Encryption by substitution

A encryption by substitution is the one which replaces each character of plain text by another character in the cipher text or cryptogram

Is based on applying the principle of confusion proposed by Shannon, hiding the text in clear to the intruder through substitutions, except for the recipient, who know the algorithm and key to recover the message

The ciphers by substitution can be classified into three groups:

• Monoalphabet monogamous substitution The encryption is done using an algorithm that maps a letter of the clear text to a single letter in the cryptogram, that is to say, a figure monograms

  Hence its monogamy encryption designation

  As regards the term monoalphabet means that it uses a single alphabet of encryption, the same as the text in clear or a mixed one, but distributed either randomly or through a mathematical transformation

  Then, if the letter M of the plain text corresponds to the letter V, or the symbol # to the alphabet of encryption, will be encrypted always the same, since there is a unique equivalence or, which is the same thing, a single alphabet encryption

• Polyalphabet monogamous substitution the encryption operation is also performed character by character, that is to say by monograms

  As regards the term polialphabetmeans that it uses multiple alphabets for encryption, applied to the same character in the text in clear or a mixed one, but distributed either randomly or through a mathematical transformation

  However, through a key, algorithm or mechanism, you get multiple alphabets of encryption so that the same letter can be encrypted with different characters, depending on their position within the text in clear

• Polygamic substitution treat the message in blocks of two or more characters on which it is applied the transformation of the cryptosystem in question, substituting n-grams of the message by n-gram of ciphertext