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Date: Fri, 1 Aug 2014 22:36:04 -0500
From: Dylan Staley <>
Subject: PKZIP and GPU acceleration


I've been playing around with John, compiled from the bleeding-edge branch
(without modifying the Makefile), and I've noticed that a lot of the
formats that have CUDA or OpenCL support are listed as such under the
format option. Now, I've read countless articles about using John on
CUDA-enabled EC2 instances, but seeing as how PKZIP *doesn't* have a CUDA
or OpenCL version listed in the format option, does it even matter?

I wanted to try and figure this out myself, so I ran john --format=PKZIP
--test on two EC2 instances:

* g2.2xlarge: 26 ECUs, 8 vCPUs, 2.6 GHz, Intel Xeon E5-2670, 15 GiB memory,
* c3.8xlarge: 108 ECUs, 32 vCPUs, 2.8 GHz, Intel Xeon E5-2680v2, 60 GiB

The results were as follows:

$ ./john --format=PKZIP --test
Will run 8 OpenMP threads
Benchmarking: PKZIP [32/64]... (8xOMP) DONE
Many salts: 50288K c/s real, 6301K c/s virtual
Only one salt: 22616K c/s real, 2837K c/s virtual

$ ./john --format=PKZIP --test
Will run 32 OpenMP threads
Benchmarking: PKZIP [32/64]... (32xOMP) DONE
Many salts: 144437K c/s real, 4519K c/s virtual
Only one salt: 33959K c/s real, 1061K c/s virtual

At this point, I was completely convinced that john is using the CPU for
PKZIP, but I wanted to see just how much its performance could be increased
in the real world. I used zip2john to get the hash for a zip file with a
fairly simple password ("mi12345"). It took the g2 instance (the one with
the GPU) 21 minutes to find the password, and the more powerful c3 instance
15 minutes to find the password.

If I'm correct in assuming that John doesn't support using a GPU on PKZIP,
what would be needed to enable this? Does anyone know of anything that is
able to use the GPU with better performance than a CPU?

Dylan Staley

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