Questions about generating keys (hash firewalls)

[David Shaw]

On Fri, Aug 24, 2007 at 09:06:24PM +0300, Oskar L. wrote:

> Do hash firewalls have any drawbacks (performance decrease, difficult to
> implement, patent issues etc.)? What's the reason DSA doesn't have one?

I suspect a major reason is the main use of DSA is really DSS - and
DSS was never intended to be used with any hash other than SHA-1.

It gets a little stickier with DSA2/DSS2 where there are several
possible hashes.  For example, a 1024/160 DSA key can use SHA1, but
also SHA224, SHA256, SHA384, or SHA512, by truncating them to 160
bits.

David