[TLS] new error alerts?

[Dave Garrett <[e-mail]>]

Hubert Kairo found quite a few more spots in need of explicit error designations, which have been amended into PR #201.
https://github.com/tlswg/tls13-spec/pull/201

I just noticed one error in the current draft text that was wrong and added a fix for that as well. The Server Hello section said that lack of acceptable group would result in an "insufficient_security" error, which is incorrect. That error is clearly defined to be for lack of acceptable cipher suite. The Negotiated Groups section says lack of acceptable group is a “handshake_failure” error. I changed the text to state the error for suites, as the other is already noted elsewhere. (this change is now in PR #201) This brings up a problem, however: there is no distinct error for lack of group support. The “handshake_failure” is a bit of a catchall, so there's no way for a client to really know what's wrong if this happens. This is also why I don't want to change the definition of the "insufficient_security" error. Clients rely on these being relatively precise in order to show error messages that are hopefully meaningful enough to get them fixed. As such, I'd like to propose adding a new error just for this and renaming the old one to focus precisely on its long defined meaning. While we're at it, a failure of client authentication doesn't have its own error alert code either.

  enum {
       handshake_failure(40),
       unsupported_cipher_suites(71),  /* formerly insufficient_security */
       unsupported_dh_groups(72),  /* new */
       client_authentication_failure(73),  /* new */
       (255)
   } AlertDescription;

Pretty straightforward. Are there any other errors that can't be clearly identified by the returned code? Debugging shouldn't be guesswork. ;)


Dave