[messaging] Zero knowledge proofs of passport

Trevor Perrin trevp at trevp.net
Mon Jul 28 11:15:18 PDT 2014

On Sun, Jul 27, 2014 at 12:45 PM, Mike Hearn <mike at plan99.net> wrote:
>> Trusting national passport agencies seems wrong for this use case.
> Now it would be. But I think it's worth remembering that at the start
> Greenwald was not a well known national security journalist, he was a
> relatively obscure columnist and blogger. He didn't expect what happened and
> wasn't using PGP as a result. All different now of course, but it's hard for
> people to learn PGP, and hard for them to predict they might want to use it.
> And that in turn means it's hard to bootstrap a secure conversation, as
> Snowden learned the hard way when he failed to do so.

That's true, but I don't think your proposal solves this.

Your proposal amounts to: Glenn, or anyone who's scanned his passport,
can register a public-key in his name by running some "SNARK" tool to
generate proof of passport fields and a public key he chooses.  Then
this proof can be published to some global directory.

Glenn still needs to generate a keypair, manage his private-key,
decrypt messages, etc.  You argue that scanning your passport is
easier than registering for an S/MIME cert or PKP key-signing / WoT
path-building, but almost no-one does these.

Better comparables - and more plausible solutions IMO - would be
publishing your fingerprint/key/proof widely (via your website, social
media, friends, etc.), or registering with keyserver(s) that
authenticate you via email.

It's worth re-iterating that your trust model allows anyone who's
scanned your passport to forge a proof for you, which is particularly
bad for the well-travelled journalists you're imagining protecting.

And in other ways this doesn't address the concrete situation of
source / journalist communications:
 - Identity-hiding and relationship-hiding are also important; the
problem is bigger than key lookup.
 - The key lookup aspect could be solved by the journalist publishing
his key or fingerprint or similar via his organization's web presence.

> Usability suffers a lot if asymmetric crypto gets directly exposed to end
> users. That's why I'm interested in the directory problem. A good key
> directory (even if the users don't really realise that's what it is) seems
> like a crucial feature for making it as brainless as possible.

Again true, preaching to choir etc.

But the problems with, say, PGP keyservers are very basic - keys can't
be deleted, and anyone can add keys for anyone (which a lot of people
will just download and immediately accept!)

There's a ton of progress that could be made by sane engineering and
fixing things like this, which is why I'm grumpy and skeptical about
new crypto exotica...


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