Minimal Example of LFSR

lfsr1.py

#https://en.wikipedia.org/wiki/Linear-feedback_shift_register
from bitstring import BitArray

def pad(x,K):
	N = len(x)
	PAD = N % K
	if PAD > 0:
		PAD = K-PAD
		# tell me better
		x = x + BitArray(bin='0'*PAD)
	return x

def asbits(x):
	if isinstance(x,BitArray):
		return x
	else:
		return BitArray(bytes=x)

def lfsr(t,k,wn=0):
	t = asbits(t)
	k = asbits(k)
	q = BitArray()
	K = len(k)
	N = len(t)
	t = pad(t,K)
	print "processing: ",N,"with key",K,"extended to",len(t)
	for i in range(0,len(t),K):
		q += t[i:i+K] ^ k
		k.rol(1)
	if wn != 0:
		q = q[0:wn]
	return q,N

def main():
	key = "ciao"
	input = "ciaomondo"

	w,wn = repeated(input,key)
	print "encrypted as",len(w),"original len",wn
	print repeated(w,key,wn)[0].bytes
if __name__ == '__main__':
	main()