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Date: Sun, 9 Jun 2013 20:39:39 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Extra functions/datatypes for external mode?

On Sun, Jun 09, 2013 at 04:35:49PM +1000, Michael Samuel wrote:
> I currently have some C code that emulates a random password generator,
> which I was looking at porting to a john external mode.
> 
> While most of the code works as 32-bit signed integers, I need to do the
> cast as double, then multiply by (1.0/2^32) trick, which I'm not really
> sure how to do in integer-only arithmatic (I'm guessing it's technically
> possible).

Can you post the relevant excerpt from your C code (along with the
relevant variable declarations)?  Did the original password generator
use the "double" data type too?

> Is there a way to define C functions that external mode can call, or just
> add more data types to external mode?

Currently, no.  Also, having an external mode call a custom C function
would defeat the purpose of using an external mode in the first place -
you could instead implement the entire thing in C as an extra cracking
mode (would be a JtR source code patch then).

I think that in your case it'd be best to go with emulating the one
conversion via "double" in 32-bit integer arithmetic in an external
mode, if having to implement that conversion is not easily avoidable.

Alexander

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