Date: Mon, 3 Jun 2013 18:16:37 +0400 From: Solar Designer <solar@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: cmp_all on gpu for descrypt-opencl Hi Sayantan, On Mon, Jun 03, 2013 at 07:12:45PM +0530, Sayantan Datta wrote: > I have implemented a password generator which can crack all numeric(upto 8 > digit) password for descrypt. I have also tested it using a few hashes from > the test-suite. The generator is integrated with finalize_keys and doesn't > use global memory. It is also very light on registers. The password are > saved to global memory only when positive. The comparisons are done in gpu. > > The code is currently in my git hub repo , bleeding-jumbo branch. > https://github.com/Sayantan2048/JohnTheRipper.git I just took a look. Overall, this is a nice experiment, but there are two major issues with the approach taken: 1. The passwords generated by JtR are totally ignored by this descrypt-opencl hack, which generates its own all-numeric candidate passwords instead. What we need is to have the GPU substitute all possible characters (out of the currently configured charset) into a few character positions, but leave the rest as generated by the host. 2. You use modulo division, which probably has high cost of its own. What speeds are you getting? After 5 minutes of running on one descrypt hash (for other than an all-numeric password, or it would get cracked within seconds) on bull's 7970, I get a reported speed of 83M c/s (not sure if the calculation is correct or not, though, as it obviously depends on correctness of your *pcount updates). This is somewhere inbetween of what we had before and what we should be able to achieve. Running on "3269 password hashes with 2243 different salts", I get reported speeds of as low as "500752c/s 684361C/s" after 2 minutes (and not a single password is cracked yet, even though several are all-numeric). Where's the new bottleneck? With password generation on host, your descrypt-opencl was ~50 times faster at this sort of test. Thanks, Alexander
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