Icon MonoDecrypt

Decrypt your enemy's secret messages!


  • Latest Version:
  • Runs on:
Windows, Linux, Mac OS
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MonoDecrypt in action Interactive mode


Do you remember your days as a child when you encrypted your top secret messages by replacing the letters? For example an A became an L, a B became a D and so on. It didn't matter with which letter another one was replaced, as long as no letter was used as a replacement for more than one other letter. This encryption algorithm is known as Monoalphabetic Substitution. Although the underlying principle is a very simple one, decrypting monoalphabetically substituted texts is not that easy. MonoDecrypt uses pattern matching and its knowledge about character frequencies in order to do decrypt such messages. Depending on the information you give it (MonoDecrypt is able to decrypt texts of any language; it only needs information on the appropriate language), the tool decrypts about 50%-100% on its own. Then you can decrypt the remaining data by filling the gaps or correcting bad guesses.
By the way MonoDecrypt can also encrypt texts using Monoalphabetic Substitution. However, this is not recommended, because your snoopy fellow men could use MonoDecrypt, too ;-).

How to use MonoDecrypt


This program requires the Java Runtime Environment (JRE) in version 6 or higher!

Download Executable File or Source Code


  • 17 August 2008:
First public release: Version 1.0.0