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Versions: 00 01 draft-ietf-tls-ticketrequests

Network Working Group                                           T. Pauly
Internet-Draft                                               D. Schinazi
Intended status: Informational                                   C. Wood
Expires: April 16, 2019                                       Apple Inc.
                                                        October 13, 2018

                          TLS Ticket Requests


   TLS session tickets enable stateless connection resumption for
   clients without server-side per-client state.  Servers vend session
   tickets to clients, at their discretion, upon connection
   establishment.  Clients store and use tickets when resuming future
   connections.  Moreover, clients should use tickets at most once for
   session resumption, especially if such keying material protects early
   application data.  Single-use tickets bound the number of parallel
   connections a client may initiate by the number of tickets received
   from a given server.  To address this limitation, this document
   describes a mechanism by which clients may specify the desired number
   of tickets needed for future connections.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://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 April 16, 2019.

Copyright Notice

   Copyright (c) 2018 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

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   (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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Ticket Requests . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   As per [RFC5077], and as described in [RFC8446], TLS servers send
   clients session tickets at their own discretion in NewSessionTicket
   messages.  Clients are in complete control of how many tickets they
   may use when establishing future and subsequent connections.  For
   example, clients may open multiple TLS connections to the same server
   for HTTP, or may race TLS connections across different network
   interfaces.  The latter is especially useful in transport systems
   that implement Happy Eyeballs [RFC8305].  Since connection
   concurrency and resumption is controlled by clients, a standard
   mechanism to request more than one ticket is desirable.

   This document specifies a new TLS extension - ticket_request - that
   may be used by clients to express their desired number of session
   tickets.  Servers may use this extension as a hint of the number of
   NewSessionTicket messages to vend.  This extension is only applicable
   to TLS 1.3 [RFC8446] and future versions of TLS.

1.1.  Requirements Language

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

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2.  Use Cases

   The ability to request one or more tickets is useful for a variety of

   o  Parallel HTTP connections: To minimize ticket reuse while still
      improving performance, it may be useful to use multiple, distinct
      tickets when opening parallel connections.  Clients must therefore
      bound the number of parallel connections they initiate by the
      number of tickets in their possession, or risk ticket re-use.

   o  Connection racing: Happy Eyeballs V2 [RFC8305] describes
      techniques for performing connection racing.  The Transport
      Services Architecture implementation from [I-D.ietf-taps-impl]
      also describes how connections may race across interfaces and
      address families.  In cases where clients have early data to send
      and want to minimize or avoid ticket re-use, unique tickets for
      each unique connection attempt are useful.  Moreover, as some
      servers may implement single-use tickets (and even session ticket
      encryption keys), distinct tickets will be needed to prevent
      premature ticket invalidation by racing.

   o  Connection priming: In some systems, connections may be primed or
      bootstrapped by a centralized service or daemon for faster
      connection establishment.  Requesting tickets on demand allows
      such services to vend tickets to clients to use for accelerated
      handshakes with early data.  (Note that if early data is not
      needed by these connections, this method SHOULD NOT be used.
      Fresh handshakes SHOULD be performed instead.)

   o  Less ticket waste: Currently, TLS servers use application-
      specific, and often implementation-specific, logic to determine
      how many tickets to issue.  By moving the burden of ticket count
      to clients, servers do not generate wasteful tickets for clients.
      Moreover, as ticket generation may involve expensive computation,
      e.g., public key cryptographic operations, avoiding waste is

3.  Ticket Requests

   Clients may indicate to servers their desired number of tickets via
   the following "ticket_request" extension:

   enum {
       ticket_request(TBD), (65535)
   } ExtensionType;

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   Clients may send this extension in ClientHello.  It contains the
   following structure:

   struct {
       uint8 count;
   } TicketRequestContents;

   count  The number of tickets desired by the client.

   A supporting server MAY vend TicketRequestContents.count
   NewSessionTicket messages to a requesting client, and SHOULD NOT send
   more than TicketRequestContents.count NewSessionTicket messages to a
   requesting client.  Servers SHOULD place a limit on the number of
   tickets they are willing to vend to clients.  Thus, the number of
   NewSessionTicket messages sent should be the minimum of the server's
   self-imposed limit and TicketRequestContents.count.  Servers MUST NOT
   send more than 255 tickets to clients.

   Servers that support ticket requests MUST NOT echo "ticket_request"
   in the EncryptedExtensions.

4.  IANA Considerations

   IANA is requested to Create an entry, ticket_requests(TBD), in the
   existing registry for ExtensionType (defined in [RFC8446]), with "TLS
   1.3" column values being set to "CH", and "Recommended" column being
   set to "Yes".

5.  Security Considerations

   Ticket re-use is a security and privacy concern.  Moreover, ticket
   pooling as a means of avoiding or amortizing handshake costs must be
   used carefully.  If servers do not rotate session ticket encryption
   keys frequently, clients may be encouraged to obtain and use tickets
   beyond common lifetime windows of, e.g., 24 hours.  Despite ticket
   lifetime hints provided by servers, clients SHOULD dispose of pooled
   tickets after some reasonable amount of time that mimics the ticket
   rotation period.

6.  Acknowledgments

   The authors would like to thank David Benjamin, Eric Rescorla, Nick
   Sullivan, and Martin Thomson for discussions on earlier versions of
   this draft.

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7.  Normative References

              Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K.,
              Jones, T., Tiesel, P., Perkins, C., and M. Welzl,
              "Implementing Interfaces to Transport Services", draft-
              ietf-taps-impl-01 (work in progress), July 2018.

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

   [RFC5077]  Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
              "Transport Layer Security (TLS) Session Resumption without
              Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
              January 2008, <https://www.rfc-editor.org/info/rfc5077>.

   [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>.

   [RFC8305]  Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
              Better Connectivity Using Concurrency", RFC 8305,
              DOI 10.17487/RFC8305, December 2017, <https://www.rfc-

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

Authors' Addresses

   Tommy Pauly
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: tpauly@apple.com

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   David Schinazi
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: dschinazi@apple.com

   Christopher A. Wood
   Apple Inc.
   One Apple Park Way
   Cupertino, California 95014
   United States of America

   Email: cawood@apple.com

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