Re: [CFRG] I-D Action: draft-irtf-cfrg-hpke-08.txt

Dear Chris,

HPKE is now in "Awaiting IRSG Reviews" status.

I would suggest updating the draft if there are updates, so that all future
reviewers could find the most up-to-date version in the datatracker.

Regards,
Stanislav

On Wed, 21 Apr 2021 at 01:04, Christopher Wood <caw@heapingbits.net> wrote:

> Thanks, Frank! We applied your suggestions in this PR:
>
>    https://github.com/cfrg/draft-irtf-cfrg-hpke/pull/217
>
> Since this was mostly editorial, we'll hold off publishing a new version
> for now. (Chairs, please let us know if you'd like to see a new version in
> order to move this document forward.)
>
> Best,
> Chris
>
> On Mon, Apr 19, 2021, at 12:51 PM, Frank Denis wrote:
> > General comments on draft-irtf-cfrg-hpke-08:
> >
> > * The document is well-written and every function is clearly specified.
> > I wrote implementations solely based on it, that were verified to be
> > interoperable with other implementations, and didn’t hit anything that
> > required additional information.
> >
> > * The test vectors also appear to be correct.
> >
> > Given this, the maturity of the scheme, and the fact that it is a
> > dependency for other protocols, I’d like to see this document move
> > forward.
> >
> >
> > ---
> >
> >
> > Additional comments:
> >
> >
> > * Section 4:
> >
> > “This function can raise an DecapError” -> “a DecapError”
> >
> >
> >
> > * Section 4: "The Seal() and Open() functions can return a
> NonceOverflowError."
> >
> > The fact that HPKE uses increasing nonces is an internal detail;
> > exposing this to applications looks like the wrong abstraction level.
> >
> > From an application perspective, a more meaningful error would be
> > `TooManyMessages` or a more generic `Overflow` error that could also
> > encompass the case of the AEAD’s internal counter reaching a limit.
> >
> > Using `NonceOverflowError` may catalyze inconsistencies between the
> > specification and its implementations.
> >
> >
> >
> > * Section 4: LabeledExtract() and LabeledExpand() functions
> >
> > The document doesn’t mention any size limits regarding the `suite_id`
> > and `label` parameters of these functions.
> >
> > This can be an issue for implementations favoring static/pre-allocated
> > storage space over heap allocations.
> >
> > Specifying reasonable limits (64 bytes?) may be useful to avoid
> > interoperability issues.
> > These limits can also be documented in section 7.2.1.
> >
> >
> >
> >
> > * Section 8.1.3
> >
> > Splitting this into 2 or 3 paragraphs would make the section more
> readable.
> >
> >
> >
> > * Section 8.4: “Further, because HPKE uses AEAD schemes that are not
> > key-committing”
> >
> > This seems to suggest that non key-committing schemes are a requirement
> > for HPKE, which is not the case.
> > Further revisions of the document can include key-committing schemes,
> > and exported keys can safely be used with such AEADs.
> >
> >
> >
> >
> >
> > Cheers,
> > -Frank.
> >
> >
> >
> > _______________________________________________
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> > CFRG@irtf.org
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> >
>
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