Let's say I came up with a very special algorithm, one that would be 
very valuable to sell.

If I distribute it as a binary executable file for something like 
Windows or Mac, then of course people can just look at the machine code 
to figure out what it's doing.

I've been looking into using a microcontroller to keep an algorithm 
private. Let's say I have an algorithm as follows:
    It takes a 128-Bit number as input and gives a 128-Bit number as output.

Now here's what I have in mind:
    I get my hands on a microcontroller that has either built-in USB or 
built-in Ethernet. I compile my algorithm for the microcontroller in 
question. I produce a device about the size of a matchbox and sell it, 
and the consumer plugs this device into their PC, perhaps into a USB 
port. The microcontroller will take input from the PC, run the algorithm 
and then give output to the PC.

Has this been done before? (Try not to throw plates at me if it has)

I've heard about the "code protect" feature of PIC chips. Does this 
feature prevent the program code from being read from the chip? Is it 
100% secure?

Lastly, how would you suggest I go about this: USB or Ethernet. Ethernet 
would be handy in that I could set it up as a webserver that takes input 
and then gives the output on a webpage. Another good thing about this is 
that it would be platform independent and would work on anything that 
has a web browser.

USB would be attractive because it's what people are "used to" and it 
seems USB ports are more ubiquitous than Ethernet ports. Also I do away 
with a batter because I can take power from the USB port. How good is 
USB though when it comes to cross-platform development?

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