Anonymous Tickets for TLS 1.3
draft-sullivan-tls-anonymous-tickets-00

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Last updated 2019-03-11
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Network Working Group                                        N. Sullivan
Internet-Draft                                                Cloudflare
Intended status: Informational                                   C. Wood
Expires: September 12, 2019                                   Apple Inc.
                                                          March 11, 2019

                     Anonymous Tickets for TLS 1.3
                draft-sullivan-tls-anonymous-tickets-00

Abstract

   This document describes a mechanism that enables unlinkable session
   resumption for TLS 1.3 without server-side state.  In contrast to
   existing ticket-based resumption in TLS 1.3, wherein servers
   construct and issue tickets to clients, this document specifies a
   mechanism by which clients request "anonymous tickets" from servers.
   When a session is resumed using an anonymous ticket, a server only
   learns that it previously engaged in a session with some client,
   rather than linking it to a specific client.  Anonymous tickets are
   only useful for clients with idempotent early data to send.

   DISCLAIMER: This draft has not seen any significant security analysis
   and may contain major errors.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 12, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Sullivan & Wood        Expires September 12, 2019               [Page 1]
Internet-Draft            tls-anonymous-tickets               March 2019

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   (https://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Preliminaries . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Anonymous Ticket Protocol . . . . . . . . . . . . . . . . . .   4
     3.1.  Anonymous Ticket Requests and Responses . . . . . . . . .   5
     3.2.  Anonymous Ticket Resumption . . . . . . . . . . . . . . .   6
     3.3.  Negotiation . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Token Derivation  . . . . . . . . . . . . . . . . . . . . . .   7
   5.  0-RTT Data Implications . . . . . . . . . . . . . . . . . . .   8
   6.  Linkability Beyond TLS  . . . . . . . . . . . . . . . . . . .   8
     6.1.  Network-Layer Linkability . . . . . . . . . . . . . . . .   8
     6.2.  Application-Layer Linkability . . . . . . . . . . . . . .   8
   7.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   DISCLAIMER: This is a work-in-progress draft and as such has not seen
   any significant security analysis and may contain major errors.

   TLS session tickets enable temporal cross-connection linkability.
   Per [RFC8446], session tickets are recommended to carry an encryption
   of the session resumption_master_secret, from which clients and
   servers derive keying material for subsequent upon resumption.  With
   such tickets, servers can stitch together resumed sessions from the
   same client over time.  This can be exploited to build a profile of
   client and application behavior.

   In this document, we describe a mechanism for TLS 1.3 [RFC8446] by
   which sessions may be resumed in a way that does compromise client
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