Now really, we want to tie the key to a person -- even if they
resleeve (a. la. Altered Carbon, [0]). Thankfully, releeving is not
(yet) possible, so we don't have to deal with that. All we have to do
is to tie a key to a real live person, and do it in a fashion that is
reproducible and testable.
Traditionally, you establish identity for a person by one or
more of:
A) Something they (and only they) have. This is previously issued
tokens of some kind (passports, id cards, secure tokens,
etc). There are three things needed to make this even the least bit
reliable:
1) You need to trust the process of deploying the thing they have;
someone must establish in some manner who the person is, before
the token is given out
2) The token should not be easily duplicated, stolen, and
reused. This requires some care on the part of the token holder
3) You can actually verify that the token is genuine and decipher
who the token was issued to without being spoofed.
B) Something that the person is. Biometrics, etc. Again, the caveats
apply about spoofing, and trusting you know what it is that the
person is supposed to be (is it really Mr X's retina scan I am
trying to match?)
C) Something they know. Shared secrets, passwords, knowledge of
events past you and the person knows, and no one else could.
Madduck seems to put a whole lot of unjustified confidence in C)
above. You might think you know the person pretending to be Mr X, but
really, most of us at debconf have done little to verify C to any
degree of reliability. If all you can say is that person owns that
email address, why are you even bothering to have a signing party? You
don't need it to ascertain that a key owner controls an email address
by some other persons signature; just send a encrypted message to that
email address and ask for a reply. Done.
So, A. Now, most countries where people are allowed to come to
my country from have to demonstrate a process by which they issue
travel documents to their citizens, and I have established for myself
that if it meets the State departments needs, then !.1 is satisfied
for me.
A.2 is somewhat harder, but being careless about your travel
documents has real world consequences, and most countries whose
citizens can travel to mine have made travel docs hard to
duplicate. Not impossible, but hard.
A.3 seems to be the part which receives most criticism; I can
surely be spoofed by a well forged travel document. But it does raise
the bar for someone who needs my signature, and I think it meets my
threshold of return on effort to sign the key, and put a modicum of
trust in the assertion that we have nailed that key to a real human
being.
So while signing keys is not about governments, as Russ said, it
is about establishing identity, and government issued identity
documents are better proxies for establishing that than I can be
bothered to do myself.
And, on my day job, people will fall over laughing about basing
identity on what someone says often enough over a period of time with
no further checks. And yes, my tummy still hurts.