Re: Fuseable Links - no guarantees??

[tcmay@got.net (Timothy C. May)]

At 3:44 AM 6/15/96, Warren wrote:
>I have never paid much attention to the protection of firmware or the
>technical issues revolving around such schemes...was wondering:
>
>I recently saw an add for a UK based group that says they can take a PIC
>OTP micro and read the prom (for a fee, of course) - How the heck is this
>done?? I have my suspicion that they (somehow) magically peel off the
>ceramic coating (without destroying the chewy center), get a circuit mask
>and 'micro probe' the I/O of the IC...they then download the secret recipe
>to the afore mentioned 'chewy center'.
>
>Is this close to accurate?? How is it 'done' ???

I don't know of any modern chips that have "ceramic coatings." (Some chips,
esp. CPUs, are still ceramic-packaged, but in these cases the metal or
ceramic lids are easily removed.)

Most chips are plastic-packaged, and plasma ashers and/or chemical baths
will expose the chip surface easily enough.

Once exposed, various methods exist to read internal voltage levels. For
example, electron beams in a scanning electron microscope (SEM) can fairly
easily read at least surface potentials. Whether a SEM in voltage-contrast
mode can read voltages on lower levels depends on a lot of things, and I
can't even make a guess here as to whether OTP (one-time programmable)
memories from particular vendors can have internal nodes probed.

With enough money, many things are possible.

--Tim May

Boycott "Big Brother Inside" software!
We got computers, we're tapping phone lines, we know that that ain't allowed.
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Timothy C. May              | Crypto Anarchy: encryption, digital money,
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