The Scope of Application of Letter Frequency Analysis in Substitution Cipher

Since its inception, substitution ciphers have been a popular type of cipher, and over time, academics have studied them in an effort to discover patterns that will allow them to be broken. They created it because substitution ciphers are a reasonably simple type of cipher. Through a survey of the literature, this paper investigates the encryption and decryption of three sub-types of monoalphabetic ciphers: shift cipher, affine cipher, and random substitution cipher. Letter frequency analysis is the foundation of the primary decryption technique. After that, two sub-kinds of monoalphabetic ciphers, Hill cipher and Playfair cipher, which are resistant to this decryption method because the letters encrypted hardly keep the original frequency, will be introduced. The paper shows that statistical analysis of letter frequency is only useful for deciphering single-table substitution ciphers.