1. Monoalphabetic Cipher :
A monoalphabetic cipher is any cipher in which the letters of the plain text are mapped to cipher text letters based on a single alphabetic key. Examples of monoalphabetic ciphers would include the Caesar-shift cipher, where each letter is shifted based on a numeric key, and the atbash cipher, where each letter is mapped to the letter symmetric to it about the center of the alphabet.
2. Polyalphabetic Cipher :
A polyalphabetic cipher is any cipher based on substitution, using multiple substitution alphabets. The Vigenère cipher is probably the best-known example of a polyalphabetic cipher, though it is a simplified special case.
Difference Between Monoalphabetic Cipher and Polyalphabetic Cipher :
SR.NO Monoalphabetic Cipher Polyalphabetic Cipher 1 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.
2 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. 3 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. 4 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. 5 It includes additive, multiplicative, affine and monoalphabetic substitution cipher. It includes autokey, Playfair, Vigenere, Hill, one-time pad, rotor, and Enigma cipher.
6 It is a simple substitution cipher. It is multiple substitutions cipher. 7 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. 8 Monoalphabetic ciphers are not that strong as compared to polyalphabetic cipher. Polyalphabetic ciphers are much stronger.