Introduction

Modern information security manifests itself in many ways, according to the situation and its requirements. It deals with such concepts as confidentiality, data integrity, access control, identification, authentication and authorization. Practical applications, closely related to information security, are private messaging, electronic money, online services and many others.

Cryptography is the study of mathematical techniques related to aspects of information security. The word is derived from the Greek kryptos, meaning hidden. Cryptography is closely related to the disciplines of cryptanalysis and cryptology. In simple words, cryptanalysis is the art of breaking cryptosystems, i.e. retrieving the original message without knowing the proper key or forging an electronic signature. Cryptology is the mathematics, such as number theory, and the application of formulas and algorithms that underpin cryptography and cryptanalysis.

Cryptology is a branch of mathematical science describing an ideal world. It is the only instrument that allows the application of strict mathematical methods to design a cryptosystem and estimate its theoretical security. However, real security deals with complex systems involving human beings from the real world. Mathematical strength in a cryptographic algorithm is a necessary but not sufficient requirement for a system to be acceptably secure.

Moreover, in the ideal mathematical world, the cryptographic security of an object can be checked only by means of proving its resistance to various kinds of known attack. Practical security does not imply that the system is secure: other, unknown, types of attack may occur.