This application note describes the design of a
microcontroller-based KEELOQ™ Hopping Encoder
using the AES encryption algorithm. This encoder is
implemented on the Microchip PIC16F636
microcontroller. A description of the encoding process,
the encoding hardware and description of the software
modules are included within this application note. The
software was designed to emulate an HCS365 dual
encoder. As it is, this design can be used to implement
a secure system transmitter that will have the flexibility
to be designed into various types of KEELOQ receiver/
decoders.
BACKGROUND
The Advanced Encryption Standard (AES) was developed
in the 1990’s to replace the widely used DES.
AES algorithm is also called the “Rijndael” algorithm,
after its designers. AES is currently adopted by the
National Institute of Standards and Technology.
Rijndael/AES is a symmetric block cipher that utilizes a
single key to encrypt data. The implementation of AES
in this application note is based on a 16-byte block of
data and a 16-byte key size as described on application
note AN1044.