[hashcash] Re: compact stamps optimization

  • From: Adam Back <adam@xxxxxxxxxxxxxxx>
  • To: hashcash@xxxxxxxxxxxxx
  • Date: Thu, 8 Dec 2005 02:50:34 -0500

I think the issue is that SHA1 is chained thru the 5x 32-bit (160-bit)
chaining/state variables A,B,C,D,E.  So in the 2nd case you have to
recompute the 2nd block even though the 2nd data doesn't change.

(It would be nice to find a way to remove the -Z options, we tried
before, and failed so far).

Adam

On Wed, Dec 07, 2005 at 11:19:11PM +0100, bas wrote:
> [...]
> changes which would require calculation of both blocks are
> 1: the string becoming longer (because the counter becomes longer), so it 
> becomes 2 blocks
> 2: a char of the counter, other than the least significant, changes, which 
> is in the first block.
> 
> what does the padding refer to? what am i missing?
> 
> i think if its possible at all to optimize -Z2 so it's like 1.1 slowdown, 
> and not 2x, this is a good idea and it should become the default, and the 
> existing -Z1 setting becomes obsolete.

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