Re: [TLS] Should we require implementations to send alerts?

[Florian Weimer <[e-mail]>]

On 09/16/2015 09:53 PM, Brian Smith wrote:

> Assume the client and the server implement the mandatory-to-implement
> parameters and that both the client and the server are otherwise
> conformant. In this scenerio, when would an alert other than the non-fatal
> close_notify be sent?

I have been told that mandatory-to-implement does not mean
mandatory-to-enable, and that it is possible to run a nominally
RFC-conforming client or server in a mode which is not interoperable
with anything else.  Under such a scenario, fatal alerts happen without
an attack.

Most fatal alerts in the wild appear to be harmless in the sense that
they are not due to attacks, but due to interoperability failures (due
to not enabling mandatory-to-implement cipher suites, self-signed
certificates, incomplete certificate chains, or just bugs).

-- 
Florian Weimer / Red Hat Product Security