Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-05

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tls                                                          D. Benjamin
Internet-Draft                                              Google, LLC.
Intended status: Standards Track                               C.A. Wood
Expires: 20 November 2020                                     Cloudflare
                                                             19 May 2020

                    Importing External PSKs for TLS
                draft-ietf-tls-external-psk-importer-05

Abstract

   This document describes an interface for importing external Pre-
   Shared Keys (PSKs) into TLS 1.3.

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
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   This Internet-Draft will expire on 20 November 2020.

Copyright Notice

   Copyright (c) 2020 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
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  PSK Import  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  External PSK Diversification  . . . . . . . . . . . . . .   4
     4.2.  Binder Key Derivation . . . . . . . . . . . . . . . . . .   5
   5.  Deprecating Hash Functions  . . . . . . . . . . . . . . . . .   6
   6.  Incremental Deployment  . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     10.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Addressing Selfie  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   TLS 1.3 [RFC8446] supports Pre-Shared Key (PSK) authentication,
   wherein PSKs can be established via session tickets from prior
   connections or externally via some out-of-band mechanism.  The
   protocol mandates that each PSK only be used with a single hash
   function.  This was done to simplify protocol analysis.  TLS 1.2
   [RFC5246], in contrast, has no such requirement, as a PSK may be used
   with any hash algorithm and the TLS 1.2 PRF.  While there is no known
   way in which the same external PSK might produce related output in
   TLS 1.3 and prior versions, only limited analysis has been done.
   Applications SHOULD provision separate PSKs for TLS 1.3 and prior
   versions when possible.

   To mitigate against any interference, this document specifies a PSK
   Importer interface by which external PSKs may be imported and
   subsequently bound to a specific KDF and hash function for use in
   (D)TLS 1.3.  In particular, it describes a mechanism for
   differentiating external PSKs by the target KDF, (D)TLS protocol
   version, and an optional context string.  This process yields a set
   of candidate PSKs, each of which are bound to a target KDF and
   protocol, that are separate from those used in (D)TLS 1.2 and prior
   versions.  This expands what would normally have been a single PSK
   and identity into a set of PSKs and identities.

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