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Date: Tue, 27 Feb 2018 15:59:44 -0600
From: Adam Lininger <>
Subject: Re: Getting full performance out of multiple GPU's


Thank you for the help. I believe I am properly using a GPU and the actual
hashing is being done there. The nvidia-smi command seems to agree. Based
on your email, I suspect the problem is that the korelogic rule generation
is still happening on the CPU rather than the GPU. Is there an easy way to
correct that? I've copied my command below.

john --wordlist=rockyou.dict --format=descrypt-opencl
--devices=1,2,3,4,5,6,7,8 --fork=8 --rules=korelogic htpasswd


On Tue, Feb 27, 2018 at 2:14 PM, Solar Designer <> wrote:

> Hi Adam,
> On Mon, Feb 26, 2018 at 01:41:34PM -0600, Adam Lininger wrote:
> > I've got an 8-gpu cracking rig that I've inherited from someone who had
> it
> > setup with hashcat. Apparently it worked well there.
> >
> > As I prefer john, I've been trying to get it set up. I have it up and
> > running, but the Utilization output from --list=opencl-devices hovers
> > around 0-1%. Is there a way to improve this?
> >
> > I'm running John the Ripper (freshly
> > re-pulled and re-built today).
> To use a GPU at all, you need to be invoking one of JtR "formats" with
> "-opencl" in its name.  You do this with an option like e.g.
> "--format=sha512crypt-opencl", but corresponding to whatever hash type
> you're actually cracking.
> And if it's one of so-called "fast hashes" - like raw MD5, and thus
> "--format=raw-md5-opencl" - then you also need to use "--mask" (and
> specify a mask suitable for your attack) in order to have candidate
> passwords at least partially generated on GPU.  You may use this mask
> mode along with another cracking mode, in which case you'd refer to that
> other mode's generated partial candidate password as "?w" in the mask.
> Then, as magnum has just pointed out in another thread, to use more than
> one GPU you need to list all GPU device numbers and also specify at
> least an equivalent number of "forks", like this: "--dev=0,1,2,3,4,5,6,7
> --fork=8".  (We got to enhance JtR to print a warning when the specified
> number of OpenCL devices is greater than the number of forks.)
> Please post your current JtR command line and explain its resulting
> behavior if you require further help, or just to share your experience
> with the community.
> Alexander

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