Relationship of Three Cryptographic Channels in the UC Framework

Abstract

The relationship of three cryptographic channels, secure channels (SC), anonymous channels (AC) and direction-indeterminable channels (DIC), was investigated by Okamoto. He showed that the three cryptographic channels are reducible to each other, but did not consider communication schedules clearly as well as composable security. This paper refines the relationship of the three channels in the light of communication schedules and composable security. We model parties by the task-probabilistic input/output automata (PIOA) to treat communication schedules, and adopt the universally composable (UC) framework by Canetti to treat composable security. We show that a class of anonymous channels, two-anonymous channels (2AC), and DIC are reducible to each other under any schedule and that DIC and SC are reducible to each other under some types of schedules, in the UC framework with the PIOA model.KeywordsSecure Channel (SC)Two-Anonymous Channel (2AC)Direction-Indeterminable Channel (DIC)Universal Composability (UC)Probabilistic Input/Output Automaton (PIOA)