Exploit for Multi-Time Pad

Problem

Given k ciphertexts encrypted using a OTP style stream cipher using the same key, decrypt the k+1th ciphertext.

Files

1. exploit-two-time-pad.py - the main script
2. ciphers.txt - txt file to enter ciphertexts one per line
3. target.txt - target ciphertext to decrypt
4. decrypt.txt - output file for the decrypted message.

Approach

The key is guessed using:

1. Given two ciphertexts c1 and c2 for plaintext messages m1 and m2 respectively, c1 xor c2 gives m1 xor m2.
2. For any character c in [a-zA-Z], c xor (space) reverses the case of the character.