On Sun, Dec 22, 2024, 2:35 PM Brian Campbell
<bcampbell=40pingidentity....@dmarc.ietf.org> wrote:
>
>
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> On Sat, Dec 21, 2024 at 1:37 PM Joseph Heenan <jos...@authlete.com> wrote:
>>
>>
>>  < ...  snip ... >
>>
>> The current text is clear that there are situations where issuer-verifier 
>> linkability can’t be fully prevented.
>>
>> Process wide, I believe if you think the text currently in the specification 
>> is inadequate, you need to make a concrete suggestion that doesn’t introduce 
>> new problems and hence can gain consensus with working group members.
>>
>
> I believe this kinda gets at the heart of things here. It does for me anyway. 
> There are indeed some legitimate and not obvious or intuitive privacy 
> considerations inherent in salted-hash based selective disclosure mechanisms 
> like SD-JWT (also SD-CWT, ISO mdoc/mDL, and probably others I'm unaware of) 
> that deserve serious treatment in a prospective RFC. The authors on this 
> draft have endeavored to provide thoughtful treatment of the topic(s) and 
> believe that the current text, while obviously not perfect, is reasonably 
> clear and provides sufficient discourse on the subject(s). Watson feels 
> otherwise, which is a completely reasonable viewpoint. However, at this stage 
> of things especially, I believe it is incumbent on him to provide a concrete 
> suggestion that doesn't introduce new/unwanted problems and can be viewed as 
> at least acceptable as rough consensus of the working group. This thread and 
> several others of a very similar vein over the last few months suggests that, 
> from my perspective as both draft author and WG participant anyway, the 
> various proposals don't meet that bar.

Brian,

I strongly object to our with your procedural summaries. I think it's
an underhanded way to admit that the current text is inadequate while
excusing inaction on your part as draft author, and try to ape the
authority of the WG chairs.  That's a bit besides the real point, but
I do want to register my profound unease with this rhetorical
strategy.

Nobody here, including you here disagrees that there are subtle issues
that deserve careful treatment.  I think, and IETF wide consensus has
said that the place for those considerations is in the security
considerations and privacy considerations of this draft. We don't
sweep those problems under the rug anymore. Saying we need another RFC
is saying "go spend x years trying to get this work that this group
isn't interested in done somewhere while I throw roadblocks in your
way, and real users face harms that we couldn't be arsed to put one
paragraph in talking about". TLS 1.3 didn't just have a securities
consideration section, it had 3 entire appendices going into careful
detail about what it does and doesn't do, how to work around it, etc.

The fact that you and everyone else feels content to shoot down text
rather than try to meet me halfway shows that this isn't an honest
attempt to achieve rough consensus or conversely say my views are in
the rough because of actually thinking through the issue.  I've been
consistent in raising this issue for over a year: to pretend that the
WGLC is at all relevant to where we are is a ridiculous excuse made
possible only by your own inaction on this issue. I've tried to tweak
the text to make it work better, at length, but it's very hard when
people say they have concerns without being clear or suggesting
alternatives. I'd appreciate you doing me the same courtesy, rather
than sitting back and saying "nah, no one agrees enough for us to
handle it". I agree that my text may be too limiting or overly
prescriptive, but the people closer to the problem need to provide
input if there is going to be a text we can live with.

The only reason this is still an issue is refusal to address it: to
add a clear description of what the issuer-verifier linkability
problem means in practice together with actionable mitigations. Why
hasn't that happened? Secondly the verifier-verifier unlinkability
really doesn't have much in the way of actual mitigations: it says you
can use one-use credentials, etc. but doesn't mandate, provide
designs, explain how to issue based on a previous credential etc. It
at least has that material.

To be absolutely clear, this is what the current text says in its most
relevant section "In considering Issuer/Verifier unlinkability, it is
important to note the potential for an asymmetric power dynamic
between Issuers and Verifiers. This dynamic can compel an otherwise
honest Verifier into collusion. For example, a governmental Issuer
might have the authority to mandate that a Verifier report back
information about the credentials presented to it. Legal requirements
could further enforce this, explicitly undermining Issuer/Verifier
unlinkability. Similarly, a large service provider issuing credentials
might implicitly pressure Verifiers into collusion by incentivizing
participation in their larger ecosystem. Deployers of SD-JWT must be
aware of these potential power dynamics, mitigate them as much as
possible, and/or make the risks transparent to the End-User."

That text has a lot of problems:

- It presents the issue as one of coercion or malfeasance, rather than
e.g. excessive logging, or some other information leak letting the
issuer see what the verifier knows.
- It says deployers must mitigate the power dynamics, rather than use
technical means, with no real guidance as to what that mitigation
looks like
- It doesn't say what the risks are that must be made transparent

It's not something that someone can use to say "no, we shouldn't do X"
for any X.

All I've been asking to add now is a specific example of what a user
might need to know and that if this can't be achieved, don't use
SD-JWT. I'm surprised by the enormous pushback to this. All I want to
know is is there some form of this we could live with, or what are the
concrete issues people have with the proposal. So far I've gotten that
actually naming mitigations is a problem. How on earth do I work with
that?

Conversely, if you think age verification with SD-JWT is fine, save me
the time and let me know.

Sincerely,
Watson
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