stubbed out cipher funcs

TODO

@@ -4,3 +4,8 @@
 --- ssh-rsa (sha1), rsa-sha2-256, rsa-sha2-512 (new default)
 - ciphers:
 -- 3des-cbc, aes128-cbc, aes192-cbc, aes256-cbc, aes128-ctr, aes192-ctr, aes256-ctr, aes128-gcm@openssh.com, aes256-gcm@openssh.com, chacha20-poly1305@openssh.com
+
+provide marshal, unmarshal for keytypes/* keys.
+https://golangexample.com/encode-and-decode-binary-message-and-file-formats-in-go/ (?)
+
+create separate package, go_sshdh