The Intrinsic Conditional Mutual Information and Perfect Secrecy

Ueli Maurer and Stefan Wolf


Conditions are derived for the possibility and impossibility of 
information-theoretic secret-key agreement by public discussion.
A new quantity, the intrinsic information, is introduced and its
relationship to secret-key agreement is investigated. A new protocol 
is described that allows secret-key agreement in situations for 
which the previous protocols fail.