byte operations (XOR) in python

Question

    #!/usr/bin/env python3

import binascii


var=binascii.a2b_qp("hello")
key=binascii.a2b_qp("supersecretkey")[:len(var)]

print(binascii.b2a_qp(var))
print(binascii.b2a_qp(key))


#here i want to do an XOR operation on the bytes in var and key and place them in 'encryption': encryption=var XOR key

print(binascii.b2a_qp(encrypted))

If someone could enlighten me on how I could accomplish this I would be very happy. Very new to the whole data-type conversions so yeah...reading through the python wiki is not as clear as I would like :(.

Answer 1

Comparison of two python3 solutions

The first one is based on zip:

    def encrypt1(var, key):
        return bytes(a ^ b for a, b in zip(var, key))

The second one uses int.from_bytes and int.to_bytes:

    def encrypt2(var, key, byteorder=sys.byteorder):
        key, var = key[:len(var)], var[:len(key)]
        int_var = int.from_bytes(var, byteorder)
        int_key = int.from_bytes(key, byteorder)
        int_enc = int_var ^ int_key
        return int_enc.to_bytes(len(var), byteorder)

Simple tests:

assert encrypt1(b'hello', b'supersecretkey') == b'\x1b\x10\x1c\t\x1d'
assert encrypt2(b'hello', b'supersecretkey') == b'\x1b\x10\x1c\t\x1d'

Performance tests with var and key being 1000 bytes long:

$ python3 -m timeit \
  -s "import test_xor;a=b'abcdefghij'*100;b=b'0123456789'*100" \
  "test_xor.encrypt1(a, b)"
10000 loops, best of 3: 100 usec per loop

$ python3 -m timeit \
  -s "import test_xor;a=b'abcdefghij'*100;b=b'0123456789'*100" \
  "test_xor.encrypt2(a, b)"
100000 loops, best of 3: 5.1 usec per loop

The integer approach seems to be significantly faster.