QUIC                                                     M. Thomson, Ed.
Internet-Draft                                                   Mozilla
Intended status: Standards Track                          S. Turner, Ed.
Expires: January 10, 2020                                          sn3rd
                                                           July 09, 2019

                        Using TLS to Secure QUIC


   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
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 10, 2020.

Copyright Notice

   Copyright (c) 2019 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
   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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   4
     2.1.  TLS Overview  . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Carrying TLS Messages . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Interface to TLS  . . . . . . . . . . . . . . . . . . . .   9
       4.1.1.  Handshake Complete  . . . . . . . . . . . . . . . . .  10
       4.1.2.  Handshake Confirmed . . . . . . . . . . . . . . . . .  10
       4.1.3.  Sending and Receiving Handshake Messages  . . . . . .  10
       4.1.4.  Encryption Level Changes  . . . . . . . . . . . . . .  12
       4.1.5.  TLS Interface Summary . . . . . . . . . . . . . . . .  13
     4.2.  TLS Version . . . . . . . . . . . . . . . . . . . . . . .  13
     4.3.  ClientHello Size  . . . . . . . . . . . . . . . . . . . .  14
     4.4.  Peer Authentication . . . . . . . . . . . . . . . . . . .  14
     4.5.  Enabling 0-RTT  . . . . . . . . . . . . . . . . . . . . .  15
     4.6.  Rejecting 0-RTT . . . . . . . . . . . . . . . . . . . . .  15
     4.7.  HelloRetryRequest . . . . . . . . . . . . . . . . . . . .  15
     4.8.  TLS Errors  . . . . . . . . . . . . . . . . . . . . . . .  16
     4.9.  Discarding Unused Keys  . . . . . . . . . . . . . . . . .  16
       4.9.1.  Discarding Initial Keys . . . . . . . . . . . . . . .  17
       4.9.2.  Discarding Handshake Keys . . . . . . . . . . . . . .  17
       4.9.3.  Discarding 0-RTT Keys . . . . . . . . . . . . . . . .  17
   5.  Packet Protection . . . . . . . . . . . . . . . . . . . . . .  18
     5.1.  Packet Protection Keys  . . . . . . . . . . . . . . . . .  18
     5.2.  Initial Secrets . . . . . . . . . . . . . . . . . . . . .  18
     5.3.  AEAD Usage  . . . . . . . . . . . . . . . . . . . . . . .  19
     5.4.  Header Protection . . . . . . . . . . . . . . . . . . . .  21
       5.4.1.  Header Protection Application . . . . . . . . . . . .  21
       5.4.2.  Header Protection Sample  . . . . . . . . . . . . . .  23
       5.4.3.  AES-Based Header Protection . . . . . . . . . . . . .  24
       5.4.4.  ChaCha20-Based Header Protection  . . . . . . . . . .  24
     5.5.  Receiving Protected Packets . . . . . . . . . . . . . . .  24
     5.6.  Use of 0-RTT Keys . . . . . . . . . . . . . . . . . . . .  25
     5.7.  Receiving Out-of-Order Protected Frames . . . . . . . . .  25
   6.  Key Update  . . . . . . . . . . . . . . . . . . . . . . . . .  26
   7.  Security of Initial Messages  . . . . . . . . . . . . . . . .  28

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   8.  QUIC-Specific Additions to the TLS Handshake  . . . . . . . .  29
     8.1.  Protocol Negotiation  . . . . . . . . . . . . . . . . . .  29
     8.2.  QUIC Transport Parameters Extension . . . . . . . . . . .  29
     8.3.  Removing the EndOfEarlyData Message . . . . . . . . . . .  30
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  30
     9.1.  Replay Attacks with 0-RTT . . . . . . . . . . . . . . . .  31
     9.2.  Packet Reflection Attack Mitigation . . . . . . . . . . .  32
     9.3.  Peer Denial of Service  . . . . . . . . . . . . . . . . .  32
     9.4.  Header Protection Analysis  . . . . . . . . . . . . . . .  32
     9.5.  Key Diversity . . . . . . . . . . . . . . . . . . . . . .  33
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  34
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  34
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  34
     11.2.  Informative References . . . . . . . . . . . . . . . . .  35
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  36
   Appendix A.  Sample Initial Packet Protection . . . . . . . . . .  36
     A.1.  Keys  . . . . . . . . . . . . . . . . . . . . . . . . . .  36
     A.2.  Client Initial  . . . . . . . . . . . . . . . . . . . . .  37
     A.3.  Server Initial  . . . . . . . . . . . . . . . . . . . . .  39
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  40
     B.1.  Since draft-ietf-quic-tls-21  . . . . . . . . . . . . . .  40
     B.2.  Since draft-ietf-quic-tls-20  . . . . . . . . . . . . . .  40
     B.3.  Since draft-ietf-quic-tls-18  . . . . . . . . . . . . . .  40
     B.4.  Since draft-ietf-quic-tls-17  . . . . . . . . . . . . . .  41
     B.5.  Since draft-ietf-quic-tls-14  . . . . . . . . . . . . . .  41
     B.6.  Since draft-ietf-quic-tls-13  . . . . . . . . . . . . . .  41
     B.7.  Since draft-ietf-quic-tls-12  . . . . . . . . . . . . . .  41
     B.8.  Since draft-ietf-quic-tls-11  . . . . . . . . . . . . . .  42
     B.9.  Since draft-ietf-quic-tls-10  . . . . . . . . . . . . . .  42
     B.10. Since draft-ietf-quic-tls-09  . . . . . . . . . . . . . .  42
     B.11. Since draft-ietf-quic-tls-08  . . . . . . . . . . . . . .  42
     B.12. Since draft-ietf-quic-tls-07  . . . . . . . . . . . . . .  42
     B.13. Since draft-ietf-quic-tls-05  . . . . . . . . . . . . . .  42
     B.14. Since draft-ietf-quic-tls-04  . . . . . . . . . . . . . .  42
     B.15. Since draft-ietf-quic-tls-03  . . . . . . . . . . . . . .  42
     B.16. Since draft-ietf-quic-tls-02  . . . . . . . . . . . . . .  42
     B.17. Since draft-ietf-quic-tls-01  . . . . . . . . . . . . . .  43
     B.18. Since draft-ietf-quic-tls-00  . . . . . . . . . . . . . .  43
     B.19. Since draft-thomson-quic-tls-01 . . . . . . . . . . . . .  43
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  44
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  44
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  44

1.  Introduction

   This document describes how QUIC [QUIC-TRANSPORT] is secured using
   TLS [TLS13].

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   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 TLS acts as a security component of QUIC.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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

   For brevity, the acronym TLS is used to refer to TLS 1.3, though a
   newer version could be used (see Section 4.2).

2.1.  TLS Overview

   TLS provides two endpoints with a way to establish a means of
   communication over an untrusted medium (that is, the Internet) that
   ensures that messages they exchange cannot be observed, modified, or

   Internally, TLS is a layered protocol, with the structure shown

   |  Handshake   |    Alerts    |  Application |
   |    Layer     |              |     Data     |
   |              |              |              |
   |                                            |
   |               Record Layer                 |
   |                                            |

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

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   Change Cipher Spec records cannot be sent in QUIC.

   The TLS authenticated key exchange occurs between two entities:
   client and server.  The client initiates the exchange and the server
   responds.  If the key exchange completes successfully, both client
   and server will agree on a secret.  TLS supports both pre-shared key
   (PSK) and Diffie-Hellman (DH) key exchanges.  PSK is the basis for
   0-RTT; the latter provides perfect forward secrecy (PFS) when the DH
   keys are destroyed.

   After completing the TLS handshake, the client will have learned and
   authenticated an identity for the server and the server is optionally
   able to learn and authenticate an identity for the client.  TLS
   supports X.509 [RFC5280] certificate-based authentication for both
   server and client.

   The TLS key exchange is resistant to tampering by attackers and it
   produces shared secrets that cannot be controlled by either
   participating peer.

   TLS provides two basic handshake modes of interest to QUIC:

   o  A full 1-RTT handshake in which the client is able to send
      application data after one round trip and the server immediately
      responds after receiving the first handshake message from the

   o  A 0-RTT handshake in which the client uses information it has
      previously learned about the server to send application data
      immediately.  This application data can be replayed by an attacker
      so it MUST NOT carry a self-contained trigger for any non-
      idempotent action.

   A simplified TLS handshake with 0-RTT application data is shown in
   Figure 1.  Note that this omits the EndOfEarlyData message, which is
   not used in QUIC (see Section 8.3).

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       Client                                             Server

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

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

       () Indicates messages protected by early data (0-RTT) keys
       {} Indicates messages protected using handshake keys
       [] Indicates messages protected using application data
          (1-RTT) keys

                    Figure 1: TLS Handshake with 0-RTT

   Data is protected using a number of encryption levels:

   o  Initial Keys

   o  Early Data (0-RTT) Keys

   o  Handshake Keys

   o  Application Data (1-RTT) Keys

   Application data may appear only in the early data and application
   data levels.  Handshake and Alert messages may appear in any level.

   The 0-RTT handshake is only possible if the client and server have
   previously communicated.  In the 1-RTT handshake, the client is
   unable to send protected application data until it has received all
   of the handshake messages sent by the server.

3.  Protocol Overview

   QUIC [QUIC-TRANSPORT] assumes responsibility for the confidentiality
   and integrity protection of packets.  For this it uses keys derived
   from a TLS handshake [TLS13], but instead of carrying TLS records
   over QUIC (as with TCP), TLS Handshake and Alert messages are carried
   directly over the QUIC transport, which takes over the
   responsibilities of the TLS record layer, as shown below.

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   +--------------+--------------+ +-------------+
   |     TLS      |     TLS      | |    QUIC     |
   |  Handshake   |    Alerts    | | Applications|
   |              |              | |  (h3, etc.) |
   |                                             |
   |                QUIC Transport               |
   |   (streams, reliability, congestion, etc.)  |
   |                                             |
   |                                             |
   |            QUIC Packet Protection           |
   |                                             |

   QUIC also relies on TLS for authentication and negotiation of
   parameters that are critical to security and performance.

   Rather than a strict layering, these two protocols are co-dependent:
   QUIC uses the TLS handshake; TLS uses the reliability, ordered
   delivery, and record layer provided by QUIC.

   At a high level, there are two main interactions between the TLS and
   QUIC components:

   o  The TLS component sends and receives messages via the QUIC
      component, with QUIC providing a reliable stream abstraction to

   o  The TLS component provides a series of updates to the QUIC
      component, including (a) new packet protection keys to install (b)
      state changes such as handshake completion, the server
      certificate, etc.

   Figure 2 shows these interactions in more detail, with the QUIC
   packet protection being called out specially.

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   +------------+                        +------------+
   |            |<- Handshake Messages ->|            |
   |            |<---- 0-RTT Keys -------|            |
   |            |<--- Handshake Keys-----|            |
   |   QUIC     |<---- 1-RTT Keys -------|    TLS     |
   |            |<--- Handshake Done ----|            |
   +------------+                        +------------+
    |         ^
    | Protect | Protected
    v         | Packet
   |   QUIC     |
   |  Packet    |
   | Protection |

                    Figure 2: QUIC and TLS Interactions

   Unlike TLS over TCP, QUIC applications which want to send data do not
   send it through TLS "application_data" records.  Rather, they send it
   as QUIC STREAM frames which are then carried in QUIC packets.

4.  Carrying TLS Messages

   QUIC carries TLS handshake data in CRYPTO frames, each of which
   consists of a contiguous block of handshake data identified by an
   offset and length.  Those frames are packaged into QUIC packets and
   encrypted under the current TLS encryption level.  As with TLS over
   TCP, once TLS handshake data has been delivered to QUIC, it is QUIC's
   responsibility to deliver it reliably.  Each chunk of data that is
   produced by TLS is associated with the set of keys that TLS is
   currently using.  If QUIC needs to retransmit that data, it MUST use
   the same keys even if TLS has already updated to newer keys.

   One important difference between TLS records (used with TCP) and QUIC
   CRYPTO frames is that in QUIC multiple frames may appear in the same
   QUIC packet as long as they are associated with the same encryption
   level.  For instance, an implementation might bundle a Handshake
   message and an ACK for some Handshake data into the same packet.

   Some frames are prohibited in different encryption levels, others
   cannot be sent.  The rules here generalize those of TLS, in that
   frames associated with establishing the connection can usually appear
   at any encryption level, whereas those associated with transferring
   data can only appear in the 0-RTT and 1-RTT encryption levels:

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

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   o  CRYPTO and CONNECTION_CLOSE frames MAY appear in packets of any
      encryption level except 0-RTT.

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

   o  All other frame types MUST only be sent in the 0-RTT and 1-RTT

   Note that it is not possible to send the following frames in 0-RTT
   for various reasons: ACK, CRYPTO, NEW_TOKEN, PATH_RESPONSE, and

   Because packets could be reordered on the wire, QUIC uses the packet
   type to indicate which level a given packet was encrypted under, as
   shown in Table 1.  When multiple packets of different encryption
   levels need to be sent, endpoints SHOULD use coalesced packets to
   send them in the same UDP datagram.

          | 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       |
          |                     |                  |           |
          | Version Negotiation | N/A              | N/A       |
          |                     |                  |           |
          | Short Header        | 1-RTT            | 0/1-RTT   |

                 Table 1: Encryption Levels by Packet Type

   Section 17 of [QUIC-TRANSPORT] shows how packets at the various
   encryption levels fit into the handshake process.

4.1.  Interface to TLS

   As shown in Figure 2, the interface from QUIC to TLS consists of
   three primary functions:

   o  Sending and receiving handshake messages

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   o  Rekeying (both transmit and receive)

   o  Handshake state updates

   Additional functions might be needed to configure TLS.

4.1.1.  Handshake Complete

   In this document, the TLS handshake is considered complete when the
   TLS stack has reported that the handshake is complete.  This happens
   when the TLS stack has both sent a Finished message and verified the
   peer's Finished message.  Verifying the peer's Finished provides the
   endpoints with an assurance that previous handshake messages have not
   been modified.  Note that the handshake does not complete at both
   endpoints simultaneously.  Consequently, any requirement that is
   based on the completion of the handshake depends on the perspective
   of the endpoint in question.

4.1.2.  Handshake Confirmed

   In this document, the TLS handshake is considered confirmed at an
   endpoint when the following two conditions are met: the handshake is
   complete, and the endpoint has received an acknowledgment for a
   packet sent with 1-RTT keys.  This second condition can be
   implemented by recording the lowest packet number sent with 1-RTT
   keys, and the highest value of the Largest Acknowledged field in any
   received 1-RTT ACK frame: once the latter is higher than or equal to
   the former, the handshake is confirmed.

4.1.3.  Sending and Receiving Handshake Messages

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

   Before starting the handshake QUIC provides TLS with the transport
   parameters (see Section 8.2) that it wishes to carry.

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

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

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   provides handshake bytes to be sent, they are appended to the current
   flow and any packet that includes the CRYPTO frame is protected using
   keys from the corresponding encryption level.

   QUIC takes the unprotected content of TLS handshake records as the
   content of CRYPTO frames.  TLS record protection is not used by QUIC.
   QUIC assembles CRYPTO frames into QUIC packets, which are protected
   using QUIC packet protection.

   When an endpoint receives a QUIC packet containing a CRYPTO frame
   from the network, it proceeds as follows:

   o  If the packet was in the TLS receiving encryption level, sequence
      the data into the input flow as usual.  As with STREAM frames, the
      offset is used to find the proper location in the data sequence.
      If the result of this process is that new data is available, then
      it is delivered to TLS in order.

   o  If the packet is from a previously installed encryption level, it
      MUST not contain data which extends past the end of previously
      received data in that flow.  Implementations MUST treat any
      violations of this requirement as a connection error of type

   o  If the packet is from a new encryption level, it is saved for
      later processing by TLS.  Once TLS moves to receiving from this
      encryption level, saved data can be provided.  When providing data
      from any new encryption level to TLS, if there is data from a
      previous encryption level that TLS has not consumed, this MUST be
      treated as a connection error of type PROTOCOL_VIOLATION.

   Each time that TLS is provided with new data, new handshake bytes are
   requested from TLS.  TLS might not provide any bytes if the handshake
   messages it has received are incomplete or it has no data to send.

   Once the TLS handshake is complete, this is indicated to QUIC along
   with any final handshake bytes that TLS needs to send.  TLS also
   provides QUIC with the transport parameters that the peer advertised
   during the handshake.

   Once the handshake is complete, TLS becomes passive.  TLS can still
   receive data from its peer and respond in kind, but it will not need
   to send more data unless specifically requested - either by an
   application or QUIC.  One reason to send data is that the server
   might wish to provide additional or updated session tickets to a

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   When the handshake is complete, QUIC only needs to provide TLS with
   any data that arrives in CRYPTO streams.  In the same way that is
   done during the handshake, new data is requested from TLS after
   providing received data.

4.1.4.  Encryption Level Changes

   As keys for new encryption levels become available, TLS provides QUIC
   with those keys.  Separately, as TLS starts using keys at a given
   encryption level, TLS indicates to QUIC that it is now reading or
   writing with keys at that encryption level.  These events are not
   asynchronous; they always occur immediately after TLS is provided
   with new handshake bytes, or after TLS produces handshake bytes.

   TLS provides QUIC with three items as a new encryption level becomes

   o  A secret

   o  An Authenticated Encryption with Associated Data (AEAD) function

   o  A Key Derivation Function (KDF)

   These values are based on the values that TLS negotiates and are used
   by QUIC to generate packet and header protection keys (see Section 5
   and Section 5.4).

   If 0-RTT is possible, it is ready after the client sends a TLS
   ClientHello message or the server receives that message.  After
   providing a QUIC client with the first handshake bytes, the TLS stack
   might signal the change to 0-RTT keys.  On the server, after
   receiving handshake bytes that contain a ClientHello message, a TLS
   server might signal that 0-RTT keys are available.

   Although TLS only uses one encryption level at a time, QUIC may use
   more than one level.  For instance, after sending its Finished
   message (using a CRYPTO frame at the Handshake encryption level) an
   endpoint can send STREAM data (in 1-RTT encryption).  If the Finished
   message is lost, the endpoint uses the Handshake encryption level to
   retransmit the lost message.  Reordering or loss of packets can mean
   that QUIC will need to handle packets at multiple encryption levels.
   During the handshake, this means potentially handling packets at
   higher and lower encryption levels than the current encryption level
   used by TLS.

   In particular, server implementations need to be able to read packets
   at the Handshake encryption level at the same time as the 0-RTT
   encryption level.  A client could interleave ACK frames that are

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   protected with Handshake keys with 0-RTT data and the server needs to
   process those acknowledgments in order to detect lost Handshake

4.1.5.  TLS Interface Summary

   Figure 3 summarizes the exchange between QUIC and TLS for both client
   and server.  Each arrow is tagged with the encryption level used for
   that transmission.

   Client                                                    Server

   Get Handshake
                        Initial ------------->
   Install tx 0-RTT Keys
                        0-RTT --------------->
                                                 Handshake Received
                                                      Get Handshake
                        <------------- Initial
                                              Install rx 0-RTT keys
                                             Install Handshake keys
                                                      Get Handshake
                        <----------- Handshake
                                              Install tx 1-RTT keys
                        <--------------- 1-RTT
   Handshake Received
   Install tx Handshake keys
   Handshake Received
   Get Handshake
   Handshake Complete
                        Handshake ----------->
   Install 1-RTT keys
                        1-RTT --------------->
                                                 Handshake Received
                                              Install rx 1-RTT keys
                                                 Handshake Complete
                                                      Get Handshake
                        <--------------- 1-RTT
   Handshake Received

            Figure 3: Interaction Summary between QUIC and TLS

4.2.  TLS Version

   This document describes how TLS 1.3 [TLS13] is used with QUIC.

   In practice, the TLS handshake will negotiate a version of TLS to
   use.  This could result in a newer version of TLS than 1.3 being

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   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.

4.3.  ClientHello Size

   QUIC requires that the first Initial packet from a client contain an
   entire cryptographic handshake message, which for TLS is the
   ClientHello.  Though a packet larger than 1200 bytes might be
   supported by the path, a client improves the likelihood that a packet
   is accepted if it ensures that the first ClientHello message is small
   enough to stay within this limit.

   QUIC packet and framing add at least 36 bytes of overhead to the
   ClientHello message.  That overhead increases if the client chooses a
   connection ID without zero length.  Overheads also do not include the
   token or a connection ID longer than 8 bytes, both of which might be
   required if a server sends a Retry packet.

   A typical TLS ClientHello can easily fit into a 1200 byte packet.
   However, in addition to the overheads added by QUIC, there are
   several variables that could cause this limit to be exceeded.  Large
   session tickets, multiple or large key shares, and long lists of
   supported ciphers, signature algorithms, versions, QUIC transport
   parameters, and other negotiable parameters and extensions could
   cause this message to grow.

   For servers, in addition to connection IDs and tokens, the size of
   TLS session tickets can have an effect on a client's ability to
   connect.  Minimizing the size of these values increases the
   probability that they can be successfully used by a client.

   A client is not required to fit the ClientHello that it sends in
   response to a HelloRetryRequest message into a single UDP datagram.

   The TLS implementation does not need to ensure that the ClientHello
   is sufficiently large.  QUIC PADDING frames are added to increase the
   size of the packet as necessary.

4.4.  Peer Authentication

   The requirements for authentication depend on the application
   protocol that is in use.  TLS provides server authentication and
   permits the server to request client authentication.

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   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 "early_data" extension with a
   max_early_data_size of 0xffffffff; the amount of data which the
   client can send in 0-RTT is controlled by the "initial_max_data"
   transport parameter supplied by the server.  A client MUST treat
   receipt of a NewSessionTicket that contains an "early_data" extension
   with any other value as a connection error of type

4.6.  Rejecting 0-RTT

   A server rejects 0-RTT by rejecting 0-RTT at the TLS layer.  This
   also prevents QUIC from sending 0-RTT data.  A server will always
   reject 0-RTT if it sends a TLS HelloRetryRequest.

   When 0-RTT is rejected, all connection characteristics that the
   client assumed might be incorrect.  This includes the choice of
   application protocol, transport parameters, and any application
   configuration.  The client therefore MUST reset the state of all
   streams, including application state bound to those streams.

   A client MAY attempt to send 0-RTT again if it receives a Retry or
   Version Negotiation packet.  These packets do not signify rejection
   of 0-RTT.

4.7.  HelloRetryRequest

   In TLS over TCP, the HelloRetryRequest feature (see Section 4.1.4 of
   [TLS13]) can be used to correct a client's incorrect KeyShare
   extension as well as for a stateless round-trip check.  From the
   perspective of QUIC, this just looks like additional messages carried
   in the Initial encryption level.  Although it is in principle
   possible to use this feature for address verification in QUIC, QUIC

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   implementations SHOULD instead use the Retry feature (see Section 8.1
   of [QUIC-TRANSPORT]).  HelloRetryRequest is still used to request key

4.8.  TLS Errors

   If TLS experiences an error, it generates an appropriate alert as
   defined in Section 6 of [TLS13].

   A TLS alert is turned into a QUIC connection error by converting the
   one-byte alert description into a QUIC error code.  The alert
   description is added to 0x100 to produce a QUIC error code from the
   range reserved for CRYPTO_ERROR.  The resulting value is sent in a

   The alert level of all TLS alerts is "fatal"; a TLS stack MUST NOT
   generate alerts at the "warning" level.

4.9.  Discarding Unused Keys

   After QUIC moves to a new encryption level, packet protection keys
   for previous encryption levels can be discarded.  This occurs several
   times during the handshake, as well as when keys are updated; see
   Section 6.

   Packet protection keys are not discarded immediately when new keys
   are available.  If packets from a lower encryption level contain
   CRYPTO frames, frames that retransmit that data MUST be sent at the
   same encryption level.  Similarly, an endpoint generates
   acknowledgements for packets at the same encryption level as the
   packet being acknowledged.  Thus, it is possible that keys for a
   lower encryption level are needed for a short time after keys for a
   newer encryption level are available.

   An endpoint cannot discard keys for a given encryption level unless
   it has both received and acknowledged all CRYPTO frames for that
   encryption level and when all CRYPTO frames for that encryption level
   have been acknowledged by its peer.  However, this does not guarantee
   that no further packets will need to be received or sent at that
   encryption level because a peer might not have received all the
   acknowledgements necessary to reach the same state.

   Though an endpoint might retain older keys, new data MUST be sent at
   the highest currently-available encryption level.  Only ACK frames
   and retransmissions of data in CRYPTO frames are sent at a previous
   encryption level.  These packets MAY also include PADDING frames.

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4.9.1.  Discarding Initial Keys

   Packets protected with Initial secrets (Section 5.2) are not
   authenticated, meaning that an attacker could spoof packets with the
   intent to disrupt a connection.  To limit these attacks, Initial
   packet protection keys can be discarded more aggressively than other

   The successful use of Handshake packets indicates that no more
   Initial packets need to be exchanged, as these keys can only be
   produced after receiving all CRYPTO frames from Initial packets.
   Thus, a client MUST discard Initial keys when it first sends a
   Handshake packet and a server MUST discard Initial keys when it first
   successfully processes a Handshake packet.  Endpoints MUST NOT send
   Initial packets after this point.

   This results in abandoning loss recovery state for the Initial
   encryption level and ignoring any outstanding Initial packets.

4.9.2.  Discarding Handshake Keys

   An endpoint MUST NOT discard its handshake keys until the TLS
   handshake is confirmed (Section 4.1.2).  An endpoint SHOULD discard
   its handshake keys as soon as it has confirmed the handshake.  Most
   application protocols will send data after the handshake, resulting
   in acknowledgements that allow both endpoints to discard their
   handshake keys promptly.  Endpoints that do not have reason to send
   immediately after completing the handshake MAY send ack-eliciting
   frames, such as PING, which will cause the handshake to be confirmed
   when they are acknowledged.

4.9.3.  Discarding 0-RTT Keys

   0-RTT and 1-RTT packets share the same packet number space, and
   clients do not send 0-RTT packets after sending a 1-RTT packet
   (Section 5.6).

   Therefore, a client SHOULD discard 0-RTT keys as soon as it installs
   1-RTT keys, since they have no use after that moment.

   Additionally, a server MAY discard 0-RTT keys as soon as it receives
   a 1-RTT packet.  However, due to packet reordering, a 0-RTT packet
   could arrive after a 1-RTT packet.  Servers MAY temporarily retain
   0-RTT keys to allow decrypting reordered packets without requiring
   their contents to be retransmitted with 1-RTT keys.  After receiving
   a 1-RTT packet, servers MUST discard 0-RTT keys within a short time;
   the RECOMMENDED time period is three times the Probe Timeout (PTO,
   see [QUIC-RECOVERY]).  A server MAY discard 0-RTT keys earlier if it

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   determines that it has received all 0-RTT packets, which can be done
   by keeping track of missing packet numbers.

5.  Packet Protection

   As with TLS over TCP, QUIC protects packets with keys derived from
   the TLS handshake, using the AEAD algorithm negotiated by TLS.

5.1.  Packet Protection Keys

   QUIC derives packet protection keys in the same way that TLS derives
   record protection keys.

   Each encryption level has separate secret values for protection of
   packets sent in each direction.  These traffic secrets are derived by
   TLS (see Section 7.1 of [TLS13]) and are used by QUIC for all
   encryption levels except the Initial encryption level.  The secrets
   for the Initial encryption level are computed based on the client's
   initial Destination Connection ID, as described in Section 5.2.

   The keys used for packet protection are computed from the TLS secrets
   using the KDF provided by TLS.  In TLS 1.3, the HKDF-Expand-Label
   function described in Section 7.1 of [TLS13] is used, using the hash
   function from the negotiated cipher suite.  Other versions of TLS
   MUST provide a similar function in order to be used with QUIC.

   The current encryption level secret and the label "quic key" are
   input to the KDF to produce the AEAD key; the label "quic iv" is used
   to derive the IV; see Section 5.3.  The header protection key uses
   the "quic hp" label; see Section 5.4.  Using these labels provides
   key separation between QUIC and TLS; see Section 9.5.

   The KDF used for initial secrets is always the HKDF-Expand-Label
   function from TLS 1.3 (see Section 5.2).

5.2.  Initial Secrets

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

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   initial_salt = 0x7fbcdb0e7c66bbe9193a96cd21519ebd7a02644a
   initial_secret = HKDF-Extract(initial_salt,

   client_initial_secret = HKDF-Expand-Label(initial_secret,
                                             "client in", "",
   server_initial_secret = HKDF-Expand-Label(initial_secret,
                                             "server in", "",

   The hash function for HKDF when deriving initial secrets and keys is
   SHA-256 [SHA].

   The connection ID used with HKDF-Expand-Label is the Destination
   Connection ID in the Initial packet sent by the client.  This will be
   a randomly-selected value unless the client creates the Initial
   packet after receiving a Retry packet, where the Destination
   Connection ID is selected by the server.

   The value of initial_salt is a 20 byte sequence shown in the figure
   in hexadecimal notation.  Future versions of QUIC SHOULD generate a
   new salt value, thus ensuring that the keys are different for each
   version of QUIC.  This prevents a middlebox that only recognizes one
   version of QUIC from seeing or modifying the contents of packets from
   future versions.

   The HKDF-Expand-Label function defined in TLS 1.3 MUST be used for
   Initial packets even where the TLS versions offered do not include
   TLS 1.3.

   Appendix A contains test vectors for the initial packet encryption.

   Note:  The Destination Connection ID is of arbitrary length, and it
      could be zero length if the server sends a Retry packet with a
      zero-length Source Connection ID field.  In this case, the Initial
      keys provide no assurance to the client that the server received
      its packet; the client has to rely on the exchange that included
      the Retry packet for that property.

5.3.  AEAD Usage

   The Authentication Encryption with Associated Data (AEAD) [AEAD]
   function used for QUIC packet protection is the AEAD that is
   negotiated for use with the TLS connection.  For example, if TLS is
   using the TLS_AES_128_GCM_SHA256, the AEAD_AES_128_GCM function is

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   Packets are protected prior to applying header protection
   (Section 5.4).  The unprotected packet header is part of the
   associated data (A).  When removing packet protection, an endpoint
   first removes the header protection.

   All QUIC packets other than Version Negotiation and Retry packets are
   protected with an AEAD algorithm [AEAD].  Prior to establishing a
   shared secret, packets are protected with AEAD_AES_128_GCM and a key
   derived from the Destination Connection ID in the client's first
   Initial packet (see Section 5.2).  This provides protection against
   off-path attackers and robustness against QUIC version unaware
   middleboxes, but not against on-path attackers.

   QUIC can use any of the ciphersuites defined in [TLS13] with the
   exception of TLS_AES_128_CCM_8_SHA256.  A ciphersuite MUST NOT be
   negotiated unless a header protection scheme is defined for the
   ciphersuite.  This document defines a header protection scheme for
   all ciphersuites defined in [TLS13] aside from
   TLS_AES_128_CCM_8_SHA256.  These ciphersuites have a 16-byte
   authentication tag and produce an output 16 bytes larger than their

   Note:  An endpoint MUST NOT reject a ClientHello that offers a
      ciphersuite that it does not support, or it would be impossible to
      deploy a new ciphersuite.  This also applies to

   The key and IV for the packet are computed as described in
   Section 5.1.  The nonce, N, is formed by combining the packet
   protection IV with the packet number.  The 62 bits of the
   reconstructed QUIC packet number in network byte order are left-
   padded with zeros to the size of the IV.  The exclusive OR of the
   padded packet number and the IV forms the AEAD nonce.

   The associated data, A, for the AEAD is the contents of the QUIC
   header, starting from the flags byte in either the short or long
   header, up to and including the unprotected packet number.

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

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

   Some AEAD functions have limits for how many packets can be encrypted
   under the same key and IV (see for example [AEBounds]).  This might
   be lower than the packet number limit.  An endpoint MUST initiate a
   key update (Section 6) prior to exceeding any limit set for the AEAD
   that is in use.

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5.4.  Header Protection

   Parts of QUIC packet headers, in particular the Packet Number field,
   are protected using a key that is derived separate to the packet
   protection key and IV.  The key derived using the "quic hp" label is
   used to provide confidentiality protection for those fields that are
   not exposed to on-path elements.

   This protection applies to the least-significant bits of the first
   byte, plus the Packet Number field.  The four least-significant bits
   of the first byte are protected for packets with long headers; the
   five least significant bits of the first byte are protected for
   packets with short headers.  For both header forms, this covers the
   reserved bits and the Packet Number Length field; the Key Phase bit
   is also protected for packets with a short header.

   The same header protection key is used for the duration of the
   connection, with the value not changing after a key update (see
   Section 6).  This allows header protection to be used to protect the
   key phase.

   This process does not apply to Retry or Version Negotiation packets,
   which do not contain a protected payload or any of the fields that
   are protected by this process.

5.4.1.  Header Protection Application

   Header protection is applied after packet protection is applied (see
   Section 5.3).  The ciphertext of the packet is sampled and used as
   input to an encryption algorithm.  The algorithm used depends on the
   negotiated AEAD.

   The output of this algorithm is a 5 byte mask which is applied to the
   protected header fields using exclusive OR.  The least significant
   bits of the first byte of the packet are masked by the least
   significant bits of the first mask byte, and the packet number is
   masked with the remaining bytes.  Any unused bytes of mask that might
   result from a shorter packet number encoding are unused.

   Figure 4 shows a sample algorithm for applying header protection.
   Removing header protection only differs in the order in which the
   packet number length (pn_length) is determined.

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   mask = header_protection(hp_key, sample)

   pn_length = (packet[0] & 0x03) + 1
   if (packet[0] & 0x80) == 0x80:
      # Long header: 4 bits masked
      packet[0] ^= mask[0] & 0x0f
      # Short header: 5 bits masked
      packet[0] ^= mask[0] & 0x1f

   # pn_offset is the start of the Packet Number field.
   packet[pn_offset:pn_offset+pn_length] ^= mask[1:1+pn_length]

                  Figure 4: Header Protection Pseudocode

   Figure 5 shows the protected fields of long and short headers marked
   with an E.  Figure 5 also shows the sampled fields.

   Long Header:
   |1|1|T T|E E E E|
   |                    Version -> Length Fields                 ...

   Short Header:
   |0|1|S|E E E E E|
   |               Destination Connection ID (0/32..144)         ...

   Common Fields:
   |E E E E E E E E E  Packet Number (8/16/24/32) E E E E E E E E...
   |   [Protected Payload (8/16/24)]             ...
   |             Sampled part of Protected Payload (128)         ...
   |                 Protected Payload Remainder (*)             ...

             Figure 5: Header Protection and Ciphertext Sample

   Before a TLS ciphersuite can be used with QUIC, a header protection
   algorithm MUST be specified for the AEAD used with that ciphersuite.
   This document defines algorithms for AEAD_AES_128_GCM,

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   AEAD_AES_128_CCM, AEAD_AES_256_GCM (all AES AEADs are defined in
   [AEAD]), and AEAD_CHACHA20_POLY1305 [CHACHA].  Prior to TLS selecting
   a ciphersuite, AES header protection is used (Section 5.4.3),
   matching the AEAD_AES_128_GCM packet protection.

5.4.2.  Header Protection Sample

   The header protection algorithm uses both the header protection key
   and a sample of the ciphertext from the packet Payload field.

   The same number of bytes are always sampled, but an allowance needs
   to be made for the endpoint removing protection, which will not know
   the length of the Packet Number field.  In sampling the packet
   ciphertext, the Packet Number field is assumed to be 4 bytes long
   (its maximum possible encoded length).

   An endpoint MUST discard packets that are not long enough to contain
   a complete sample.

   To ensure that sufficient data is available for sampling, packets are
   padded so that the combined lengths of the encoded packet number and
   protected payload is at least 4 bytes longer than the sample required
   for header protection.  The ciphersuites defined in [TLS13] - other
   than TLS_AES_128_CCM_8_SHA256, for which a header protection scheme
   is not defined in this document - have 16-byte expansions and 16-byte
   header protection samples.  This results in needing at least 3 bytes
   of frames in the unprotected payload if the packet number is encoded
   on a single byte, or 2 bytes of frames for a 2-byte packet number

   The sampled ciphertext for a packet with a short header can be
   determined by the following pseudocode:

   sample_offset = 1 + len(connection_id) + 4

   sample = packet[sample_offset..sample_offset+sample_length]

   For example, for a packet with a short header, an 8 byte connection
   ID, and protected with AEAD_AES_128_GCM, the sample takes bytes 13 to
   28 inclusive (using zero-based indexing).

   A packet with a long header is sampled in the same way, noting that
   multiple QUIC packets might be included in the same UDP datagram and
   that each one is handled separately.

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   sample_offset = 6 + len(destination_connection_id) +
                       len(source_connection_id) +
                       len(payload_length) + 4
   if packet_type == Initial:
       sample_offset += len(token_length) +

   sample = packet[sample_offset..sample_offset+sample_length]

5.4.3.  AES-Based Header Protection

   This section defines the packet protection algorithm for
   AEAD_AES_128_GCM, AEAD_AES_128_CCM, and AEAD_AES_256_GCM.
   AEAD_AES_128_GCM and AEAD_AES_128_CCM use 128-bit AES [AES] in
   electronic code-book (ECB) mode.  AEAD_AES_256_GCM uses 256-bit AES
   in ECB mode.

   This algorithm samples 16 bytes from the packet ciphertext.  This
   value is used as the input to AES-ECB.  In pseudocode:

   mask = AES-ECB(hp_key, sample)

5.4.4.  ChaCha20-Based Header Protection

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

   The first 4 bytes of the sampled ciphertext are interpreted as a
   32-bit number in little-endian order and are used as the block count.
   The remaining 12 bytes are interpreted as three concatenated 32-bit
   numbers in little-endian order and used as the nonce.

   The encryption mask is produced by invoking ChaCha20 to protect 5
   zero bytes.  In pseudocode:

   counter = DecodeLE(sample[0..3])
   nonce = DecodeLE(sample[4..7], sample[8..11], sample[12..15])
   mask = ChaCha20(hp_key, counter, nonce, {0,0,0,0,0})

5.5.  Receiving Protected Packets

   Once an endpoint successfully receives a packet with a given packet
   number, it MUST discard all packets in the same packet number space
   with higher packet numbers if they cannot be successfully unprotected
   with either the same key, or - if there is a key update - the next
   packet protection key (see Section 6).  Similarly, a packet that

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   appears to trigger a key update, but cannot be unprotected
   successfully MUST be discarded.

   Failure to unprotect a packet does not necessarily indicate the
   existence of a protocol error in a peer or an attack.  The truncated
   packet number encoding used in QUIC can cause packet numbers to be
   decoded incorrectly if they are delayed significantly.

5.6.  Use of 0-RTT Keys

   If 0-RTT keys are available (see Section 4.5), the lack of replay
   protection means that restrictions on their use are necessary to
   avoid replay attacks on the protocol.

   A client MUST only use 0-RTT keys to protect data that is idempotent.
   A client MAY wish to apply additional restrictions on what data it
   sends prior to the completion of the TLS handshake.  A client
   otherwise treats 0-RTT keys as equivalent to 1-RTT keys, except that
   it MUST NOT send ACKs with 0-RTT keys.

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

   A server MUST NOT use 0-RTT keys to protect packets; it uses 1-RTT
   keys to protect acknowledgements of 0-RTT packets.  A client MUST NOT
   attempt to decrypt 0-RTT packets it receives and instead MUST discard

   Once a client has installed 1-RTT keys, it MUST NOT send any more
   0-RTT packets.

   Note:  0-RTT data can be acknowledged by the server as it receives
      it, but any packets containing acknowledgments of 0-RTT data
      cannot have packet protection removed by the client until the TLS
      handshake is complete.  The 1-RTT keys necessary to remove packet
      protection cannot be derived until the client receives all server
      handshake messages.

5.7.  Receiving Out-of-Order Protected Frames

   Due to reordering and loss, protected packets might be received by an
   endpoint before the final TLS handshake messages are received.  A
   client will be unable to decrypt 1-RTT packets from the server,
   whereas a server will be able to decrypt 1-RTT packets from the

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   Even though 1-RTT keys are available to a server after receiving the
   first handshake messages from a client, it is missing assurances on
   the client state:

   o  The client is not authenticated, unless the server has chosen to
      use a pre-shared key and validated the client's pre-shared key
      binder; see Section 4.2.11 of [TLS13].

   o  The client has not demonstrated liveness, unless a RETRY packet
      was used.

   o  Any received 0-RTT data that the server responds to might be due
      to a replay attack.

   Therefore, the server's use of 1-RTT keys is limited before the
   handshake is complete.  A server MUST NOT process data from incoming
   1-RTT protected packets before the TLS handshake is complete.
   Because sending acknowledgments indicates that all frames in a packet
   have been processed, a server cannot send acknowledgments for 1-RTT
   packets until the TLS handshake is complete.  Received packets
   protected with 1-RTT keys MAY be stored and later decrypted and used
   once the handshake is complete.

   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 its 1-RTT packets coalesced with a handshake
   packet containing a copy of the CRYPTO frame that carries the
   Finished message, until one of the handshake packets is acknowledged.
   This enables immediate server processing for those packets.

   A server could receive packets protected with 0-RTT keys prior to
   receiving a TLS ClientHello.  The server MAY retain these packets for
   later decryption in anticipation of receiving a ClientHello.

6.  Key Update

   Once the handshake is confirmed, it is possible to update the keys.
   The KEY_PHASE bit in the short header is used to indicate whether key
   updates have occurred.  The KEY_PHASE bit is initially set to 0 and
   then inverted with each key update.

   The KEY_PHASE bit allows a recipient to detect a change in keying
   material without necessarily needing to receive the first packet that
   triggered the change.  An endpoint that notices a changed KEY_PHASE
   bit can update keys and decrypt the packet that contains the changed

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   This mechanism replaces the TLS KeyUpdate message.  Endpoints MUST
   NOT send a TLS KeyUpdate message.  Endpoints MUST treat the receipt
   of a TLS KeyUpdate message as a connection error of type 0x10a,
   equivalent to a fatal TLS alert of unexpected_message (see
   Section 4.8).

   An endpoint MUST NOT initiate the first key update until the
   handshake is confirmed (Section 4.1.2).  An endpoint MUST NOT
   initiate a subsequent key update until it has received an
   acknowledgment for a packet sent at the current KEY_PHASE.  This can
   be implemented by tracking the lowest packet number sent with each
   KEY_PHASE, and the highest acknowledged packet number in the 1-RTT
   space: once the latter is higher than or equal to the former, another
   key update can be initiated.

   Endpoints MAY limit the number of keys they retain to two sets for
   removing packet protection and one set for protecting packets.  Older
   keys can be discarded.  Updating keys multiple times rapidly can
   cause packets to be effectively lost if packets are significantly
   reordered.  Therefore, an endpoint SHOULD NOT initiate a key update
   for some time after it has last updated keys; the RECOMMENDED time
   period is three times the PTO.  This avoids valid reordered packets
   being dropped by the peer as a result of the peer discarding older

   A receiving endpoint detects an update when the KEY_PHASE bit does
   not match what it is expecting.  It creates a new secret (see
   Section 7.2 of [TLS13]) and the corresponding read key and IV using
   the KDF function provided by TLS.  The header protection key is not

   If the packet can be decrypted and authenticated using the updated
   key and IV, then the keys the endpoint uses for packet protection are
   also updated.  The next packet sent by the endpoint MUST then use the
   new keys.  Once an endpoint has sent a packet encrypted with a given
   key phase, it MUST NOT send a packet encrypted with an older key

   An endpoint does not always need to send packets when it detects that
   its peer has updated keys.  The next packet that it sends will simply
   use the new keys.  If an endpoint detects a second update before it
   has sent any packets with updated keys, it indicates that its peer
   has updated keys twice without awaiting a reciprocal update.  An
   endpoint MUST treat consecutive key updates as a fatal error and
   abort the connection.

   An endpoint SHOULD retain old keys for a period of no more than three
   times the PTO.  After this period, old keys and their corresponding

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   secrets SHOULD be discarded.  Retaining keys allow endpoints to
   process packets that were sent with old keys and delayed in the
   network.  Packets with higher packet numbers always use the updated
   keys and MUST NOT be decrypted with old keys.

   This ensures that once the handshake is complete, packets with the
   same KEY_PHASE will have the same packet protection keys, unless
   there are multiple key updates in a short time frame succession and
   significant packet reordering.

      Initiating Peer                    Responding Peer

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

                           Figure 6: Key Update

   A packet that triggers a key update could arrive after the receiving
   endpoint successfully processed a packet with a higher packet number.
   This is only possible if there is a key compromise and an attack, or
   if the peer is incorrectly reverting to use of old keys.  Because the
   latter cannot be differentiated from an attack, an endpoint MUST
   immediately terminate the connection if it detects this condition.

   In deciding when to update keys, endpoints MUST NOT exceed the limits
   for use of specific keys, as described in Section 5.5 of [TLS13].

7.  Security of Initial Messages

   Initial packets are not protected with a secret key, so they are
   subject to potential tampering by an attacker.  QUIC provides
   protection against attackers that cannot read packets, but does not
   attempt to provide additional protection against attacks where the
   attacker can observe and inject packets.  Some forms of tampering -
   such as modifying the TLS messages themselves - are detectable, but
   some - such as modifying ACKs - are not.

   For example, an attacker could inject a packet containing an ACK
   frame that makes it appear that a packet had not been received or to
   create a false impression of the state of the connection (e.g., by
   modifying the ACK Delay).  Note that such a packet could cause a
   legitimate packet to be dropped as a duplicate.  Implementations

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   SHOULD use caution in relying on any data which is contained in
   Initial packets that is not otherwise authenticated.

   It is also possible for the attacker to tamper with data that is
   carried in Handshake packets, but because that tampering requires
   modifying TLS handshake messages, that tampering will cause the TLS
   handshake to fail.

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 Negotiation

   QUIC requires that the cryptographic handshake provide authenticated
   protocol negotiation.  TLS uses Application Layer Protocol
   Negotiation (ALPN) [RFC7301] to select an application protocol.
   Unless another mechanism is used for agreeing on an application
   protocol, endpoints MUST use ALPN for this purpose.  When using ALPN,
   endpoints MUST immediately close a connection (see Section 10.3 in
   [QUIC-TRANSPORT]) if an application protocol is not negotiated with a
   no_application_protocol TLS alert (QUIC error code 0x178, see
   Section 4.8).  While [RFC7301] only specifies that servers use this
   alert, QUIC clients MUST also use it to terminate a connection when
   ALPN negotiation fails.

   An application-layer protocol MAY restrict the QUIC versions that it
   can operate over.  Servers MUST select an application protocol
   compatible with the QUIC version that the client has selected.  If
   the server cannot select a compatible combination of application
   protocol and QUIC version, it MUST abort the connection.  A client
   MUST abort a connection if the server picks an incompatible
   combination of QUIC version and ALPN identifier.

8.2.  QUIC Transport Parameters Extension

   QUIC transport parameters are carried in a TLS extension.  Different
   versions of QUIC might define a different format for this struct.

   Including transport parameters in the TLS handshake provides
   integrity protection for these values.

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      enum {
         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 struct when the version of QUIC defined in
   [QUIC-TRANSPORT] is used.

   The quic_transport_parameters extension is carried in the ClientHello
   and the EncryptedExtensions messages during the handshake.  Endpoints
   MUST send the quic_transport_parameters extension; endpoints that
   receive ClientHello or EncryptedExtensions messages without the
   quic_transport_parameters extension MUST close the connection with an
   error of type 0x16d (equivalent to a fatal TLS missing_extension
   alert, see Section 4.8).

   While the transport parameters are technically available prior to the
   completion of the handshake, they cannot be fully trusted until the
   handshake completes, and reliance on them should be minimized.
   However, any tampering with the parameters will cause the handshake
   to fail.

   Endpoints MUST NOT send this extension in a TLS connection that does
   not use QUIC (such as the use of TLS with TCP defined in [TLS13]).  A
   fatal unsupported_extension alert MUST be sent by an implementation
   that supports this extension if the extension is received when the
   transport is not QUIC.

8.3.  Removing the EndOfEarlyData Message

   The TLS EndOfEarlyData message is not used with QUIC.  QUIC does not
   rely on this message to mark the end of 0-RTT data or to signal the
   change to Handshake keys.

   Clients MUST NOT send the EndOfEarlyData message.  A server MUST
   treat receipt of a CRYPTO frame in a 0-RTT packet as a connection
   error of type PROTOCOL_VIOLATION.

   As a result, EndOfEarlyData does not appear in the TLS handshake

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.

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

9.1.  Replay Attacks with 0-RTT

   As described in Section 8 of [TLS13], use of TLS early data comes
   with an exposure to replay attack.  The use of 0-RTT in QUIC is
   similarly vulnerable to replay attack.

   Endpoints MUST implement and use the replay protections described in
   [TLS13], however it is recognized that these protections are
   imperfect.  Therefore, additional consideration of the risk of replay
   is needed.

   QUIC is not vulnerable to replay attack, except via the application
   protocol information it might carry.  The management of QUIC protocol
   state based on the frame types defined in [QUIC-TRANSPORT] is not
   vulnerable to replay.  Processing of QUIC frames is idempotent and
   cannot result in invalid connection states if frames are replayed,
   reordered or lost.  QUIC connections do not produce effects that last
   beyond the lifetime of the connection, except for those produced by
   the application protocol that QUIC serves.

   Note:  TLS session tickets and address validation tokens are used to
      carry QUIC configuration information between connections.  These
      MUST NOT be used to carry application semantics.  The potential
      for reuse of these tokens means that they require stronger
      protections against replay.

   A server that accepts 0-RTT on a connection incurs a higher cost than
   accepting a connection without 0-RTT.  This includes higher
   processing and computation costs.  Servers need to consider the
   probability of replay and all associated costs when accepting 0-RTT.

   Ultimately, the responsibility for managing the risks of replay
   attacks with 0-RTT lies with an application protocol.  An application
   protocol that uses QUIC MUST describe how the protocol uses 0-RTT and
   the measures that are employed to protect against replay attack.  An
   analysis of replay risk needs to consider all QUIC protocol features
   that carry application semantics.

   Disabling 0-RTT entirely is the most effective defense against replay

   QUIC extensions MUST describe how replay attacks affect their
   operation, or prohibit their use in 0-RTT.  Application protocols
   MUST either prohibit the use of extensions that carry application
   semantics in 0-RTT or provide replay mitigation strategies.

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9.2.  Packet Reflection Attack Mitigation

   A small ClientHello that results in a large block of handshake
   messages from a server can be used in packet reflection attacks to
   amplify the traffic generated by an attacker.

   QUIC includes three defenses against this attack.  First, the packet
   containing a ClientHello MUST be padded to a minimum size.  Second,
   if responding to an unverified source address, the server is
   forbidden to send more than three UDP datagrams in its first flight
   (see Section 8.1 of [QUIC-TRANSPORT]).  Finally, because
   acknowledgements of Handshake packets are authenticated, a blind
   attacker cannot forge them.  Put together, these defenses limit the
   level of amplification.

9.3.  Peer Denial of Service

   QUIC, TLS, and HTTP/2 all contain messages that have legitimate uses
   in some contexts, but that can be abused to cause a peer to expend
   processing resources without having any observable impact on the
   state of the connection.  If processing is disproportionately large
   in comparison to the observable effects on bandwidth or state, then
   this could allow a malicious peer to exhaust processing capacity
   without consequence.

   While there are legitimate uses for some redundant packets,
   implementations SHOULD track redundant packets and treat excessive
   volumes of any non-productive packets as indicative of an attack.

9.4.  Header Protection Analysis

   Header protection relies on the packet protection AEAD being a
   pseudorandom function (PRF), which is not a property that AEAD
   algorithms guarantee.  Therefore, no strong assurances about the
   general security of this mechanism can be shown in the general case.
   The AEAD algorithms described in this document are assumed to be

   The header protection algorithms defined in this document take the

   protected_field = field XOR PRF(hp_key, sample)

   This construction is secure against chosen plaintext attacks (IND-
   CPA) [IMC].

   Use of the same key and ciphertext sample more than once risks
   compromising header protection.  Protecting two different headers

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   with the same key and ciphertext sample reveals the exclusive OR of
   the protected fields.  Assuming that the AEAD acts as a PRF, if L
   bits are sampled, the odds of two ciphertext samples being identical
   approach 2^(-L/2), that is, the birthday bound.  For the algorithms
   described in this document, that probability is one in 2^64.

   Note:  In some cases, inputs shorter than the full size required by
      the packet protection algorithm might be used.

   To prevent an attacker from modifying packet headers, the header is
   transitively authenticated using packet protection; the entire packet
   header is part of the authenticated additional data.  Protected
   fields that are falsified or modified can only be detected once the
   packet protection is removed.

   An attacker could guess values for packet numbers and have an
   endpoint confirm guesses through timing side channels.  Similarly,
   guesses for the packet number length can be trialed and exposed.  If
   the recipient of a packet discards packets with duplicate packet
   numbers without attempting to remove packet protection they could
   reveal through timing side-channels that the packet number matches a
   received packet.  For authentication to be free from side-channels,
   the entire process of header protection removal, packet number
   recovery, and packet protection removal MUST be applied together
   without timing and other side-channels.

   For the sending of packets, construction and protection of packet
   payloads and packet numbers MUST be free from side-channels that
   would reveal the packet number or its encoded size.

9.5.  Key Diversity

   In using TLS, the central key schedule of TLS is used.  As a result
   of the TLS handshake messages being integrated into the calculation
   of secrets, the inclusion of the QUIC transport parameters extension
   ensures that handshake and 1-RTT keys are not the same as those that
   might be produced by a server running TLS over TCP.  To avoid the
   possibility of cross-protocol key synchronization, additional
   measures are provided to improve key separation.

   The QUIC packet protection keys and IVs are derived using a different
   label than the equivalent keys in TLS.

   To preserve this separation, a new version of QUIC SHOULD define new
   labels for key derivation for packet protection key and IV, plus the
   header protection keys.  This version of QUIC uses the string "quic".
   Other versions can use a version-specific label in place of that

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   The initial secrets use a key that is specific to the negotiated QUIC
   version.  New QUIC versions SHOULD define a new salt value used in
   calculating initial secrets.

10.  IANA Considerations

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

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

11.  References

11.1.  Normative References

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

   [AES]      "Advanced encryption standard (AES)", National Institute
              of Standards and Technology report,
              DOI 10.6028/nist.fips.197, November 2001.

   [CHACHA]   Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
              Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,

              Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
              and Congestion Control", draft-ietf-quic-recovery-22 (work
              in progress), July 2019.

              Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
              Multiplexed and Secure Transport", draft-ietf-quic-
              transport-22 (work in progress), July 2019.

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

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   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
              July 2014, <https://www.rfc-editor.org/info/rfc7301>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [SHA]      Dang, Q., "Secure Hash Standard", National Institute of
              Standards and Technology report,
              DOI 10.6028/nist.fips.180-4, July 2015.

              Salowey, J. and S. Turner, "IANA Registry Updates for TLS
              and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,

   [TLS13]    Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,

11.2.  Informative References

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

   [IMC]      Katz, J. and Y. Lindell, "Introduction to Modern
              Cryptography, Second Edition", ISBN 978-1466570269,
              November 2014.

              Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
              QUIC", draft-ietf-quic-http-22 (work in progress), July

   [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818,
              DOI 10.17487/RFC2818, May 2000,

   [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,

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11.3.  URIs

   [1] https://mailarchive.ietf.org/arch/search/?email_list=quic

   [2] https://github.com/quicwg

   [3] https://github.com/quicwg/base-drafts/labels/-tls

Appendix A.  Sample Initial Packet Protection

   This section shows examples of packet protection for Initial packets
   so that implementations can be verified incrementally.  These packets
   use an 8-byte client-chosen Destination Connection ID of
   0x8394c8f03e515708.  Values for both server and client packet
   protection are shown together with values in hexadecimal.

A.1.  Keys

   The labels generated by the HKDF-Expand-Label function are:

   client in:  00200f746c73313320636c69656e7420696e00

   server in:  00200f746c7331332073657276657220696e00

   quic key:  00100e746c7331332071756963206b657900

   quic iv:  000c0d746c733133207175696320697600

   quic hp:  00100d746c733133207175696320687000

   The initial secret is common:

   initial_secret = HKDF-Extract(initial_salt, cid)
       = 4496d3903d3f97cc5e45ac5790ddc686

   The secrets for protecting client packets are:

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       = HKDF-Expand-Label(initial_secret, "client in", _, 32)
       = 8a3515a14ae3c31b9c2d6d5bc58538ca

   key = HKDF-Expand-Label(client_initial_secret, "quic key", _, 16)
       = 98b0d7e5e7a402c67c33f350fa65ea54

   iv  = HKDF-Expand-Label(client_initial_secret, "quic iv", _, 12)
       = 19e94387805eb0b46c03a788

   hp  = HKDF-Expand-Label(client_initial_secret, "quic hp", _, 16)
       = 0edd982a6ac527f2eddcbb7348dea5d7

   The secrets for protecting server packets are:

       = HKDF-Expand-Label(initial_secret, "server in", _, 32)
       = 47b2eaea6c266e32c0697a9e2a898bdf

   key = HKDF-Expand-Label(server_initial_secret, "quic key", _, 16)
       = 9a8be902a9bdd91d16064ca118045fb4

   iv  = HKDF-Expand-Label(server_initial_secret, "quic iv", _, 12)
       = 0a82086d32205ba22241d8dc

   hp  = HKDF-Expand-Label(server_initial_secret, "quic hp", _, 16)
       = 94b9452d2b3c7c7f6da7fdd8593537fd

A.2.  Client Initial

   The client sends an Initial packet.  The unprotected payload of this
   packet contains the following CRYPTO frame, plus enough PADDING
   frames to make an 1163 byte payload:

   060040c4010000c003036660261ff947 cea49cce6cfad687f457cf1b14531ba1
   4131a0e8f309a1d0b9c4000006130113 031302010000910000000b0009000006
   736572766572ff01000100000a001400 12001d00170018001901000101010201
   03010400230000003300260024001d00 204cfdfcd178b784bf328cae793b136f
   2aedce005ff183d7bb14952072366470 37002b0003020304000d0020001e0403
   05030603020308040805080604010501 060102010402050206020202002d0002

   The unprotected header includes the connection ID and a 4 byte packet
   number encoding for a packet number of 2:


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   Protecting the payload produces output that is sampled for header
   protection.  Because the header uses a 4 byte packet number encoding,
   the first 16 bytes of the protected payload is sampled, then applied
   to the header:

   sample = 65f354ebb400418b614f73765009c016

   mask = AES-ECB(hp, sample)[0..4]
        = 519bd343ff

   header[0] ^= mask[0] & 0x0f
        = c2
   header[17..20] ^= mask[1..4]
        = 9bd343fd
   header = c2ff000015508394c8f03e51570800449f9bd343fd

   The resulting protected packet is:

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   c2ff000015508394c8f03e5157080044 9f9bd343fd65f354ebb400418b614f73
   765009c0162d594777f9e6ddeb32fba3 865cffd7e26e3724d4997cdde8df34f8
   868772fed2412d43046f44dc7c6adf5e e10da456d56c892c8f69594594e8dcab
   edb10d591130ca464588f2834eab931b 10feb963c1947a05f57062692c242248
   ad0133b31f6dcc585ba344ca5beb382f b619272e65dfccae59c08eb00b7d2a5b
   bccd888582df1d1aee040aea76ab4dfd cae126791e71561b1f58312edb31c164
   ff1341fd2820e2399946bad901e425da e58a9859ef1825e7d757a6291d9ba6ee
   1a8c836dc0027cd705bd2bc67f56bad0 024efaa3819cbb5d46cefdb7e0df3ad9
   2b0689650e2b49ac29e6398bedc75554 1a3f3865bc4759bec74d721a28a0452c
   1260189e8e92f844c91b27a00fc5ed6d 14d8fceb5a848bea0a3208162c7a9578
   2fcf9a045b20b76710a2565372f25411 81030e4350e199e62fa4e2e0bba19ff6
   6662ab8cc6815eeaa20b80d5f31c41e5 51f558d2c836a215ccff4e8afd2fec4b
   fcb9ea9d051d12162f1b14842489b69d 72a307d9144fced64fc4aa21ebd310f8
   97cf00062e90dad5dbf04186622e6c12 96d388176585fdb395358ecfec4d95db
   4429f4473a76210866fd180eaeb60da4 33500c74c00aef24d77eae81755faa03
   e71a8879937b32d31be2ba51d41b5d7a 1fbb4d952b10dd2d6ec171a3187cf3f6
   4d520afad796e4188bc32d153241c083 f225b6e6b845ce9911bd3fe1eb4737b7
   1c8d55e3962871b73657b1e2cce368c7 400658d47cfd9290ed16cdc2a6e3e7dc
   ea77fb5c6459303a32d58f62969d8f46 70ce27f591c7a59cc3e7556eda4c58a3
   2e9f53fd7f9d60a9c05cd6238c71e3c8 2d2efabd3b5177670b8d595151d7eb44
   aa401fe3b5b87bdb88dffb2bfb6d1d0d 8868a41ba96265ca7a68d06fc0b74bcc
   ac55b038f8362b84d47f52744323d08b 46bfec8c421f991e1394938a546a7482
   a17c72be109ea4b0c71abc7d9c0ac096 0327754e1043f18a32b9fb402fc33fdc
   b6a0b4fdbbddbdf0d85779879e98ef21 1d104a5271f22823f16942cfa8ace68d
   0c9e5b52297da9702d8f1de24bcd0628 4ac8aa1068fa21a82abbca7e7454b848
   d7de8c3d43560541a362ff4f6be06c01 15e3a733bff44417da11ae668857bba2
   c53ba17db8c100f1b5c7c9ea960d3f3d 3b9e77c16c31a222b498a7384e286b9b
   7c45167d5703de715f9b06708403562d cff77fdf2793f94e294888cebe8da4ee
   88a53e38f2430addc161e8b2e2f2d405 41d10cda9a7aa518ac14d0195d8c2012
   0b4f1d47d6d0909e69c4a0e641b83c1a d4fff85af4751035bc5698b6141ecc3f
   bffcf2f55036880071ba118927400796 7f64468172854d140d229320d689f576
   60f6c445e629d15ff2dcdff4b71a41ec 0c24bd2fd8f5ad13b2c3688e0fdb8dbc
   ce42e6cf49cf60d022ccd5b19b4fd5d9 8dc10d9ce3a626851b1fdd23e1fa3a96
   1f9b0333ab8d632e48c944b82bdd9e80 0fa2b2b9e31e96aee54b40edaf6b79ec
   211fdc95d95ef552aa532583d76a539e 988e416a0a10df2550cdeacafc3d61b0
   b0a79337960a0be8cf6169e4d55fa6e7 a9c2e8efabab3da008f5bcc38c1bbabd
   b6c10368723da0ae83c4b1819ff54946 e7806458d80d7be2c867d46fe1f029c5

A.3.  Server Initial

   The server sends the following payload in response, including an ACK
   frame, a CRYPTO frame, and no PADDING frames:

   0d0000000018410a020000560303eefc e7f7b37ba1d1632e96677825ddf73988
   cfc79825df566dc5430b9a045a120013 0100002e00330024001d00209d3c940d
   89690b84d08a60993c144eca684d1081 287c834d5311bcf32bb9da1a002b0002

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   The header from the server includes a new connection ID and a 2-byte
   packet number encoding for a packet number of 1:


   As a result, after protection, the header protection sample is taken
   starting from the third protected octet:

   sample = 6176fa3b713f272a9bf03ee28d3c8add
   mask   = 5bd74a846c
   header = caff00001505f067a5502a4262b5004074d74b

   The final protected packet is then:

   caff00001505f067a5502a4262b50040 74d74b7e486176fa3b713f272a9bf03e
   e28d3c8addb4e805b3a110b663122a75 eee93c9177ac6b7a6b548e15a7b8f884
   65e9eab253a760779b2e6a2c574882b4 8d3a3eed696e50d04d5ec59af85261e4
   cdbe264bd65f2b076760c69beef23aa7 14c9a174d69034c09a2863e1e1863508

Appendix B.  Change Log

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

   Issue and pull request numbers are listed with a leading octothorp.

B.1.  Since draft-ietf-quic-tls-21

   o  No changes

B.2.  Since draft-ietf-quic-tls-20

   o  Mandate the use of the QUIC transport parameters extension (#2528,

   o  Define handshake completion and confirmation; define clearer rules
      when it encryption keys should be discarded (#2214, #2267, #2673)

B.3.  Since draft-ietf-quic-tls-18

   o  Increased the set of permissible frames in 0-RTT (#2344, #2355)

   o  Transport parameter extension is mandatory (#2528, #2560)

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B.4.  Since draft-ietf-quic-tls-17

   o  Endpoints discard initial keys as soon as handshake keys are
      available (#1951, #2045)

   o  Use of ALPN or equivalent is mandatory (#2263, #2284)

B.5.  Since draft-ietf-quic-tls-14

   o  Update the salt used for Initial secrets (#1970)

   o  Clarify that TLS_AES_128_CCM_8_SHA256 isn't supported (#2019)

   o  Change header protection

      *  Sample from a fixed offset (#1575, #2030)

      *  Cover part of the first byte, including the key phase (#1322,

   o  TLS provides an AEAD and KDF function (#2046)

      *  Clarify that the TLS KDF is used with TLS (#1997)

      *  Change the labels for calculation of QUIC keys (#1845, #1971,

   o  Initial keys are discarded once Handshake are avaialble (#1951,

B.6.  Since draft-ietf-quic-tls-13

   o  Updated to TLS 1.3 final (#1660)

B.7.  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

      *  Separate QUIC packet number spaces are used for the handshake

      *  Changed Retry to be independent of the cryptographic handshake

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      *  Limit the use of HelloRetryRequest to address TLS needs (like
         key shares)

   o  Changed codepoint of TLS extension (#1395, #1402)

B.8.  Since draft-ietf-quic-tls-11

   o  Encrypted packet numbers.

B.9.  Since draft-ietf-quic-tls-10

   o  No significant changes.

B.10.  Since draft-ietf-quic-tls-09

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

B.11.  Since draft-ietf-quic-tls-08

   o  Specify value for max_early_data_size to enable 0-RTT (#942)

   o  Update key derivation function (#1003, #1004)

B.12.  Since draft-ietf-quic-tls-07

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

B.13.  Since draft-ietf-quic-tls-05

   No significant changes.

B.14.  Since draft-ietf-quic-tls-04

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

B.15.  Since draft-ietf-quic-tls-03

   No significant changes.

B.16.  Since draft-ietf-quic-tls-02

   o  Updates to match changes in transport draft

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B.17.  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,

   o  The QUIC header is included as AEAD Associated Data (#226, #243,

   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)

B.18.  Since draft-ietf-quic-tls-00

   o  Changed bit used to signal key phase

   o  Updated key phase markings during the handshake

   o  Added TLS interface requirements section

   o  Moved to use of TLS exporters for key derivation

   o  Moved TLS error code definitions into this document

B.19.  Since draft-thomson-quic-tls-01

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

   o  Updated authors/editors list

   o  Added status note

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   This document has benefited from input from Dragana Damjanovic,
   Christian Huitema, Jana Iyengar, Adam Langley, Roberto Peon, Eric
   Rescorla, Ian Swett, and many others.


   Ryan Hamilton was originally an author of this specification.

Authors' Addresses

   Martin Thomson (editor)

   Email: mt@lowentropy.net

   Sean Turner (editor)

   Email: sean@sn3rd.com

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