Re: [saag] Revision of "Attacks on Cryptographic Hashes in Internet Protocols"

Paul Hoffman <paul.hoffman@vpnc.org> Wed, 14 November 2012 23:42 UTC

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From: Paul Hoffman <paul.hoffman@vpnc.org>
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To: Andrey Jivsov <openpgp@brainhub.org>
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Subject: Re: [saag] Revision of "Attacks on Cryptographic Hashes in Internet Protocols"
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On Nov 14, 2012, at 3:35 PM, Andrey Jivsov <openpgp@brainhub.org> wrote:

> On 11/14/2012 02:33 PM, Paul Hoffman wrote:
>> On Nov 14, 2012, at 1:40 PM, Andrey Jivsov <openpgp@brainhub.org> wrote:
>> 
>>> SHA-2 is well-supported today, but there are no solid reasons why SHA-3 will not be supported equally well in the future.
>> 
>> In that future, we can re-look at support for it in IETF protocols. For now, algorithm agility might be sufficient.
> 
> I would agree, but the document such as RFC 4270 influence the future. If the message it sends is that the SHA-3 is an odd bifurcation in the SHA line, SHA-3 won't gain critical mass.

If we have suggested that in the draft, we should change the text. Can you say where you got that feeling?

>>> Let's say there is a protocols that is hardwired to SHA1 or MD5. Are we telling people thinking about its improvement to go with the SHA-2?
>> 
>> Yes.
>> 
>>> What about newly designed protocols?
>> 
>> The same.
>> 
>>> If you are a maintainer, what would you prefer: worry about explaining to others that "my SHA-2 use doesn't depend on collision resistance and is not vulnerable to extension attacks", v.s. I "use SHA-3".
>> 
>> Nowhere did we say that you should not use SHA-3. In fact, we said the opposite. We said there was no need to push that.
>> 
>>> I suggest that the document at least softens the statements on SHA-2 v.s. SHA-3. Ideally, I would like to see a path on which we move to the universally supported SHA-3 and, hopefully, the hardware manufacturers are comfortable to jump in.
>> 
>> That's one view; we took a different one. So far, we have had good support in the IETF community for our view, but at some point that might change.
>> 
> 
> It would be useful for me and others to see more details behind the arguments that the SHA-2 is preferred to SHA-3 at IETF. I suspect there are a lot of assumptions here that may not apply to every particular case.

Instead of speaking for others, I'll let them chime in here.

> One of the parameters is the timeline. The transition to a new hash algorithm may take years in protocols and formats without algorithm agility, while the plans for which route to take are being made today.

Noted.

> For example, in OpenPGP there is a hardwired SHA1 fingerprint. It still seems wrong to me to move to SHA-2 and not SHA-3. I am leaning toward non-agile solution here because of space constrains and the fact that the agility will only be a benefit if Keccak is broken (so instead of adding SHA-2 + agility, add hardwired SHA-3 which is good for a few decades, at least).

The OpenPGP people can speak for themselves; I certainly don't represent them.

--Paul Hoffman