OTP/XOR Cracking two ciphertexts that have the same key

Question

How can I crack two ciphertexts that have used the same key twice? For example, plaintext1 uses the key "abcdefg", and plaintext2 uses the key "abcdefg".

I know that ciphertext2 ^ ciphertext1 is equal to plaintext1 ^ plaintext2. And the method to crack plaintext1 ^ plaintext2 is the same method to crack a "book cipher" (also sometimes called a "running key cipher", although a running key cipher isn't the same as a book cipher, right?)

I know that I'm supposed to use a dictionary attack, but I'm not sure which dictionary/wordlist I should use, and the algorithm used in cracking this. Can anyone provide me with a link, or some code that shows how to crack it?

I'm new to cryptography, and I just wanted to do this for fun. Can anyone help me out? Thanks.

Answer 1

The most common attack is to "slide" a common (but not too short) word along and XOR it against successive positions in the combined stream. Where the word was used in one stream, the XOR will (usually) produce readable text for the other stream.