On Thu, 11 Feb 2010, Johansson wrote:

> Xiaofan Chen:
> >I mean those with encryption.
> 
> Using encryption doesn't automatically mean that things become safe. If you
> encrypt your harddrive, would that mean you can't get viruses in your
> computer?

Johansson I think you've missed the point a bit :-)

Your analogy of encrypting the harddrive is the wrong one. You should 
instead be thinking of scrambling a phone conversation with someone 
listening in and occationally saying something to make two friends think 
the other is being rude. If the line is scrambled then the friends can't 
hear understand the troublemaker.

If you used a bootloader with encryption then it becomes very hard for a 
third party to "just" upload code into your device. Your bootloader will 
disregard any invalid attempts to load new code into the FLASH (including 
a new bootloader) if the uploader does not encrypt and send the code 
CORRECTLY!!! This means that unless the person doing the modification (the 
bad guy between you and your client) knows how the encryption works and 
what keys to use then he is VERY EFFECTIVLY blocked from uploading new 
code to your device.

It is MUCH easier to change the contents of a PIC using ICSP than it is to 
change it using a bootloader with encryption.

Regards
Sergio Masci
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