PGP chain of trust tools

[Jeremy C. Reed]

I am looking for a way to count the "degrees of separation" or shortest 
path between public PGP keys.

Any tools or libraries I should look at?

I am researching to see if it would be useful for allowing mail (default 
deny stance / guilty-until-proven-innocent since most mail is unwanted) if 
the sender's signature is within 2 or 3 hops from recipient. Or scoring 
the mail up based on the lowest hops.

Anyone know of anything like this? Any research? How far can this scale?

(I now see a spamassassin plugin but doesn't score based on hops away.)

  Jeremy C. Reed