Keybase

[Peter S. May]

Hiya —

So, I've just redeemed an alpha invite to a new service called Keybase
(https://keybase.io) that I haven't seen mentioned yet in gnupg-users.
GnuPG is pretty central to it, or at least it can be, and I'm writing
mostly to get it on everyone's radar and register a couple of first
impressions.

I'm also curious what you might have to say about the soundness of the
"proofs" used by this scheme, whether the holes I've imagined are real,
and whether I've missed anything larger.


What it claims to be
--------------------

From the front:

"Get a public key, safely, starting just with someone's social media
username(s). From there, unbounded potential!"

"And have you ever been invited to a key party? Yeah, we neither :-("

The front page appears to describe, in some vagueness, a system of
exchanging usernames that is somehow a suitable substitute for actual
offline key exchange.

(I find such a claim questionable; however, I haven't taken the time to
completely map it out. But let's say some person other than me signs an
assertion saying "My name is Eve, public key signature is ABCDEFGH, and
@psmay is my Twitter account". Let's say, for the sake of argument, that
I don't treat my Twitter password with the same respect with which I
treat my passphrase, and the attacker tweets the assertion. Then, let's
say someone else tries to look up a public key for @psmay and finds that
assertion. Private messages intended for me are now going to my
doppelganger. I think this serves to suggest that the assertion itself
may tend to be only as strong as a weaker link than the signature
itself.)

(I'm also a little more offended than I should be by the key party
comment. I ran one once.)

What it actually seems to be
----------------------------

Keybase, from what I've determined so far, is each of

*   a set of client idioms for
    *   direct exchange and verification of "proofs", i.e. signed
        assertions
        *   authoring a canonicalized JSON assertion that an online
            asset, either cryptographic in nature (like a bitcoin
            address) or not so cryptographic (such as a social
            networking username), belongs to a keyholder
        *   signing said assertion
        *   posting a signed assertion (or some sort of surrogate
            signature sufficient to determine that such an assertion has
            been signed) to demonstrate control of the asset
            *   Examples:
                *   Control of a Github account is demonstrated by
                    posting a Markdown document containing the assertion
                    and signature as a Gist
                *   Control of a Twitter account is demonstrated by
                    posting, as a tweet, a truncated signature and a
                    link to a signed assertion to which that truncated
                    signature is associated.

        *   verifying found assertions made by another user against that
            user's public key

    *   discovery and exchange of proofs by way of the central directory
        implemented by the website
    *   generic sign, encrypt, decrypt, verify operations, with asserted
        usernames as an available substitute for key ids

*   a command-line program, `keybase`, that implements the client idioms
    in terms of GnuPG
*   a web application, `http://keybase.io`, the also implements the
    client idioms
*   an online directory (also part of `http://keybase.io`) for discovery
    and exchange of proofs (which is intended, by design, not to be
    strictly necessary for authoring, signing, exchanging, or verifying
    proofs, but merely a convenient place for these things to happen)

Of particular note is that the website itself implements the client
protocol, though it is not the only option (there is the command-line
client, and crypto operations for the website can also be accomplished
through supplied, auditable shell commands involving gpg, perl, and
curl). A user may post a client-encrypted copy of a private key to be
stored on the server, after which crypto operations can be executed
directly in the browser in JavaScript. (They acknowledge that "Some
people have strong feelings about this, for good reason." I'm among
them.)

The players
-----------

The co-founders of Keybase are also co-founders of OkCupid. As sketchy
as that might sound now, the history of OkCupid reaches farther back to
a pre-social-networking social networking site called SparkMatch, a
subsite of TheSpark, with roots in the fabled academic communities of
Harvard and MIT. Do with that what you will.


Cheers

___
Peter S. May
http://psmay.com/
A0E6 3851 9ABB 112E 7303
DD91 7A2E 91FB 7885 DAFC