used to signal that no more data is to be encrypted: this is used
to flush and possibly pad the final block through the BIO.
-BIO_set_cipher() sets the cipher of BIO <b> to B<cipher> using key B<key>
+BIO_set_cipher() sets the cipher of BIO B<b> to B<cipher> using key B<key>
and IV B<iv>. B<enc> should be set to 1 for encryption and zero for
decryption.