Deniability of Symmetric Encryption Based on Computational Indistinguishability from Probabilistic Ciphering

It is proposed as a novel interpretation of the notion of the shared-key deniable encryption, extended model of the coercive adversary, set of the design criteria, and a new practical approach to designing the shared-key deniable encryption algorithms, which is characterized using computational indistinguishability from probabilistic ciphering. The approach is implemented in several described algorithms relating to the plan-ahead shared-key deniable encryption schemes. The algorithms encrypt simultaneously secret and fake messages and produce the single cryptogram that is computationally indistinguishable from the ciphertext produced by some probabilistic cipher, while encrypting the fake message. The proposed algorithms are based on block conversion functions (hash-functions and block ciphers) and satisfy criterion of complete coincidence of the algorithms for recovering the fake and secret messages. Due to possibility to perform the inverse transformation the block ciphers used as the base block conversion function provide higher speed of the deniable encryption. It is also proposed as a general design of fast block deniable encryption algorithms satisfying the proposed design criteria.