Projektowanie szyfratorow dla ochrony informacji

In the paper methods of the design of enciphering systems are presented. The discussion is confined to the case of construction of symmetric cryptosystems. All the reasoning is based on the Shannon's idea, which consists in the construction of complex enciphering systems for appropriate product ciphers. Extended by Feisel, this idea has become the basis for the construction of all existing symmetric cryptosystems (the enciphering algorithm). In the first part of the paper requirements to be satisfied when constructing cryptosystems are formulated. If these requirements are not met, a cipher generated by the cryptosystem is easy to break. The Feistel's cryptosystem and DES algortithm are considered as examples of enciphering systems satisfying all the requirements mentioned. Moreover, the concept of enciphering module is introduced. It is shown that an arbitrarily complex cryptosystem can be constructed of enciphering modules. The described method of the design of complex enciphering systems having modular structure is illustrated with numerous examples.