[Openid-specs-fapi] A simpler signing solution

Dave Tonge dave.tonge at momentumft.co.uk
Thu Oct 29 14:09:26 UTC 2020


Hi Francis, Brian

I am proposing that we define a new mechanism for http signing in the FAPI
WG.
Obviously it should use existing standards where at all applicable.

As discussed on the call, it would be good to come up with a document that
we can present to the WG.
It seems that we have two options at the moment:

*1. Build on the OBE spec*
*2. Build on dPOP*

At first I was leaning towards option 1, but after further review of the
OBE spec I personally am very much leaning towards option 2. I think the
OBE spec is not fit for purpose, it adds lots of unnecessary complexity
just because its trying to join draft-cavage and  an earlier version of the
UK OpenBanking signing spec together. I may try and show some worked
examples as I think my suggestion will result in a small http payload even
if some header values are repeated.

I will send through an example shortly.

Dave





On Thu, 29 Oct 2020 at 14:12, Brian Campbell via Openid-specs-fapi <
openid-specs-fapi at lists.openid.net> wrote:

>
> 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
>> CTO
>> [image: Moneyhub Enterprise]
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>> Moneyhub Financial Technology, 5th Floor, 10 Temple Back, Bristol, BS1 6FL
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>>
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-- 
Dave Tonge
CTO
[image: Moneyhub Enterprise]
<http://www.google.com/url?q=http%3A%2F%2Fmoneyhubenterprise.com%2F&sa=D&sntz=1&usg=AFQjCNGUnR5opJv5S1uZOVg8aISwPKAv3A>
Moneyhub Financial Technology, 5th Floor, 10 Temple Back, Bristol, BS1 6FL
t: +44 (0)117 280 5120

Moneyhub Enterprise is a trading style of Moneyhub Financial Technology
Limited which is authorised and regulated by the Financial Conduct
Authority ("FCA"). Moneyhub Financial Technology is entered on the
Financial Services Register (FRN 809360) at fca.org.uk/register.
Moneyhub Financial
Technology is registered in England & Wales, company registration number
06909772 .
Moneyhub Financial Technology Limited 2018 ©

DISCLAIMER: This email (including any attachments) is subject to copyright,
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Whilst reasonable efforts are made to ensure that any attachments are
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attachments) are those of the author and do not necessarily represent the
opinions of Moneyhub Financial Technology Limited or of any other group
company.

-- 


Moneyhub Enterprise is a trading style of Moneyhub Financial Technology 
Limited which is authorised and regulated by the Financial Conduct 
Authority ("FCA"). Moneyhub Financial Technology is entered on the 
Financial Services Register (FRN 809360) at https://register.fca.org.uk/ 
<https://register.fca.org.uk/>. Moneyhub Financial Technology is registered 
in England & Wales, company registration number 06909772. Moneyhub 
Financial Technology Limited 2020 © Moneyhub Enterprise, Regus Building, 
Temple Quay, 1 Friary, Bristol, BS1 6EA. 

DISCLAIMER: This email 
(including any attachments) is subject to copyright, and the information in 
it is confidential. Use of this email or of any information in it other 
than by the addressee is unauthorised and unlawful. Whilst reasonable 
efforts are made to ensure that any attachments are virus-free, it is the 
recipient's sole responsibility to scan all attachments for viruses. All 
calls and emails to and from this company may be monitored and recorded for 
legitimate purposes relating to this company's business. Any opinions 
expressed in this email (or in any attachments) are those of the author and 
do not necessarily represent the opinions of Moneyhub Financial Technology 
Limited or of any other group company.
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