secure against chosen plaintext attacks (IND-
CPA) [IMC].
Use of the same key and ciphertext sample more than once risks
compromising header protection. Protecting two different headers
with the same key and ciphertext sample reveals the exclusive OR of
the protected fields. Assuming that the AEAD acts as a PRF, if L
bits are sampled, the odds of two ciphertext samples being identical
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approach 2^(-L/2), that is, the birthday bound. For the algorithms
described in this document, that probability is one in 2^64.
Note: In some cases, inputs shorter than the full size required by
the packet protection algorithm might be used.
To prevent an attacker from modifying packet headers, the header is
transitively authenticated using packet protection; the entire packet
header is part of the authenticated additional data. Protected
fields that are falsified or modified can only be detected once the
packet protection is removed.
An attacker could guess values for packet numbers and have an
endpoint confirm guesses through timing side channels. Similarly,
guesses for the packet number length can be trialed and exposed. If
the recipient of a packet discards packets with duplicate packet
numbers without attempting to remove packet protection they could
reveal through timing side-channels that the packet number matches a
received packet. For authentication to be free from side-channels,
the entire process of header protection removal, packet number
recovery, and packet protection removal MUST be applied together
without timing and other side-channels.
For the sending of packets, construction and protection of packet
payloads and packet numbers MUST be free from side-channels that
would reveal the packet number or its encoded size.
9.5. Key Diversity
In using TLS, the central key schedule of TLS is used. As a result
of the TLS handshake messages being integrated into the calculation
of secrets, the inclusion of the QUIC transport parameters extension
ensures that handshake and 1-RTT keys are not the same as those that
might be produced by a server running TLS over TCP. To avoid the
possibility of cross-protocol key synchronization, additional
measures are provided to improve key separation.
The QUIC packet protection keys and IVs are derived using a different
label than the equivalent keys in TLS.
To preserve this separation, a new version of QUIC SHOULD define new
labels for key derivation for packet protection key and IV, plus the
header protection keys. This version of QUIC uses the string "quic".
Other versions can use a version-specific label in place of that
string.
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The initial secrets use a key that is specific to the negotiated QUIC
version. New QUIC versions SHOULD define a new salt value used in
calculating initial secrets.
10. IANA Considerations
This document does not create any new IANA registries, but it
registers the values in the following registries:
o TLS ExtensionsType Registry [TLS-REGISTRIES] - IANA is to register
the quic_transport_parameters extension found in Section 8.2. The
Recommended column is to be marked Yes. The TLS 1.3 Column is to
include CH and EE.
11. References
11.1. Normative References
[AEAD] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
[AES] "Advanced encryption standard (AES)", National Institute
of Standards and Technology report,
DOI 10.6028/nist.fips.197, November 2001.
[CHACHA] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,
<https://www.rfc-editor.org/info/rfc8439>.
[QUIC-RECOVERY]
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", draft-ietf-quic-recovery-19 (work
in progress), March 2019.
[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic-
transport-19 (work in progress), March 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>.
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[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[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>.
[SHA] Dang, Q., "Secure Hash Standard", National Institute of
Standards and Technology report,
DOI 10.6028/nist.fips.180-4, July 2015.
[TLS-REGISTRIES]
Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/info/rfc8447>.
[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
11.2. Informative References
[AEBounds]
Luykx, A. and K. Paterson, "Limits on Authenticated
Encryption Use in TLS", March 2016,
<http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>.
[CCM] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for
Transport Layer Security (TLS)", RFC 6655,
DOI 10.17487/RFC6655, July 2012,
<https://www.rfc-editor.org/info/rfc6655>.
[IMC] Katz, J. and Y. Lindell, "Introduction to Modern
Cryptography, Second Edition", ISBN 978-1466570269,
November 2014.
[QUIC-HTTP]
Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
QUIC", draft-ietf-quic-http-19 (work in progress), March
2019.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
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[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
11.3. URIs
[1] https://mailarchive.ietf.org/arch/search/?email_list=quic
[2] https://github.com/quicwg
[3] https://github.com/quicwg/base-drafts/labels/-tls
Appendix A. Sample Initial Packet Protection
This section shows examples of packet protection for Initial packets
so that implementations can be verified incrementally. These packets
use an 8-byte client-chosen Destination Connection ID of
0x8394c8f03e515708. Values for both server and client packet
protection are shown together with values in hexadecimal.
A.1. Keys
The labels generated by the HKDF-Expand-Label function are:
client in: 00200f746c73313320636c69656e7420696e00
server in: 00200f746c7331332073657276657220696e00
quic key: 00100e746c7331332071756963206b657900
quic iv: 000c0d746c733133207175696320697600
quic hp: 00100d746c733133207175696320687000
The initial secret is common:
initial_secret = HKDF-Extract(initial_salt, cid)
= 4496d3903d3f97cc5e45ac5790ddc686
683c7c0067012bb09d900cc21832d596
The secrets for protecting client packets are:
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client_initial_secret
= HKDF-Expand-Label(initial_secret, "client in", _, 32)
= 8a3515a14ae3c31b9c2d6d5bc58538ca
5cd2baa119087143e60887428dcb52f6
key = HKDF-Expand-Label(client_initial_secret, "quic key", _, 16)
= 98b0d7e5e7a402c67c33f350fa65ea54
iv = HKDF-Expand-Label(client_initial_secret, "quic iv", _, 12)
= 19e94387805eb0b46c03a788
hp = HKDF-Expand-Label(client_initial_secret, "quic hp", _, 16)
= 0edd982a6ac527f2eddcbb7348dea5d7
The secrets for protecting server packets are:
server_initial_secret
= HKDF-Expand-Label(initial_secret, "server in", _, 32)
= 47b2eaea6c266e32c0697a9e2a898bdf
5c4fb3e5ac34f0e549bf2c58581a3811
key = HKDF-Expand-Label(server_initial_secret, "quic key", _, 16)
= 9a8be902a9bdd91d16064ca118045fb4
iv = HKDF-Expand-Label(server_initial_secret, "quic iv", _, 12)
= 0a82086d32205ba22241d8dc
hp = HKDF-Expand-Label(server_initial_secret, "quic hp", _, 16)
= 94b9452d2b3c7c7f6da7fdd8593537fd
A.2. Client Initial
The client sends an Initial packet. The unprotected payload of this
packet contains the following CRYPTO frame, plus enough PADDING
frames to make an 1163 byte payload:
060040c4010000c003036660261ff947 cea49cce6cfad687f457cf1b14531ba1
4131a0e8f309a1d0b9c4000006130113 031302010000910000000b0009000006
736572766572ff01000100000a001400 12001d00170018001901000101010201
03010400230000003300260024001d00 204cfdfcd178b784bf328cae793b136f
2aedce005ff183d7bb14952072366470 37002b0003020304000d0020001e0403
05030603020308040805080604010501 060102010402050206020202002d0002
0101001c00024001
The unprotected header includes the connection ID and a 4 byte packet
number encoding for a packet number of 2:
c3ff000012508394c8f03e51570800449f00000002
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Protecting the payload produces output that is sampled for header
protection. Because the header uses a 4 byte packet number encoding,
the first 16 bytes of the protected payload is sampled, then applied
to the header:
sample = 0000f3a694c75775b4e546172ce9e047
mask = AES-ECB(hp, sample)[0..4]
= 020dbc1958
header[0] ^= mask[0] & 0x0f
= c1
header[17..20] ^= mask[1..4]
= 0dbc195a
header = c1ff000012508394c8f03e51570800449f0dbc195a
The resulting protected packet is:
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c1ff000012508394c8f03e5157080044 9f0dbc195a0000f3a694c75775b4e546
172ce9e047cd0b5bee5181648c727adc 87f7eae54473ec6cba6bdad4f5982317
4b769f12358abd292d4f3286934484fb 8b239c38732e1f3bbbc6a003056487eb
8b5c88b9fd9279ffff3b0f4ecf95c462 4db6d65d4113329ee9b0bf8cdd7c8a8d
72806d55df25ecb66488bc119d7c9a29 abaf99bb33c56b08ad8c26995f838bb3
b7a3d5c1858b8ec06b839db2dcf918d5 ea9317f1acd6b663cc8925868e2f6a1b
da546695f3c3f33175944db4a11a346a fb07e78489e509b02add51b7b203eda5
c330b03641179a31fbba9b56ce00f3d5 b5e3d7d9c5429aebb9576f2f7eacbe27
bc1b8082aaf68fb69c921aa5d33ec0c8 510410865a178d86d7e54122d55ef2c2
bbc040be46d7fece73fe8a1b24495ec1 60df2da9b20a7ba2f26dfa2a44366dbc
63de5cd7d7c94c57172fe6d79c901f02 5c0010b02c89b395402c009f62dc053b
8067a1e0ed0a1e0cf5087d7f78cbd94a fe0c3dd55d2d4b1a5cfe2b68b86264e3
51d1dcd858783a240f893f008ceed743 d969b8f735a1677ead960b1fb1ecc5ac
83c273b49288d02d7286207e663c45e1 a7baf50640c91e762941cf380ce8d79f
3e86767fbbcd25b42ef70ec334835a3a 6d792e170a432ce0cb7bde9aaa1e7563
7c1c34ae5fef4338f53db8b13a4d2df5 94efbfa08784543815c9c0d487bddfa1
539bc252cf43ec3686e9802d651cfd2a 829a06a9f332a733a4a8aed80efe3478
093fbc69c8608146b3f16f1a5c4eac93 20da49f1afa5f538ddecbbe7888f4355
12d0dd74fd9b8c99e3145ba84410d8ca 9a36dd884109e76e5fb8222a52e1473d
a168519ce7a8a3c32e9149671b16724c 6c5c51bb5cd64fb591e567fb78b10f9f
6fee62c276f282a7df6bcf7c17747bc9 a81e6c9c3b032fdd0e1c3ac9eaa5077d
e3ded18b2ed4faf328f49875af2e36ad 5ce5f6cc99ef4b60e57b3b5b9c9fcbcd
4cfb3975e70ce4c2506bcd71fef0e535 92461504e3d42c885caab21b782e2629
4c6a9d61118cc40a26f378441ceb48f3 1a362bf8502a723a36c63502229a462c
c2a3796279a5e3a7f81a68c7f81312c3 81cc16a4ab03513a51ad5b54306ec1d7
8a5e47e2b15e5b7a1438e5b8b2882dbd ad13d6a4a8c3558cae043501b68eb3b0
40067152337c051c40b5af809aca2856 986fd1c86a4ade17d254b6262ac1bc07
7343b52bf89fa27d73e3c6f3118c9961 f0bebe68a5c323c2d84b8c29a2807df6
63635223242a2ce9828d4429ac270aab 5f1841e8e49cf433b1547989f419caa3
c758fff96ded40cf3427f0761b678daa 1a9e5554465d46b7a917493fc70f9ec5
e4e5d786ca501730898aaa1151dcd318 29641e29428d90e6065511c24d3109f7
cba32225d4accfc54fec42b733f95852 52ee36fa5ea0c656934385b468eee245
315146b8c047ed27c519b2c0a52d33ef e72c186ffe0a230f505676c5324baa6a
e006a73e13aa8c39ab173ad2b2778eea 0b34c46f2b3beae2c62a2c8db238bf58
fc7c27bdceb96c56d29deec87c12351b fd5962497418716a4b915d334ffb5b92
ca94ffe1e4f78967042638639a9de325 357f5f08f6435061e5a274703936c06f
c56af92c420797499ca431a7abaa4618 63bca656facfad564e6274d4a741033a
ca1e31bf63200df41cdf41c10b912bec
A.3. Server Initial
The server sends the following payload in response, including an ACK
frame, a CRYPTO frame, and no PADDING frames:
0d0000000018410a020000560303eefc e7f7b37ba1d1632e96677825ddf73988
cfc79825df566dc5430b9a045a120013 0100002e00330024001d00209d3c940d
89690b84d08a60993c144eca684d1081 287c834d5311bcf32bb9da1a002b0002
0304
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The header from the server includes a new connection ID and a 2-byte
packet number encoding for a packet number of 1:
c1ff00001205f067a5502a4262b50040740001
As a result, after protection, the header protection sample is taken
starting from the third protected octet:
sample = c4c2a2303d297e3c519bf6b22386e3d0
mask = 75f7ec8b62
header = c4ff00001205f067a5502a4262b5004074f7ed
The final protected packet is then:
c4ff00001205f067a5502a4262b50040 74f7ed5f01c4c2a2303d297e3c519bf6
b22386e3d0bd6dfc6612167729803104 1bb9a79c9f0f9d4c5877270a660f5da3
6207d98b73839b2fdf2ef8e7df5a51b1 7b8c68d864fd3e708c6c1b71a98a3318
15599ef5014ea38c44bdfd387c03b527 5c35e009b6238f831420047c7271281c
cb54df7884
Appendix B. Change Log
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
Issue and pull request numbers are listed with a leading octothorp.
B.1. Since draft-ietf-quic-tls-18
o Increased the set of permissible frames in 0-RTT (#2344, #2355)
B.2. Since draft-ietf-quic-tls-17
o Endpoints discard initial keys as soon as handshake keys are
available (#1951, #2045)
o Use of ALPN or equivalent is mandatory (#2263, #2284)
B.3. Since draft-ietf-quic-tls-14
o Update the salt used for Initial secrets (#1970)
o Clarify that TLS_AES_128_CCM_8_SHA256 isn't supported (#2019)
o Change header protection
* Sample from a fixed offset (#1575, #2030)
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* Cover part of the first byte, including the key phase (#1322,
#2006)
o TLS provides an AEAD and KDF function (#2046)
* Clarify that the TLS KDF is used with TLS (#1997)
* Change the labels for calculation of QUIC keys (#1845, #1971,
#1991)
o Initial keys are discarded once Handshake are avaialble (#1951,
#2045)
B.4. Since draft-ietf-quic-tls-13
o Updated to TLS 1.3 final (#1660)
B.5. Since draft-ietf-quic-tls-12
o Changes to integration of the TLS handshake (#829, #1018, #1094,
#1165, #1190, #1233, #1242, #1252, #1450)
* The cryptographic handshake uses CRYPTO frames, not stream 0
* QUIC packet protection is used in place of TLS record
protection
* Separate QUIC packet number spaces are used for the handshake
* Changed Retry to be independent of the cryptographic handshake
* Limit the use of HelloRetryRequest to address TLS needs (like
key shares)
o Changed codepoint of TLS extension (#1395, #1402)
B.6. Since draft-ietf-quic-tls-11
o Encrypted packet numbers.
B.7. Since draft-ietf-quic-tls-10
o No significant changes.
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B.8. Since draft-ietf-quic-tls-09
o Cleaned up key schedule and updated the salt used for handshake
packet protection (#1077)
B.9. Since draft-ietf-quic-tls-08
o Specify value for max_early_data_size to enable 0-RTT (#942)
o Update key derivation function (#1003, #1004)
B.10. Since draft-ietf-quic-tls-07
o Handshake errors can be reported with CONNECTION_CLOSE (#608,
#891)
B.11. Since draft-ietf-quic-tls-05
No significant changes.
B.12. Since draft-ietf-quic-tls-04
o Update labels used in HKDF-Expand-Label to match TLS 1.3 (#642)
B.13. Since draft-ietf-quic-tls-03
No significant changes.
B.14. Since draft-ietf-quic-tls-02
o Updates to match changes in transport draft
B.15. Since draft-ietf-quic-tls-01
o Use TLS alerts to signal TLS errors (#272, #374)
o Require ClientHello to fit in a single packet (#338)
o The second client handshake flight is now sent in the clear (#262,
#337)
o The QUIC header is included as AEAD Associated Data (#226, #243,
#302)
o Add interface necessary for client address validation (#275)
o Define peer authentication (#140)
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o Require at least TLS 1.3 (#138)
o Define transport parameters as a TLS extension (#122)
o Define handling for protected packets before the handshake
completes (#39)
o Decouple QUIC version and ALPN (#12)
B.16. Since draft-ietf-quic-tls-00
o Changed bit used to signal key phase
o Updated key phase markings during the handshake
o Added TLS interface requirements section
o Moved to use of TLS exporters for key derivation
o Moved TLS error code definitions into this document
B.17. Since draft-thomson-quic-tls-01
o Adopted as base for draft-ietf-quic-tls
o Updated authors/editors list
o Added status note
Acknowledgments
This document has benefited from input from Dragana Damjanovic,
Christian Huitema, Jana Iyengar, Adam Langley, Roberto Peon, Eric
Rescorla, Ian Swett, and many others.
Contributors
Ryan Hamilton was originally an author of this specification.
Authors' Addresses
Martin Thomson (editor)
Mozilla
Email: mt@lowentropy.net
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Sean Turner (editor)
sn3rd
Email: sean@sn3rd.com
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