digest preferences [was: Re: diverging from upstream defaults]

[Robert J. Hansen]

> --default-preference-list indicates what algorithms to advertise in a
> newly-generated key.  For most modern 64-bit computers, sha-512 is
> faster to compute at any reasonable size, so it looks to me like the
> published preference order should be changed to indicate a preference
> for SHA512 by default.  People with special hardware or custom needs can
> always edit their configuration.

Begging pardon, but this seems like a very weak justification to me.
SHA512 versus SHA256 timings will be significant only for people doing
lots of signatures on extremely large files in soft-realtime
environments.  Outside of that, really, who cares if SHA512 is a
millisecond quicker when signing an email if you're handling under a
thousand documents a day?

I'm not saying SHA512 is a poor choice, mind you: I think it's probably
the right choice.  But I think this justification is pretty weak.
"People with special hardware or custom needs" describes people who
would benefit from SHA512's speed edge as much as it describes people
who would benefit from SHA256.