Design of an error-free perfect secrecy system for unknown inputs

This paper studies the behaviour of a crypto-system in a situation where an encoder P_X´R´|U´ is used to encrypt a source U which may be different from the source U´ considered to design the encoder. The original crypto-system is designed to achieve perfect secrecy under P_U´. The resulting system also achieves perfect secrecy regardless of the source distribution. Finally the mismatch in the system resources are calculated when the actual source distribution is known. The number of channel uses remains unchanged at the value for which the system is designed. Upper and lower bounds for the expected key consumption are derived.