Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-03
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2020-02-21
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draft-wood-tls-external-psk-importer
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Joseph Salowey <joe@salowey.net>
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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
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 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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Internet-Draft Importing External PSKs for TLS February 2020
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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