Abstract: In contrast to most or all commonly known symmetric encryption algorithm designs (including the AES candilates such as Rijndacl and Twofish),the Polymorphic Cipher (PMC) can immunize differential power attack. The algorithm is mostly used to encrypt disk files. The problem that would be solved is to improve the Polymorphic Cipher in P2P,and to provide mass produced session keys for two parties across a communication channel. A strong oncway function satisfing the Strict Avalanche Criterion (SAC) was constructed. The security of the function was analyzed by some experimental results and correlated theories.

Key words: Polymorphic cipher, Bit independence criterion, Strong one-way function