On Tue, Apr 28, 2015 at 10:14 AM, Derek Atkins <derek(_at_)ihtfp(_dot_)com>
wrote:
Phillip Hallam-Baker <phill(_at_)hallambaker(_dot_)com> writes:
The idea is that when someone is typing in the fingerprint, the client
can perform a parity check to see if the fingerprint data is correct
as the user is typing rather than waiting to the end.
Why would someone type in a fingerprint? Could you give me a use-case
for that?
The only use case I've ever seen is that you copy-and-paste it onto your
business card (or presentation, or other printed/distributed material),
and then the verifier performs a visual match later between the printed
material and their verification screen.
Well, I would flip it round then and say, why would a user ever
interact with a fingerprint other than on a business card?
There are many other cases where devices will be exchanging
fingerprints under the covers. But I don't expect the user to ever see
those. If we meet at IETF and bump iPhones then I don't expect to see
a fingerprint unless I open up an 'advanced' tab.
Same for email. Lets imagine this email had a header that said:
Fingerprint: ufi:xxxx-xxxx-xxxx-xxxx-xxxx-xxxx;
holder=phill(_at_)hallambaker(_dot_)com
Your email client could collect that automatically and take it as
probable cause to suspect that the specified fingerprint might be
associated with phill(_at_)hallambaker(_dot_)com.
Now as stated, that would not be proof but we can add in mechanisms
that would enable a challenge-response verification to be performed
automatically and transparently. that is slightly more complex than it
sounds because we have to avoid getting fooled by mailing lists, etc.
But at this point any mailing list that isn't giving the correct SMTP
headers is likely being spam filtered away anyhow.
But for these applications we can use a 256 or even 512 bit
fingerprint and it isn't necessary to base32 encode it either unless
we think it might get translated to a little-fingerprint at some
point.
Same goes for QR codes. There really is no need for the QR code to be
based on the base32 encoding, it can be calculated from the binary or
base64.
When it comes down to it, business cards and legal documents are the
only places I expect the base32 fingerprint to be seen.
That said, I am really on the fence on Base32C. Another way to skin
the same cat would be to have an interactive protocol with whatever
service uses fingerprints as index terms. With a population of a
million keys (2^20) a fingerprint should start to become unique after
the fourth letter is typed. So the service could easily construct a
'did you mean' concordance.
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