QUIC                                                     M. Thomson, Ed.
Internet-Draft                                                   Mozilla
Intended status: Standards Track                          S. Turner, Ed.
Expires: July 18, 2017                                             sn3rd
                                                        January 14, 2017

          Using Transport Layer Security (TLS) to Secure QUIC


   This document describes how Transport Layer Security (TLS) can be
   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 .

   Working Group information can be found at https://github.com/quicwg ;
   source code and issues list for this draft can be found at
   https://github.com/quicwg/base-drafts/labels/tls .

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
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   This Internet-Draft will expire on July 18, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  TLS Overview  . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  TLS Handshake . . . . . . . . . . . . . . . . . . . . . .   6
   4.  TLS Usage . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Handshake and Setup Sequence  . . . . . . . . . . . . . .   7
     4.2.  Interface to TLS  . . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Handshake Interface . . . . . . . . . . . . . . . . .   9
       4.2.2.  Key Ready Events  . . . . . . . . . . . . . . . . . .  10
       4.2.3.  Secret Export . . . . . . . . . . . . . . . . . . . .  11
       4.2.4.  TLS Interface Summary . . . . . . . . . . . . . . . .  11
   5.  QUIC Packet Protection  . . . . . . . . . . . . . . . . . . .  11
     5.1.  Installing New Keys . . . . . . . . . . . . . . . . . . .  12
     5.2.  QUIC Key Expansion  . . . . . . . . . . . . . . . . . . .  12
       5.2.1.  0-RTT Secret  . . . . . . . . . . . . . . . . . . . .  12
       5.2.2.  1-RTT Secrets . . . . . . . . . . . . . . . . . . . .  13
       5.2.3.  Packet Protection Key and IV  . . . . . . . . . . . .  14
     5.3.  QUIC AEAD Usage . . . . . . . . . . . . . . . . . . . . .  15
     5.4.  Packet Numbers  . . . . . . . . . . . . . . . . . . . . .  15
   6.  Key Phases  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     6.1.  Packet Protection for the TLS Handshake . . . . . . . . .  17
       6.1.1.  Initial Key Transitions . . . . . . . . . . . . . . .  17
       6.1.2.  Retransmission and Acknowledgment of Unprotected
               Packets . . . . . . . . . . . . . . . . . . . . . . .  18
     6.2.  Key Update  . . . . . . . . . . . . . . . . . . . . . . .  19
   7.  Pre-handshake QUIC Messages . . . . . . . . . . . . . . . . .  21
     7.1.  Unprotected Packets Prior to Handshake Completion . . . .  22
       7.1.1.  STREAM Frames . . . . . . . . . . . . . . . . . . . .  22
       7.1.2.  ACK Frames  . . . . . . . . . . . . . . . . . . . . .  22
       7.1.3.  WINDOW_UPDATE Frames  . . . . . . . . . . . . . . . .  23
       7.1.4.  Denial of Service with Unprotected Packets  . . . . .  23
     7.2.  Use of 0-RTT Keys . . . . . . . . . . . . . . . . . . . .  24
     7.3.  Protected Packets Prior to Handshake Completion . . . . .  24
   8.  QUIC-Specific Additions to the TLS Handshake  . . . . . . . .  25
     8.1.  Protocol and Version Negotiation  . . . . . . . . . . . .  25

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     8.2.  QUIC Extension  . . . . . . . . . . . . . . . . . . . . .  26
     8.3.  Source Address Validation . . . . . . . . . . . . . . . .  26
     8.4.  Priming 0-RTT . . . . . . . . . . . . . . . . . . . . . .  26
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
     9.1.  Packet Reflection Attack Mitigation . . . . . . . . . . .  27
     9.2.  Peer Denial of Service  . . . . . . . . . . . . . . . . .  27
   10. Error codes . . . . . . . . . . . . . . . . . . . . . . . . .  28
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  30
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  30
     12.2.  Informative References . . . . . . . . . . . . . . . . .  31
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  31
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  31
   Appendix C.  Change Log . . . . . . . . . . . . . . . . . . . . .  32
     C.1.  Since draft-ietf-quic-tls-00: . . . . . . . . . . . . . .  32
     C.2.  Since draft-thomson-quic-tls-01:  . . . . . . . . . . . .  32
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  32

1.  Introduction

   QUIC [QUIC-TRANSPORT] provides a multiplexed transport.  When used
   for HTTP [RFC7230] semantics [QUIC-HTTP] it provides several key
   advantages over HTTP/1.1 [RFC7230] or HTTP/2 [RFC7540] over TCP

   This document describes how QUIC can be secured using Transport Layer
   Security (TLS) version 1.3 [I-D.ietf-tls-tls13].  TLS 1.3 provides
   critical latency improvements for connection establishment over
   previous versions.  Absent packet loss, most new connections can be
   established and secured within a single round trip; on subsequent
   connections between the same client and server, the client can often
   send application data immediately, that is, zero round trip setup.

   This document describes how the standardized TLS 1.3 can act 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 words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
   document.  It's not shouting; when they are capitalized, they have
   the special meaning defined in [RFC2119].

   This document uses the terminology established in [QUIC-TRANSPORT].

   For brevity, the acronym TLS is used to refer to TLS 1.3.

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   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 [I-D.ietf-tls-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 ---->|            |
   |            |<---- Handshake -----|            |
   |   QUIC     |                     |    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 1 and associated packets.  Stream 1 is reserved for a TLS

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   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.

   This arrangement means that some TLS messages receive redundant
   protection from both the QUIC packet protection and the TLS record
   protection.  These messages are limited in number; the TLS connection
   is rarely needed once the handshake completes.

3.1.  TLS Overview

   TLS provides two endpoints 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

   TLS features can be separated into two basic functions: an
   authenticated key exchange and record protection.  QUIC primarily
   uses the authenticated key exchange provided by TLS; QUIC provides
   its own packet protection.

   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 exchange.  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 certificate-based authentication [RFC5280] 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.

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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
      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 immediately.  This
      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, see [I-D.ietf-tls-tls13] for more options and details.

       Client                                             Server

      (0-RTT Application Data)  -------->
                                <--------      [Application Data]
      {Finished}                -------->

      [Application Data]        <------->      [Application Data]

                    Figure 2: TLS Handshake with 0-RTT

   This 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 Section 8.3).

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   o  A pre-shared key mode can be used for subsequent handshakes to
      avoid public key operations.  This is the basis for 0-RTT data,
      even if the remainder of the connection is protected by a new
      Diffie-Hellman exchange.

4.  TLS Usage

   QUIC reserves stream 1 for a TLS connection.  Stream 1 contains a
   complete TLS connection, which includes the TLS record layer.  Other
   than the definition of a QUIC-specific extension (see Section-TBD),
   TLS is unmodified for this use.  This means that TLS will apply
   confidentiality and integrity protection to its records.  In
   particular, TLS record protection is what provides confidentiality
   protection for the TLS handshake messages sent by the server.

   QUIC permits a client to send frames on streams starting from the
   first packet.  The initial packet from a client contains a stream
   frame for stream 1 that contains the first TLS handshake messages
   from the client.  This allows the TLS handshake to start with the
   first packet that a client sends.

   QUIC packets are protected using a scheme that is specific to QUIC,
   see Section 5.  Keys are exported from the TLS connection when they
   become available using a TLS exporter (see Section 7.3.3 of
   [I-D.ietf-tls-tls13] and Section 5.2).  After keys are exported from
   TLS, QUIC manages its own key schedule.

4.1.  Handshake and Setup Sequence

   The integration of QUIC with a TLS handshake is shown in more detail
   in Figure 3.  QUIC "STREAM" frames on stream 1 carry the TLS
   handshake.  QUIC performs loss recovery [QUIC-RECOVERY] for this
   stream and ensures that TLS handshake messages are delivered in the
   correct order.

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       Client                                             Server

   @C QUIC STREAM Frame(s) <1>:
          + QUIC Extension
                           0-RTT Key => @0

   @0 QUIC STREAM Frame(s) <any stream>:
      Replayable QUIC Frames

                                         QUIC STREAM Frame <1>: @C
                                     {TLS Handshake Messages}
                           1-RTT Key => @1

                                              QUIC Frames <any> @1
   @1 QUIC STREAM Frame(s) <1>:

   @1 QUIC Frames <any>        <------->      QUIC Frames <any> @1

                     Figure 3: QUIC over TLS Handshake

   In Figure 3, symbols mean:

   o  "<" and ">" enclose stream numbers.

   o  "@" indicates the key phase that is currently used for protecting
      QUIC packets.

   o  "(" and ")" enclose messages that are protected with TLS 0-RTT
      handshake or application keys.

   o  "{" and "}" enclose messages that are protected by the TLS
      Handshake keys.

   If 0-RTT is not attempted, then the client does not send packets
   protected by the 0-RTT key (@0).  In that case, the only key
   transition on the client is from unprotected packets (@C) to 1-RTT
   protection (@1), which happens before it sends its final set of TLS
   handshake messages.

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   The server sends TLS handshake messages without protection (@C).  The
   server transitions from no protection (@C) to full 1-RTT protection
   (@1) after it sends the last of its handshake messages.

   Some TLS handshake messages are protected by the TLS handshake record
   protection.  These keys are not exported from the TLS connection for
   use in QUIC.  QUIC packets from the server are sent in the clear
   until the final transition to 1-RTT keys.

   The client transitions from cleartext (@C) to 0-RTT keys (@0) when
   sending 0-RTT data, and subsequently to to 1-RTT keys (@1) for its
   second flight of TLS handshake messages.  This creates the potential
   for unprotected packets to be received by a server in close proximity
   to packets that are protected with 1-RTT keys.

   More information on key transitions is included in Section 6.1.

4.2.  Interface to TLS

   As shown in Figure 1, the interface from QUIC to TLS consists of
   three primary functions: Handshake, Key Ready Events, and Secret

   Additional functions might be needed to configure TLS.

4.2.1.  Handshake Interface

   In order to drive the handshake, TLS depends on being able to send
   and receive handshake messages on stream 1.  There are two basic
   functions on this interface: one where QUIC requests handshake
   messages and one where QUIC provides handshake packets.

   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 1

   Each time that an endpoint receives data on stream 1, it delivers the
   octets to TLS if it is able.  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.

   Once the TLS handshake is complete, this is indicated to QUIC along
   with any final handshake octets that TLS needs to send.  Once the
   handshake is complete, TLS becomes passive.  TLS can still receive
   data from its peer and respond in kind that data, but it will not

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   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

   When the handshake is complete, QUIC only needs to provide TLS with
   any data that arrives on stream 1.  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.

4.2.2.  Key Ready Events

   TLS provides QUIC with signals when 0-RTT and 1-RTT keys are ready
   for use.  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 has enough information to generate 1-RTT keys, it indicates
   their availability.  On the client, this occurs after receiving the
   entirety of the first flight of TLS handshake messages from the
   server.  A server indicates that 1-RTT keys are available after it
   sends its handshake messages.

   This ordering ensures that a client sends its second flight of
   handshake messages protected with 1-RTT keys.  More importantly, it
   ensures that the server sends its flight of handshake messages
   without protection.

   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 0-RTT keys are ready.  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 both sending and receiving packets.  0-RTT
   keys are only used to protect packets that the client sends.

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4.2.3.  Secret Export

   Details how secrets are exported from TLS are included in
   Section 5.2.

4.2.4.  TLS Interface Summary

   Figure 4 summarizes the exchange between QUIC and TLS for both client
   and server.

   Client                                                    Server

   Get Handshake
   0-RTT Key Ready
                         --- send/receive --->
                                                 Handshake Received
                                                    0-RTT Key Ready
                                                      Get Handshake
                                                   1-RTT Keys Ready
                        <--- send/receive ---
   Handshake Received
   1-RTT Keys Ready
   Get Handshake
   Handshake Complete
                         --- send/receive --->
                                                 Handshake Received
                                                      Get Handshake
                                                 Handshake Complete
                        <--- send/receive ---
   Handshake Received
   Get Handshake

            Figure 4: Interaction Summary between QUIC and TLS

5.  QUIC Packet Protection

   QUIC packet protection provides authenticated encryption of packets.
   This provides confidentiality and integrity protection for the
   content of packets (see Section 5.3).  Packet protection uses keys
   that are exported from the TLS connection (see Section 5.2).

   Different keys are used for QUIC packet protection and TLS record
   protection.  Having separate QUIC and TLS record protection means
   that TLS records can be protected by two different keys.  This
   redundancy is limited to a only a few TLS records, and is maintained
   for the sake of simplicity.

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5.1.  Installing New Keys

   As TLS reports the availability of keying material, the packet
   protection keys and initialization vectors (IVs) are updated (see
   Section 5.2).  The selection of AEAD function is also updated to
   match the AEAD negotiated by TLS.

   For packets other than any unprotected handshake packets (see
   Section 6.1), once a change of keys has been made, packets with
   higher packet numbers MUST use 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 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.  QUIC Key Expansion

   QUIC uses a system of packet protection secrets, keys and IVs that
   are modelled on the system used in TLS [I-D.ietf-tls-tls13].  The
   secrets that QUIC uses as the basis of its key schedule are obtained
   using TLS exporters (see Section 7.3.3 of [I-D.ietf-tls-tls13]).

   QUIC uses the Pseudo-Random Function (PRF) hash function negotiated
   by TLS for key derivation.  For example, if TLS is using the
   TLS_AES_128_GCM_SHA256, the SHA-256 hash function is used.

5.2.1.  0-RTT Secret

   0-RTT keys are those keys that are used in resumed connections prior
   to the completion of the TLS handshake.  Data sent using 0-RTT keys
   might be replayed and so has some restrictions on its use, see
   Section 7.2.  0-RTT keys are used after sending or receiving a

   The secret is exported from TLS using the exporter label "EXPORTER-
   QUIC 0-RTT Secret" and an empty context.  The size 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.

          = TLS-Exporter("EXPORTER-QUIC 0-RTT Secret"
                         "", Hash.length)

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5.2.2.  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 protecting packets sent by the server.

   The initial client packet protection secret is exported from TLS
   using the exporter label "EXPORTER-QUIC client 1-RTT Secret"; the
   initial server packet protection secret uses the exporter label
   "EXPORTER-QUIC server 1-RTT Secret".  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.

          = TLS-Exporter("EXPORTER-QUIC client 1-RTT Secret"
                         "", Hash.length)
          = TLS-Exporter("EXPORTER-QUIC server 1-RTT Secret"
                         "", Hash.length)

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

   After a key update (see Section 6.2), these secrets are updated using
   the HKDF-Expand-Label function defined in Section 7.1 of
   [I-D.ietf-tls-tls13].  HKDF-Expand-Label uses the the PRF hash
   function negotiated by TLS.  The replacement secret is derived using
   the existing Secret, a Label of "QUIC client 1-RTT Secret" for the
   client and "QUIC server 1-RTT Secret" for the server, an empty
   HashValue, and the same output Length as the hash function selected
   by TLS for its PRF.

          = HKDF-Expand-Label(client_pp_secret_<N>,
                              "QUIC client 1-RTT Secret",
                              "", Hash.length)
          = HKDF-Expand-Label(server_pp_secret_<N>,
                              "QUIC server 1-RTT Secret",
                              "", Hash.length)

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

   HKDF-Expand-Label uses HKDF-Expand [RFC5869] with a specially
   formatted info parameter.  The info parameter that includes the
   output length (in this case, the size of the PRF hash output) encoded
   on two octets in network byte order, the length of the prefixed Label

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   as a single octet, the value of the Label prefixed with "TLS 1.3, ",
   and a zero octet to indicate an empty HashValue.  For example, the
   client packet protection secret uses an info parameter of:

      info = (HashLen / 256) || (HashLen % 256) || 0x21 ||
             "TLS 1.3, QUIC client 1-RTT secret" || 0x00

5.2.3.  Packet Protection Key and IV

   The complete key expansion uses an identical process for key
   expansion as defined in Section 7.3 of [I-D.ietf-tls-tls13], using
   different values for the input secret.  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 use the QUIC 0-RTT secret.  This uses the HKDF-
   Expand-Label with the PRF hash function negotiated by TLS.

   The length of the 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 [I-D.ietf-tls-tls13], the IV length is
   the larger of 8 or N_MIN (see Section 4 of [RFC5116]).

      client_0rtt_key = HKDF-Expand-Label(client_0rtt_secret,
                                          "key", "", key_length)
      client_0rtt_iv = HKDF-Expand-Label(client_0rtt_secret,
                                         "iv", "", iv_length)

   Similarly, the packet protection key and IV used to protect 1-RTT
   packets sent by both client and server use the current packet
   protection secret.

      client_pp_key_<N> = HKDF-Expand-Label(client_pp_secret_<N>,
                                            "key", "", key_length)
      client_pp_iv_<N> = HKDF-Expand-Label(client_pp_secret_<N>,
                                           "iv", "", iv_length)
      server_pp_key_<N> = HKDF-Expand-Label(server_pp_secret_<N>,
                                            "key", "", key_length)
      server_pp_iv_<N> = HKDF-Expand-Label(server_pp_secret_<N>,
                                           "iv", "", iv_length)

   The client protects (or encrypts) packets with the client packet
   protection key and IV; the server protects packets with the server
   packet protection key.

   The QUIC record protection initially starts without keying material.
   When the TLS state machine reports that the ClientHello has been
   sent, the 0-RTT keys can be generated and installed for writing.

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   When the TLS state machine reports completion of the handshake, the
   1-RTT keys can be generated and installed for writing.

5.3.  QUIC AEAD Usage

   The Authentication Encryption with Associated Data (AEAD) [RFC5116]
   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.

   Regular QUIC packets are protected by an AEAD [RFC5116].  Version
   negotiation and public reset packets are not protected.

   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, for the AEAD is either the client packet protection key
   (client_pp_key_n) or the server packet protection key
   (server_pp_key_n), derived as defined in Section 5.2.

   The nonce, N, for the AEAD is formed by combining either the packet
   protection IV (either client_pp_iv_n or server_pp_iv_n) with packet
   numbers.  The 64 bits of the reconstructed QUIC packet number in
   network byte order is 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 an empty sequence.

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

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

   Prior to TLS providing keys, no record protection is performed and
   the plaintext, P, is transmitted unmodified.

5.4.  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

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   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 packet number is not reset and it is not permitted to go higher
   than its maximum value of 2^64-1.  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) 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 1.  This
   sequence number is not visible to QUIC.

6.  Key Phases

   As TLS reports the availability 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

   Every time that a new set of keys is used for protecting outbound
   packets, the KEY_PHASE bit in the public flags is toggled.  The
   exception is the transition from 0-RTT keys to 1-RTT keys, where the
   presence of the version field and its associated bit is used (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 the first packet that triggered the change.  An
   endpoint that notices a changed KEY_PHASE bit can update keys and
   decrypt the packet that contains the changed bit, see Section 6.2.

   The KEY_PHASE bit is the third bit of the public flags (0x04).

   Transitions between keys during the handshake are complicated by the
   need to ensure that TLS handshake messages are sent with the correct
   packet protection.

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6.1.  Packet Protection for the TLS Handshake

   The initial exchange of packets are sent without protection.  These
   packets are marked with a KEY_PHASE of 0.

   TLS handshake messages that are critical to the TLS key exchange
   cannot be protected using QUIC packet protection.  A KEY_PHASE of 0
   is used for all of these packets, even during retransmission.  The
   messages critical to key exchange are the TLS ClientHello and any TLS
   handshake message from the server, except those that are sent after
   the handshake completes, such as NewSessionTicket.

   The second flight of TLS handshake messages from the client, and any
   TLS handshake messages that are sent after completing the TLS
   handshake do not need special packet protection rules.  This includes
   the EndOfEarlyData message that is sent by a client to mark the end
   of its 0-RTT data.  Packets containing these messages use the packet
   protection keys that are current at the time of sending (or

   Like the client, a server MUST send retransmissions of its
   unprotected handshake messages or acknowledgments for unprotected
   handshake messages sent by the client in unprotected packets

6.1.1.  Initial Key Transitions

   Once the TLS key exchange is complete, keying material is exported
   from TLS and QUIC packet protection commences.

   Packets protected with 1-RTT keys have a KEY_PHASE bit set to 1.
   These packets also have a VERSION bit set to 0.

   If the client is unable to send 0-RTT data - or it does not have
   0-RTT data to send - packet protection with 1-RTT keys starts with
   the packets that contain its second flight of TLS handshake messages.
   That is, the flight containing the TLS Finished handshake message and
   optionally a Certificate and CertificateVerify message.

   If the client sends 0-RTT data, it marks packets protected with 0-RTT
   keys with a KEY_PHASE of 1 and a VERSION bit of 1.  Setting the
   version bit means that all packets also include the version field.
   The client removes the VERSION bit when it transitions to using 1-RTT
   keys, but it does not change the KEY_PHASE bit.

   Marking 0-RTT data with the both KEY_PHASE and VERSION bits ensures
   that the server is able to identify these packets as 0-RTT data in
   case the packet containing the TLS ClientHello is lost or delayed.

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   Including the version also ensures that the packet format is known to
   the server in this case.

   Using both KEY_PHASE and VERSION also ensures that the server is able
   to distinguish between cleartext handshake packets (KEY_PHASE=0,
   VERSION=1), 0-RTT protected packets (KEY_PHASE=1, VERSION=1), and
   1-RTT protected packets (KEY_PHASE=1, VERSION=0).  Packets with all
   of these markings can arrive concurrently, and being able to identify
   each cleanly ensures that the correct packet protection keys can be
   selected and applied.

   A server might choose to retain 0-RTT packets that arrive before a
   TLS ClientHello.  The server can then use those packets once the
   ClientHello arrives.  However, the potential for denial of service
   from buffering 0-RTT packets is significant.  These packets cannot be
   authenticated and so might be employed by an attacker to exhaust
   server resources.  Limiting the number of packets that are saved
   might be necessary.

   The server transitions to using 1-RTT keys after sending its first
   flight of TLS handshake messages.  From this point, the server
   protects all packets with 1-RTT keys.  Future packets are therefore
   protected with 1-RTT keys and marked with a KEY_PHASE of 1.

6.1.2.  Retransmission and Acknowledgment of Unprotected Packets

   The first flight of TLS handshake messages from both client and
   server (ClientHello, or ServerHello through to the server's Finished)
   are critical to the key exchange.  The contents of these messages
   determines the keys used to protect later messages.  If these
   handshake messages are included in packets that are protected with
   these keys, they will be indecipherable to the recipient.

   Even though newer keys could be available when retranmitting,
   retransmissions of these handshake messages MUST be sent in
   unprotected packets (with a KEY_PHASE of 0).  An endpoint MUST also
   generate ACK frames for these messages that are sent in unprotected

   The TLS handshake messages that are affected by this rule are

   o  A client MUST NOT restransmit a TLS ClientHello with 0-RTT keys.
      The server needs this message in order to determine the 0-RTT

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   o  A server MUST NOT retransmit any of its TLS handshake messages
      with 1-RTT keys.  The client needs these messages in order to
      determine the 1-RTT keys.

   A HelloRetryRequest handshake message might be used to reject an
   initial ClientHello.  A HelloRetryRequest handshake message and any
   second ClientHello that is sent in response MUST also be sent without
   packet protection.  This is natural, because no new keying material
   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 a HelloRetryRequest.

   Note:  TLS handshake data that needs to be sent without protection is
      all the handshake data acquired from TLS before the point that
      1-RTT keys are provided by TLS (see Section 4.2.2).

   The KEY_PHASE and VERSION bits ensure that protected packets are
   clearly distinguished from unprotected packets.  Loss or reordering
   might cause unprotected packets to arrive once 1-RTT keys are in use,
   unprotected packets are easily distinguished from 1-RTT packets.

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

   To limit the number of key phases that could be active, an endpoint
   MUST NOT initiate a key update while there are any unacknowledged
   handshake messages, see Section 6.2.

6.2.  Key Update

   Once the TLS handshake is complete, the KEY_PHASE bit allows for
   refreshes of keying material by either peer.  Endpoints start using
   updated keys immediately without additional signaling; the change in
   the KEY_PHASE bit indicates that a new key is in use.

   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.

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   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 5.2) 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 sequence numbers lower than
   the lowest sequence 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: 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

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   be received by a peer.  Once both sending and receiving keys have
   been updated,

   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.

7.  Pre-handshake QUIC Messages

   Implementations MUST NOT exchange data on any stream other than
   stream 1 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

   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 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
   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 the handshake
      if they can't be authenticated

   o  save them and use them when they 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.

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   o  Transport parameters and options are made usable and authenticated
      as part of the TLS handshake (see Section 8.2).

   o  Most unprotected messages are treated as fatal errors when
      received except for the small number necessary to permit the
      handshake to complete (see Section 7.1).

   o  Protected packets can either be discarded or saved and later used
      (see Section 7.3).

7.1.  Unprotected Packets Prior to Handshake Completion

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

7.1.1.  STREAM Frames

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

   Receiving unprotected "STREAM" frames for other streams MUST be
   treated as a fatal error.

7.1.2.  ACK Frames

   "ACK" frames are permitted prior to the handshake being complete.
   Information learned from "ACK" frames cannot be entirely relied upon,
   since an attacker is able to 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

   Endpoints MUST NOT use an unprotected "ACK" frame to acknowledge data
   that was protected by 0-RTT or 1-RTT keys.  An endpoint MUST ignore
   an unprotected "ACK" frame if it claims to acknowledge data that was
   sent in a protected packet.  Such an acknowledgement can only serve
   as a denial of service, since an endpoint that can read protected
   data is always able to send protected data.

   ISSUE:  What about 0-RTT data?  Should we allow acknowledgment of
      0-RTT with unprotected frames?  If we don't, then 0-RTT data will
      be unacknowledged until the handshake completes.  This isn't a
      problem if the handshake completes without loss, but it could mean

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      that 0-RTT stalls when a handshake packet disappears for any

   An endpoint SHOULD use data from unprotected or 0-RTT-protected "ACK"
   frames only during the initial handshake and while they have
   insufficient information from 1-RTT-protected "ACK" frames.  Once
   sufficient information has been obtained from protected messages,
   information obtained from less reliable sources can be discarded.

7.1.3.  WINDOW_UPDATE Frames

   "WINDOW_UPDATE" frames MUST NOT be sent unprotected.

   Though data is exchanged on stream 1, the initial flow control window
   is is sufficiently large to allow the TLS handshake to complete.
   This limits the maximum size of the TLS handshake and would prevent a
   server or client from using an abnormally large certificate chain.

   Stream 1 is exempt from the connection-level flow control window.

7.1.4.  Denial of Service with Unprotected Packets

   Accepting unprotected - specifically unauthenticated - packets
   presents a denial of service risk to endpoints.  An attacker that is
   able to inject unprotected packets can cause a recipient to drop even
   protected packets with a matching sequence number.  The spurious
   packet shadows the genuine packet, causing the genuine packet to be
   ignored 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 in the
   clear, an attacker is able to force implementations to rely 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 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.

   ISSUE:  This would not be an issue if QUIC had a randomized starting
      sequence number.  If we choose to randomize, we fix this problem
      and reduce the denial of service exposure to on-path attackers.
      The only possible problem is in authenticating the initial value,
      so that peers can be sure that they haven't missed an initial

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   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 9.2 for a discussion of these

   To avoid receiving TLS 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 is received prior to the end of the handshake
   MUST be treated as a fatal error.

7.2.  Use of 0-RTT Keys

   If 0-RTT keys are available, the lack of replay protection means that
   restrictions on their use are necessary to avoid replay attacks on
   the protocol.

   A client MUST only use 0-RTT keys to protect data that is idempotent.
   A client MAY wish to apply additional restrictions on what data it
   sends prior to the completion of the TLS handshake.  A client
   otherwise treats 0-RTT keys as equivalent to 1-RTT keys.

   A client that receives an indication that its 0-RTT data has been
   accepted by a server can send 0-RTT data until it receives all of the
   server's handshake messages.  A client SHOULD stop sending 0-RTT data
   if it receives an indication that 0-RTT data has been rejected.

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

7.3.  Protected Packets Prior to Handshake Completion

   Due to reordering and loss, protected packets might be received by an
   endpoint before the final handshake messages are received.  If these
   can be decrypted successfully, such packets MAY be stored and used
   once the handshake is complete.

   Unless expressly permitted below, encrypted packets MUST NOT be used
   prior to completing the TLS handshake, in particular the receipt of a
   valid Finished message and any authentication of the peer.  If
   packets are processed prior to completion of the handshake, an
   attacker might use the willingness of an implementation to use these
   packets to mount attacks.

   TLS handshake messages are covered by record protection during the
   handshake, once key agreement has completed.  This means that
   protected messages need to be decrypted to determine if they are TLS
   handshake messages or not.  Similarly, "ACK" and "WINDOW_UPDATE"
   frames might be needed to successfully complete the TLS handshake.

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   Any timestamps present in "ACK" frames MUST be ignored rather than
   causing a fatal error.  Timestamps on protected frames MAY be saved
   and used once the TLS handshake completes successfully.

   An endpoint MAY save the last protected "WINDOW_UPDATE" frame it
   receives for each stream and apply the values once the TLS handshake
   completes.  Failing to do this might result in temporary stalling of
   affected streams.

8.  QUIC-Specific Additions to the TLS Handshake

   QUIC uses the TLS handshake for more than just negotiation of
   cryptographic parameters.  The TLS handshake validates protocol
   version selection, provides preliminary values for QUIC transport
   parameters, and allows a server to perform return routeability checks
   on clients.

8.1.  Protocol and Version Negotiation

   The QUIC version negotiation mechanism is used to negotiate the
   version of QUIC that is used prior to the completion of the
   handshake.  However, this packet is not authenticated, enabling an
   active attacker to force a version downgrade.

   To ensure that a QUIC version downgrade is not forced by an attacker,
   version information is copied into the TLS handshake, which provides
   integrity protection for the QUIC negotiation.  This does not prevent
   version downgrade during the handshake, though it means that such a
   downgrade causes a handshake failure.

   Protocols that use the QUIC transport MUST use Application Layer
   Protocol Negotiation (ALPN) [RFC7301].  The ALPN identifier for the
   protocol MUST be specific to the QUIC version that it operates over.
   When constructing a ClientHello, clients MUST include a list of all
   the ALPN identifiers that they support, regardless of whether the
   QUIC version that they have currently selected supports that

   Servers SHOULD select an application protocol based solely on the
   information in the ClientHello, not using the QUIC version that the
   client has selected.  If the protocol that is selected is not
   supported with the QUIC version that is in use, the server MAY send a
   QUIC version negotiation packet to select a compatible version.

   If the server cannot select a combination of ALPN identifier and QUIC
   version it MUST abort the connection.  A client MUST abort a
   connection if the server picks an incompatible version of QUIC
   version and ALPN.

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8.2.  QUIC Extension

   QUIC defines an extension for use with TLS.  That extension defines
   transport-related parameters.  This provides integrity protection for
   these values.  Including these in the TLS handshake also make the
   values that a client sets available to a server one-round trip
   earlier than parameters that are carried in QUIC packets.  This
   document does not define that extension.

8.3.  Source Address Validation

   QUIC implementations describe a source address token.  This is an
   opaque blob that a server might provide to clients when they first
   use a given source address.  The client returns this token in
   subsequent messages as a return routeability check.  That is, the
   client returns this token to prove that it is able to receive packets
   at the source address that it claims.  This prevents the server from
   being used in packet reflection attacks (see Section 9.1).

   A source address token is opaque and consumed only by the server.
   Therefore it can be included in the TLS 1.3 pre-shared key identifier
   for 0-RTT handshakes.  Servers that use 0-RTT are advised to provide
   new pre-shared key identifiers after every handshake to avoid
   linkability of connections by passive observers.  Clients MUST use a
   new pre-shared key identifier for every connection that they
   initiate; if no pre-shared key identifier is available, then
   resumption is not possible.

   A server that is under load might include a source address token in
   the cookie extension of a HelloRetryRequest.

8.4.  Priming 0-RTT

   QUIC uses TLS without modification.  Therefore, it is possible to use
   a pre-shared key that was obtained in a TLS connection over TCP to
   enable 0-RTT in QUIC.  Similarly, QUIC can provide a pre-shared key
   that can be used to enable 0-RTT in TCP.

   All the restrictions on the use of 0-RTT apply, with the exception of
   the ALPN label, which MUST only change to a label that is explicitly
   designated as being compatible.  The client indicates which ALPN
   label it has chosen by placing that ALPN label first in the ALPN

   The certificate that the server uses MUST be considered valid for
   both connections, which will use different protocol stacks and could
   use different port numbers.  For instance, HTTP/1.1 and HTTP/2
   operate over TLS and TCP, whereas QUIC operates over UDP.

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   Source address validation is not completely portable between
   different protocol stacks.  Even if the source IP address remains
   constant, the port number is likely to be different.  Packet
   reflection attacks are still possible in this situation, though the
   set of hosts that can initiate these attacks is greatly reduced.  A
   server might choose to avoid source address validation for such a
   connection, or allow an increase to the amount of data that it sends
   toward the client without source validation.

9.  Security Considerations

   There are likely to be some real clangers here eventually, but the
   current set of issues is well captured in the relevant sections of
   the main text.

   Never assume that because it isn't in the security considerations
   section it doesn't affect security.  Most of this document does.

9.1.  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.

   A client SHOULD also pad [RFC7685] its ClientHello to at least 1024
   octets.  A server is less likely to generate a packet reflection
   attack if the data it sends is a small multiple of the data it
   receives.  A server SHOULD use a HelloRetryRequest if the size of the
   handshake messages it sends is likely to exceed the size of the

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.

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   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 SHOULD NOT send TLS application data records unless it is
   to hide the length of QUIC records.  QUIC packet protection does not
   include any allowance for padding; padded TLS application data
   records can be used to mask the length of QUIC frames.

   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.  Error codes

   The portion of the QUIC error code space allocated for the crypto
   handshake is 0xB000-0xFFFF.  The following error codes are defined
   when TLS is used for the crypto handshake:

   TLS_HANDSHAKE_FAILED (0xB01c):  Crypto errors.  Handshake failed.

   TLS_MESSAGE_OUT_OF_ORDER (0xB01d):  Handshake message received out of

   TLS_TOO_MANY_ENTRIES (0xB01e):  Handshake message contained too many

   TLS_INVALID_VALUE_LENGTH (0xB01f):  Handshake message contained an
      invalid value length.

   TLS_MESSAGE_AFTER_HANDSHAKE_COMPLETE (0xB020):  A handshake message
      was received after the handshake was complete.

   TLS_INVALID_RECORD_TYPE (0xB021):  A handshake message was received
      with an illegal record type.

   TLS_INVALID_PARAMETER (0xB022):  A handshake message was received
      with an illegal parameter.

   TLS_INVALID_CHANNEL_ID_SIGNATURE (0xB034):  An invalid channel id
      signature was supplied.

   TLS_MESSAGE_PARAMETER_NOT_FOUND (0xB023):  A handshake message was
      received with a mandatory parameter missing.

   TLS_MESSAGE_PARAMETER_NO_OVERLAP (0xB024):  A handshake message was
      received with a parameter that has no overlap with the local

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   TLS_MESSAGE_INDEX_NOT_FOUND (0xB025):  A handshake message was
      received that contained a parameter with too few values.

   TLS_UNSUPPORTED_PROOF_DEMAND (0xB05e):  A demand for an unsupported
      proof type was received.

   TLS_INTERNAL_ERROR (0xB026):  An internal error occured in handshake

   TLS_VERSION_NOT_SUPPORTED (0xB027):  A handshake handshake message
      specified an unsupported version.

   TLS_HANDSHAKE_STATELESS_REJECT (0xB048):  A handshake handshake
      message resulted in a stateless reject.

   TLS_NO_SUPPORT (0xB028):  There was no intersection between the
      crypto primitives supported by the peer and ourselves.

   TLS_TOO_MANY_REJECTS (0xB029):  The server rejected our client hello
      messages too many times.

   TLS_PROOF_INVALID (0xB02a):  The client rejected the server's
      certificate chain or signature.

   TLS_DUPLICATE_TAG (0xB02b):  A handshake message was received with a
      duplicate tag.

   TLS_ENCRYPTION_LEVEL_INCORRECT (0xB02c):  A handshake message was
      received with the wrong encryption level (i.e. it should have been
      encrypted but was not.)

   TLS_SERVER_CONFIG_EXPIRED (0xB02d):  The server config for a server
      has expired.

   TLS_SYMMETRIC_KEY_SETUP_FAILED (0xB035):  We failed to set up the
      symmetric keys for a connection.

      message arrived, but we are still validating the previous
      handshake message.

      update arrived before the handshake is complete.

   TLS_CLIENT_HELLO_TOO_LARGE (0xB05a):  ClientHello cannot fit in one

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11.  IANA Considerations

   This document has no IANA actions.  Yet.

12.  References

12.1.  Normative References

              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-18 (work in progress),
              October 2016.

              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport".

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5116]  McGrew, D., "An Interface and Algorithms for Authenticated
              Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,

   [RFC5869]  Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
              Key Derivation Function (HKDF)", RFC 5869,
              DOI 10.17487/RFC5869, May 2010,

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,

   [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, <http://www.rfc-editor.org/info/rfc7301>.

   [RFC7685]  Langley, A., "A Transport Layer Security (TLS) ClientHello
              Padding Extension", RFC 7685, DOI 10.17487/RFC7685,
              October 2015, <http://www.rfc-editor.org/info/rfc7685>.

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12.2.  Informative References

              Luykx, A. and K. Paterson, "Limits on Authenticated
              Encryption Use in TLS", March 2016,

              Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over

              Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
              and Congestion Control".

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,

   [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,

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,

   [RFC7924]  Santesson, S. and H. Tschofenig, "Transport Layer Security
              (TLS) Cached Information Extension", RFC 7924,
              DOI 10.17487/RFC7924, July 2016,

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.

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Appendix C.  Change Log

      *RFC Editor's Note:* Please remove this section prior to
      publication of a final version of this document.

C.1.  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.2.  Since draft-thomson-quic-tls-01:

   o  Adopted as base for draft-ietf-quic-tls.

   o  Updated authors/editors list.

   o  Added status note.

Authors' Addresses

   Martin Thomson (editor)

   Email: martin.thomson@gmail.com

   Sean Turner (editor)

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