[TLS] Should we require implementations to send alerts?

[Eric Rescorla <[e-mail]>]

Issue: https://github.com/tlswg/tls13-spec/issues/242

In https://github.com/tlswg/tls13-spec/pull/231, Brian Smith argues:

"Nobody must ever be *required* to send an alert. Any requirement for
sending an alert should be SHOULD, at most."

As Dave Garrett notes in the same thread, this is a common requirement
throughout
the specification and we recently have had requests to add more of these
requirements.
This is a global specification issue, so seems appropriate to discuss
on-list.

FWIW, I would note that the just approved session-hash draft contains such
requirements as well:
https://tools.ietf.org/html/draft-ietf-tls-session-hash-06#section-5.2
"In the following, we use the phrase "abort the handshake" as shorthand for
terminating the handshake by sending a fatal "handshake_failure" alert."

so it could be argued that this reflects recent WG consensus.

-Ekr