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Date: Thu, 4 Jul 2013 22:17:44 +0400
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: cryptocurrency mining fallback in JtR (was: Parallella: scrypt)

Rafael,

I've changed the Subject because this sub-project has little to do with
Parallella.  The only relevance is that some of the experience you'd
gain would also be useful when you proceed to implement Litecoin mining
on Epiphany - hopefully, soon.  You'll revert the Subject on messages
pertaining to that then.

On Thu, Jul 04, 2013 at 06:45:39PM +0100, Rafael Waldo Delgado Doblas wrote:
> Ok, then the cgminer integration with JtR, Is it just call from JtR to
> cgminer?

Almost, but also a few things more:

1. The settings from cgminer should be input via john.conf rather than
via command-line - although, for simplicity, you may keep cgminer's
command-line parsing and have it work on a "command line" passed via a
john.conf setting (e.g., it can be "cgminer = ...").

2. We'll need to come up with and implement the condition of when the
call to cgminer code is made vs. when it is skipped - e.g., the call is
only made when the corresponding configuration settings are present in
john.conf and the current cracking session (that has just ended) took
more than N minutes and it was not interrupted, and it's been at least M
minutes since last keypress.  Something like that.

3. If JtR was running a GPU-enabled format, we also need:

> I don't get what do you mean here: "Also, when JtR was using a GPU for
> password cracking, it's the exact same GPU that should be used for that JtR
> invocation's Litecoin mining when the cracking has completed."

Consider a multi-GPU system.  Someone ran JtR such that it was using
e.g. GPU device #2 on OpenCL platform #1.  When that cracking session
has completed, that specific GPU is about to become idle.  We don't want
it to stay idle, we want to make use of it for the mining.  Not some
other GPU, nor CPU.  (Other GPUs and some CPU cores may already be in
use by other JtR invocations, manual cgminer invocations, or whatever.)

...

I gave this more thought, and I think you should keep cgminer's Bitcoin
support as well (on GPU only) when you integrate it into JtR.

Thanks,

Alexander

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