Re: Handling NULL key exchange for NULL_ ciphersuite

Ned Smith wrote:
> 
> What is the correct way to interpret handling of the NULL ciphersuite
> for key exchange?
> 
> The TLS spec (excerpts provided below) appears to be vague in its
> description of how key exchange handling is done if the NULL
> ciphersuite is negotiated. I don't recall seeing any statement
> indicating it is illegal to negotiate a NULL ciphersuite. My
> assumption is the NULL ciphersuite could be negotiated anytime it is
> legal to negotiate any other ciphersuite (its regular).

I assume you mean TLS_NULL_WITH_NULL_NULL.  Although the spec does not
explicitly forbid negotiating to this cipher suite, it should.  If an
implementation allows negotiation to this cipher suite, it is open to
a rollback attack.

-- 
You should only break rules of style if you can    | Tom Weinstein
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