Monoalphabetic substitution is a simple encryption technique in which each letter of the plaintext is replaced by a fixed letter of the ciphertext, based on a substitution table or key. For example, the letter "A" in the plaintext might be replaced by the letter "Q" in the ciphertext, and so on.
This substitution is consistent throughout the entire message, so the same letter in the plaintext always gets replaced by the same letter in the ciphertext.
Monoalphabetic substitution is a type of substitution cipher and is vulnerable to several cryptanalysis techniques, including frequency analysis. As a result, it is not considered a strong encryption technique and is not recommended for secure communications.
Example of monoalphabetic cipher
Message to crypt : "Hello World"
The correspondant key is: QWERTYUIOPASDFGHJKLZXCVBNM
The encrypted message is: "Itssg Vgksr"