Crack a One Time Pad

Used properly, a One Time Pad is unbreakable. But if the same pad is used for more than one message, it is no longer secure. This is a tool to help you crack two messages encrypted with the same one time pad.

Choose a pair of excerpts: or copy and paste your own ciphertexts into the boxes below.

Click on part of one ciphertext and type a letter to guess the plaintext. The computer will calculate the "shift" between the ciphertext and plaintext, and apply the same shift to the other ciphertext. A good way to start is to enter a crib (an educated guess at a word or phrase of plaintext). Move the crib through one ciphertext until an intelligible word shows up in the other message. The excerpts available here have spaces and punctuation left in, making the process easier. For a much harder challenge, try some with all the spaces and punctuation removed.

Ciphertext 1: Ciphertext 2:


arrow keysMove around the ciphertext
tabSwitch between ciphertexts
returnLeave crib in current location
escapeTurn crib on or off