Re: [CFRG] Questions for the group from the HPKE presentation

Richard Barnes <rlb@ipv.sx> Fri, 06 August 2021 22:49 UTC

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From: Richard Barnes <rlb@ipv.sx>
Date: Fri, 6 Aug 2021 12:49:21 -1000
Message-ID: <CAL02cgTc34pSUOYqFiCKkfcobtj8y5=LashfsDNdabQ6g6P=gQ@mail.gmail.com>
To: Nick Sullivan <nick=40cloudflare.com@dmarc.ietf.org>
Cc: CFRG <cfrg@irtf.org>, Dan Harkins <dharkins@lounge.org>
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Subject: Re: [CFRG] Questions for the group from the HPKE presentation
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1. I don't think this question is well-formed.  HPKE isn't an API, it is a
construction.  In fact, the "API considerations" section of the HPKE spec
is there precisely because there might be different APIs to an HPKE
implementation.  Given all that, I would be in favor of no action here.
There are several existing ways for an HPKE-based protocol to deal with
out-of-order delivery.

2. Personally, I don't have a use case for either of these.

On Fri, Aug 6, 2021 at 12:31 PM Nick Sullivan <nick=
40cloudflare.com@dmarc.ietf.org> wrote:

> Dear CFRG participants,
>
> At IETF 111, Dan Harkins made a presentation
> <https://datatracker.ietf.org/meeting/111/materials/slides-111-cfrg-new-kems-and-aeads-for-hpke-00>
> with two proposals:
> - a proposal to define new codepoints for HPKE representing new KEMs for
> compressed NIST points
> - a proposal to define new codepoints to support deterministic
> authenticated encryption schemes that don't use a nonce. This is in service
> of the use case of out-of-order delivery of ciphertexts. *In the
> discussion, it was noted that HPKE uses a nonce to ensure that it never
> leaks whether the same plaintext was encrypted twice and that this proposal
> does not provide this security property.*
>
> Also during the discussion, an alternative proposal was made to solve the
> out-of-order use case: modify the API for HPKE to enable the user to reset
> the nonce counter. This API would enable out-of-order delivery of
> ciphertexts with existing HPKE AEADs.
>
> The chairs would like to ask the group a few questions:
> 1) Does the research group support adding an API to HPKE for resetting the
> nonce counter?
> 2) Is there interest in pursuing a work item to explore defining either of
> the following:
> - new codepoints for compressed curve points in HPKE?
> - new codepoints for deterministic authenticated encryption in HPKE (given the
> answer to (1) was no)?
>
>
>
> Regards,
> Nick (for the chairs)
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