Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-02
tls D. Benjamin
Internet-Draft Google, LLC.
Intended status: Standards Track C. Wood
Expires: May 7, 2020 Apple, Inc.
November 04, 2019
Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-02
Abstract
This document describes an interface for importing external PSK (Pre-
Shared Key) into TLS 1.3.
Status of This Memo
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This Internet-Draft will expire on May 7, 2020.
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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
5. Deprecating Hash Functions . . . . . . . . . . . . . . . . . 5
6. Incremental Deployment . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Appendix B. Addressing Selfie . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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. However, importantly, it requires no change to the TLS
1.3 key schedule.
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2. Conventions and Definitions
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