OAEP-padded encryption, as defined by PKCS #1 v2.1.
The same hash function is used for padding and MGF. MGF is MGF1 as defined in PKCS #1 2.1.
Keys must have a minimum of
2 + 2 * hlen + len(message) bytes, where
hlen is the hash length.
encrypt ~g ~label ~key message is OAEP-padded and encrypted
message, using the optional