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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 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 consider stegosystems of fingerprints and collusion attacs on them. The structure of the system of fingerprints, necessary to oppose such attack, is investigated. We propose a method for identifying counter-fitters through a fake fingerprint. Also, in the set of all collective attacks, we identify the riskiest one, the majorizing attack.

In this paper we describe the attacks on the full block cipher GOST 28147-89. This attack consists of related-key, differential and boomerang attacks. For the attack we need 2 or 4 related keys depending on properties of s-boxes.

The paper considers the peculiarities of authentication in multi-tier environment and corresponding security problems. The authentication protocol for multi-tier system based on commutative encryption is provided.

Admissible sets of digital watermarks resistant to collusion attacks are defined in the paper. Some properties of such sets are considered. The problem of collusion paticipants identification is discussed, and some partial solutions are suggested for it.