I'm not sure what you mean by out of band

If you mean that it is communicated over TCP/IP(what i gathered from reading the doc), what is stopping someone who has access to whatever is connected to your IP from redirecting traffic to that port in order to do what was already discussed.

if you mean that it is shared in person off the internet, then what is the point of this program. Diffe Hellman, ECC, zero Knowledge proofs are all dependent on the discrete log problem being hard, so you might as well just start broadcasting to their ip with the key that they gave you in person instead of going through the trouble(and increase in vulnerability) of trying to establish that the person is who they say they are. maybe I'm wrong but I don't think that math is wrong.

in any case, I feel like the problem for this program stems from the fact that validating the IP address of the person is much more complicated than it seems. Its pretty much the reason centralized databases are needed for connections between people(those are bad things in our world now).

this is pretty much what is needed for this http://en.wikipedia.org/wiki/Web_of_trust

I wonder if the pubkeys could be maintained in a system such as namecoin? [never used namecoin, but it sounds right]