A.A. Kostina - Research Scientist, Institute for Informatics and Automation RAS (Saint Petersburg). E-mail: maa1305@yandex.ru
N.A. Moldovyan - Dr. Sc. (Eng.), Professor, Head of Laboratory, Institute for Informatics and Automation RAS (Saint Petersburg). E-mail: nmold@mail.ru
E.V. Morozova - Ph. D. (Eng.), Associate Professor of Research Institute «Vector» (Saint Petersburg). E-mail: lenmor@mail.ru

Traditional cryptographic algorithms are not resistant to so called coercive attacks when attacker can force the legal user to decrypt the sent or received ciphertext. The deniable encryption algorithms provide security to coercive attacks using possibility to decrypt the ciphertext in two different ways: one of the plaintexts is true and the second one is fake. The fake message is obtained as decryption of the ciphertext using the fake key. For the first time it is proposed commutative deniable encryption algorithm based on computationally difficulty of the discrete logarithm problem. The commutativity property provides possibility legal users to incipher and decipher the message without using any shared keys. The sent ciphertexts are computationally indistinguishable from the ciphertexts produced as result of the encryption of the fake message with some probabilistic commutative-encryption algorithm using the fake key. The associated probabilistic commutative-encryption algorithm is also to be presented to the coercer.

 

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