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Versions: 00 01 draft-ietf-quic-tls

Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Standards Track                             R. Hamilton
Expires: September 22, 2016                                       Google
                                                          March 21, 2016


             Porting QUIC to Transport Layer Security (TLS)
                       draft-thomson-quic-tls-00

Abstract

   The QUIC experiment defines a custom security protocol.  This was
   necessary to gain handshake latency improvements.  This document
   describes how that security protocol might be replaced with 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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 22, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
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   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.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Handshake Overview  . . . . . . . . . . . . . . . . . . .   4
   3.  QUIC over TLS Structure . . . . . . . . . . . . . . . . . . .   5
   4.  Mapping of QUIC to QUIC over TLS  . . . . . . . . . . . . . .   6
     4.1.  Protocol and Version Negotiation  . . . . . . . . . . . .   7
     4.2.  Source Address Validation . . . . . . . . . . . . . . . .   8
   5.  Record Protection . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  TLS Handshake Encryption  . . . . . . . . . . . . . . . .   9
     5.2.  Key Update  . . . . . . . . . . . . . . . . . . . . . . .   9
     5.3.  Sequence Number Reconstruction  . . . . . . . . . . . . .  10
     5.4.  Alternative Design: Exporters . . . . . . . . . . . . . .  10
   6.  Pre-handshake QUIC Messages . . . . . . . . . . . . . . . . .  11
     6.1.  QUIC Extension  . . . . . . . . . . . . . . . . . . . . .  11
     6.2.  Unprotected Frames Prior to Handshake Completion  . . . .  15
       6.2.1.  STREAM Frames . . . . . . . . . . . . . . . . . . . .  15
       6.2.2.  ACK Frames  . . . . . . . . . . . . . . . . . . . . .  15
       6.2.3.  WINDOW_UPDATE Frames  . . . . . . . . . . . . . . . .  15
       6.2.4.  FEC Packets . . . . . . . . . . . . . . . . . . . . .  16
     6.3.  Protected Frames Prior to Handshake Completion  . . . . .  16
   7.  Connection ID . . . . . . . . . . . . . . . . . . . . . . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     10.2.  Informative References . . . . . . . . . . . . . . . . .  18
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   QUIC [I-D.tsvwg-quic-protocol] provides a multiplexed transport for
   HTTP [RFC7230] semantics that provides several key advantages over
   HTTP/1.1 [RFC7230] or HTTP/2 [RFC7540] over TCP [RFC0793].

   The custom security protocol designed for QUIC provides critical
   latency improvements for connection establishment.  Absent packet
   loss, most new connections can be established with 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.  TLS 1.3 uses a similar design and aims to provide
   the same set of improvements.

   This document describes how the standardized TLS 1.3 might serve as a
   security layer for QUIC.  The same design could work for TLS 1.2,



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   though few of the benefits QUIC provides would be realized due to the
   handshake latency in versions of TLS prior to 1.3.

   Alternative Designs:  There are other designs that are possible; and
      many of these alternative designs are likely to be equally good.
      The point of this document is to articulate a coherent single
      design.  Notes like this throughout the document are used describe
      points where alternatives were considered.

   Note:  This is a rough draft.  Many details have not been ironed out.
      Ryan is not responsible for any errors or omissions.

1.1.  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].

2.  Protocol Overview

   QUIC [I-D.tsvwg-quic-protocol] can be separated into several modules:

   1.  The basic frame envelope describes the common packet layout.
       This layer includes connection identification, version
       negotiation, and includes the indicators that allow the framing,
       public reset, and FEC modules to be identified.

   2.  The public reset is an unprotected frame that allows an
       intermediary (an entity that is not part of the security context)
       to request the termination of a QUIC connection.

   3.  The forward error correction (FEC) module provides redundant
       entropy that allows for frames to be repaired in event of loss.

   4.  Framing comprises most of the QUIC protocol.  Framing provides a
       number of different types of frame, each with a specific purpose.
       Framing supports frames for both congestion management and stream
       multiplexing.  Framing additionally provides a liveness testing
       capability (the PING frame).

   5.  Crypto provides confidentiality and integrity protection for
       frames.  All frames are protected after the handshake completes
       on stream 1.  Prior to this, data is protected with the 0-RTT
       keys.

   6.  Multiplexed streams are the primary payload of QUIC.  These
       provide reliable, in-order delivery of data and are used to carry
       the encryption handshake and transport parameters (stream 1),



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       HTTP header fields (stream 3), and HTTP requests and responses.
       Frames for managing multiplexing include those for creating and
       destroying streams as well as flow control and priority frames.

   7.  Congestion management includes packet acknowledgment and other
       signal required to ensure effective use of available link
       capacity.

   8.  HTTP mapping provides an adaptation to HTTP that is based on
       HTTP/2.

   The relative relationship of these components are pictorally
   represented in Figure 1.

      +----+------+
      | HS | HTTP |
      +----+------+------------+
      |  Streams  | Congestion |
      +-----------+------------+
      |        Frames          |
      +           +------------+
      |           |    FEC     +--------+
      +  +--------+------------+ Public |
      |  |     Crypto          | Reset  |
      +--+---------------------+--------+
      |              Envelope           |
      +---------------------------------+
      |                UDP              |
      +---------------------------------+

                                *HS = Crypto Handshake

                         Figure 1: QUIC Structure

   This document describes a replacement of the cryptographic parts of
   QUIC.  This includes the handshake messages that are exchanged on
   stream 1, plus the record protection that is used to encrypt and
   authenticate all other frames.

2.1.  Handshake Overview

   TLS 1.3 provides two basic handshake modes of interest to QUIC:

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





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   o  A 0-RTT handshake in which the client uses information 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.

       Client                                             Server

       ClientHello
      (Finished)
      (0-RTT Application Data)
      (end_of_early_data)        -------->
                                                     ServerHello
                                            {EncryptedExtensions}
                                            {ServerConfiguration}
                                                    {Certificate}
                                              {CertificateVerify}
                                                       {Finished}
                                <--------      [Application Data]
      {Finished}                -------->

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

                    Figure 2: TLS Handshake with 0-RTT

   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 might also be
      used to verify that the client is correctly able to receive
      packets on the address it claims to have (see Section 4.2).

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

3.  QUIC over TLS Structure

   QUIC completes its cryptographic handshake on stream 1, which means
   that the negotiation of keying material happens within the QUIC
   protocol.  QUIC over TLS does the same, relying on the ordered




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   delivery guarantees provided by QUIC to ensure that the TLS handshake
   packets are delivered reliably and in order.

      +-----+---------+
      | TLS |  HTTP   |
      +-----+----------+------------+
      |    Streams     | Congestion |
      +----------------+------------+
      |          Frames             |
      |                +------------+
      |                |    FEC     +--------+
      |     +----------+------------+ Public |
      |     | TLS Record Protection | Reset  |
      +-----+-----------------------+--------+
      |               Envelope               |
      +--------------------------------------+
      |                 UDP                  |
      +--------------------------------------+

                          Figure 3: QUIC over TLS

   In this design the QUIC envelope carries QUIC frames until the TLS
   handshake completes.  After the handshake successfully completes the
   key exchange, QUIC frames are then protected by TLS record
   protection.

   QUIC stream 1 is used to exchange TLS handshake packets.  QUIC
   provides for reliable and in-order delivery of the TLS handshake
   messages.

   Prior to the completion of the TLS handshake, QUIC frames can be
   exchanged.  However, these frames are not authenticated or
   confidentiality protected.  Section 6 covers some of the implications
   of this design.

   Alternative Design:  TLS could be used to protect the entire QUIC
      envelope.  QUIC version negotiation could be subsumed by TLS and
      ALPN [RFC7301].  The only unprotected packets are then public
      resets and ACK frames, both of which could be given first octet
      values that would easily distinguish them from other TLS packets.
      This requires that the QUIC sequence numbers be moved to the
      outside of the record.

4.  Mapping of QUIC to QUIC over TLS

   Several changes to the structure of QUIC are necessary to make a
   layered design practical.




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   These changes produce the handshake shown in Figure 4.  In this
   handshake, QUIC STREAM frames on stream 1 carry the TLS handshake.
   QUIC is responsible for ensuring that the handshake packets are re-
   sent in case of loss and that they can be ordered correctly.

   QUIC operates without any record protection until the handshake
   completes, just as TLS over TCP does not include record protection
   for the handshake messages.  Once complete, QUIC frames and forward
   error control (FEC) messages are encapsulated in using TLS record
   protection.

       Client                                             Server

      QUIC STREAM Frame <stream 1>
       ClientHello
        + QUIC Setup Parameters
      (Finished)                 -------->
      (Replayable QUIC Frames <any stream>)
      (end_of_early_data <1>) -------->
                                            QUIC STREAM Frame <1>
                                                     ServerHello
                                            {EncryptedExtensions}
                                            {ServerConfiguration}
                                                    {Certificate}
                                              {CertificateVerify}
                                                       {Finished}
                                <--------       [QUIC Frames/FEC]
      QUIC STREAM Frame <1>
      {Finished}                -------->

      [QUIC Frames/FEC]         <------->       [QUIC Frames/FEC]

                     Figure 4: QUIC over TLS Handshake

   The remainder of this document describes the changes to QUIC and TLS
   that allow the protocols to operate together.

4.1.  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 doesn't prevent
   version downgrade during the handshake, though it does prevent a



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   connection from completing with a downgraded version, see
   Section 6.1.

   ISSUE:  The QUIC version negotiation has poor performance in the
      event that a client is forced to downgrade from their preferred
      version.

4.2.  Source Address Validation

   QUIC implementations describe a source address token.  This is an
   opaque blob that a server provides 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.

   Since this token is opaque and consumed only by the server, it can be
   included in the TLS 1.3 configuration identifier for 0-RTT
   handshakes.  Servers that use 0-RTT are advised to provide new
   configuration identifiers after every handshake to avoid passive
   linkability of connections from the same client.

   A server that is under load might include the same information in the
   cookie extension/field of a HelloRetryRequest.  (Note: the current
   version of TLS 1.3 does not include the ability to include a cookie
   in HelloRetryRequest.)

5.  Record Protection

   Each TLS record is encapsulated in the QUIC envelope.  This provides
   length information, which means that the length field can be dropped
   from the TLS record.

   The sequence number used by TLS record protection is changed to deal
   with the potential for packets to be dropped or lost.  The QUIC
   sequence number is used in place of the monotonically increasing TLS
   record sequence number.  This means that the TLS record protection
   employed is closer to DTLS in both its form and the guarantees that
   are provided.

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




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   QUIC does not rely on there being a continuous sequence of
   application data packets; QUIC uses authenticated repair mechansims
   that operate above the layer of encryption.  QUIC can therefore
   operate without restarting sequence numbers.

5.1.  TLS Handshake Encryption

   TLS 1.3 adds encryption for handshake messages.  This introduces an
   additional transition between different record protection keys during
   the handshake.  A consequence of this is that it becomes more
   important to explicitly identify the transition from one set of keys
   to the next (see Section 5.2).

5.2.  Key Update

   Each time that the TLS record protection keys are changed, the
   message initiating the change could be lost.  This results in
   subsequent packets being indecipherable to the peer that receives
   them.  Key changes happen at the conclusion of the handshake and and
   immediately after a KeyUpdate message.

   TLS relies on an ordered, reliable transport and therefore provides
   no other mechanism to ensure that a peer receives the message
   initiating a key change prior to receiving the subsequent messages
   that are protected using the new key.  A similar mechanism here would
   introduce head-of-line blocking.

   The simplest solution here is to steal a single bit from the
   unprotected part of the QUIC header that signals key updates, similar
   to how DTLS signals the epoch on each packet.  The epoch bit is
   encoded into 0x80 of the QUIC public flags.

   Each time the epoch bit changes, an attempt is made to update the
   keys used to read.  Peers are prohibited from sending multiple
   KeyUpdate messages until they see a reciprocal KeyUpdate to prevent
   the chance that a transition is undetected as a result of two changes
   in this bit.

   The transition from cleartext to encrypted packets is exempt from
   this limit of one key change.  Two key changes occur during the
   handshake.  The server sends packets in the clear, plus packets
   protected using handshake and application data keys.  With only a
   single bit available to discriminate between keys, packets protected
   with the application data keys will have the same bit value as
   cleartext packets.  This condition will be easily identified and
   handled, likely by discarding the application data, since the
   encrypted packets will be highly unlikely to be valid.




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5.3.  Sequence Number Reconstruction

   Each peer maintains a 48-bit send sequence number that is incremented
   with each packet that is sent (even retransmissions).  The least
   significant 8-, 16-, 32-, or 48-bits of this number is encoded in the
   QUIC sequence number field in every packet.  A 16-bit send epoch
   number is maintained; the epoch is incremented each time new record
   protection keying material is used.  The least significant bit of the
   epoch number is encoded into the epoch bit (0x80) of the QUIC public
   flags.

   A receiver maintains the same values, but recovers values based on
   the packets it receives.  This is based on the sequence number of
   packets that it has received.  A simple scheme predicts the receive
   sequence number of an incoming packet by incrementing the sequence
   number of the most recent packet to be successfully decrypted by one
   and expecting the sequence number to be within a range centered on
   that value.  The receive epoch value is incremented each time that
   the epoch bit (0x80) changes.

   The sequence number used for record protection is the 64-bit value
   obtained by concatenating the epoch and sequence number, both in
   network byte order.

5.4.  Alternative Design: Exporters

   An exporter could be used to provide keying material for a QUIC-
   specific record protection.  This could draw on the selected cipher
   suite and the TLS record protection design so that the overall effort
   required to design and analyze is kept minimal.

   One concern with using exporters is that TLS doesn't define an
   exporter for use prior to the end of the handshake.  That means the
   creation of a special exporter for use in protecting 0-RTT data.
   That's a pretty sharp object to leave lying around, and it's not
   clear what the properties we could provide.  (That doesn't mean that
   there wouldn't be demand for such a thing, the possibility has
   already been raised.)

   An exporter-based scheme might opt not to use the handshake traffic
   keys to protect QUIC packets during the handshake, relying instead on
   separate protection for the TLS handshake records.  This complicates
   implementations somewhat, so an exporter might still be used.

   In the end, using an exporter doesn't alter the design significantly.
   Given the risks, a modification to the record protocol is probably
   safer.




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6.  Pre-handshake QUIC Messages

   Implementations MUST NOT exchange data on any stream other than
   stream 1 prior to the TLS handshake completing.  However, QUIC
   requires the use of several types of frame for managing loss
   detection and recovery.  In addition, it might be useful to use the
   data acquired during the exchange of unauthenticated messages for
   congestion management.

   The actions that a peer takes as a result of receiving an
   unauthenticated packet needs tobe 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.

   o  Transport parameters and options are made usable and authenticated
      as part of the TLS handshake (see Section 6.1).

   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 6.2).

   o  Protected packets can be discarded, but can be saved and later
      used (see Section 6.3).

6.1.  QUIC Extension

   A client describes characteristics of the transport protocol it
   intends to conduct with the server in a new QUIC-specific extension
   in its ClientHello.  The server uses this information to determine



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   whether it wants to continue the connection, request source address
   validation, or reject the connection.  Having this information
   unencrypted permits this check to occur prior to committing the
   resources needed to complete the initial key exchange.

   If the server decides to complete the connection, it generates a
   corresponding response and includes it in the EncryptedExtensions
   message.

   These parameters are not confidentiality-protected when sent by the
   client, but the server response is protected by the handshake traffic
   keys.  The entire exchange is integrity protected once the handshake
   completes.

   This information is not used by TLS, but can be passed to the QUIC
   protocol as initialization parmeters.

   The "quic_parameters" extension contains a declarative set of
   parameters that establish QUIC operating parameters and constrain the
   behaviour of a peer.  The connection identifier and version are first
   negotiated using QUIC, and are included in the TLS handshake in order
   to provide integrity protection.





























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      enum {
          receive_buffer(0),
          (65535)
      } QuicTransportParameterType;

      struct {
          QuicTransportParameterType type;
          uint32 value;
      } QuicTransportParameter;

      uint32 QuicVersion;

      enum {
          (65535)
      } QuicOption;

      struct {
          uint64 connection_id;
          QuicVersion quic_version;
          QuicVersion supported_quic_versions<0..2^8-1>;
          uint32 connection_initial_window;
          uint32 stream_initial_window;
          uint32 implicit_shutdown_timeout;
          QuicTransportParameter transport_parameters<0..2^16-1>;
          QuicOption options<0..2^8-2>;
      } QuicParametersExtension;

   This extension MUST be included if a QUIC version is negotiated.  A
   server MUST NOT negotiate QUIC if this extension is not present.

   Based on the values offered by a client a server MAY use the values
   in this extension to determine whether it wants to continue the
   connection, request source address validation, or reject the
   connection.  Since this extension is initially unencrypted, the
   server can use the information prior to committing the resources
   needed to complete a key exchange.

   If the server decides to use QUIC, this extension MUST be included in
   the EncryptedExtensions message.

   The parameters are:

   connection_id:  The 64-bit connection identifier for the connection,
      as selected by the client.

   quic_version:  The currently selected QUIC version that is used for
      the connection.  This is the version negotiated using the
      unauthenticated QUIC version negotiation (Section 4.1).



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   supported_quic_versions:  This is a list of supported QUIC versions
      for each peer.  A client sends an empty list if the version of
      QUIC being used is their preferred version; however, a client MUST
      include their preferred version if this was not negotiated using
      QUIC version negotiation.  A server MUST include all versions that
      it supports in this list.

   connection_initial_window:  The initial value for the connection flow
      control window for the endpoint, in octets.

   connection_initial_window:  The initial value for the flow control
      window of new streams created by the peer endpoint, in octets.

   implicit_shutdown_timeout:  The time, in seconds, that a connection
      can remain idle before being implicitly shutdown.

   transport_parameters:  A list of parameters for the QUIC connection,
      expressed as key-value pairs of arbitrary length.  The
      QuicTransportParameterType identifies each parameter; duplicate
      types are not permitted and MUST be rejected with a fatal
      illegal_parameter alert.  Type values are taken from a single
      space that is shared by all QUIC versions.

      ISSUE:  There is currently no way to update the value of
         parameters once the connection has started.  QUIC crypto
         provided a SCFG message that could be sent after the connection
         was established.

   options:  A list of options that can be negotiated for a given
      connection.  These are set during the initial handshake and are
      fixed thereafter.  These options are used to enable or disable
      optional features in the protocol.  The set of features that are
      supported across different versions might vary.  A client SHOULD
      include all options that it is willing to use.  The server MAY
      select any subset of those options that apply to the version of
      QUIC that it selects.  Only those options selected by the server
      are available for use.

      Note:  This sort of optional behaviour seems like it could be
         accommodated adequately by defining new versions of QUIC for
         each experiment.  However, as an evolving protocol, multiple
         experiments need to be conducted concurrently and continuously.
         The options parameter provides a flexible way to regulate which
         experiments are enabled on a per-connection basis.







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6.2.  Unprotected Frames 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.

6.2.1.  STREAM Frames

   "STREAM" frames for stream 1 are permitted.  These carry the TLS
   handshake messages.

   Receiving unprotected "STREAM" frames that do not contain TLS
   handshake messages MUST be treated as a fatal error.

6.2.2.  ACK Frames

   "ACK" frames are permitted prior to the handshake being complete.
   However, an unauthenticated "ACK" frame can only be used to obtain
   NACK ranges.  Timestamps MUST NOT be included in an unprotected ACK
   frame, since these might be modified by an attacker with the intent
   of altering congestion control response.  Information on FEC-revived
   packets is redundant, since use of FEC in this phase is prohibited.

   "ACK" frames MAY be sent a second time once record protection is
   enabled.  Once protected, timestamps can be included.

   Editor's Note:  This prohibition might be a little too strong, but
      this is the only obviously safe option.  If the amount of damage
      that an attacker can do by modifying timestamps is limited, then
      it might be OK to permit the inclusion of timestamps.  Note that
      an attacker need not be on-path to inject an ACK.

6.2.3.  WINDOW_UPDATE Frames

   Sending a "WINDOW_UPDATE" on stream 1 might be necessary to permit
   the completion of the TLS handshake, particularly in cases where the
   certification path is lengthy.  To avoid stalling due to flow control
   exhaustion, "WINDOW_UPDATE" frames with stream 1 are permitted.

   Receiving a "WINDOW_UPDATE" frame on streams other than 1 MUST be
   treated as a fatal error.

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





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   The position of the flow control window MUST be reset to defaults
   once the TLS handshake is complete.  This might result in the window
   position for either the connection or stream 1 being smaller than the
   number of octets that have been sent on those streams.  A
   "WINDOW_UPDATE" frame might therefore be necessary to prevent the
   connection from being stalled.

   Note:  This is only potentially problematic for servers, who might
      need to send large certificate chains.  In other cases, this is
      unlikely given that QUIC - like HTTP [RFC7230] - is a protocol
      where the server is unable to exercise the opportunity TLS
      presents to send first.

      If a server has a large certificate chain, or later modifications
      or extensions to QUIC permit the server to send first, a client
      might reduce the chance of stalling due to flow control in this
      first round trip by setting larger values for the initial stream
      and connection flow control windows using the "quic_parameters"
      extension (Section 6.1).

   Editor's Note:  Unlike "ACK", the prohibition on "WINDOW_UPDATE" is
      much less of an imposition on implementations.  And, given that a
      spurious "WINDOW_UPDATE" might be used to create a great deal of
      memory pressure on an endpoint, the restriction seems justifiable.
      Besides, I understand this one a lot better.

6.2.4.  FEC Packets

   FEC packets MUST NOT be sent prior to completing the TLS handshake.
   Endpoints MUST treat receipt of an unprotected FEC packet as a fatal
   error.

6.3.  Protected Frames 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



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   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.

   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 MUST save the last protected "WINDOW_UPDATE" frame it
   receives for each stream and apply the values once the TLS handshake
   completes.

   Editor's Note:  Ugh.  This last one is pretty ugly.  Maybe we should
      just make the TLS handshake exempt from flow control up to the
      Finished message.  Then we can prohibit unauthenticated
      "WINDOW_UPDATE" messages.  We would still likely want to account
      for the packets sent and received, since to do otherwise would
      create some hairy special cases.  That means that stalling is
      possible, but it means that we can avoid ugly rules like the
      above.

7.  Connection ID

   The QUIC connection identifier serves to identify a connection and to
   allow a server to resume an existing connection from a new client
   address in case of mobility events.  However, this creates an
   identifier that a passive observer [RFC7258] can use to correlate
   connections.

   TLS 1.3 offers connection resumption using pre-shared keys, which
   also allows a client to send 0-RTT application data.  This mode could
   be used to continue a connection rather than rely on a publicly
   visible correlator.  This only requires that servers produce a new
   ticket on every connection and that clients do not resume from the
   same ticket more than once.

   The advantage of relying on 0-RTT modes for mobility events is that
   this is also more robust.  If the new point of attachment results in
   contacting a new server instance - one that lacks the session state -
   then a fallback is easy.

   The main drawback with a clean restart or anything resembling a
   restart is that accumulated state can be lost.  Aside from progress
   on incomplete requests, the state of the HPACK header compression
   table could be quite valuable.  Existing QUIC implementations use the
   connection ID to route packets to the server that is handling the
   connection, which avoids this sort of problem.




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   A lightweight state resurrection extension might be used to avoid
   having to recreate any expensive state.

8.  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.  IANA Considerations

   This document has no IANA actions.  Yet.

10.  References

10.1.  Normative References

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-11 (work in progress),
              December 2015.

   [I-D.tsvwg-quic-protocol]
              Hamilton, R., Iyengar, J., Swett, I., and A. Wilk, "QUIC:
              A UDP-Based Secure and Reliable Transport for HTTP/2",
              draft-tsvwg-quic-protocol-02 (work in progress), January
              2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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>.

10.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <http://www.rfc-editor.org/info/rfc793>.





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   [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,
              <http://www.rfc-editor.org/info/rfc7230>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

Appendix A.  Acknowledgments

   Christian Huitema's knowledge of QUIC is far better than my own.
   This would be even more inaccurate and useless if not for his
   assistance.  This document has variously benefited from a long series
   of discussions with Ryan Hamilton, Jana Iyengar, Adam Langley,
   Roberto Peon, Ian Swett, and likely many others who are merely
   forgotten by a faulty meat computer.

Authors' Addresses

   Martin Thomson
   Mozilla

   Email: martin.thomson@gmail.com


   Ryan Hamilton
   Google

   Email: rch@google.com
















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