http://nksecur5aoxbew7x4t2jebk7ordomil3a4xubeamno76zexicppwhiad.onion/how-to-pgp.html
PGP also has an feature to "sign" another person's key which builds a web of trust . Alice might talk to Bob, Alice can certify that Bob is who he says he is. Charlie doesn't know Bob, but does know Alice.