Re: Security for embedded device

From: Joris Dobbelsteen (none.of_at_your.business)
Date: 06/30/04 

Date: Wed, 30 Jun 2004 21:17:29 +0200

"Guy Macon" <http://www.guymacon.com> wrote in message
news:10e5qsubharrtf9@corp.supernews.com...
>
> Joris Dobbelsteen <none.of@your.business> says...
>
> >The disadvantage is that a sensor can be designed that accepts any key.
>
> You must face one inconvenient fact; the technology for cracking
> PC-based copy protection is so advanced that anyone who wishes to
> can break your security scheme on the PC side and then design a new
> sensor that works with the cracked version of your software. They
> can also extract the key that is on the PC and they can figure out
> whatever your cipher on the PC side is doing.

Indeed, the PC software is the vulternability, but because the software is
unlikely to be very widely used, it will be not a significant problem.
The cost of using my equipment should already outweight any attempts on
doing it yourself. Its mainly aimed at hobbyists, so the planned price is
low already.
In even relative low volumes the processor I'm planning to use will be close
the the cheapest on the planet. The cost of buying a simple processor would
probably be close to a single sensor.

> I think that you should release your software under the GNU license
> and encourage them to write their own software. You are not going to
> make money selling software that reads a sensor, but you can make
> money selling sensors. You can't protect the code on the PC, so why try?

The software was planned for a small price and most likely bundled with a
sensor. So the cost of the sensor should justify the effort put in the
software.
The software will be more than just reading it, but will make a complete
piece of work to get the job done. If you want to make your own

> >Implementation
> >
> >The sensor has its ROM protected. The downside is that I cannot use the
> >Flash ROM, but this is needed to prevent anyone from simply reading it.
> >
> >The device stores a serial number which is always readable and uniquely
> >identifies the device.
> >It also contains a 'security code' which cannot be read and is known by
> >myself only or a user who has paid for the sensor. The 'security code'
> >consists of an 'activation number' and 'encryption number'.
> >Of cause every device (identified with a serial) has a random activation
and
> >random encryption number.
>
> Good so far...
>
> >The device sends out a challenge and the PC must activate the device with
> >the activation code.
>
> That takes care of the obvious crack, which is to replace the part of
> the PC sofware that refuses to run with NOPs.
>
> Does the PC know that activation code? If so you might as well unprotect
> that ROM, because it is so simple to get it from the PC.

When the code can be obtained from the PC, it is already paid for...

- Joris

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