I. Basic Terminology

Suppose that someone wants to send a message to a receiver, mid wants... (быть уверенным) that no-one else can read the message. However,... (существует вероятность) that someone (vise opens the letter or hears the electronic communication. In cryptographic terminology, the message... (называется) plaintext or cleartext. Encoding the contents of the message in such a way that hides its contents from outsiders is called encryption. The encrypted message is called the ciphertext. The process of retrieving the plaintext from the ciphertext is called decryption. Encryption and decryption usually make use of a key, and the coding method is such that decryption... (может быть выполнена) only by knowing the proper key.

Cryptography is the art or science of keeping messages secret. Cryptanalysis is the art of breaking ciphers, i.e. retrieving the plaintext... (без знания) the proper key. People who do cryptography are cryptographers, and practitioners of cryptanalysis are crypt analysts.

Cryptography deals with all aspects of secure messaging, authentication, digital signatures, electronic money, and other applications. Cryptology... (является отраслью) of mathematics that studies the mathematical foundations of cryptographic methods.