Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-00
tls D. Benjamin
Internet-Draft Google, LLC.
Intended status: Experimental C. Wood
Expires: November 15, 2019 Apple, Inc.
May 14, 2019
Importing External PSKs for TLS
draft-ietf-tls-external-psk-importer-00
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.
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This Internet-Draft will expire on November 15, 2019.
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Benjamin & Wood Expires November 15, 2019 [Page 1]
Internet-Draft Importing External PSKs for TLS May 2019
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 2
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
4. Key Import . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Label Values . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Deprecating Hash Functions . . . . . . . . . . . . . . . . . 5
7. Backwards Compatibility and Incremental Deployment . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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
hash function when used in TLS 1.3, even if they are associated with
a different KDF (and 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 different hash
algorithms to produce a set of candidate PSKs, each of which are
bound to a specific hash function. This expands what would normally
have been a single PSK identity into a set of PSK identities.
However, it requires no change to the TLS 1.3 key schedule.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
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