Monoalphabetic Cipher is a #Substitution Cryptographic #algorithm that shuffle the letters arbitrarily (random) which has a key size of 26 letters. The total number of keys are \(26! = 4.03 \times 10^{26}\). However, since in Monoalphabetic Cipher the relationship between the letter in a plaintext to the letter in a ciphertext is always one-to-one, it is vulnerable to Frequency Analysis# due to the fact the frequency of the letters is not altered.
Examples of Monoalphabetic Cipher including:
Polyalphabetic Cipher is a Substitution Cryptographic #algorithm where the same plaintext letter could be replaced by several ciphertext letters depending on its position in plaintext. The relationship between a character in the plaintext and a character in the ciphertext is one-to-many, thus make it hard to crack using Frequency Analysis# and more secure than Monoalphabetic Cipher.
Playfair Cipher is a #Monoalphabetic Cipher #algorithm invented by Charles Wheatstone in 1854, that encrypts two letters (digram) at once instead of encrypts only one letter. It is resilient against Frequency Analysis since there are 676 digrams to analyse (\(26 \times 26\)) therefore more ciphertext needed to crack. However, given enough amount of letters, it could be easily cracked especially after computer was invented since it still retains much of plaintext structure.
Hill Cipher is a #Monoalphabetic Cipher #algorithm which substitutes blocks of characters in group, usually in pairs known as bigrams, in a block matrix using linear algebra. It was invented by Lester S. Hill in 1929.