# substitution cipher

The substitution cipher is a simple encryption method in which the characters of a word are replaced by assigned cipher characters. Depending on the method, the substitution can be made by an assigned character from a cipher table, the substitution box, as in the Atbash c ipher or the Caesar cipher, or several cipher tables can be used alternately for the substitution, as in the Vigenère cipher.

There are different substitution methods, for example the monoalphabetic substitution where single letters are always replaced by the same cipher. In this method, a single cipher step is used repeatedly. In polyalphabetic substitution, several cipher steps are applied. In this method, the same plaintext letters are replaced by different cipher letters or digits.

In the second basic cryptographic method, transposition, the characters in the ciphertext have a different sequence than those in the plaintext. Thus a change of the character sequence takes place. The plaintext "letter" could then be transposed to "chatsuebb". Combining the substitution cipher with the transpositioncipher produces the product cipher.