> From MPritchard@xxxxxxxxxxxxxxxxxxx Thu Nov 12 17:33:51 1998
> To: "'stella@xxxxxxxxxxx'" <stella@xxxxxxxxxxx>
> Subject: RE: [stella] Atari 7800
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>
> It's a 126 byte public/private key thingie. Bruce Tomlin has the full scoop
> on it.
I have seen Bruce's document on how to modify the 7800 to accept and EPROM (as a way of by passing the validation key), but I have never seen any info from him on the actual encryption algorithm. If you have anything can you forward it to the list?
>
> The code/data is not actually encrypted, it is just used to generate the
> encryption key which is processed with the 126 byte key to determine that
> the cart is valid. That is what it is doing when it shows the Atari logo on
> power up.
>
> The Encryption does not have to cover the entire cart. A Byte in the top of
> the cart indicates what portion of the cart to use to generate the
> encryption check. it can be as little as 4K, I think the 6502 vectors have
> to point into the encryption key area. Bank Switched data is not used for
> encryption of course. Harry Dodgson's monitor cart (believe it or not, I
> got one of these from cart hunting in the wild) only "encrypts" the top 4K
> and the vectors immediately jump out to point in the "unencrypted" space.
>
I am not following you on how Harry got around the encryption. Did he just put data from a real cart in the top 4K and point the reset vector out of the range?
Dan Boris
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