Date: Sat, 14 Apr 2012 07:57:39 +0200 From: Frank Dittrich <frank_dittrich@...mail.com> To: john-dev@...ts.openwall.com Subject: Re: JtR:Multi-GPU Setups On 04/14/2012 05:48 AM, SAYANTAN DATTA wrote: > On Sat, Apr 14, 2012 at 7:07 AM, Solar Designer <solar@...nwall.com> wrote: > >> For slow hashes, multiple instances of JtR are perfectly capable of >> fully loading multiple GPUs in the same machine at once. I experimented >> with that the other day, got over 1.5M c/s combined speed at phpass with >> incremental mode on my AMD + Nvidia cards. >> > > I have a question here. In this mode do we use two gpus to crack a single > hash or two instances john is run on both the GPUs. Since Alexander mentioned "multiple instances of JtR", I am pretty sure he did start JtR twice. If you do that, you manually make sure that there is no (or very little) overlapping in what these two instances do. Either you use two password files (the original passwords split by salts, so that no salt appears in both input files). For slow hashes any many password hashes with different salts, the overhead of generating the same password candidate twice can be neglected. Alternatively, you try different cracking modes (e.g., the first instance runs incremental mode for length 1-7, the second one incremental mode for length 8). Frank
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