Guidance for External PSK Usage in TLS
draft-dt-tls-external-psk-guidance-00

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Last updated 2020-03-09
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tls                                                           R. Housley
Internet-Draft                                            Vigil Security
Intended status: Informational                                J. Hoyland
Expires: 10 September 2020                               Cloudflare Ltd.
                                                                M. Sethi
                                                                Ericsson
                                                               C.A. Wood
                                                            9 March 2020

                 Guidance for External PSK Usage in TLS
                 draft-dt-tls-external-psk-guidance-00

Abstract

   This document provides usage guidance for external Pre-Shared Keys
   (PSKs) in TLS.  It lists TLS security properties provided by PSKs
   under certain assumptions and demonstrates how violations of these
   assumptions lead to attacks.  This document also discusses PSK use
   cases, provisioning processes, and TLS stack implementation support
   in the context of these assumptions.  It provides advice for
   applications in various use cases to help meet these assumptions.

Note to Readers

   Source for this draft and an issue tracker can be found at
   https://github.com/tlswg/external-psk-design-team
   (https://github.com/tlswg/external-psk-design-team).

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 https://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 10 September 2020.

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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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  PSK Security Properties . . . . . . . . . . . . . . . . . . .   3
   4.  Recommendations for External PSK Usage  . . . . . . . . . . .   4
   5.  Privacy Properties  . . . . . . . . . . . . . . . . . . . . .   4
   6.  External PSK Use Cases and Provisioning Processes . . . . . .   5
     6.1.  Provisioning Examples . . . . . . . . . . . . . . . . . .   6
     6.2.  Provisioning Constraints  . . . . . . . . . . . . . . . .   7
     6.3.  Stack Interfaces  . . . . . . . . . . . . . . . . . . . .   7
       6.3.1.  PSK Identity encoding and comparison  . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   This document provides usage guidance for external Pre-Shared Keys
   (PSKs) in TLS.  It lists TLS security properties provided by PSKs
   under certain assumptions and demonstrates how violations of these
   assumptions lead to attacks.  This document also discusses PSK use
   cases, provisioning processes, and TLS stack implementation support
   in the context of these assumptions.  It provides advice for
   applications in various use cases to help meet these assumptions.

   The guidance provided in this document is applicable across TLS
   [RFC8446], DTLS [I-D.ietf-tls-dtls13], and Constrained TLS
   [I-D.rescorla-tls-ctls].

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2.  Conventions and Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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