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Re: [Uta] updated I-Ds

Yaron Sheffer <yaronf.ietf@gmail.com> Wed, 26 February 2014 08:43 UTC

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Date: Wed, 26 Feb 2014 10:43:05 +0200
From: Yaron Sheffer <yaronf.ietf@gmail.com>
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To: Stephen Farrell <stephen.farrell@cs.tcd.ie>, Daniel Kahn Gillmor <dkg@fifthhorseman.net>, Watson Ladd <watsonbladd@gmail.com>
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Archived-At: http://mailarchive.ietf.org/arch/msg/uta/K8vfrpJTPD4Fh2bxZO8pRPX_-xY
Cc: uta@ietf.org
Subject: Re: [Uta] updated I-Ds
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The document recommends ECDHE over DHE, because DHE parameters cannot be 
negotiated and so some people will be stuck with DH-1024. See 
http://tools.ietf.org/id/draft-sheffer-tls-bcp-02.html#rfc.section.4.2

But for those people who cannot switch to ECDHE, the tradeoff is exactly 
between RSA-2048 and DH-1024. Stephen would recommend DH-1024 in this 
case, because the NSA can get at the server's private key and then, if 
you don't have PFS, you're hosed.

I would recommend RSA-2048 in this case, because DH-1024 can be broken 
today with commercially available compute power (buy a few Amazon extra 
large instances and let them run for a few months). Also, and this is a 
value judgment, I think the cryptographic break is a higher risk than 
wholesale theft of the private keys.

Thanks,
	Yaron

On 02/26/2014 12:40 AM, Stephen Farrell wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
>
>
> On 02/25/2014 09:42 PM, Daniel Kahn Gillmor wrote:
>> Yes, agreed.  DHE-1024 needs to be deprecated.
>>
>
> True. But I would hope UTA WG BCPs can be broadly
> implemented without waiting for a massive upgrade
> so its possible we could have to live with DH-1024.
>
> Much better if that's only a niche or just gets fixed,
> but that's the kind of trade off that needs to be
> considered. And an important part of that trade off
> is not between DH-1024 and RSA-2048, but rather
> between PFS and non-PFS ciphersuites.
>
> S.
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