Re: [TLS] draft-sheffer-tls-bcp: DH recommendations

Xuelei Fan <xuelei.fan@vimino.com> Mon, 16 September 2013 10:43 UTC

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Date: Mon, 16 Sep 2013 18:43:09 +0800
From: Xuelei Fan <xuelei.fan@vimino.com>
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To: Michael D'Errico <mike-list@pobox.com>
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Subject: Re: [TLS] draft-sheffer-tls-bcp: DH recommendations
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It's another worry that there is no way to negotiate the ephemeral DH 
key size.  A robust client may have to support 756/1024/1536/2048-bit 
keys. And a wildly deployed server may have to always use the wildly 
supported DH key sizes, for example 1024-bit, in order to server more 
clients.  If we want a new extension for ephemeral DH keys, it would be 
nice to support ephemeral DH key size negotiation.

Xuelei

On 9/16/2013 5:21 AM, Michael D'Errico wrote:
> DH can be sped up if you incorporate a medium-sized (e.g.
> 256-bit) prime q into the parameters.  See for example
> Cryptography Engineering, pages 187-188.  Since q is
> missing from the signed ServerDHParams, adding it would
> require an extension.
>
> We all know how hard it is to new get extensions deployed,
> but perhaps there's now sufficient incentive....
>
> Mike
>
>
> Stephen Farrell wrote:
>>
>> On 09/15/2013 08:56 PM, Yoav Nir wrote:
>>> So no, I don't think we should give up of PFS.
>>
>> +1024 :-)
>>
>> S.
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