da_crypt.py: The smallest encryption library you will ever find!

Here is a small library that I wrote just for fun. If you provide a key that is the same length as the file/bytes to be encrypted, this algorithm is unbreakable (see XOR_cipher and One Time Pad).


class Key:

def __init__(self, bytesKey):
self.__key = bytesKey

def getAt(self, x):
x = x % len(self.__key)
return self.__key[x]

class Crypt_Xor:

def __init__(self, key):
self.__key = key

def encrypt(self, bytesToCrypt):
bytesCrypt = bytearray(len(bytesToCrypt))
x = 0
for byte in bytesToCrypt:
key_node = self.__key.getAt(x)
bytesCrypt[x] = byte ^ key_node
x += 1
return bytesCrypt

def decrypt(self, bytesToDecrypt):
bytesDeCrypt = bytearray(len(bytesToDecrypt))
x = 0
lstDecrypted = []
for char in bytesToDecrypt:
key_node = self.__key.getAt(x)
bytesDeCrypt[x] = bytesToDecrypt[x] ^ key_node
x += 1

return bytesDeCrypt

The amazing thing is that it can be fully implemented with very little code (31 lines in this case).
I got the idea reading the excellent book 'Computer Networks by Andrew S.Tanenbaum -- 8.1.4'.

Here is a small test function:

def _test_crypt_object( crypt ):
data_orig = b'I am a simple string to be encrypted.'
print( 'data_orig: %s' % data_orig )

testKey = b'My secret key... \x123\x456\x798'

crypt = crypt( Key(testKey) )
data_encoded = crypt.encrypt(data_orig)
print( 'data_encoded: %s' % data_encoded )
data_decoded = crypt.decrypt(data_encoded)
print( 'data_decoded: %s' % data_decoded )

assert data_decoded == data_orig

def test_module():
print( 'da_crypt test start' )
print( 'da_crypt test end' )

if __name__ == '__main__':

You can check the updated code at:
It also contains a small extension that allows file encryption.

Be careful though: the implementation uses a circular key (for simplicity's sake). If you use a key that is not random or a key that is less than the size of the data to be encrypted then it becomes relatively easy to crack.


No comments: