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mgeeky-Penetration-Testing-.../others/xor-key-recovery.py

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2018-02-02 22:22:43 +01:00
#!/usr/bin/python
#
# Simple XOR brute-force Key recovery script - given a cipher text, plain text and key length
# it searches for proper key that could decrypt cipher into text.
#
# Mariusz B., 2016
#
import sys
def xorstring(s, k):
out = [0 for c in range(len(s))]
key = []
if type(k) == type(int):
key = [k,]
else:
key = [ki for ki in k]
for i in range(len(key)):
for j in range(i, len(s), len(key)):
out[j] = chr(ord(s[j]) ^ key[i])
return ''.join(out)
def brute(input_xored, expected_output, key_len):
key = []
if len(input_xored) != len(expected_output):
print '[!] Input xored and expected output lengths not match!'
return False
for i in range(key_len):
cipher_letters = [ input_xored[x] for x in range(i, len(input_xored), key_len)]
plaintext_letters = [ expected_output[x] for x in range(i, len(input_xored), key_len)]
found = False
for k in range(256):
found = True
for j in range(key_len):
if chr(ord(cipher_letters[j]) ^ k) != plaintext_letters[j]:
found = False
break
if found:
key.append(k)
break
found = False
if not found:
print '[!] Could not found partial key value.'
break
return key, xorstring(input_xored, key) == expected_output
def main(argv):
if len(argv) < 4:
print 'Usage: %s <cipher> <plain> <key-len>'
return False
cipher = argv[1]
plain = argv[2]
keylen = int(argv[3])
if len(cipher) != len(plain):
print '[!] Cipher text and plain text must be of same length!'
return False
if len(cipher) % keylen != 0:
print '[!] Cipher text and plain text lengths must be divisble by keylen!'
return False
print "Cipher text:\t%s" % cipher
print "Plain text:\t%s" % plain
print "Key length:\t%d" % keylen
key, status = brute(cipher, plain, keylen)
if status:
print '[+] Key recovered!'
print '\tKey:\t\t\t', str(key)
print '\tDecrypted string:\t' + xorstring(cipher, key)
else:
print '[!] Key not found.'
if __name__ == '__main__':
main(sys.argv)