Rewrite cryptopunk

[v6ak]

Crypto is currently handled by openssl CLI. (Except for scrypt, which calls Perl.) See cryptopunk.py file. This is a high-latency solution that makes some assumptions (attacker can't read /proc, which is justifiable in dom0) that I would like to get rid off.

Maybe the best available alternative would be nacl/sodium. For Python, we could use python3-pynacl or python3-libnacl. But I can't see those packages in Fedora 23. If Qubes 4.0 updates dom0 to Fedora 24 or newer (not sure), we can go this way. Until then, I'd wait. Or maybe someone will suggest a better solution that we can use without waiting for Qubes 4.0.