I've been hacking with the hashing method used in noise.sys and decided to throw it away, since it did more to overestimate the entropy. Until I find something better an xor-checksum of the ast N samples seems to do fine. Alternating samples generate no entropy and samples with periods <= N seem to generate less than 1 bit per sample. The method (in pseudo-code) is as follows: delta = abs( LastSample - sample ) LastSample = sample hash ^= delta /* until I can think of a better hashing algorithm */ swap delta, lastNtable[ indexNtable ] indexNtable = (indexNtable+1) mod N hash ^= delta t = counter /* counts the number of samples so far */ counter++ swap t, lastseen[ hash & (TABLESIZE-1) ] diff = lastseen[ hash & (TABLESIZE-1) ] - t if diff<=N, assume no entropy (or fractional entropy?) otherwise return log2(diff) Comments? Rob. --- Send a blank message with the subject "send pgp-key" to <WlkngOwl@unix.asb.com> for a copy of my PGP key.