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In order to protect both data confidentiality and legality, a concept of a watermarking cipher (also called a w-cipher) is defined. The main idea of this cjncept is as follows: the transformation of a plaintext x by the composition of encryption and decryption operations using some encryption and decryption keys yields a proper text x/ containing a unique watermark w. The encryption and decryption keys in the w-cipher are connected with each other and with the given watermark w in some way. In contrast with the ciphers usually studied in cryptography, the encryption function in a w-cipher is not compulsorily invertible. Thus in fact w-ciphers are not ciphers in the known sense of the word, but the ciphers are w-ciphers of a certain partial type, and all terms, notions and notations related to ciphers are quite applicable to w-ciphers. It is shown how data watermarking can be performed by applying a w-cipher in such a way that the concealment of a watermark into a plaintext is accomplished by this w-cipher either in the encryption or in the decryption processes. Some examples of w-ciphers constructed on the basis of symmetric stream ciphers are presented in the paper.

In the paper, a technology for solving logical cryptanalysis problems in desktop grids is described. The technology was validated by successful solving of cryptanalysis problems for some keystream generators in the desktop grid based on BOINC platform.

In this paper we describe a differential attack on a block cipher in a general case. We calculate the attack complexity for different cipher parameters.

In this paper we propose an approach to steganographic system optimization. Corresponding cover message model is explained. Our method is aimed at steganographic security and capacity maximization and can be adapted to different types of digital cover messages.