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.