This paper provides a general treatment of privacy amplification by pu
blic discussion, a concept introduced by Bennett, Brassard, and Robert
for a special scenario, Privacy amplification is a process that allow
s two parties to distill a secret key from a common random variable ab
out which an eavesdropper has partial information, The two parties gen
erally know nothing about the eavesdropper's information except that i
t satisfies a certain constraint, The results have applications to unc
onditionally secure secret-key agreement protocols and quantum cryptog
raphy, and they yield results on wiretap and broadcast channels for a
considerably strengthened definition of secrecy capacity.