Re: [TLS] Next steps for Client Certificate URL

[Nikos Mavrogiannopoulos <nmav@xxxxxxxxxx>]

Nelson B Bolyard wrote:

>>>> Given this, would everyone be OK with updating the existing
>>>> client_certificate_url extension so that including the hash is
>>>> mandatory (client MUST send, server MUST NOT accept without hash)?
>>>> This behavior would be independent of the negotiated TLS version.
>>> I'm trying to understand the attack against which this hash is going
>>> to protect, that is not already adequately protected without it.
>>> Can someone outline that attack here?
>> Usually even if you do not have an attack at hand, it might be good to 
>> prove that a modification to a security protocol makes it no less 
>> secure. By adding the hash (and considering it ideal) it is not hard to 
>> prove that the modified scheme is as strong as by sending the 
>> certificate itself.
> 
> Given two protocols of equivalent security, the one with less overhead is
> preferable in the marketplace.  If the best thing that can be said about
> the addition of the hash is that it makes the protocol no less secure,
> that is hardly a compelling reason to make it mandatory, as Pasi proposed.

At least for me it is not obvious that the two protocols have equivalent 
security (but I cannot really say I have thoroughly studied them).


regards,
Nikos
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