On Sun, Sep 09, 2012 at 03:35:12PM +0200, Arno Wagner wrote: > On Sun, Sep 09, 2012 at 10:27:44AM +0200, Milan Broz wrote: [...] > > (And the same random test perhaps should be in tests for large > > enough blocks - see tests/differ.c, there is nice fixme :-) > > Will have a look. Question for that, is the "R" option one random thing replaced with another random thing? If so, I can fix that test by XORing both and calculating entropy on the result. Will still require -lm for the log() though. And an update on the 0.85 threshold: I have checked 10 Million random 512B blocks and the sample entroy never went below 0.92. For larger blocks the probability will be even lower. I think 0.85 is quite adequate as threshold. However, the test in differ.c will probably need to go back to a count of differing bits for blocks significantly smaller than 512B or use a lower threshold. Is it used for small blocks, e.g. keys? Arno > > I am just not sure introducing floating point in libcryptsetup > > is good idea. > > While this can be done without, it is really hard. Basically > you eiher need to simulate the logarithm in fixed-point integer > or build up huffman tree as direct entropy estimator. Easiest way > would probably be fixed-point and a 1000-entry table for the > log(). > > > But perhaps this can be compile time option, > > if some ancient/embedded CPU/distro has problems here, > > so it can be compiled-out. > > I like that idea much better. > > So, next step, make it use luks.h and put it in misc/ ? > > Arno > -- > Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno@xxxxxxxxxxx > GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F > ---- > One of the painful things about our time is that those who feel certainty > are stupid, and those with any imagination and understanding are filled > with doubt and indecision. -- Bertrand Russell > _______________________________________________ > dm-crypt mailing list > dm-crypt@xxxxxxxx > http://www.saout.de/mailman/listinfo/dm-crypt > -- Arno Wagner, Dr. sc. techn., Dipl. Inform., Email: arno@xxxxxxxxxxx GnuPG: ID: 1E25338F FP: 0C30 5782 9D93 F785 E79C 0296 797F 6B50 1E25 338F ---- One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision. -- Bertrand Russell _______________________________________________ dm-crypt mailing list dm-crypt@xxxxxxxx http://www.saout.de/mailman/listinfo/dm-crypt
