[Openid-specs-fapi] A simpler signing solution

Brian Campbell bcampbell at pingidentity.com
Thu Oct 29 13:11:57 UTC 2020


On Thu, Oct 29, 2020 at 5:10 AM Francis Pouatcha <
Francis.Pouatcha at adorsys.com> wrote:

> I agree with Dave we shall not define a new signature mechanism.
>

As I understood the message that started this thread and the discussion
about it during the call yesterday, Dave is very much proposing that we
define a new mechanism. Maybe there's some semantic difference or
miscommunication here but I'm confused by your statement.


> As for the replacement of RFC3230 with
> https://datatracker.ietf.org/doc/draft-ietf-httpbis-digest-headers/,
> adding a signature header field to indicate the mechanism used to digest
> the http body might solve the problem.
>

What problem? I just wanted to note that there was work underway to
update/obsolete RFC3230 as it seemed relevant given Dave's initial proposal
relied on RFC3230. But I don't understand what problem you're suggesting
would be introduced by the new document or how that would solve it.

I am a bit concerned (or rather just don't really understand the
implications of) about RFC3230 and it's successor digesting the "instance"
or "representation" of the resource as opposed to the payload of the
message itself. But as far as I can tell RFC3230 and
https://datatracker.ietf.org/doc/draft-ietf-httpbis-digest-headers/ are the
same in this regard but just use different language to describe it.





>
> ------------------------------
> *From:* Openid-specs-fapi <openid-specs-fapi-bounces at lists.openid.net> on
> behalf of Brian Campbell via Openid-specs-fapi <
> openid-specs-fapi at lists.openid.net>
> *Sent:* Monday, October 26, 2020 10:05 AM
> *To:* FAPI Working Group List <openid-specs-fapi at lists.openid.net>
> *Cc:* Brian Campbell <bcampbell at pingidentity.com>
> *Subject:* Re: [Openid-specs-fapi] A simpler signing solution
>
> As someone who has expressed distaste for pretty much every HTTP signature
> scheme attempted and also tried to keep the scope of DPoP to
> proof-of-possession so that it doesn't try to be yet another HTTP signature
> scheme, I don't actually hate this idea as much as you might expect. It
> does seem simpler than others and maybe finds a pragmatic place in the
> continuum of doing enough to address the basic need while not going
> overboard. Maybe anyway.
>
> Is there only need to have a signature for requests? It'd become a lot
> more than building on DPoP with one additional claim, if it needs to cover
> responses.
>
> I've not looked at either in detail, TBH, but there is work underway that
> aims to obsolete RFC 3230
> https://datatracker.ietf.org/doc/draft-ietf-httpbis-digest-headers/ which
> should be considered if this is pursued.
>
>
>
>
>
>
>
> On Fri, Oct 23, 2020 at 7:41 AM Dave Tonge via Openid-specs-fapi <
> openid-specs-fapi at lists.openid.net> wrote:
>
> Dear WG
>
> After looking in more detail at the proposed OBE signing spec, I'm really
> quite concerned and think that this WG should work on something else
> simpler as soon as possible.
>
> My suggestion is:
>  - abandon "detached" jwts
>  - build on dPoP by defining one additional claim - `htd` - the http body
> digest
>  - recommend that any info in headers that needs to be integrity protected
> is put in the body
>
> So you would end up with a JWT with a standard header (no need for any
> `crit` claims), and a body that would be something like this:
>
> {
>      "jti":"-BwC3ESc6acc2lTc",
>      "htm":"POST",
>      "htu":"https://server.example.com/payment",
>
>      "htd":"SHA-256=+xeh7JAayYPh8K13UnQCBBcniZzsyat+KDiuy8aZYdI=",
>      "iat":1562262616
> }
> The `htd` value would be created according to the instructions in RFC3230
>
> Verification rules would be the same as dPoP, but with the addition of the
> verification of the `htd` value.
>
> The advantage of this approach:
>  - should be supported by all standard JWT libraries
>  - should be much easier to get interoperability as there aren't the same
> serialisation problems as draft-cavage or the OBE profile.
>  - only one additional claim needs to be registered in the IANA registry
>
> Any feedback?
>
> @anders - I know you will suggest rather using rfc8785, and I think that
> as a WG we should definitely keep monitoring support for that, but the
> reality is that at the moment there isn't widespread adoption.
>
> Thanks
>
> Dave
>
>
>
>
> --
> Dave Tonge
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