Build your own dongle

[taos]

Originally Posted by redbull

I found this design project on Amtel AVR 2004 design contest web site.

hxxp://www.circuitcellar.com/avr2004/DA3824.html
The ATmega8L-8AI microprocessor-based Intelligent Security Serial Dongle effectively ... by a random number generator.
No external power source is needed.(RS-232)

You can make a similar project with PIC (16F87X,etc...) I made one last year.
Use a usb interface with the PIC (like USB to RS232 FT232 converter), the Quartz crystall oscilator and the power supply filtering capacitors.The cost maybe 5-9 $. Use virtual USB-serial drivers (you can use the USB like a com serial port). You don't need external supply (USB has a VDC line). Then you can do this:
Your EXE open virtual com port, send a string to the PIC ("0ABBAA00"), the PIC convert this into a string like ("CALL BBAA00" opcodes), send this string to your EXE, then your EXE writes this in memory a jumps.
It's like a VM engine, you can also shares info between PIC & EXE (HD serial,etc...), stores seeds in PIC flash memory, make jumps calculations,etc...
But any cracker can put a BP AFTER your send/receive ports commands and rebuild the EXE.
So the problem is that you can not execute x86 opcodes in the pic. If you stores some procedures of your EXE in the pic and then upload this to the EXE you make a hardware dependent dongle. So for a newbaby cracker you can use this but it's more easy to protect with Execryptor (for example) to avoid them.