EPROM PROTECTION???

[Richard]

Hi masters,

I have always wandered if there is any of the chip family 27C256,
28C256, 29C256, 27SF256, etc. with internal protection, like a fuse or
anything alike, that could be set to prevent reading in a device
programmer and still being accesible by the circuit it is intended
for. This for avoiding the hard to develop code to be copied without
permission (stolen).

If there is no such a device, is there anything that could be done to
prevent or make dificult to read the programmed code?

Thanks in advance for any help you could bring. It will be greatly
appreciated.

Richard

 

[Tim Wescott]

A processor reads the device exactly the same way that a programmer would,
so there really isn't any way to make that happen. Someone (Intel, I think)
made a device which encrypted the data, but that doesn't help the poor
processor than needs it to boot! Pretty much anything that's going to let
the processor access the data on an external chip is going to make the data
available for hacking.

Depending on the level of security you need and the amount you're willing
pay there are things you can do, however. The three that I can think of
are:

1. Get a modern microcontroller with a security fuse. These things _can_
be protected from reading by the programmer, because the memory and
processor are all on one chip. There are a lot of 8- and 16-bit devices
these days that do this for you, but not many 32-bit ones, so it may not do
the job for you.

2. For 'lite' security just scramble the address and data pins on the
board. A friend of mine used to be partners in a business in a very
competitive market which was rife with piracy. They just swapped pins
around on the chips as needed for convenience in laying out the board then
mixed and matched the image on the chip to match. This would raise cain
with block organization on flash unless you restricted yourself to only
swapping the lower-order address pins.

3. For tighter (yet still not perfect) security, encrypt the data on your
ROM and use a protected processor to decrypt it into the main processor's
memory. If someone wanted to use the data they'd have to get there hands on
a working board and do some serious engineering to get an entire image. You
could get more elaborate by encrypting data for the particular system it's
in, but at some point you'll spend more money than you would just giving
your code away.

Have fun.

-------------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

"Richard" <zilog357@hotmail.com> wrote in message
news:d22a8817.0401062043.10caba13@posting.google.com...

Hi masters,

I have always wandered if there is any of the chip family 27C256,
28C256, 29C256, 27SF256, etc. with internal protection, like a fuse or
anything alike, that could be set to prevent reading in a device
programmer and still being accesible by the circuit it is intended
for. This for avoiding the hard to develop code to be copied without
permission (stolen).

If there is no such a device, is there anything that could be done to
prevent or make dificult to read the programmed code?

Thanks in advance for any help you could bring. It will be greatly
appreciated.

Richard

 

[zilog357]

Thanks a lot for your reply Tim, I greatly appreciate your help. It
definitely cleared things up to me.

 

[helder Varela]

lol, of course not, if it can be read, how can the microprocessor read the
information. To be almost(almost) secure, use a microcontroler with internal
eprom(program memory), the most secure is the dallas family.....


"Richard" <zilog357@hotmail.com> escreveu na mensagem
news:d22a8817.0401062043.10caba13@posting.google.com...

Hi masters,

I have always wandered if there is any of the chip family 27C256,
28C256, 29C256, 27SF256, etc. with internal protection, like a fuse or
anything alike, that could be set to prevent reading in a device
programmer and still being accesible by the circuit it is intended
for. This for avoiding the hard to develop code to be copied without
permission (stolen).

If there is no such a device, is there anything that could be done to
prevent or make dificult to read the programmed code?

Thanks in advance for any help you could bring. It will be greatly
appreciated.

Richard

 

[Sensei S]

well actually depends on what you're doing. if you're looking for straight
eeprom memory storage, you cannot write protect however if you've played
with the basic stamp or oopic, you can see that there are ways to protect
your code by setting lock bits. but that means your code would have to be
based on a microprocessor design.


"Richard" <zilog357@hotmail.com> wrote in message
news:d22a8817.0401062043.10caba13@posting.google.com...

Hi masters,

I have always wandered if there is any of the chip family 27C256,
28C256, 29C256, 27SF256, etc. with internal protection, like a fuse or
anything alike, that could be set to prevent reading in a device
programmer and still being accesible by the circuit it is intended
for. This for avoiding the hard to develop code to be copied without
permission (stolen).

If there is no such a device, is there anything that could be done to
prevent or make dificult to read the programmed code?

Thanks in advance for any help you could bring. It will be greatly
appreciated.

Richard