What is Classical Cipher

Classical ciphers are used to encrypt plaintext messages written in a natural language in such a way that they are readable for sender or intended recipient only. Many classical ciphers can be broken by brute-force search through the key-space. One of the pertinent problems arising in automated cryptanalysis is the plaintext recognition. A computer should be able to decide which of many possible decrypts are meaningful. This can be accomplished by means of a text scoring function, based, e.g. on n-grams or other text statistics. A scoring function can also be used in conjunction with AI methods to speedup cryptanalysis.