Kelly Marquardt wrote:
>
> Hi,
>
> I'm new to this list (and female for whoever was keeping track :)).  I've used
> the 16C57 on a previous project and I'm looking into using the 17C44 on a new
> project.
>
> I'm concerned about the security of the PIC's code protection feature.  From
> what I understand, after the code protect fuse is blown, a scrambled version
> of the code can still be read from the part.  The scramble is an exclusive-nor
> of the most and least significant bytes of the opcode (16 bit program words).
>
> The question is, just how much information would this give to an adversary
> who wanted to reverse engineer the algorithm that was implemented by the code?
> Clearly it would be a difficult problem.  I more or less believe that it is
> difficult enough to provide for adequate security, but its difficult to
> quantify this in any meaningful way.
>
> Has anyone else struggled with this?  Any thoughts?  I'm trying to get a
> response from Microchip, but wondered if this group had any ideas for me.
>
> Thanks,
>
> Kelly Marquardt

The first thing to do is to fill the unused memory with code snippets
from
old projects, or random junk. This way, your code cannot be discovered
by XORing with retlw 255.

--
Friendly Regards

Tjaart van der Walt
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