CORE 139 Methods and Issues in Cryptology Spring 2004

Vigenere Cipher Cracker Tool #2

Use this tool to crack a Vigenere-encrypted message with a long or unknown-length key. Enter the ciphertext in the appropriate box and click the "initialize" button. Dashes indicate unknown letters in the plaintext and keyword.

To decrypt, guess a letter in the plaintext or the keyword - replace the dash with the desired letter. Click "update keyword" to update the keyword based on the current plaintext or "update plaintext" to update the plaintext based on the current keyword. (Note that "update plaintext" will not change any plaintext letters for which the corresponding keyword letter is unknown ("-"); use "reset plaintext" instead to set the plaintext according to exactly what is in the keyword.) To "unguess" a plaintext or keyword letter, replace it with a dash. You can start over from scratch by clicking "initialize".

To facilitate guessing parts of the plaintext, use the "plaintext guesser" section: Enter a section of plaintext in the "substring" box (and press enter); slide it along the ciphertext using the arrows below the "substring" box. You can also enter an offset directly in the "offset" box (press enter to force it to take effect) - the beginning of the substring will be lined up at this point in the ciphertext. Clicking "commit" will update the keyword and plaintext accordingly.

ciphertext:
Set up the plaintext and keyword to begin decryption.
Reset the plaintext to only the letters known based on the current state of the keyword.
Update the plaintext based on the current state of the keyword. Plaintext letters for which the keyword entry is "-" are not changed.
Reset the keyword to only the letters known based on the current state of the plaintext.
Update the keyword based on the current state of the plaintext.
keyword:
 plaintext:
plaintext guesser:

keyword: substring:
plaintext: offset:
ciphertext:

sbridgeman@mail.colgate.edu last updated: --Wed Jan 28 19:50:33 Eastern Standard Time 2004--