Instructions for Using the Aguilar Cipher

Since 2005 I have offered a $5000 reward to anybody who could break my cipher using a known plaintext attack.  This means that the attacker is given the ciphertext for known plaintext as well as the ciphertext for a secret message, both encrypted with the same key, and is asked to decrypt the secret message.  Since this prize goes unclaimed, you can assume that my cipher is secure.

Encrypt/Decrypt Messages

Permanent Key (30 Characters)
Temporary Key (30 Characters)

Key Alphabet Scramble

The Java Applet above is for creating a key strip for use when encrypting with pencil and paper. For example, your spies may not be able to possess a laptop or get to an internet cafe because they are living on the street and will thus have to write their reports by hand. Computer users can ignore this Applet.

Click here for a PDF file of the cipher wheel.

Click here for instructions to the quick, three-stage Aguilar Cipher.

Click here for a PDF file of the form for doing three-stage encryption by hand.

Click here for instructions to the full six-stage Aguilar Cipher.

1) The 30-character permanent key consist of letters, numbers and spaces but no punctuation.  This is a phrase that you have memorized and which you use every time you send or receive a message.  It must be exactly 30 characters long; you cannot have a shorter key.

2) The temporary key should be gibberish and should be different every time; just randomly poke at the keyboard until you get your 30 characters.  Decryptors may leave the temporary key box empty as it is only needed when encrypting.

3) The input box has the message that is to be encrypted or decrypted.  It consists of letters, numbers, spaces (or underscores, _) and these punctuation marks:  .  ,  -  '  “  ?  Capitalization is optional; the Applet does not distinguish lowercase from uppercase letters.

4) Click on “Encrypt” or “Decrypt” and the ciphertext or plaintext, respectively, will appear in the output box.  All letters will be lowercase except L to distinguish it from 1.  Spaces will be represented by underscores, _.  Right click on the output to copy it into an e-mail, text message or other communication device.