EPOC (Efficient Probabilistic Public Key Encryption) is aprobabilisticpublic-keyencryption scheme.
EPOC was developed in 1999 by T. Okamoto, S. Uchiyama and E. Fujisaki ofNTT Labs in Japan. It is based on therandom oracle model, in which a primitive public-key encryption function is converted to a secure encryption scheme by use of a truly random hash function; the resulting scheme is designed to besemantically secure against achosen ciphertext attack.
EPOC's primitive encryption function is the OU (Okamoto–Uchiyama) function, in which to invert the OU function is proven to be as hard asfactoring a composite integer public key. There are three versions of EPOC:
EPOC-1 is designed for key distribution; EPOC-2 and EPOC-3 are designed for both key distribution and encrypted data transfer.
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