密码算法.zip

# MANY TIME PASS HACK ------------------------ INSTRUCTIONS TO RUN THE PROGRAM ------------------------ The following command must be executed to run the program: python3 manytimepass.py ------------------------ ALGORITHM ------------------------ In Many Time Pass Hack, we exploit the properties of xor. When messages m1 and m2 are encrypted using the same one time pass key, we get a relation which relates the ciphertext c1 and c2 with the messages, verbosely, c1 xor c2 = (m1 xor key) xor (m2 xor key) c1 xor c2 = m1 xor m2 It turns out that English language and ASCII encoding has enough redundancy to decode the ciphertexts. That is, whenever we encounter the xor of a space ' ' and a character we get the same character with inverted case. So this implies that whenever there is a space in m1 and m2 and not in the other, we can get the original alphabet with inverted case. We carry this on for all the strings and in the last apply a guessing heuristic to get the result based on maximum occurences of the possibilities. If we encounter the xor of a weird punctuation mark with a space or something else, we get inconsistent letters which can be seen as having many different alphabets in the same possibility position. If we get such possibilities or occurences spanned over more than one letter, then they are probably a weird punctuation mark or a number else it is a space. ------------------------