Every letter in the coded message was encrypted using another letter of the alphabet.  Type the coded letter to highlight it and then the letter you think it represent.  The guessed letter will appear in blue under the corresponding letters of the coded message in green.  Once you have more than 90% of the message correctly guessed, the rest of the message will get decoded automatically.  A single wrongly guessed letter will prevent this.  To erase a guess, simply type the coded letter, then hit the spacebar.

Done:

• Basic decoding: can guess the correct letters.
• Guess percentage: It shows how much of the message you have guessed, correctly or not.  When it gets over 90% without wrong guesses, the message gets totally decoded and you get a "Done!" message.
• Random message: A random message from a random plot from the plot folder is chosen when you practice cryptography.
• Sound effects
• Background music (.mp3) in played from the Music\Crypto folder, but none are in there by default.

Left to do:

• Erase guesses button.
• Hint button: Decodes a letter, but that takes some time.  Every time you hit this button, it will add a hour of game time.
• Difficulty levels: At the local level, you get a free guess.  At the national level, you get no guess and no extra difficulty.  At the regional level, more than one letter in the coded message could mean the same letter; every letter will appear at least once in the coded message.  At the global level, punctuation and spaces are removed.
• Icon for the window.
• Appropriate music that is free to redistribute.
• Ability to use the mouse instead of the keyboard.

Ideas for improvements:

• Add information about the sender and the receiver at the top of the window.  It would show their name, city, organization and role, provided that you already know them.