ABSTRACT
The ciphers (also called ciphersystems or cryptosystems) should provide security, which means that plaintext extraction from the ciphertext is practically impossible. While using a ciphersystem, our secrets depend on its security. Therefore, designers of the encryption systems should estimate the security of their algorithms. Security estimation is performed analyzing different possible attacks against a cipher. The aim of the cryptographic attack is to discover the key or the plaintext (this is called breaking the encryption algorithm), a process also known as cryptanalysis. Thus, the design and analysis of ciphers are two indivisible parts of cryptography, although some authors distinguish between cryptography and cryptanalysis, calling cryptography the science of designing ciphers and cryptanalysis the art of breaking the cryptosystems. The science comprising both parts is called cryptology. The reader should note that the terms cryptography and cryptology are often used as words having the same meaning, namely, the art and science of designing both encryption methods and techniques for breaking the cryptosystems.
