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PICList Thread
'GUARANTEED CODE PROTECTION'
1996\05\24@155630 by rdmiller

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On Fri, 24 May 1996, Eric T. Brewer wrote:
> At 8:32 AM 5/23/96, John Payson wrote:
[...]
> >[2] too much voltage on a port pin, with current to back it up [e.g. rect-
> >    ified raw power line--170v DC!]  Note: even this didn't blow up the whole
> >    chip--just the affected port pins.  Unfortunately, blowing up PB7 leaves
> >    the chip's code in a somewhat permanent state (the code that was in there
> >    still ran, but there was no way to change it)
>
> Sounds like a good way to really code protect your devices! Just blow away
> PB6 and PB7 on the newer (ISP) devices! ;)

Now we have an answer for the truly paranoid.
One hundred percent code protection, guaranteed.

Rick Miller

1996\05\24@175838 by Eric T. Brewer

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At 12:56 PM 5/24/96, Rick Miller wrote:
>On Fri, 24 May 1996, Eric T. Brewer wrote:
>> At 8:32 AM 5/23/96, John Payson wrote:
>[...]
>> >[2] too much voltage on a port pin, with current to back it up [e.g. rect-
>> >    ified raw power line--170v DC!]  Note: even this didn't blow up the
>>whole
>> >    chip--just the affected port pins.  Unfortunately, blowing up PB7 leaves
>> >    the chip's code in a somewhat permanent state (the code that was in
>>there
>> >    still ran, but there was no way to change it)
>>
>> Sounds like a good way to really code protect your devices! Just blow away
>> PB6 and PB7 on the newer (ISP) devices! ;)
>
>Now we have an answer for the truly paranoid.
>One hundred percent code protection, guaranteed.
>
>Rick Miller

Almost perfect. Someone can still use invasive techniques on the chip to
get a the code. This is what chip companies do. They take electron micrographs
of the chip and figure out the circuits. They can also probe the part to figure
out what bits are set to what. The downside, is the patient dies in the process!

But all in all, I think it is pretty good if you don't mind losing a port
pin or two!

eric

1996\05\24@181136 by Eric Smith

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On Fri, 24 May 1996, Eric T. Brewer wrote:
> Sounds like a good way to really code protect your devices! Just blow away
> PB6 and PB7 on the newer (ISP) devices! ;)

Rick Miller <spam_OUTrickTakeThisOuTspamDIGALOGSYS.COM> replied:
> Now we have an answer for the truly paranoid.
> One hundred percent code protection, guaranteed.

Not guaranteed.  There is at least one company in the UK (I forgot the
name, saw an ad a few months back in Nuts & Volts) that dumps PIC code
by deencapsulating the chip.  My guess is that they mask most of the chip
and UV erase the code protect cell (which won't work on newer PIC that have
the code protect cell covered by metallization).  But if they deencapsulate
the chip it is a small step for them to also do wafer probing to bypass the
blown I/O port or otherwise tap internal circuit nodes.

There is nothing that can be done to guarantee code protection short of not
programming the code into a part in the first place.

This technique might be useful on the '84 to thwart the published techniques.
However, even if the only obvious damage to the part is a failure of PB6
and PB7, the reliability of the entire part is suspect at best.  As with
overclocking, it would be very bad engineering practice to do this in an
an actual product.

For many (but by no means all) PIC applications I have seen, it is
sufficiently easy to determine what the PIC software does that it would be
more cost effective for me to write equivalent code from scratch rather than
send a locked PIC off to a company specializing in extracting protected code.

As an example:

Malik Dad previously asked how to extract code from a protected 16C54
used in a Sony PlayStation modification that circumvents the country code
restrictions.  I suspect that some clever engineer went to a lot of work
to reverse engineer the relevant part of the behavior of the PlayStation.

But I'd be willing to bet that a good engineer with one of the modified
PlayStations could easily figure out the behavior of the PIC and write
equivalent code from scratch in much less time than was required for the
original design.

If anyone wants to give me a modified PlayStation, I'd be willing to give
it a try :-)

Cheers,
Eric

1996\05\31@115249 by Pedro Polonia

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Attachment converted: wonderlandthree:_tar.863.Re__GUARANTEED_COD (????/----) (000043E4)

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