Wikipedia article on Man-in-the-middle attack mentions, in the list of defenses against it, some method called "Carry-forward verification", but it does not explain it. I am curious about different MITM defense methods in general. Can someone describe this method or point to description? (Of course googling does not give anything except wikipedia itself with its clones.)
ps. Would be grateful also if someone points me to more elaborated survey of MITM defense methods (and especially for key exchange).