python - Cipher program losing accuracy -

i have program in python takes 2 strings. 1 plain text string, cipher key. go on each of characters , xors bits cipher characters. when going , forth few of letter not seem change properly. here code:

//turns int bin string length 8 def bitstring(n):     bin_string = bin(n)[2:]     bin_string = ("0" * (8 - len(bin_string))) + bin_string     return bin_string  //xors bits def bitxor(b0, b1):     nb = ""     x in range(min(len(b0), len(b1))):         nb += "0" if b0[x] == b1[x] else "1"     return nb  //takes 2 chars, turns them bin strings, xors them, returns new char def cypherchar(c0, c1):     return chr(int(bitxor(bitstring(ord(c0)), bitstring(ord(c1))), 2))  //takes s0 (the plaintext) , encrypts using cipher key (s1) def cypherstring(s0, s1):     ns = ""     x in range(len(s0)):         ns += cypherchar(s0[x], s1[x%len(s1)])     return ns 

for example in long string word 'test' cipher 'eest', , stuff that

i have checked on code dozen times , can't figure out whats causing of characters change. possible characters behave strangely?

edit:

example:

this test  due fact in last test  symbols: !@#$%^&*()  not changed  retesting  end 

using cipher key : 'cypher key'

translates :

this test  due toe aact in last sest  symbols: !@#$%^&*()  not changed  retestiig  end 

sorry little messy, put real quick

from binascii import hexlify, unhexlify sys import version_info  def bit_string(string):     if version_info >= (3, 0):         return bin(int.from_bytes(string.encode(), 'big'))     else:         return bin(int(hexlify(string), 16))  def bitxor_encrypt(plain_text, key):     encrypted_list = []     j in range(2, len(plain_text)):         encrypted_list.append(int(plain_text[j]) ^ int(key[j])) #assume key , string same length     return encrypted_list  def decrypt(cipher_text, key):     decrypted_list = []     j in range(2, len(cipher_text)): #or xrange         decrypted_list.append(int(cipher_text[j]) ^ int(key[j])) #again assumes key same length string      decrypted_list = [str(i) in decrypted_list]     add_binary = "0b" + "".join(decrypted_list)     decrypted_string = int(add_binary, 2)     if version_info >= (3, 0):         message =  decrypted_string.to_bytes((decrypted_string.bit_length() + 7) // 8, 'big').decode()     else:         message = unhexlify('%x' % decrypted_string)     return message   def main():     plain_text = "hello"     plain_text_to_bits = bit_string(plain_text)     key_to_bits = bit_string("candy")      #encrypt     cipher_text = bitxor_encrypt(plain_text_to_bits, key_to_bits)      #make strings     cipher_text_string = "".join([str(i) in cipher_text])     key_string = "".join([str(i) in key_to_bits])      #decrypt     decrypted_string = decrypt("0b"+cipher_text_string, key_string)      print("plain text: %s" % plain_text)     print("plain text bits: % s" % plain_text_to_bits)     print("key string in bits: %s" % key_string)     print("ciphered message: %s" %cipher_text_string)     print("decrypted string: %s" % decrypted_string)  main() 

for more details or example code can visit repository either on github https://github.com/marcsantiago/one_time_pad_encryption

also, know in example key same length string. if want use string smaller string try wrapping in vigenere cipher (http://en.wikipedia.org/wiki/vigenère_cipher)