It was a challenge from CTF (ended), but I didn't solve it.
p, q = keygen(512) n = p * q flag = bytes_to_long(flag) enc = pow(n + 1, flag, n**3)
So we have module and encrypted flag. We don't know module's factors (p,q). I have tried some ways, search another writeups and read many topics, but I didn't find any information how solve it.