updating default digest preferences

[Daniel Kahn Gillmor]

On 07/09/2009 03:45 AM, Werner Koch wrote:
> On Mon,  6 Jul 2009 23:52, dkg at fifthhorseman.net said:
> 
>> with new versions of gpg pending, is there any chance of getting the
>> default key preferences updated, as referenced here:
> 
> Done a bit different for 2.0; the default hash algo order is now:
> 
>       SHA-256, SHA-1, SHA-384, SHA-512, SHA-224.

Great news, thank you Werner!

> Ordering SHA-1 before SHA-384 might be viewed as a bit strange; it is
> done because we expect that soon enough SHA-3 will be available and at
> that point there should be no more need for SHA-384 etc.  Anyway this
> order is just a default and can easily be changed by a config option.

I'm not certain i understand this logic.  doesn't the same reasoning
apply in both directions?  That is, when SHA-3 is finalized in 2012,
won't it obsolete both SHA-384 *and* SHA-1?  Since SHA-1 is assumed to
be present in the list by every RFC 4880 client, the only thing this
preference ordering does is that it precludes the use of stronger
digests by every client that respects the ordering.

It seems to me like the defaults should prefer the strongest known
digest that the implementation is capable of supporting.  If other
implementations can't produce the stronger digests, they would fall back
to weaker ones with no problem, right?  I don't see the advantage of
deprecating these other stronger digests now.  Are there computational
or efficiency issues that i'm unaware of?  Can you explain more?

	--dkg

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