Pseudo-probabilistic block ciphers and their randomization
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There is considered implementation of the plan-ahead share-key deniable encryption algorithms that produce the cryptogram that satisfy criterion of the computational indistinguishability from probabilistic encryption of the fake message. This paper introduces a general design of the pseudo-probabilistic block ciphers. The proposed method includes encryption of the secret message block and the fake message block followed by a transformation procedure mapping the pair of intermediate ciphertext blocks into a single block of the output ciphertext. The transformation procedure is implemented in the following two variants: (1) simultaneous encryption of the intermediate ciphertext blocks and (2) solving the system of two linear congruencies. The second variant provides natural possibility to construct pseudo-probabilistic block ciphers in which recovering fake or secret message is performed using the same single decryption algorithm. To provide higher security there are proposed randomized pseudo-probabilistic ciphers. There are also considered designs with different size of the input data blocks corresponding to fake and secret messages.
KeywordsBlock ciphers Plan-ahead deniable encryption Shared-key deniable encryption Pseudo-probabilistic cipher Randomization
The reported study was funded by Russian Foundation for Basic Research (project #18-57-54002-Viet_a) and by Vietnam Academy of Science and Technology (project # QTRU01.08/18-19).