by Joseph Watson » Fri Oct 10, 2014 5:43 am
After looking AN662 over, I think that the implication is that it is possible to implement the KEELOQ® decoder algorithm on many PIC microcontrollers but that there is important information needed about the details of the decryption algorithm that are not disclosed in AN662. They are, however, disclosed in AN652. Once you have the details of the algorithm, it looks like you can implement the decoder yourself but to get the details of the algorithm, you will need to enter into a non-disclosure agreement with Microchip.
Near the bottom of the first page of AN662, it says, "Notice: This is a non-restricted version of Application Note AN652 which is available under the KEELOQ License Agreement. The license agreement can be ordered from the Microchip Literature Center as DS40149."
On page 11, it says, "The confidential and proprietary information contained in this section of AN652 has been removed. The full application note is available under a license agreement and can be ordered as DS40149 from Microchip Technology Inc."
That license agreement will doubtless place you under certain limitations on what you can legally do with the algorithm information. You could try ordering the license agreement to see what it says.
About 35 years ago, when remote locks were first available for cars, a remote transmitter always transmitted the same code when a button was pressed. That made it possible for a crook to build a code grabber that could be used to capture the code when someone locked their car and walked into a store. Later, the crook could transmit the open door command using the captured code and break into the person's car. That is why systems like KEELOQ® were created. They transmit a different code each time the button is pressed. In general, the receiver rejects a code that was previously received, thus preventing the use of such code grabbers. The encryption scheme is used to provide subsequent valid codes that the decoder will be able to recognize and decipher. Good luck with your project.
NCR once refused to hire me because I was too short. I'm still waiting on my growth spurt.