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Re: Signature Crypto Algorithm Details

From: Brian Campbell <bcampbell@pingidentity.com>
Date: Fri, 14 Jan 2022 13:58:45 -0700
Message-ID: <CA+k3eCQ1bCUf-BEiC66c+NKh=ze0jPrkrPzDdpk6ZDCw5w=tTg@mail.gmail.com>
To: Justin Richer <jricher@mit.edu>
Cc: HTTP Working Group <ietf-http-wg@w3.org>
I'd +1 the r and s concatenation approach.

On Fri, Jan 14, 2022 at 9:42 AM Justin Richer <jricher@mit.edu> wrote:

> Hi all,
>
> In the Signatures draft, we’ve got a bunch of strictly-defined algorithms
> for people to be able to use out of the box. Crypto primitives are often
> parameterized, giving a lot of flexibility and choice. The idea here though
> is that if you’re pulling something out of the named algorithm registry,
> you wouldn’t have choices to make about how to apply it. (You can, as
> always, go off and do your own algorithm within your own ecosystem without
> using the registry values.)
>
> In any event, two elliptic curve algorithms have caught my attention the
> last couple weeks and I am looking to drum up feedback. First, Edwards
> curve algorithms, specifically ed25519. It’s been requested by a number of
> people out there that we add this, so I’ve been working out what parameters
> we’d need within the spec text to make it interoperable. From early
> implementations and feedback, we’ve settled on a PureEdDSA algorithm with
> no pre-hash of the message input, since that seems to be the most common
> and accepted version of this. We’re preparing text to add this to the
> draft, and I’m looking to confirm that choice if anyone has any strong
> feelings on the matter.
>
> Second, the ECDSA algorithm that we define over curve P256 has its own
> snag that we didn’t realize: the signature in the mathematical model is two
> separate numbers, r and s. We need to encode a single value, and all the
> libraries that I used take the approach that you just concatenate the two
> into a single 64-byte array and call that the signature. However some
> implementors have gotten back to me that their libraries use an alternative
> method of encoding, using ASN.1 to wrap the two integers into an ASN.1
> structure. A quick survey shows that this is supported on many libraries,
> but it does have the drawback of pulling in explicit ASN.1 into the
> signature definition where it isn’t needed elsewhere. I’m currently leaning
> towards more carefully defining the concatenation approach, similar to what
> JOSE uses in this case, but I am seeking feedback on this choice.
>
> I know that this is a question more for the security/crypto crowd, and
> we’ll be reaching out there as well for sure, but I wanted to get a feel
> for any preference within this community that would be implementing and
> dealing with this spec on the other side. What do your libraries support
> for ECDSA and EdDSA inputs and outputs? Do you have a strong feeling on
> either of these choices?
>
> Thanks,
>  — Justin
>

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Received on Friday, 14 January 2022 21:00:25 UTC

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