wdiff draft-ietf-quic-tls-12.txt draft-ietf-quic-tls-13.txt

QUIC M. Thomson, Ed.
Internet-Draft Mozilla
Intended status: Standards Track S. Turner, Ed.
Expires: November 23, December 30, 2018 sn3rd
May 22,
June 28, 2018

Using Transport Layer Security (TLS) to Secure QUIC
draft-ietf-quic-tls-12
draft-ietf-quic-tls-13

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
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This Internet-Draft will expire on November 23, December 30, 2018.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4
3. Protocol 3
2.1. TLS Overview . . . . . . . . . . . . . . . . . . . . . . 4
3.1. TLS
3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.2. TLS Handshake . . . . . . . . . . . . . . . . . . . . . . 6
4. Carrying TLS Usage . . . . . . Messages . . . . . . . . . . . . . . . . . . . . 7
4.1. Handshake and Setup Sequence . . . . . . . . . . . . . . 8
4.2. Interface to TLS . . . . . . . . . . . . . . . . . . . . 9
4.2.1. 8
4.1.1. Sending and Receiving Handshake Interface . . . . . . . . . . . . . . . . . 10
4.2.2. Source Address Validation . . . . . . . . . . . . . . 11
4.2.3. Key Ready Events . . . . . . . . . . . . . . . . . . 12
4.2.4. Secret Export Messages . . . . . . 9
4.1.2. Encryption Level Changes . . . . . . . . . . . . . . 12
4.2.5. 10
4.1.3. TLS Interface Summary . . . . . . . . . . . . . . . . 12
4.3. 11
4.2. TLS Version . . . . . . . . . . . . . . . . . . . . . . . 13
4.4. 12
4.3. ClientHello Size . . . . . . . . . . . . . . . . . . . . 13
4.5. 12
4.4. Peer Authentication . . . . . . . . . . . . . . . . . . . 14
4.6. Rejecting 12
4.5. Enabling 0-RTT . . . . . . . . . . . . . . . . . . . . . 14
4.7. TLS Errors . . . . . . . . . . . . . . . . . . . . . . . 15
5. QUIC Packet Protection . . . . . . . . . . . . . . . . . . . 15
5.1. Installing New Keys . . . . . . . . . . . . . . . . . . . 15
5.2. Enabling 13
4.6. Rejecting 0-RTT . . . . . . . . . . . . . . . . . . . . . 15
5.3. QUIC Key Expansion . . . . . . . . . . . . . . . . . . . 16
5.3.1. QHKDF-Expand . 13
4.7. HelloRetryRequest . . . . . . . . . . . . . . . . . . . 16
5.3.2. Handshake Secrets . 13
4.8. TLS Errors . . . . . . . . . . . . . . . . . 17
5.3.3. 0-RTT Secret . . . . . . 14
5. QUIC Packet Protection . . . . . . . . . . . . . . 17
5.3.4. 1-RTT Secrets . . . . . 14
5.1. QUIC Packet Encryption Keys . . . . . . . . . . . . . . . 18
5.3.5. Updating 1-RTT 14
5.1.1. Initial Secrets . . . . . . . . . . . . . . . 18
5.3.6. Packet Protection Keys . . . . . . . . . . . . . . . 18
5.4. 14
5.2. QUIC AEAD Usage . . . . . . . . . . . . . . . . . . . . . 19
5.5. Packet Numbers . . . . . . . . . . . . . . . . . . . . . 20
5.6. 15
5.3. Packet Number Protection . . . . . . . . . . . . . . . . 21
5.6.1. 16
5.3.1. AES-Based Packet Number Protection . . . . . . . . . 22
5.6.2. 17
5.3.2. ChaCha20-Based Packet Number Protection . . . . . . . 22
5.7. 18
5.4. Receiving Protected Packets . . . . . . . . . . . . . . . 22
6. Key Phases . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.1. Packet Protection for the TLS Handshake . . . . . . . . . 23
6.1.1. Initial Key Transitions . . . . . . . . . . . . . . . 24
6.1.2. Retransmission and Acknowledgment 18
5.5. Use of Unprotected
Packets . . . . . . . . . . . . . . . . . . . . . . . 24
6.2. Key Update . . . . . . . . . . . . . . . . . . . . . . . 25
7. Client Address Validation . . . . . . . . . . . . . . . . . . 27
7.1. HelloRetryRequest Address Validation . . . . . . . . . . 27
7.1.1. Stateless Address Validation . . . . . . . . . . . . 28
7.1.2. Sending HelloRetryRequest . . . . . . . . . . . . . . 28
7.2. NewSessionTicket Address Validation . . . . . . . . . . . 29
7.3. Address Validation Token Integrity . . . . . . . . . . . 29
8. Pre-handshake QUIC Messages . . . . . . . . . . . . . . . . . 29
8.1. Unprotected Packets Prior to Handshake Completion . . . . 30
8.1.1. STREAM Frames 0-RTT Keys . . . . . . . . . . . . . . . . . . . . 31
8.1.2. ACK 18
5.6. Receiving Out-of-Order Protected Frames . . . . . . . . . 19
6. Key Update . . . . . . . . . . . . 31
8.1.3. Updates to Data and Stream Limits . . . . . . . . . . 31
8.1.4. Handshake Failures . . . . . . . . . . . . . . . . . 32
8.1.5. Address Verification . . . . . . . . . . . . . . . . 32
8.1.6. Denial of Service with Unprotected Packets . . . . . 32
8.2. Use 19
7. Security of 0-RTT Keys . . . . . . . . . . . . . Initial Messages . . . . . . . 33
8.3. Receiving Out-of-Order Protected Frames . . . . . . . . . 33
9. 21
8. QUIC-Specific Additions to the TLS Handshake . . . . . . . . 34
9.1. 21
8.1. Protocol and Version Negotiation . . . . . . . . . . . . 34
9.2. 22
8.2. QUIC Transport Parameters Extension . . . . . . . . . . . 34
10. 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 35
10.1. 23
9.1. Packet Reflection Attack Mitigation . . . . . . . . . . 35
10.2. . 23
9.2. Peer Denial of Service . . . . . . . . . . . . . . . . . 35
10.3. 23
9.3. Packet Number Protection Analysis . . . . . . . . . . . 36
11. Error Codes . 24
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
11. References . . . 37
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
13. . 25
11.1. Normative References . . . . . . . . . . . . . . . . . . 25
11.2. Informative References . . . . . . . 38
13.1. Normative References . . . . . . . . . . 26
11.3. URIs . . . . . . . . 38
13.2. Informative References . . . . . . . . . . . . . . . . . 39
13.3. URIs . 26
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 27
A.1. Since draft-ietf-quic-tls-12 . . . . . 40
Appendix A. Contributors . . . . . . . . . 27
A.2. Since draft-ietf-quic-tls-11 . . . . . . . . . . . 40
Appendix B. Acknowledgments . . . 27
A.3. Since draft-ietf-quic-tls-10 . . . . . . . . . . . . . . 27
A.4. Since draft-ietf-quic-tls-09 . . . . . . . 40
Appendix C. Change Log . . . . . . . 27
A.5. Since draft-ietf-quic-tls-08 . . . . . . . . . . . . . . 40
C.1. 27
A.6. Since draft-ietf-quic-tls-10 draft-ietf-quic-tls-07 . . . . . . . . . . . . . . 41
C.2. 28
A.7. Since draft-ietf-quic-tls-09 draft-ietf-quic-tls-05 . . . . . . . . . . . . . . 41
C.3. 28
A.8. Since draft-ietf-quic-tls-08 draft-ietf-quic-tls-04 . . . . . . . . . . . . . . 41
C.4. 28
A.9. Since draft-ietf-quic-tls-07 draft-ietf-quic-tls-03 . . . . . . . . . . . . . . 41
C.5. 28
A.10. Since draft-ietf-quic-tls-05 draft-ietf-quic-tls-02 . . . . . . . . . . . . . . 41
C.6. 28
A.11. Since draft-ietf-quic-tls-04 draft-ietf-quic-tls-01 . . . . . . . . . . . . . . 41
C.7. 28
A.12. Since draft-ietf-quic-tls-03 draft-ietf-quic-tls-00 . . . . . . . . . . . . . . 41
C.8. 29
A.13. Since draft-ietf-quic-tls-02 draft-thomson-quic-tls-01 . . . . . . . . . . . . . 29
Acknowledgments . 41
C.9. Since draft-ietf-quic-tls-01 . . . . . . . . . . . . . . 41
C.10. Since draft-ietf-quic-tls-00 . . . . . . . . . . 29
Contributors . . . . . . . . . . . 42
C.11. Since draft-thomson-quic-tls-01 . . . . . . . . . . . . . 42 . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42 29

1. Introduction

This document describes how QUIC [QUIC-TRANSPORT] is secured using
Transport Layer Security (TLS) version 1.3 [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.

This document describes how the standardized TLS 1.3 acts as a
security component of QUIC. The same design could work for TLS 1.2, though
few of the benefits QUIC provides would be realized due to the
handshake latency in versions of TLS prior to 1.3.

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.

TLS terminology is used when referring to parts of TLS. Though TLS
assumes a continuous stream of octets, it divides that stream into
_records_. Most relevant to QUIC are the records that contain TLS
_handshake messages_, which are discrete messages that are used for
key agreement, authentication and parameter negotiation. Ordinarily,
TLS records can also contain _application data_, though in the QUIC
usage there is no use of TLS application data.

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 1.3 connection [TLS13]; QUIC also relies on TLS 1.3 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 and ordered
delivery provided by QUIC streams.

This document defines how QUIC interacts with TLS. This includes a
description of how TLS is used, how keying material is derived from
TLS, and the application of that keying material to protect QUIC
packets. Figure 1 shows the basic interactions between TLS and QUIC,
with the QUIC packet protection being called out specially.

+------------+ +------------+
| |------ Handshake ------>| |
| |<-- Validate Address ---| |
| |-- OK/Error/Validate -->| |
| |<----- Handshake -------| |
| QUIC |------ Validate ------->| TLS |
| | | |
| |<------ 0-RTT OK -------| |
| |<------ 1-RTT OK -------| |
| |<--- Handshake Done ----| |
+------------+ +------------+
| ^ ^ |
| Protect | Protected | |
v | Packet | |
+------------+ / /
| QUIC | / /
| Packet |-------- Get Secret -------' /
| Protection |<-------- Secret -----------'
+------------+

Figure 1: QUIC and TLS Interactions

The initial state of a QUIC connection has packets exchanged without
any form of protection. In this state, QUIC is limited to using
stream 0 and associated packets. Stream 0 is reserved for a TLS
connection. This is a complete TLS connection as it would appear
when layered over TCP; the only difference is that QUIC provides the
reliability and ordering that would otherwise be provided by TCP.

At certain points during the TLS handshake, keying material is
exported from the TLS connection for use by QUIC. This keying
material is used to derive packet protection keys. Details on how
and when keys are derived and used are included in Section 5.

3.1.

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 features can be separated into two basic functions: an
authenticated key exchange and record protection. QUIC primarily
uses is a layered protocol, with the authenticated key exchange provided by structure shown
below:

Each upper layer (handshake, alerts, and application data) is carried
as a series of typed TLS but records. Records are individually
cryptographically protected and then transmitted over a reliable
transport (typically TCP) which provides its
own packet protection. sequencing and guaranteed
delivery.

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
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 resistent to tampering by attackers and it
produces shared secrets that cannot be controlled by either
participating peer.

3.2. TLS Handshake

TLS 1.3 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 1.3 handshake with 0-RTT application data is shown
in Figure 2, 1, see [TLS13] for more options and details.

Client Server

ClientHello
(0-RTT Application Data) -------->
ServerHello
{EncryptedExtensions}
{Finished}
<-------- [Application Data]
(EndOfEarlyData)
{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 2: 1: TLS Handshake with 0-RTT

This

Data is protected using a number of encryption levels:

o Plaintext

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.

Two additional variations on this basic handshake exchange are
relevant to this document:

o The server can respond to a ClientHello with a HelloRetryRequest,
which adds an additional round trip prior to the basic exchange.
This is needed if the server wishes to request a different key
exchange key from the client. HelloRetryRequest is also used to
verify that the client is correctly able to receive packets on the
address it claims to have (see [QUIC-TRANSPORT]).

o A pre-shared key mode can be used for subsequent handshakes to
reduce the number of public key operations. This is the basis

3. Protocol Overview

QUIC [QUIC-TRANSPORT] assumes responsibility for
0-RTT data, even if the remainder confidentiality
and integrity protection of the connection is protected
by packets. For this it uses keys derived
from a new Diffie-Hellman exchange.

4. TLS Usage

QUIC reserves stream 0 for a 1.3 handshake [TLS13], but instead of carrying TLS connection. Stream 0 contains a
complete records
over QUIC (as with TCP), TLS connection, which includes Handshake and Alert messages are carried
directly over the TLS record layer. Other
than QUIC transport, which takes over the definition
responsibilities of a QUIC-specific extension (see Section 9.2),
TLS is unmodified for this use. This means that TLS will apply
confidentiality and integrity protection to its records. In
particular, the TLS record protection is what provides confidentiality
protection for the layer, as shown below.

QUIC also relies on streams starting from the
first packet. The initial packet from a client contains a stream
frame TLS 1.3 for stream 0 authentication and negotiation of
parameters that contains are critical to security and performance.

Rather than a strict layering, these two protocols are co-dependent:
QUIC uses the first TLS handshake messages
from the client. This allows the handshake; TLS handshake to start with uses the
first packet that a client sends. reliability and ordered
delivery provided by QUIC packets are protected using streams.

At a scheme that is specific to QUIC,
see Section 5. Keys high level, there are exported from two main interactions between the TLS connection when they
become available using a TLS exporter (see Section 7.5 of [TLS13] and
Section 5.3). After keys are exported from TLS,
QUIC manages its own
key schedule.

4.1. Handshake and Setup Sequence components:

o The integration of TLS component sends and receives messages via the QUIC
component, with a TLS handshake is shown in more detail
in Figure 3. QUIC "STREAM" frames on providing a reliable stream 0 carry the abstraction to
TLS.

o The TLS
handshake. component provides a series of updates to the QUIC performs loss recovery [QUIC-RECOVERY] for this
stream and ensures that TLS
component, including (a) new packet protection keys to install (b)
state changes such as handshake messages are delivered completion, the server
certificate, etc.

Figure 2 shows these interactions in more detail, with the
correct order.

Client Server

@H QUIC STREAM Frame(s) <0>:
ClientHello
+ QUIC Extension
-------->
packet protection being called out specially.

@0 Keys -------| |
| |<--- Handshake Keys-----| |
| QUIC STREAM Frame(s) <any stream>:
Replayable |<---- 1-RTT Keys -------| TLS |
| |<--- Handshake Done ----| |
+------------+ +------------+
| ^
| Protect | Protected
v | Packet
+------------+
| QUIC Frames
--------> |
| Packet |
| Protection |
+------------+

Figure 2: QUIC STREAM Frame <0>: @H
ServerHello
{TLS Handshake Messages}
<--------
1-RTT Key => @1 and TLS Interactions

Unlike TLS over TCP, QUIC Frames <any> @1
<--------
@H applications which want to send data do not
send it through TLS "application_data" records. Rather, they send it
as QUIC STREAM Frame(s) <0>:
(EndOfEarlyData)
{Finished}
-------->

@1 QUIC Frames <any> <-------> frames which are then carried in QUIC Frames <any> @1

Figure 3: packets.

4. Carrying TLS Messages

QUIC over carries TLS Handshake

In Figure 3, symbols mean:

o "<" handshake data in CRYPTO frames, each of which
consists of a contiguous block of handshake data identified by an
offset and ">" enclose stream numbers.

o "@" indicates the keys that length. Those frames are used for protecting the packaged into QUIC
packet (H = handshake, using keys from the well-known cleartext
packet secret; 0 = 0-RTT keys; 1 = 1-RTT keys).

o "(" packets and ")" enclose messages that are protected
encrypted under the current TLS encryption level. As with TLS 0-RTT over
TCP, once TLS handshake or application keys.

o "{" and "}" enclose messages data has been delivered to QUIC, it is QUIC's
responsibility to deliver it reliably. Each chunk of data that are protected is
produced by the TLS
Handshake keys.

If 0-RTT is not attempted, then the client does not send packets
protected by associated with the 0-RTT key (@0). In set of keys that case, the only key
transition on the client TLS is from handshake packets (@H)
currently using. If QUIC needs to 1-RTT
protection (@1), which happens after retransmit that data, it sends its final set of TLS
handshake messages.

Note: two different types of packet are used during MUST use
the handshake by
both client and server. The Initial packet carries a same keys even if TLS ClientHello
message; the remainder of the has already updated to newer keys.

One important difference between TLS handshake 1.3 records (used with TCP) and
QUIC CRYPTO frames is carried that in Handshake
packets. The Retry QUIC multiple frames may appear in the
same QUIC packet carries as long as they are associated with the same
encryption level. For instance, an implementation might bundle a TLS HelloRetryRequest, if it is
needed,
Handshake message and an ACK for some Handshake packets carry data into the remainder same
packet.

Each encryption level has a specific list of the server
handshake.

The server sends TLS handshake messages without protection (@H). frames which may appear
in it. The
server transitions from no protection (@H) to full 1-RTT protection
(@1) after it sends the last rules here generalize those of its handshake messages.

Some TLS handshake messages are protected by the TLS handshake record
protection. These keys are not exported from TLS, in that frames
associated with establishing the TLS connection for
use can usually appear at any
encryption level, whereas those associated with transferring data can
only appear in QUIC. QUIC packets from the server are sent 0-RTT and 1-RTT encryption levels

o CRYPTO frames MAY appear in packets of any encryption level.

o CONNECTION_CLOSE MAY appear in packets of any encryption level
other than 0-RTT.

o PADDING and PING frames MAY appear in packets of any encryption
level.

o ACK frames MAY appear in packets of any encryption level other
than 0-RTT, but can only acknowledge packets which appeared in
that encryption level.

o STREAM frames MUST ONLY appear in the clear
until the final transition to 1-RTT keys.

The client transitions from handshake (@H) to 0-RTT keys (@0) when
sending 0-RTT data, and subsequently to to 1-RTT keys (@1) after its
second flight of TLS handshake messages. This creates levels.

o All other frame types MUST only appear at the potential
for unprotected 1-RTT levels.

Because packets to could be received by reordered on the wire, QUIC uses the packet
type to indicate which level a server given packet was encrypted under, as
shown in close proximity Table 1. When multiple packets of different encryption
levels need to be sent, endpoints SHOULD use coalesced packets that are protected with 1-RTT keys.

More information on key transitions is included to
send them in the same UDP datagram.

+-----------------+------------------+-----------+
| 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 6.1.

4.2. 6.3 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 1, 2, the interface from QUIC to TLS consists of four
three primary functions: Handshake, Source Address Validation, Key Ready
Events,

o Sending and receiving handshake messages

o Rekeying (both transmit and Secret Export. receive)
o Handshake state updates

Additional functions might be needed to configure TLS.

4.2.1.

4.1.1. Sending and Receiving Handshake Interface Messages

In order to drive the handshake, TLS depends on being able to send
and receive handshake messages on stream 0. 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 9.2) 8.2) that it wishes to carry.

A QUIC client starts TLS by requesting TLS handshake octets from TLS.
The client acquires handshake octets before sending its first packet.
A QUIC server starts the process by providing TLS with stream 0 the client's
handshake octets.

At any given time, the TLS stack at an endpoint will have a current
sending encryption level and receiving encryption level. Each time
encryption level is associated with a different flow of bytes, which
is reliably transmitted to the peer in CRYPTO frames. When TLS
provides handshake octets 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.

When an endpoint receives data on stream 0, a QUIC packet containing a CRYPTO frame
from the network, it delivers proceeds as follows:

o If the
octets 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 if 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 able. 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 octets
are requested from TLS. TLS might not provide any octets if the
handshake messages it has received are incomplete or it has no data
to send.

At the server, when TLS provides handshake octets, it also needs to
indicate whether the octets contain a HelloRetryRequest. A
HelloRetryRequest MUST always be sent in a Retry packet, so the QUIC
server needs to know whether the octets are a HelloRetryRequest.

Once the TLS handshake is complete, this is indicated to QUIC along
with any final handshake octets 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
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 on stream 0. 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 STREAM frame that carries the
Finished message in multiple packets. This enables immediate
server processing for those packets.

4.2.2. Source Address Validation

During the processing of the TLS ClientHello, TLS requests that the
transport make a decision about whether to request source address
validation from the client.

An initial TLS ClientHello that resumes a session includes an address
validation token in the session ticket; this includes all attempts at
0-RTT. If the client does not attempt session resumption, no token
will be present. While processing the initial ClientHello, TLS
provides QUIC with any token that is present. In response, QUIC
provides one

4.1.2. Encryption Level Changes

At each change of three responses:

o proceed with the connection,

o ask for client address validation, or

o abort the connection.

If QUIC requests source address validation, it also provides a new
address validation token. TLS includes that along with any
information it requires encryption level in the cookie extension of a TLS
HelloRetryRequest message. In the other cases, the connection either
proceeds or terminates with a handshake error.

The client echoes the cookie extension in a second ClientHello. A
ClientHello that contains a valid cookie extension will always be in
response to a HelloRetryRequest. If address validation was requested
by QUIC, then this will include an address validation token. direction, TLS
makes a second address validation request of signals
QUIC, including the
value extracted from the cookie extension. In response to this
request, QUIC cannot ask for client address validation, it can only
abort or permit the connection attempt to proceed.

QUIC can provide a new address validation token for use in session
resumption at any time after providing the handshake is complete. Each time a new token is provided TLS generates a NewSessionTicket message, with
the token included in the ticket.

See Section 7 for more details on client address validation.

4.2.3. Key Ready Events

TLS provides QUIC with signals when 0-RTT level and 1-RTT keys are ready
for use. the encryption keys. These events
are not asynchronous, they always occur immediately after TLS is
provided with new handshake octets, or after TLS produces handshake
octets.

When TLS completed its handshake, 1-RTT keys can be provided to QUIC.
On both client and server, this occurs after sending the TLS Finished
message.

This ordering means that there could be frames that carry TLS
handshake messages ready to send at the same time that application
data is available. An implementation MUST ensure that TLS handshake
messages are always sent in packets protected with handshake keys
(see Section 5.3.2). Separate packets are required for data that
needs protection from 1-RTT keys.

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 octets, the TLS
stack might signal that the change to 0-RTT keys are ready. keys. On the server, after
receiving handshake octets that contain a ClientHello message, a TLS
server might signal that 0-RTT keys are available.

1-RTT keys are used for packets in both directions. 0-RTT keys are

Note that although TLS only used 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 in Handshake encryption) may
send STREAM data (in 1-RTT encryption). However, if the Finished is
lost, the client would have to protect packets sent by retransmit the client.

4.2.4. Secret Export

Details how secrets are exported from TLS are included Finished, in
Section 5.3.

4.2.5. which case
it would use Handshake encryption.

4.1.3. TLS Interface Summary

Figure 4 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.

Client Server

Get Handshake
Initial ------------>
Rekey tx to 0-RTT Key Ready
--- send/receive ---> Keys
0-RTT -------------->
Handshake Received
Get Handshake
<------------ Initial
Rekey rx to 0-RTT Key Ready keys
Handshake Received
Rekey rx to Handshake keys
Get Handshake
<----------- Handshake
Rekey tx to 1-RTT Keys Ready
<--- send/receive --- keys
Handshake Received
Rekey rx to Handshake keys
Handshake Received
Get Handshake
Handshake Complete
Rekey tx to 1-RTT Keys Ready
--- send/receive ---> keys
Handshake ---------->
Handshake Received
Rekey rx to 1-RTT keys
Get Handshake
Handshake Complete
<--- send/receive ---
<--------------- 1-RTT
Handshake Received
Get Handshake

Figure 4: 3: Interaction Summary between QUIC and TLS

4.3.

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.

4.4.

4.3. ClientHello Size

QUIC requires that the initial handshake packet from a client fit
within the payload of a single packet. The size limits on QUIC
packets mean that a record containing a ClientHello needs to fit
within 1129 octets, though endpoints can reduce the size of their
connection ID to increase by up to 22 octets.

A TLS ClientHello can fit within this limit with ample space
remaining. However, there are several variables that could cause
this limit to be exceeded. Implementations are reminded that large
session tickets or HelloRetryRequest cookies, 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, the size of the session tickets and HelloRetryRequest
cookie extension can have an effect on a client's ability to connect.
Choosing a small value increases the probability that these values
can be successfully used by a client.

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.

4.5.

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
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 "max_early_data" extension with the value
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 a "max_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
results in early exporter keys being unavailable, thereby preventing
the use of
also prevents QUIC from sending 0-RTT for QUIC. data. A client that attempts
0-RTT MUST also consider 0-RTT to be rejected if it receives a Retry or
Version Negotiation packet.

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.

4.7. HelloRetryRequest

In TLS Errors

Errors in the TLS connection SHOULD be signaled using TLS alerts on
stream 0. A failure in over TCP, the handshake MUST HelloRetryRequest feature (see Section 4.1.4 of
[TLS13]) can be treated used to correct a client's incorrect KeyShare
extension as well as for a QUIC
connection error stateless round-trip check. From the
perspective of type TLS_HANDSHAKE_FAILED. Once QUIC, this just looks like additional messages carried
in the handshake Initial encryption level. Although it is
complete, an error in principle
possible to use this feature for address verification in QUIC, QUIC
implementations SHOULD instead use the Retry feature (see
Section 4.4.2 of [QUIC-TRANSPORT]). HelloRetryRequest is still used
to request key shares.

4.8. TLS connection that causes a Errors

If TLS experiences an error, it generates an appropriate alert to
be sent or received MUST be treated as
defined in Section 6 of [TLS13].

A TLS alert is turned into a QUIC connection error of
type TLS_FATAL_ALERT_GENERATED or TLS_FATAL_ALERT_RECEIVED
respectively.

5. by converting the
one-octet alert description into a QUIC Packet Protection error code. The alert
description is added to 0x100 to produce a QUIC packet protection provides authenticated encryption of packets.
This provides confidentiality and integrity protection for the
content of packets (see Section 5.4). Packet protection uses keys
that are exported error code from the TLS connection (see Section 5.3).

Different keys are used
range reserved for CRYPTO_ERROR. The resulting value is sent in a
QUIC packet protection and TLS record
protection. CONNECTION_CLOSE frame.

The alert level of all TLS handshake messages are protected solely with alerts is "fatal"; a TLS
record protection, but post-handshake messages are redundantly
protected with both stack MUST NOT
generate alerts at the "warning" level.

5. QUIC packet protection and the TLS record
protection. These messages are limited in number, and so the
additional overhead is small.

5.1. Installing New Keys Packet Protection

As with TLS reports the availability of keying material, the packet
protection over TCP, QUIC encrypts packets with keys and initialization vectors (IVs) are updated (see
Section 5.3). The selection of AEAD function is also updated to
match derived from
the TLS handshake, using the AEAD algorithm negotiated by TLS.

For packets other than any handshake packets (see Section 6.1), once
a change of keys has been made, packets with higher

5.1. QUIC Packet Encryption Keys

QUIC derives packet numbers
MUST be sent with the new keying material. The KEY_PHASE bit on
these packets is inverted each time new keys are installed to signal
the use of the new encryption keys to the recipient (see Section 6 for details).

An endpoint retransmits stream data in a new packet. New packets
have new packet numbers and use the latest packet protection keys.
This simplifies key management when there are key updates (see
Section 6.2).

5.2. Enabling 0-RTT

In order to be usable for 0-RTT, same way as TLS MUST provide 1.3: Each
encryption level/direction pair has a NewSessionTicket
message that contains the "max_early_data" extension with the value
0xffffffff; the amount of data secret value, which the client can send in 0-RTT is
controlled by the "initial_max_data" transport parameter supplied by then
used to derive the server. A client MUST treat receipt of a NewSessionTicket that
contains a "max_early_data" extension with any other value traffic keys using as a
connection error described in Section 7.3 of type PROTOCOL_VIOLATION.

Early data within the TLS connection MUST NOT be used. As it is
[TLS13]

The keys for
other TLS application data, a server MUST treat receiving early data
on the TLS connection as a connection error of type
PROTOCOL_VIOLATION.

5.3. QUIC Key Expansion

QUIC uses a system of packet protection secrets, keys and IVs that Initial encryption level are modelled computed based on the system used in TLS [TLS13]. The secrets that
QUIC uses
client's initial Destination Connection ID, as the basis of its key schedule are obtained using TLS
exporters (see described in
Section 7.5 of [TLS13]).

5.3.1. QHKDF-Expand

QUIC uses the Hash-based Key Derivation Function (HKDF) [HKDF] with
the same hash function negotiated by TLS 5.1.1.

The keys for key derivation. For
example, if TLS is using the TLS_AES_128_GCM_SHA256, the SHA-256 hash
function is used.

Most key derivations remaining encryption level are computed in this document use the QHKDF-Expand function,
which uses the HKDF expand function and is modelled on same
fashion as the HKDF-
Expand-Label function from corresponding TLS 1.3 keys (see Section 7.1 7 of [TLS13]).
QHKDF-Expand differs from HKDF-Expand-Label in [TLS13]),
except that it uses a
different base label and omits the Context argument.

QHKDF-Expand(Secret, Label, Length) =
HKDF-Expand(Secret, QhkdfExpandInfo, Length)

The HKDF-Expand function used by QHKDF-Expand uses the PRF hash
function negotiated by TLS, except label for handshake secrets and keys
derived from them (see Section 5.3.2).

Where HKDF-Expand-Label uses the "info" parameter of HKDF-Expand is an encoded
"QhkdfExpandInfo" structure:

struct {
uint16 length = Length;
opaque label<6..255> = "QUIC prefix "quic " + Label;
} QhkdfExpandInfo;

For example, assuming a hash function with a 32 octet output,
derivation for a client packet protection
rather than "tls13 ". A different label provides key would use HKDF-Expand
with an "info" parameter of 0x00200851554943206b6579.

5.3.2. Handshake Secrets

Packets that carry the separation
between TLS handshake (Initial, Retry, and Handshake) QUIC.

5.1.1. Initial Secrets

Initial packets are protected with a secret derived from the
Destination Connection ID field from the client's first Initial packet.
packet of the connection. Specifically:

handshake_salt

initial_salt = 0x9c108f98520a5c5c32968e950e8a2c5fe06d6c38
handshake_secret
initial_secret =
HKDF-Extract(handshake_salt,
HKDF-Extract(initial_salt, client_dst_connection_id)

client_handshake_secret

client_initial_secret =
QHKDF-Expand(handshake_secret,
HKDF-Expand-Label(initial_secret, "client hs", in", Hash.length)
server_handshake_secret
server_initial_secret =
QHKDF-Expand(handshake_secret,
HKDF-Expand-Label(initial_secret, "server hs", in", Hash.length)

Note that if the server sends a Retry, the client's Initial will
correspond to a new connection and thus use the server provided
Destination Connection ID.

The hash function for HKDF when deriving handshake secrets and keys
is SHA-256 [SHA]. The connection ID used with QHKDF-Expand HKDF-Expand-Label is
the
connection ID chosen by the client. initial Destination Connection ID.

The handshake salt value of initial_salt is a 20 octet 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 handshake
packets from future versions.

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
handshake 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.

5.3.3. 0-RTT Secret

0-RTT keys are those keys that are

5.2. QUIC AEAD Usage

The Authentication Encryption with Associated Data (AEAD) [AEAD]
function used in resumed connections prior
to for QUIC packet protection is the completion of AEAD that is
negotiated for use with the TLS handshake. Data sent using 0-RTT keys
might be replayed and so has some restrictions on its use, see
Section 8.2. 0-RTT keys are used after sending or receiving a
ClientHello.

The secret is exported from connection. For example, if TLS is
using the exporter label "EXPORTER- TLS_AES_128_GCM_SHA256, the AEAD_AES_128_GCM function is
used.

QUIC 0rtt" and an empty context. packets are protected prior to applying packet number encryption
(Section 5.3). The size unprotected packet number is part of the secret MUST be the
size of the hash output for the PRF hash function negotiated by TLS.
This uses the TLS early_exporter_secret. The QUIC 0-RTT secret is
only used for protection of packets sent by the client.

client_0rtt_secret =
TLS-Early-Exporter("EXPORTER-QUIC 0rtt", "", Hash.length)

5.3.4. 1-RTT Secrets

1-RTT keys are used by both client and server after the TLS handshake
completes. There are two secrets used at any time: one is used to
derive packet protection keys for packets sent by the client, the
other for packet protection keys on packets sent by the server.

The initial client packet protection secret is exported from TLS
using the exporter label "EXPORTER-QUIC client 1rtt"; the initial
server packet protection secret uses the exporter label "EXPORTER-
QUIC server 1rtt". Both exporters use an empty context. The size of
the secret MUST be the size of the hash output for the PRF hash
function negotiated by TLS.

client_pp_secret<0> =
TLS-Exporter("EXPORTER-QUIC client 1rtt", "", Hash.length)
server_pp_secret<0> =
TLS-Exporter("EXPORTER-QUIC server 1rtt", "", Hash.length)

These secrets are used to derive the initial client and server packet
protection keys.

5.3.5. Updating 1-RTT Secrets

After a key update (see Section 6.2), the 1-RTT secrets are updated
using QHKDF-Expand. Updated secrets are derived from the existing
packet protection secret. A Label parameter of "client 1rtt" is used
for the client secret and "server 1rtt" for the server. The Length
is the same as the native output of the PRF hash function.

client_pp_secret<N+1> =
QHKDF-Expand(client_pp_secret<N>, "client 1rtt", Hash.length)
server_pp_secret<N+1> =
QHKDF-Expand(server_pp_secret<N>, "server 1rtt", Hash.length)

This allows for a succession of new secrets to be created as needed.

5.3.6. Packet Protection Keys

The complete key expansion uses a similar process for key expansion
to that defined in Section 7.3 of [TLS13], using QHKDF-Expand in
place of HKDF-Expand-Label. QUIC uses the AEAD function negotiated
by TLS.

The packet protection key and IV used to protect the 0-RTT packets
sent by a client are derived from the QUIC 0-RTT secret. The packet
protection keys and IVs for 1-RTT packets sent by the client and
server are derived from the current generation of client and server
1-RTT secrets (client_pp_secret and server_pp_secret)
respectively.

The length of the QHKDF-Expand output is determined by the
requirements of the AEAD function selected by TLS. The key length is
the AEAD key size. As defined in Section 5.3 of [TLS13], the IV
length is the larger of 8 or N_MIN (see Section 4 of [AEAD]; all
ciphersuites defined in [TLS13] have N_MIN set to 12).

The size of the packet protection key is determined by the packet
protection algorithm, see Section 5.6.

For any secret S, the AEAD key uses a label of "key", the IV uses a
label of "iv", packet number encryption uses a label of "pn":

key = QHKDF-Expand(S, "key", key_length)
iv = QHKDF-Expand(S, "iv", iv_length)
pn_key = QHKDF-Expand(S, "pn", pn_key_length)

Separate keys are derived for packet protection by clients and
servers. Each endpoint uses the packet protection key of its peer to
remove packet protection. For example, client packet protection keys
and IVs - which are also used by the server to remove the protection
added by a client - for AEAD_AES_128_GCM are derived from 1-RTT
secrets as follows:

client_pp_key = QHKDF-Expand(client_pp_secret, "key", 16)
client_pp_iv = QHKDF-Expand(client_pp_secret, "iv", 12)
client_pp_pn = QHKDF-Expand(client_pp_secret, "pn", 12)

The QUIC packet protection initially starts with keying material
derived from handshake keys. For a client, when the TLS state
machine reports that the ClientHello has been sent, 0-RTT keys can be
generated and installed for writing, if 0-RTT is available. Finally,
the TLS state machine reports completion of the handshake and 1-RTT
keys can be generated and installed for writing.

5.4. QUIC AEAD Usage

The Authentication Encryption with Associated Data (AEAD) [AEAD]
function used for QUIC packet protection is 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.

QUIC packets are protected prior to applying packet number encryption
(Section 5.6). The unprotected packet number is part of the
associated data (A). When removing packet protection, an endpoint
first removes
associated data (A). When removing packet protection, an endpoint
first removes the protection from the packet number.

All QUIC packets other than Version Negotiation and Stateless Reset 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 client's destination connection ID in the client's first
Initial packet (see Section 5.3.2). 5.1.1). This provides protection against
off-path attackers and robustness against QUIC version unaware
middleboxes, but not against on-path attackers.

All ciphersuites currently defined for TLS 1.3 - and therefore QUIC -
have a 16-byte authentication tag and produce an output 16 bytes
larger than their input.

Once TLS has provided a key, the contents of regular QUIC packets
immediately after any TLS messages have been sent are protected by
the AEAD selected by TLS.

The key, K, is either the client packet protection key
(client_pp_key) or and IV for the server packet protection key
(server_pp_key), derived are computed as defined described in
Section 5.3. 5.1. The nonce, N, is formed by combining the packet
protection IV (either
client_pp_iv or server_pp_iv) with the packet number. The 64 bits of the
reconstructed QUIC packet number in network byte order is
left-padded 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 octet in either the short or long
header.

The input plaintext, P, for the AEAD is the content of the QUIC frame
following the header, as described in [QUIC-TRANSPORT].

The output ciphertext, C, of the AEAD is transmitted in place of P.

5.5. Packet Numbers

QUIC has a single, contiguous packet number space. In comparison,
TLS restarts its sequence number each time that record protection
keys are changed. The sequence number restart in TLS ensures that a
compromise of the current traffic keys does not allow an attacker to
truncate the data that is sent after a key update by sending
additional packets under the old key (causing new packets to be
discarded).

QUIC does not assume a reliable transport and is required to handle
attacks where packets are dropped in other ways. QUIC is therefore
not affected by this form of truncation.

The QUIC packet number is not reset and it is not permitted to go
higher than its maximum value of 2^62-1. This establishes a hard
limit on the number of packets that can be sent.

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 6.2) 6) prior to exceeding any limit set for the AEAD
that is in use.

TLS maintains a separate sequence number that is used for record
protection on the connection that is hosted on stream 0. This
sequence number is not visible to QUIC.

5.6.

5.3. Packet Number Protection

QUIC packets packet numbers are protected using a key that is derived from
the current set of secrets. The key derived using the "pn" label is
used to protect the packet number from casual observation. The
packet number protection algorithm depends on the negotiated AEAD.

Packet number protection is applied after packet protection is
applied (see Section 5.4). 5.2). The ciphertext of the packet is sampled
and used as input to an encryption algorithm.

In sampling the packet ciphertext, the packet number length is
assumed to be the smaller of the 4 octets (its maximum possible encoded length), unless
there is insufficient space in the packet for sampling. The sampled
ciphertext starts after allowing for a 4 octet packet number
encoding (4 octets), or unless
this would cause the size sample to extend past the end of the protected packet minus packet. If
the
minimum expansion for sample would extend past the AEAD. end of the packet, the end of the
packet is sampled.

For example, the sampled ciphertext for a packet with a short header
can be determined by:

"sample_offset

sample_offset = min(1 1 + connection_id_length len(connection_id) + 4

if sample_offset + 4, sample_length > packet_length then
sample_offset = packet_length -
aead_expansion) sample_length
sample = packet[sample_offset..sample_offset+sample_length] "

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

To ensure that this process does not sample the packet number, packet
number protection algorithms MUST NOT sample more ciphertext than the
minimum expansion of the corresponding AEAD.

Packet number protection is applied to the packet number encoded as
described in Section 4.8 of [QUIC-TRANSPORT]. Since the length of
the packet number is stored in the first octet of the encoded packet
number, it may be necessary to progressively decrypt the packet
number.

Before a TLS ciphersuite can be used with QUIC, a packet protection
algorithm MUST be specifed 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 [RFC5116]), [AEAD]), and AEAD_CHACHA20_POLY1305 ([CHACHA]).

5.6.1.

5.3.1. AES-Based Packet Number 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 counter (CTR) mode. AEAD_AES_256_GCM, and
AEAD_AES_256_CCM use 256-bit AES in CTR mode.

This algorithm samples 16 octets from the packet ciphertext. This
value is used as the counter input to AES-CTR.

encrypted_pn = AES-CTR(pn_key, sample, packet_number)

5.6.2.

5.3.2. ChaCha20-Based Packet Number Protection

When AEAD_CHACHA20_POLY1305 is in use, packet number protection uses
the raw ChaCha20 function as defined in Section 2.4 of [CHACHA].
This uses a 256-bit key and 16 octets sampled from the packet
protection output.

The first 4 octets 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 octets are interpreted as three concatenated 32-bit
numbers in little-endian order and used as the nonce.

The encoded packet number is then encrypted with ChaCha20 directly.
In pseudocode:

counter = DecodeLE(sample[0..3])
nonce = DecodeLE(sample[4..7], sample[8..11], sample[12..15])
encrypted_pn = ChaCha20(pn_key, counter, nonce, packet_number)

5.7.

5.4. 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 6.2). 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.

6. Key Phases

As TLS reports the availability

5.5. Use of 0-RTT and 1-RTT keys, new keying
material can be exported from TLS and used for QUIC packet
protection. At each transition during the handshake a new secret is
exported from TLS and packet protection keys are derived from that
secret.

Every time that a new set of keys is used for protecting outbound
packets, the KEY_PHASE bit in the public flags is toggled. Keys

If 0-RTT
protected packets use the QUIC long header, they do not use the
KEY_PHASE bit to select the correct keys are available (see Section 6.1.1).

Once the connection is fully enabled, the KEY_PHASE bit allows a
recipient to detect a change in keying material without necessarily
needing to receive 4.5), the first packet lack of replay
protection means that triggered restrictions on their use are necessary to
avoid replay attacks on the change. An
endpoint that notices a changed KEY_PHASE bit can update protocol.

A client MUST only use 0-RTT keys and
decrypt the packet to protect data that contains the changed bit, see Section 6.2.

The KEY_PHASE bit is included as the 0x20 bit of the QUIC short
header.

Transitions between keys during the handshake are complicated by the
need idempotent.
A client MAY wish to apply additional restrictions on what data it
sends prior to ensure that TLS handshake messages are sent with the correct
packet protection.

6.1. Packet Protection for the TLS Handshake

The initial exchange completion of packets that carry the TLS handshake are
AEAD-protected using the handshake secrets generated handshake. A client
otherwise treats 0-RTT keys as described in
Section 5.3.2. All TLS handshake messages up equivalent to the TLS Finished
message sent by either endpoint use packets protected 1-RTT keys, except that
it MUST NOT send ACKs with handshake 0-RTT keys.

Any TLS handshake messages

A client that are sent after completing the TLS
handshake do not need special packet protection rules. Packets
containing these messages use the packet protection keys receives an indication that are
current at the time of sending (or retransmission).

Like the client, its 0-RTT data has been
accepted by a server MUST can send retransmissions 0-RTT data until it receives all of its
unprotected handshake messages or acknowledgments for unprotected
handshake messages sent by the client in packets protected with
handshake keys.

6.1.1. Initial Key Transitions

Once the TLS
server's handshake is complete, keying material is exported from
TLS and used to protect QUIC packets.

Packets protected with 1-RTT keys initially have a KEY_PHASE bit set
to 0. This bit inverts with each subsequent key update (see
Section 6.2).

If the messages. A client sends SHOULD stop sending 0-RTT data, data
if it uses the 0-RTT packet type. The
packet receives an indication that contains the TLS EndOfEarlyData and Finished messages are
sent in packets protected with handshake keys.

Using distinct packet types during the handshake for handshake
messages, 0-RTT data, and 1-RTT data ensures that the has been rejected.

A server is able MUST NOT use 0-RTT keys to distinguish between the different protect packets; it uses 1-RTT
keys used to remove packet
protection. All protect acknowledgements of these packets can arrive concurrently at a
server.

A server might choose 0-RTT packets. Clients MUST NOT
attempt to retain decrypt 0-RTT packets that arrive before a
TLS ClientHello. The server it receives and instead MUST discard
them.

Note: 0-RTT data can then use those packets once the
ClientHello arrives. However, be acknowledged by the potential for denial server as it receives
it, but any packets containing acknowledgments of service
from buffering 0-RTT packets data
cannot have packet protection removed by the client until the TLS
handshake is significant. These packets complete. The 1-RTT keys necessary to remove packet
protection cannot be
authenticated derived until the client receives all server
handshake messages.

5.6. Receiving Out-of-Order Protected Frames

Due to reordering and so loss, protected packets might be employed received by an attacker to exhaust
server resources. Limiting
endpoint before the number of packets that final TLS handshake messages are saved
might received. A
client will be necessary.

The server transitions unable to using decrypt 1-RTT keys after sending its first
flight of TLS handshake messages, ending in the Finished. From this
point, packets from the server,
whereas a server protects all packets with will be able to decrypt 1-RTT keys. Future packets are therefore protected with 1-RTT keys. Initially, these
are marked with from the
client.

However, a KEY_PHASE of 0.

6.1.2. Retransmission and Acknowledgment of Unprotected Packets

TLS handshake messages server MUST NOT process data from both incoming 1-RTT protected
packets before verifying either the client and Finished message or - in
the case that the server are critical has chosen to use a pre-shared key - the
pre-shared key exchange. The contents binder (see Section 4.2.11 of [TLS13]). Verifying
these messages determine values provides the keys
used to protect later messages. If these handshake messages are
included in packets server with an assurance that are the
ClientHello has not been modified. Packets protected with these keys, they will be
indecipherable to the recipient.

Even though newer 1-RTT keys could be available when retransmitting,
retransmissions of these handshake messages MUST
MAY be sent in packets
protected with handshake keys. An endpoint MUST generate ACK frames
for these messages stored and later decrypted and send them in packets protected with handshake
keys.

A HelloRetryRequest handshake message might be used to reject an
initial ClientHello. A HelloRetryRequest once the handshake message is sent
in a Retry packet; any second ClientHello that is sent in response
uses a Initial packet type. These
complete.

A server could receive packets are only protected with a
predictable key (see Section 5.3.2). This is natural, because no
shared secret will be available when these messages need to be sent.
Upon receipt of a HelloRetryRequest, a client SHOULD cease any
transmission of 0-RTT data; 0-RTT data will only be discarded by any
server that sends keys prior to
receiving a HelloRetryRequest. TLS ClientHello. The packet type ensures that protected packets are clearly
distinguished from unprotected packets. Loss or reordering might
cause unprotected server MAY retain these packets to arrive once 1-RTT keys are for
later decryption in use,
unprotected packets are easily distinguished from 1-RTT packets using
the packet type. anticipation of receiving a ClientHello.

6. Key Update

Once the 1-RTT keys are available to an endpoint, it no longer needs established and the
TLS handshake messages that are carried in unprotected packets.
However, a server might need to retransmit its TLS handshake messages short header is in response use,
it is possible to receiving an unprotected packet that contains ACK
frames. A server MUST process ACK frames in unprotected packets
until update the TLS handshake is reported as complete, or it receives an
ACK frame keys. The KEY_PHASE bit in a protected packet that acknowledges all of its
handshake messages.

To limit the number of short
header is used to indicate whether key phases that could be active, an endpoint
MUST NOT initiate a updates have occurred. The
KEY_PHASE bit is initially set to 0 and then inverted with each key
update while there are any unacknowledged
handshake messages, see Section 6.2.

6.2. Key Update

Once the TLS handshake is complete, the 6.

The KEY_PHASE bit allows for
refreshes of a recipient to detect a change in keying
material by either peer. Endpoints start using
updated keys immediately without additional signaling; necessarily needing to receive the change in first packet that
triggered the change. An endpoint that notices a changed KEY_PHASE
bit indicates can update keys and decrypt the packet that a new key is in use. contains the changed
bit, see Section 6.

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. Note that
when 0-RTT is attempted the value of the KEY_PHASE bit will be
different on packets sent by either peer.

A receiving endpoint detects an update when the KEY_PHASE bit doesn't
match what it is expecting. It creates a new secret (see Section 5.3) 7.2
of [TLS13]) and the corresponding read key and IV. If the packet can
be decrypted and authenticated using these values, then the keys it
uses for packet protection are also updated. The next packet sent by
the endpoint will then use the new keys.

An endpoint doesn't need to send packets immediately 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 short period to allow it to
decrypt packets with smaller packet numbers than the packet that
triggered the key update. This allows an endpoint to consume packets
that are reordered around the transition between keys. Packets with
higher packet numbers always use the updated keys and MUST NOT be
decrypted with old keys.

Keys and their corresponding secrets SHOULD be discarded when an
endpoint has received all packets with packet numbers lower than the
lowest packet number used for the new key. An endpoint might discard
keys if it determines that the length of the delay to affected
packets is excessive.

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.

Initiating Peer Responding Peer

@M QUIC Frames
New Keys -> @N
@N QUIC Frames
-------->
QUIC Frames @M
New Keys -> @N
QUIC Frames @N
<--------

Figure 5: 4: Key Update

As shown in Figure 3 and Figure 5, there is never a situation where
there are more than two different sets of keying material that might
be received by a peer. Once both sending and receiving keys have
been updated, the peers immediately begin to use them.

A server cannot initiate a key update until it has received the
client's Finished message. Otherwise, packets protected by the
updated keys could be confused for retransmissions of handshake
messages. A client cannot initiate a key update until all of its
handshake messages have been acknowledged by the server.

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.

7. Client Address Validation

Two tools are provided by TLS to enable validation of client source
addresses at a server: the cookie in the HelloRetryRequest message,
and the ticket in the NewSessionTicket message.

7.1. HelloRetryRequest Address Validation

The cookie extension in the TLS HelloRetryRequest message allows a
server to perform source address validation during the handshake.

When QUIC requests address validation during the processing of the
first ClientHello, the token it provides is included in the cookie
extension of a HelloRetryRequest. As long as the cookie cannot be
successfully guessed by a client, the server can be assured that the
client received the HelloRetryRequest if it includes the value in a
second ClientHello.

An initial ClientHello never includes a cookie extension. Thus, if a
server constructs a cookie that contains all the information
necessary to reconstruct state, it can discard local state after
sending a HelloRetryRequest. Presence of a valid cookie in a
ClientHello indicates that the ClientHello is a second attempt from
the client.

An address validation token can be extracted from a second
ClientHello and passed to the transport for further validation. If
that validation fails, the server MUST fail the TLS handshake and
send an illegal_parameter alert.

Combining address validation with the other uses of HelloRetryRequest
ensures that there are fewer ways in which an additional round-trip
can be added to the handshake. In particular, this makes it possible
to combine a request for address validation with a request for a
different client key share.

If TLS needs to send a HelloRetryRequest for other reasons, it needs
to ensure that it can correctly identify the reason that the
HelloRetryRequest was generated. During the processing of a second
ClientHello, TLS does not need to consult the transport protocol
regarding address validation if address validation was not requested
originally. In such cases, the cookie extension could either be
absent or it could indicate that an address validation token is not
present.

7.1.1. Stateless Address Validation

A server can use the cookie extension to store all state necessary to
continue the connection. This allows a server to avoid committing
state for clients that have unvalidated source addresses.

For instance, a server could use a statically-configured key to
encrypt the information that it requires and include that information
in the cookie. In addition to address validation information, a
server that uses encryption also needs to be able recover the hash of
the ClientHello and its length, plus any information it needs in
order to reconstruct the HelloRetryRequest.

7.1.2. Sending HelloRetryRequest

A server does not need to maintain state for the connection when
sending a HelloRetryRequest message. This might be necessary to
avoid creating a denial of service exposure for the server. However,
this means that information about the transport will be lost at the
server. This includes the stream offset Security of stream 0, the packet
number that the server selects, and any opportunity to measure round
trip time.

A server MUST send a TLS HelloRetryRequest in a Retry packet. Using
a Retry packet causes the client to reset stream offsets. It also
avoids the need for the server select an initial packet number, which
would need to be remembered so that subsequent packets could be
correctly numbered.

A HelloRetryRequest message MUST NOT be split between multiple Retry
packets. This means that HelloRetryRequest is subject to the same
size constraints as a ClientHello (see Section 4.4).

A client might send multiple Initial packets in response to loss. If
a server sends a Retry packet in response to an Messages

Initial packet, it
does not have to generate the same Retry packet each time.
Variations in Retry packet, if used by a client, could lead to
multiple connections derived from the same ClientHello. Reuse of the
client nonce is not supported by TLS and could lead to security
vulnerabilities. Clients that receive multiple Retry packets MUST
use only one and discard the remainder.

7.2. NewSessionTicket Address Validation

The ticket in the TLS NewSessionTicket message allows a server to
provide a client with a similar sort of token. When a client resumes
a TLS connection - whether or are not 0-RTT is attempted - it includes
the ticket in the handshake message. As protected with the HelloRetryRequest
cookie, the server includes the address validation token in the
ticket. TLS provides the token it extracts from the session ticket
to the transport when it asks whether source address validation is
needed.

If both a HelloRetryRequest cookie and a session ticket secret key, so they are present
in the ClientHello, only the token from the cookie is passed to the
transport. The presence of a cookie indicates that this is a second
ClientHello - the token from the session ticket will have been
provided to the transport when it appeared in the first ClientHello.

A server can send a NewSessionTicket message at any time. This
allows it to update the state - and the address validation token -
that is included in the ticket. This might be done to refresh the
ticket or token, or it might be generated in response
subject to changes in
the state of the connection. QUIC can request that a
NewSessionTicket be sent potential tampering by providing a new address validation token.

A server that intends to support 0-RTT SHOULD provide an address
validation token immediately after completing the TLS handshake.

7.3. Address Validation Token Integrity

TLS MUST provide integrity protection for address validation token
unless the transport guarantees integrity protection by other means.
For a NewSessionTicket that includes confidential information - such
as the resumption secret - including the token under authenticated
encryption ensures that the token gains both confidentiality and
integrity attacker. QUIC provides
protection without duplicating the overheads of against attackers that
protection.

8. Pre-handshake QUIC Messages

Implementations MUST NOT exchange data on any stream other than
stream 0 without packet protection. QUIC requires the use of several
types of frame for managing loss detection and recovery during this
phase. In addition, it might be useful to use the data acquired
during the exchange of unauthenticated messages for congestion
control.

This section generally only applies to TLS handshake messages from
both peers and acknowledgments of the packets carrying those
messages. In many cases, the need for servers cannot read packets, but does not
attempt to provide
acknowledgments is minimal, since the messages that clients send are
small and implicitly acknowledged by the server's responses.

The actions that a peer takes as a result of receiving an
unauthenticated packet needs to be limited. In particular, state
established by these packets cannot be retained once record additional protection commences.

There are several approaches possible for dealing with
unauthenticated packets prior to handshake completion:

o discard and ignore them

o use them, but reset any state that is established once the
handshake completes

o use them and authenticate them afterwards; failing against attacks where the handshake
if they can't be authenticated

o save them and use them when they
attacker can be properly authenticated

o treat them as a fatal error

Different strategies are appropriate for different types of data.
This document proposes that all strategies are possible depending on
the type of message.

o Transport parameters are made usable observe and authenticated as part inject packets. Some forms of
the TLS handshake (see Section 9.2).

o Most unprotected messages are treated tampering -
such as fatal errors when
received except for the small number necessary to permit the
handshake to complete (see Section 8.1).

o Protected packets can either be discarded or saved and later used
(see Section 8.3).

8.1. Unprotected Packets Prior to Handshake Completion

This section describes the handling of messages that are sent and
received prior to the completion of modifying the TLS handshake.

Sending and receiving unprotected messages is hazardous. Unless
expressly permitted, receipt of an unprotected message of any kind
MUST be treated as a fatal error.

8.1.1. STREAM Frames

"STREAM" frames for stream 0 are permitted. These carry the TLS
handshake messages. Once 1-RTT keys themselves - are available, unprotected
"STREAM" frames on stream 0 can be ignored.

Receiving unprotected "STREAM" frames for other streams MUST be
treated detectable, but
some - such as a fatal error.

8.1.2. ACK Frames

"ACK" frames modifying ACKs - are permitted prior to the handshake being complete.
Information learned from "ACK" frames cannot be entirely relied upon,
since not.

For example, an attacker is able to could inject these packets. Timing and packet
retransmission information from "ACK" frames is critical to the
functioning of the protocol, but these frames might be spoofed or
altered.

Endpoints MUST NOT use an "ACK" frame in an unprotected a packet to
acknowledge packets that were protected by 0-RTT or 1-RTT keys. An
endpoint MUST treat receipt of containing an "ACK" ACK
frame in an unprotected
packet that claims to acknowledge protected packets as a connection
error of type OPTIMISTIC_ACK. An endpoint that can read protected
data is always able to send protected data.

Note: 0-RTT data can be acknowledged by the server as makes 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.

An endpoint SHOULD use data from "ACK" frames carried in unprotected
packets or packets protected with 0-RTT keys only during the initial
handshake. All "ACK" frames contained in unprotected packets appear that
are received after successful receipt of a packet protected with
1-RTT keys MUST be discarded. An endpoint SHOULD therefore include
acknowledgments for unprotected and any packets protected with 0-RTT
keys until it sees an acknowledgment for a packet that is both
protected with 1-RTT keys and contains an "ACK" frame.

8.1.3. Updates to Data and Stream Limits

"MAX_DATA", "MAX_STREAM_DATA", "BLOCKED", "STREAM_BLOCKED", and
"MAX_STREAM_ID" frames MUST NOT be sent unprotected.

Though data is exchanged on stream 0, the initial flow control window
on that stream is sufficiently large to allow the TLS handshake to
complete. This limits the maximum size of the TLS handshake and
would prevent a server had not been received or client from using an abnormally large
certificate chain.

Stream 0 is exempt from the connection-level flow control window.

Consequently, there is no need to signal being blocked on flow
control.

Similarly, there is no need to increase
create a false impression of the number state of allowed streams
until the handshake completes.

8.1.4. Handshake Failures

The "CONNECTION_CLOSE" frame MAY be sent by either endpoint in a
Handshake packet. This allows an endpoint to signal a fatal error
with connection establishment. A "STREAM" frame carrying a TLS alert
MAY be included in the same packet.

8.1.5. Address Verification

In order to perform source-address verification before (e.g., by
modifying the handshake
is complete, "PATH_CHALLENGE" and "PATH_RESPONSE" frames MAY be
exchanged unprotected.

8.1.6. Denial of Service with Unprotected Packets

Accepting unprotected - specifically unauthenticated - packets
presents a denial of service risk to endpoints. An attacker ACK Delay). Note that is
able to inject unprotected packets can cause a recipient to drop even
protected packets with such a matching packet number. The spurious packet
shadows the genuine packet, causing the genuine could cause a
legitimate packet to be ignored dropped as redundant.

Once the TLS handshake is complete, both peers MUST ignore
unprotected packets. From that point onward, unprotected messages
can be safely dropped.

Since only TLS handshake packets and acknowledgments are sent a duplicate. Implementations
SHOULD use caution in the
clear, an attacker is able to force implementations to rely relying on
retransmission for packets that are lost or shadowed. Thus, an
attacker that intends to deny service to an endpoint has to drop or
shadow protected packets any data which is contained in order to ensure that their victim
continues to accept unprotected packets. The ability to shadow
packets means that an attacker does not need to be on path.

In addition to causing valid packets to be dropped, an attacker can
generate packets with an intent of causing the recipient to expend
processing resources. See Section 10.2 for a discussion of these
risks.

To avoid receiving TLS
Initial packets that contain no useful data, a TLS
implementation MUST reject empty TLS handshake records and any record
that is not permitted by the TLS state machine. Any TLS application
data or alerts that are received prior to the end of the handshake
MUST be treated as a connection error of type PROTOCOL_VIOLATION.

8.2. Use of 0-RTT Keys

If 0-RTT keys are available (see Section 5.2), the lack of replay
protection means that restrictions on their use are necessary to
avoid replay attacks on otherwise authenticated.

It is also possible for the protocol.

A client MUST only use 0-RTT keys attacker to protect tamper with 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.

A client that receives an indication
carried in Handshake packets, but because that its 0-RTT data has been
accepted by a server can send 0-RTT data until it receives all of the
server's tampering requires
modifying TLS handshake messages. A client SHOULD stop sending 0-RTT data
if it receives an indication messages, that 0-RTT data has been rejected.

A server MUST NOT use 0-RTT keys to protect packets.

If a server rejects 0-RTT, then the TLS stream tampering will not include any
TLS records protected with 0-RTT keys.

8.3. Receiving Out-of-Order Protected Frames

Due to reordering and loss, protected packets might be received by an
endpoint before cause 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.

Packets protected with 1-RTT keys MAY be stored and later decrypted
and used once the handshake is complete. A server MUST NOT use 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 4.2.8 of [TLS13]). Verifying
these values provides the server with an assurance that the
ClientHello has not been modified.

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.

Receiving and verifying the TLS Finished message is critical in
ensuring the integrity of the TLS handshake. A server MUST NOT use
protected packets from the client prior to verifying the client
Finished message if its response depends on client authentication.

9. fail.

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.

9.1.

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.

TLS uses Application Layer Protocol Negotiation (ALPN) [RFC7301] to
select an application protocol. The 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.

9.2.

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(26),
quic_transport_parameters(0xffa5), (65535)
} ExtensionType;

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 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.

10.

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.

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.

10.1.

9.1. 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.

Certificate caching [RFC7924] can reduce the size of the server's
handshake messages significantly.

QUIC requires that includes three defenses against this attack. First, the packet
containing a ClientHello MUST be padded to a minimum size. A server is less likely to generate a packet
reflection attack Second,
if responding to an unverified source address, the data it sends is a small multiple of this
size. A server SHOULD use a HelloRetryRequest if the size of the
handshake messages it sends is likely
forbidden to significantly exceed the
size send more than three UDP datagrams in its first flight
(see Section 4.4.3 of [QUIC-TRANSPORT]). Finally, because
acknowledgements of Handshake packets are authenticated, a blind
attacker cannot forge them. Put together, these defenses limit the packet containing the ClientHello.

10.2.
level of amplification.

9.2. Peer Denial of Service

QUIC, TLS and HTTP/2 all contain a 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.

TLS records SHOULD always contain at least one octet of a handshake
messages or alert. Records containing only padding are permitted
during the handshake, but an excessive number might be used to
generate unnecessary work. Once the TLS handshake is complete,
endpoints MUST NOT send TLS application data records. Receiving TLS
application data MUST be treated as a connection error of type
PROTOCOL_VIOLATION.

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.

10.3.

9.3. Packet Number Protection Analysis

Packet number 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 packet number protection algorithms defined in this document take
the form:

"encrypted_pn

encrypted_pn = packet_number XOR PRF(pn_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 packet number protection. Protecting two different
packet numbers with the same key and ciphertext sample reveals the
exclusive OR of those packet numbers. Assuming that the AEAD acts as
a PRF, if L bits are sampled, the odds of two ciphertext samples
being identical 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 numbers, values of
packet numbers are transitively authenticated using packet
protection; packet numbers are part of the authenticated additional
data. A falsified or modified packet number can only be detected
once the packet protection is removed.

An attacker can guess values for packet numbers and have an endpoint
confirm guesses through timing side channels. 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 packet number 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.

11. Error Codes

This section defines error codes from the error code space used in
[QUIC-TRANSPORT].

The following error codes are defined when TLS is used for the crypto
handshake:

TLS_HANDSHAKE_FAILED (0x201): The TLS handshake failed.

TLS_FATAL_ALERT_GENERATED (0x202): A TLS fatal alert was sent,
causing the TLS connection to end prematurely.

TLS_FATAL_ALERT_RECEIVED (0x203): A TLS fatal alert was received,
causing the TLS connection to end prematurely.

12.

10. IANA Considerations

This document does not create any new IANA registries, but it
registers the values in the following registries:

o QUIC Transport Error Codes Registry [QUIC-TRANSPORT] - IANA is to
register the three error codes found in Section 11, these are
summarized in Table 1.

o TLS ExtensionsType Registry [TLS-REGISTRIES] - IANA is to register
the quic_transport_parameters extension found in Section 9.2.
Assigning 26 to the extension would be greatly appreciated. 8.2. The
Recommended column is to be marked Yes. The TLS 1.3 Column is to
include CH and EE.

o TLS Exporter Label Registry [TLS-REGISTRIES] - IANA is requested
to register "EXPORTER-QUIC 0rtt" from Section 5.3.3; "EXPORTER-
QUIC client 1rtt" and "EXPORTER-QUIC server 1-RTT" from
Section 5.3.4. The DTLS column is to be marked No. The
Recommended column is to be marked Yes.

Table 1: QUIC Transport Error Codes for TLS

13.

11. References

13.1.

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 7539, DOI 10.17487/RFC7539, May 2015,
<https://www.rfc-editor.org/info/rfc7539>.

[HKDF] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.

[QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", draft-ietf-quic-
transport-12
transport-13 (work in progress), May June 2018.

[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>.

[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.

[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
Transport Layer Security (TLS) and DTLS", draft-ietf-tls-iana-registry-updates-04 Datagram Transport
Layer Security (DTLS)", draft-ietf-tls-iana-registry-
updates-05 (work in progress), February May 2018.

[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-21 (work in progress),
July 2017.

13.2.

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>.

[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-12 draft-ietf-quic-http-13 (work in progress), May June
2018.

[QUIC-RECOVERY]
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control", draft-ietf-quic-recovery-11 draft-ietf-quic-recovery-13 (work
in progress), May June 2018.

[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.

[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>.

[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016,
<https://www.rfc-editor.org/info/rfc7924>.

13.3.

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. Contributors

Ryan Hamilton was originally an author of this specification.

Appendix B. 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.

Appendix C. 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.

C.1.

A.1. 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)

A.2. Since draft-ietf-quic-tls-11

o Encrypted packet numbers.

A.3. Since draft-ietf-quic-tls-10

o No significant changes.

C.2.

A.4. Since draft-ietf-quic-tls-09

o Cleaned up key schedule and updated the salt used for handshake
packet protection (#1077)

C.3.

A.5. 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)

C.4.

A.6. Since draft-ietf-quic-tls-07

o Handshake errors can be reported with CONNECTION_CLOSE (#608,
#891)

C.5.

A.7. Since draft-ietf-quic-tls-05

No significant changes.

C.6.

A.8. Since draft-ietf-quic-tls-04

o Update labels used in HKDF-Expand-Label to match TLS 1.3 (#642)

C.7.

A.9. Since draft-ietf-quic-tls-03

No significant changes.

C.8.

A.10. Since draft-ietf-quic-tls-02

o Updates to match changes in transport draft

C.9.

A.11. 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)

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)

C.10.

A.12. 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

C.11.

A.13. 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: martin.thomson@gmail.com

Sean Turner (editor)
sn3rd

Email: sean@sn3rd.com