87 lines
2.3 KiB
Python
87 lines
2.3 KiB
Python
#!/usr/bin/python
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#
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# Simple XOR brute-force Key recovery script - given a cipher text, plain text and key length
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# it searches for proper key that could decrypt cipher into text.
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#
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# Mariusz Banach, 2016
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#
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import sys
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def xorstring(s, k):
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out = [0 for c in range(len(s))]
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key = []
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if type(k) == type(int):
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key = [k,]
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else:
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key = [ki for ki in k]
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for i in range(len(key)):
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for j in range(i, len(s), len(key)):
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out[j] = chr(ord(s[j]) ^ key[i])
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return ''.join(out)
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def brute(input_xored, expected_output, key_len):
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key = []
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if len(input_xored) != len(expected_output):
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print '[!] Input xored and expected output lengths not match!'
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return False
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for i in range(key_len):
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cipher_letters = [ input_xored[x] for x in range(i, len(input_xored), key_len)]
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plaintext_letters = [ expected_output[x] for x in range(i, len(input_xored), key_len)]
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found = False
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for k in range(256):
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found = True
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for j in range(key_len):
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if chr(ord(cipher_letters[j]) ^ k) != plaintext_letters[j]:
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found = False
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break
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if found:
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key.append(k)
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break
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found = False
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if not found:
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print '[!] Could not found partial key value.'
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break
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return key, xorstring(input_xored, key) == expected_output
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def main(argv):
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if len(argv) < 4:
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print 'Usage: %s <cipher> <plain> <key-len>'
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return False
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cipher = argv[1]
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plain = argv[2]
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keylen = int(argv[3])
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if len(cipher) != len(plain):
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print '[!] Cipher text and plain text must be of same length!'
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return False
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if len(cipher) % keylen != 0:
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print '[!] Cipher text and plain text lengths must be divisble by keylen!'
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return False
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print "Cipher text:\t%s" % cipher
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print "Plain text:\t%s" % plain
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print "Key length:\t%d" % keylen
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key, status = brute(cipher, plain, keylen)
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if status:
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print '[+] Key recovered!'
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print '\tKey:\t\t\t', str(key)
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print '\tDecrypted string:\t' + xorstring(cipher, key)
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else:
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print '[!] Key not found.'
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if __name__ == '__main__':
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main(sys.argv)
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