Since I don’t have George here to tell me his fingerprint in person, I’ll go through a few extra steps. I’ve already confirmed that my trusted introducer, Mike Burns, has signed George’s key. Next, I’ll ask George to give me his fingerprint in a couple of different locations: an email from George’s thoughtbot address, our company’s Slack room, and his Twitter account . Once it’s been confirmed in those locations, and given that I know George personally and he gave me the key id to download in the first place, I’m willing to sign his key and confirm that I believe it to be controlled by George.
Full article: http://robots.thoughtbot.com/pgp-and-you