follow_the_current_source.py

import os
import zlib
def keystream():
	key = os.urandom(2)
	index = 0
	while 1:
		index+=1
		if index >= len(key):
			key += zlib.crc32(key).to_bytes(4,'big')
		yield key[index]
ciphertext = []
with open("plain","rb") as f:
	plain = f.read()
	assert b"actf{" in plain
	k = keystream()
	for i in plain:
		ciphertext.append(i ^ next(k))
with open("enc","wb") as g:
	g.write(bytes(ciphertext))