EPOC (Efficient Probabilistic Public Key Encryption) is a
probabilistic public-key
Public-key cryptography, or asymmetric cryptography, is the field of cryptographic systems that use pairs of related keys. Each key pair consists of a public key and a corresponding private key. Key pairs are generated with cryptographic alg ...
encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can de ...
scheme.
EPOC was developed in 1999 by T. Okamoto, S. Uchiyama and E. Fujisaki of
NTT Labs in Japan. It is based on the
random 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 be
semantically secure In cryptography, a semantically secure cryptosystem is one where only negligible information about the plaintext can be feasibly extracted from the ciphertext. Specifically, any probabilistic, polynomial-time algorithm (PPTA) that is given the cip ...
against a
chosen ciphertext attack
A chosen-ciphertext attack (CCA) is an attack model for cryptanalysis where the cryptanalyst can gather information by obtaining the decryptions of chosen ciphertexts. From these pieces of information the adversary can attempt to recover the hidd ...
.
EPOC's primitive encryption function is the OU (Okamoto–Uchiyama) function, in which to invert the OU function is proven to be as hard as
factoring a composite integer public key. There are three versions of EPOC:
* EPOC-1 uses a one-way
trapdoor function
In theoretical computer science and cryptography, a trapdoor function is a function that is easy to compute in one direction, yet difficult to compute in the opposite direction (finding its inverse) without special information, called the "trap ...
and a random function (hash function);
* EPOC-2 uses a one-way trapdoor function, two random functions (hash functions) and a symmetric-key encryption (e.g., one-time padding and block-ciphers);
* EPOC-3 uses the Okamoto–Uchiyama one-way trapdoor function and two random functions (hash functions) as well as any symmetric encryption scheme such as the one-time pad, or any classical block cipher.
EPOC-1 is designed for key distribution; EPOC-2 and EPOC-3 are designed for both key distribution and encrypted data transfer.
See also
*
Cryptography
Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...
*
Computational complexity theory
In theoretical computer science and mathematics, computational complexity theory focuses on classifying computational problems according to their resource usage, and relating these classes to each other. A computational problem is a task solved ...
*
Okamoto–Uchiyama cryptosystem The Okamoto–Uchiyama cryptosystem is a public key cryptosystem proposed in 1998 by Tatsuaki Okamoto and Shigenori Uchiyama. The system works in the multiplicative group of integers modulo n, (\mathbb/n\mathbb)^*, where ''n'' is of the form ''p' ...
References
* T. Okamoto, S. Uchiyama and E. Fujisaki (1999).
EPOC: Efficient Probabilistic Public-Key Encryption, Contribution to IEEE – describes EPOC-1 and EPOC-2.
* T. Okamoto and D. Pointcheval (2000).
, Contribution to IEEE – describes EPOC-3.
*
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Public-key encryption schemes