lfsr.py

def gen_8_bits(state, length=128):
    output=0
    for i in range(8):
      next_out = state%2
      next_state_bit = next_out ^ ((state>>1)%2) ^ ((state>>2)%2) ^ ((state>>7)%2)
      state = (state >> 1) | (next_state_bit << (length-1))
      output = (output << 1) | next_out
    return output, state

key = int("".join(['1' for i in range(128)]),2)

#hex digest to hex digest
def hex_crypt(plain, key):
	cipher = ''
	state = key
	for hc in [plain[i:i+2] for i in range(0,len(plain),2)]:
		output, state = gen_8_bits(state)
		cipher += hex(int(hc,16)^output)[2:-1].zfill(2)
	return cipher

import binascii

def encrypt(plain, key):
	digest = binascii.hexlify(plain)
	return hex_crypt(digest, key)

def decrypt(ct, key):
	pt_hex = hex_crypt(ct, key)
	return binascii.unhexlify(pt_hex)

ct = encrypt("*** *** *** *** Andy is the best.", key)
print ct
print decrypt(ct, key)

#BTW binascii.unhexlify(ct) == '\xd5\xd5\xd5\xdf\xd5\xd5\xd5\xdf\xd5\xd5\xd5\xdf\xd5\xd5\xd5\xdfAndy is the gre\x1ctest. Just waiK\xdd'