Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-03

Document Type Active Internet-Draft (tls WG)
Last updated 2020-02-21 (latest revision 2020-02-15)
Replaces draft-wood-tls-external-psk-importer
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tls                                                          D. Benjamin
Internet-Draft                                              Google, LLC.
Intended status: Standards Track                               C.A. Wood
Expires: 18 August 2020                                      Apple, Inc.
                                                        15 February 2020

                    Importing External PSKs for TLS
                draft-ietf-tls-external-psk-importer-03

Abstract

   This document describes an interface for importing external PSK (Pre-
   Shared Key) 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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

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   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on 18 August 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
   Provisions Relating to IETF Documents (https://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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Key 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  . . . . . . . . . . . . . . . . . . .   7
   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  . . . . . . . . . . . . . . . . . . . . . . .  10

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.  This means that
   external PSKs could possibly be re-used in two different contexts
   with the same hash functions during key derivation.  Moreover, it
   requires external PSKs to be provisioned for specific hash functions.

   To mitigate these problems, external PSKs can be bound to a specific
   KDF and hash function when used in TLS 1.3, even if they are
   associated with a different hash function when provisioned.  This
   document specifies an interface by which external PSKs may be
   imported for use in a TLS 1.3 connection to achieve this goal.  In
   particular, it describes how KDF-bound PSKs can be differentiated by
   the target (D)TLS protocol version and KDF for which the PSK will be
   used.  This produces a set of candidate PSKs, each of which are bound
   to a specific target protocol and KDF.  This expands what would
   normally have been a single PSK identity into a set of PSK
   identities.

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