The difference between monoalphabetic cipher and polyalphabetic cipher are:
| Monoalphabetic Cipher | Polyalphabetic Cipher |
|---|---|
| Monoalphabetic cipher is one where each symbol in plain text is mapped to a fixed symbol in cipher text. | Polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. |
| The relationship between a character in the plain text and the characters in the cipher text is one-to-one. | The relationship between a character in the plain text and the characters in the cipher text is one-to-many. |
| Each alphabetic character of plain text is mapped onto a unique alphabetic character of a cipher text. | Each alphabetic character of plain text can be mapped onto ‘m’ alphabetic characters of a cipher text. |
| A stream cipher is a monoalphabetic cipher if the value of key does not depend on the position of the plain text character in the plain text stream. | A stream cipher is a polyalphabetic cipher if the value of key does depend on the position of the plain text character in the plain text stream. |
| It includes additive, multiplicative, affine and monoalphabetic substitution cipher. | It includes autokey, Playfair, Vigenere, Hill, one-time pad, rotor, and Enigma cipher. |
| It is a simple substitution cipher. | It is multiple substitutions cipher. |
| Monoalphabetic Cipher is described as a substitution cipher in which the same fixed mappings from plain text to cipher letters across the entire text are used. | Polyalphabetic Cipher is described as substitution cipher in which plain text letters in different positions are enciphered using different cryptoalphabets. |
| Monoalphabetic ciphers are not that strong as compared to polyalphabetic cipher. | Polyalphabetic ciphers are much stronger. |
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