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Re: [TLS] Call for consensus to remove anonymous DH

Viktor Dukhovni <ietf-dane@dukhovni.org> Thu, 17 September 2015 00:42 UTC

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Date: Thu, 17 Sep 2015 00:42:07 +0000
From: Viktor Dukhovni <ietf-dane@dukhovni.org>
To: tls@ietf.org
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Subject: Re: [TLS] Call for consensus to remove anonymous DH
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On Wed, Sep 16, 2015 at 08:31:41PM -0400, Daniel Kahn Gillmor wrote:

> For those worried about computational cost: the raw public key or
> certificate themselves do not have to be valid mathematical objects if
> the peer is not inclined to check them.

That's not generally possible.  Many servers support a mixture of
clients, some of which authenticate, and others not.  If a server
agrees to a cipher that requires signatures, it needs to sign.

> The signed_params itself could
> also be all 0xff or anything you like as long as the peer isn't
> checking.  

Without "anon_(EC)DH" ciphers in the client HELLO, there's no "I'm
not checking" signal.

> For those concerned about bandwidth, these objects do not
> have to be large.

Absent a client signal, this is generally not viable.

-- 
	Viktor.

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