Re: [stella] Official Atari St 2600/7800 Dev Kit.

Subject: Re: [stella] Official Atari St 2600/7800 Dev Kit.
From: bwmott@xxxxxxxxxxxx
Date: Sat, 14 Mar 1998 23:23:56 -0500 (EST)
> Wow!  Anyone try to copy this yet?  I'm not sure I understand how this
> works, but might it be possible?
> Actually, how is the encryption done on a regular cart?  If we can pool
> all the known data, we might be able to get it to work.  Personally, I
> don't know anything...but I'm willing to spend time on work arounds once
> I know how the scheme is set up.

Here's my understanding of 7800 carts.  First of all 7800 cartridges are 
NOT encrypted.  However, they do contain what I would call a digital 
signature.  The idea is that the 7800 BIOS computes a digital signature 
for the ROM before it transfers control to the ROM's code.  Once the 
digital signature is computed it's "compared" with the digital signature 
embedded in the ROM.  If the two do not "match" then the 7800 does not 
execute the code in the ROM.

I'm sure it's more complicated than this, however, that's the basic idea.  


Bradford W. Mott (bwmott@xxxxxxx)          Computer Science Department           North Carolina State University

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