Olivier Galibert wrote:
>
> I have 32768 16bit values that are the result of the hardware
> decryption of the same value (ffff) at 32768 consecutive adresses
> (starting at f0000). Nobody knows how the encryption work, except
> that it only depends on the address and the 16 bit value at that
> address (no hidden state).
>
> With these 36768 values, it should at least be possible to get a clue
> on how the address indluences the process. Problem is, I have no idea
> where to start. So it would be nice if you could point me to
> resources (books, websites, whatever) on the subject. All I can find
> is of the "algorithm known, key unknown" category.

Spot the guy who is trying to hack a ROM. What's the bets its in a
phone?

BTW, I did this once, many years ago - it helps to remember that
whatever the algorithm is is likely to be realisable in a relatively
small number of gates, and not involve arithmetic (as such). Since it
also has to be reversible (or, to put it another way, entropy
conserving), it is likely to be entirely composed of transpositions and
XORs.

Cheers,

Ben.

--
http://www.apache-ssl.org/ben.html
"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff

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