2. Cryptographic methods for protecting information 2.1. Terms and Definitions

Cryptographic methods for protecting information constitute the basis of the security subsystems of modern information systems, providing confidentiality, integrity and authentication services.

2.1. Terms and Definitions

Cryptography is the science of methods and means of transforming information into a form that makes unauthorized operations with it difficult or impossible, including methods and means of creating, storing and distributing keys - special information objects that implement these sanctions.

The basic concept of cryptography is the concept of cipher. A cipher is a set of injective (reversible) transformations of a set of plain text elements into a set of ciphertext elements indexed by elements from a set of keys:

{F _k : X ® S, kÎK},

where XÎ X - encoded message from a variety of open texts;

SÎ S is a ciphertext from a set of possible encoded texts;

k - encryption key;

F is the mapping performed by the cipher.

The cipher injectivity property means that there exists a mapping F ^-1 such that

{F _k ^-1 : X ® S, kÎK}

The process of converting plaintext to the ciphertext is called encryption. The inverse transformation of ciphertext to plaintext is called decryption .

Cryptanalysis is the science (and practice of its application) about the methods and methods of opening ciphers. An autopsy is the task of obtaining the corresponding plaintext and / or encryption key by a known encryption test.

Cryptography and cryptanalysis together form cryptology .