  In this paper we try to unify the frameworks of definitions of semantic
security, indistinguishability and non-malleability by defining semantic
security in comparison based framework. This facilitates the study of relations
among these goals against different attack models and makes the proof of the
equivalence of semantic security and indistinguishability easier and more
understandable. Besides, our proof of the equivalence of semantic security and
indistinguishability does not need any intermediate goals such as non
devidability to change the definition framework.
