Design issues for hybrid key exchange in TLS 1.3
draft-stebila-tls-hybrid-design-01

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Network Working Group                                         D. Stebila
Internet-Draft                                    University of Waterloo
Intended status: Informational                                S. Fluhrer
Expires: January 9, 2020                                   Cisco Systems
                                                               S. Gueron
                                           U. Haifa, Amazon Web Services
                                                           July 08, 2019

            Design issues for hybrid key exchange in TLS 1.3
                   draft-stebila-tls-hybrid-design-01

Abstract

   Hybrid key exchange refers to using multiple key exchange algorithms
   simultaneously and combining the result with the goal of providing
   security even if all but one of the component algorithms is broken,
   and is motivated by transition to post-quantum cryptography.  This
   document categorizes various design considerations for using hybrid
   key exchange in the Transport Layer Security (TLS) protocol version
   1.3 and outlines two concrete instantiations for consideration.

Status of This Memo

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   This Internet-Draft will expire on January 9, 2020.

Copyright Notice

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

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Stebila, et al.          Expires January 9, 2020                [Page 1]
Internet-Draft          stebila-tls-hybrid-design              July 2019

   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Revision history  . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Motivation for use of hybrid key exchange . . . . . . . .   4
     1.4.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.5.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.6.  Related work  . . . . . . . . . . . . . . . . . . . . . .   7
   2.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   3.  Design options  . . . . . . . . . . . . . . . . . . . . . . .  10
     3.1.  (Neg) How to negotiate hybridization and component
           algorithms? . . . . . . . . . . . . . . . . . . . . . . .  10
       3.1.1.  Key exchange negotiation in TLS 1.3 . . . . . . . . .  10
       3.1.2.  (Neg-Ind) Negotiating component algorithms
               individually  . . . . . . . . . . . . . . . . . . . .  10
       3.1.3.  (Neg-Comb) Negotiating component algorithms as a
               combination . . . . . . . . . . . . . . . . . . . . .  11
       3.1.4.  Benefits and drawbacks  . . . . . . . . . . . . . . .  12
     3.2.  (Num) How many component algorithms to combine? . . . . .  13
       3.2.1.  (Num-2) Two . . . . . . . . . . . . . . . . . . . . .  13
       3.2.2.  (Num-2+) Two or more  . . . . . . . . . . . . . . . .  13
       3.2.3.  Benefits and Drawbacks  . . . . . . . . . . . . . . .  13
     3.3.  (Shares) How to convey key shares?  . . . . . . . . . . .  13
       3.3.1.  (Shares-Concat) Concatenate key shares  . . . . . . .  13
       3.3.2.  (Shares-Multiple) Send multiple key shares  . . . . .  14
       3.3.3.  (Shares-Ext-Additional) Extension carrying additional
               key shares  . . . . . . . . . . . . . . . . . . . . .  14
       3.3.4.  Benefits and Drawbacks  . . . . . . . . . . . . . . .  14
     3.4.  (Comb) How to use keys? . . . . . . . . . . . . . . . . .  14
       3.4.1.  (Comb-Concat) Concatenate keys  . . . . . . . . . . .  15
       3.4.2.  (Comb-KDF-1) KDF keys . . . . . . . . . . . . . . . .  16
       3.4.3.  (Comb-KDF-2) KDF keys . . . . . . . . . . . . . . . .  17
       3.4.4.  (Comb-XOR) XOR keys . . . . . . . . . . . . . . . . .  18