Astrum Astrum - 13 days ago 5
Python Question

XOR cipher in python - odd length string

I'm trying to make a cipher using the xor operator. Right now this is what I have:

from binascii import hexlify, unhexlify
from itertools import cycle

s = '636174'
key = '13'
def cipherkey(s, key):
bin_key = bin(int(key))[2:]
bin_s = bin(int(s, 16))[2:]
k = []
if len(bin_key) < len(bin_s):
for i, j in zip(cycle(bin_key), bin_s):
k.append('{}'.format(i))
else:
for i, j in zip(bin_key, cycle(bin_s)):
k.append('{}'.format(i))
return int("".join(k),2)

def xor_cipher(s,key):
n = cipherkey(s, key)
out = n ^ int(s,16)
return hex(out)
print(unhexlify(xor_cipher(s, key)))


I'm sure this is super inefficient code, but I'd like to keep as much of it as possible. I've startched my head over this for a while now and haven't found the mistake.There must be a mistake in how I'm iterating over
zip(cycle(bin_key), bin_s)
.

Answer

Try to replace the last line:

print(unhexlify(xor_cipher(s, key)))

with this code:

res=xor_cipher(s, key)[2:] # remove '0x' from the begining of the hex code
if res.__len__()%2 ==1:    # if res length is odd,
   res="0{}".format(res)   #     append '0' at the begining to make it even
print unhexlify(res)
Comments