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Re: IETF mail server and SSLv3

Viktor Dukhovni <ietf-dane@dukhovni.org> Thu, 25 February 2016 08:57 UTC

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Subject: Re: IETF mail server and SSLv3
From: Viktor Dukhovni <ietf-dane@dukhovni.org>
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Date: Thu, 25 Feb 2016 03:57:13 -0500
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> On Feb 25, 2016, at 3:07 AM, Martin Rex <mrex@sap.com> wrote:
> 
> I'm sorry, but this information is strange.
> 
> There exists *NO* downgrade vulnerability in TLS.
> 
> There is a well-known-stupid unprotected "downgrade dance" implemented
> in a few web browsers, but that is something entirely different, and
> not a property of TLS or SSLv3.
> 
> Btw. even SSLv3 still provides *ALL* the security properties officially
> documented for TLSv1.2 in rfc5246 Appendix F.
> 
> What SSLv3 does not provide, however, is additional protection against
> obvious abuses of the TLS protocol beyond its original security goals,
> such as by ^SSL VPNs and Web Browsers.  For authentication-less
> SMTP and programmatic clients, the original scope of TLS is sufficient,
> and therefore SSLv3 a perfectly sensible option.
> 
> Disabling SSLv3 can not possibly provide any security benefit here,
> but may cause interop problems and less security for a few old peers.

Would you then go further and say that SMTP servers should leave SSLv2
and/or EXPORT ciphers or single-DES enabled?  If not, why not?

-- 
	Viktor.

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