Алгоритм перестройки

def bytes2reg(m):
    L = 8
    pol = []
    dic = {'1' : 1, '0' : 0}
    for i in m:
        b = bin(ord(i)).split('b')
        b = b[1]
        b = '0'*(L - len(b)) + b
        for c in b:
            pol.append(dic[c])
    return pol
 
 
def reg2bytes(pol):
    res = ""
    if len(pol) % 8 != 0:
        pol.extend([0 for _ in range(8 - (len(pol) % 8))])
    b = [int(i) for i in pol]
    for i in range(4):
        ch = 0
        pw = 7
        for _ in range(8):
            ch += b.pop(0) * (2**pw)
            pw -= 1
        res += chr(ch)
    return res
 
 
def encrypt(m, k):
    enc = [i for i in m]
    enc.extend([0 for _ in range(32)])
    for i in range(32):
        enc[32+i] = enc[31+i] ^ enc[16+i] ^ enc[1+i] ^ enc[i] ^ k[i]
    return enc[32:]
 
 
f = open("fl1.png", 'r')
file = f.read()
f.close()
enc = open("file.png", 'w')
enc.write(file[:file.find("IDAT")])
 
cnt = 0
while file[cnt:].find("IDAT") != -1:
    enc.write("IDAT")
    p = file[cnt:].find("IDAT") + cnt
    length = int(file[p-4:p].encode('hex'), 16)
    data = file[p+4:p+length+4]
    crc = file[p+length+4:p+length+8]
    key = bytes2reg(crc)
    l = length - (length % 4)
    for i in range(0, l, 4):
        block = data[i:i+4]
        block = bytes2reg(block)
        e = encrypt(block, key)
        enc.write(reg2bytes(e))
    enc.write(data[l:length])
    cnt = p + 4 + length + 4
    e = encrypt(key, key)
    enc.write(reg2bytes(e))
enc.write(file[cnt:])
enc.close()