A monoalphabetic cipher decryption program is an application that can find keys to unencrypt messages that have been encoded with a monoalphabetic cipher. Because monoalphabetic ciphers involve only a single transformation of each letter in the alphabet, there are a number of different types of programs that can perform this function. Some generate solution keys automatically and others work with input from the user.
A monoalphabetic cipher is a method of cryptology that maps every letter in an alphabet to another letter. This transformation occurs once and only uses sets of letters from one alphabet. These ciphers are used to encrypt and decrypt hidden messages. However, by applying some knowledge about common language patterns and letter frequencies, it is possible to create a program that can generate solutions to these types of ciphers.
Some monoalphabetic cipher decryption programs are manual, which means the user must enter letter substitutions in an attempt to decrypt text. The user does this by making estimates about the language patterns of the message they are decrypting. For example, single-letter words might be "a" or "i," and letters that occur frequently might be "e." After spending some time working this way, it is possible to develop a solution key. Automatic monoalphabetic cipher decryption programs go through this process automatically.