code protection for microprocessor

[jtronix]

In microprocessor it doesn't have internal memory for code but it stored on external flash which is non protected and anybody can copy. So how people are protect their processor based device ??

I have gone through cryptography but in cryptography it store key in external flash so it won't secure the device..

kindly advice

[Kilrah]

You don't.

If you need to there are processors that are made specifically for this and have a small internal memory to put a key in as well as hardware modules to do the decryption transparently.

[ataradov]

which is non protected and anybody can copy. So how people are protect their processor based device ??

That depends on your device. Most MCUs that can execute code from external interfaces support scrambling on those interfaces.

[mikerj]

That depends on your device. Most MCUs that can execute code from external interfaces support scrambling on those interfaces.

Most?  I suspect those devices are in the minority.

[ataradov]

Most?  I suspect those devices are in the minority.

Well, I don't have the stats, but my thinking is, manufacturer must be pretty dumb to release a product with no IP protection. Who would design such a thing into a real product?

[mikeselectricstuff]

Most?  I suspect those devices are in the minority.

Well, I don't have the stats, but my thinking is, manufacturer must be pretty dumb to release a product with no IP protection. Who would design such a thing into a real product?

Not every product is at risk from code copying - most standard MCUs can be unprotected for a few hundred dollars, so it doesn't offer protection from more than casual copying.
Microprocessors are pretty rare nowadays as pretty much everything from within the last couple of decades will have at leas some I/O and/or memory built in.
Back in the days when microprocessors were common, for those that did want some protection, it was common to use a GAL or other PLD to provide some level of protection, but again this was only good against fairly low-level attacks.
Another tactic that was used was to fill unused areas with "random" data or have hidden functionality to display a copyright message ( that was obfuscated in the ROM image), so if code was copied it was very easy to prove.