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KEELOQ with XTEA encryption receiver/decoder

Posted: 10 Sep 2009     Print Version  Bookmark and Share

Keywords:receiver decoder  XTEA encryption  KEELOQ MCU 

This application note describes a KEELOQ with XTEA encryption algorithm code hopping decoder implemented on a Microchip mid-range enhanced flash MCU (PIC16F886). The purpose of this implementation is to demonstrate how the KEELOQ code hopping technology can be implemented with the XTEA encryption algorithm for even greater security. This allows for a higher level of security solutions for keyless entry systems and access control systems. The software has been designed as a group of independent modules written in C.

XTEA stands for Tiny Encryption Algorithm Version 2. This encryption algorithm is an improvement over the original TEA algorithm. It was developed by David Wheeler and Roger Needham of the Cambridge Computer Laboratory. XTEA is practical both for its security and the small size of its algorithm. XTEA security is achieved by the number of iterations it goes through. The implementation in this KEELOQ hopping decoder uses 32 iterations. If a higher level of security is needed, 64 iterations can be used.

KEELOQ code hopping creates a unique transmission on every use by using a cycle counter. The cycle counter is then used to validate the transmission. The combined XTEA KEELOQ algorithm uses a programmable 128bit encryption key unique to each device to generate a 64bit hopping code. The key length and code hopping combination increases the security for remote control and access systems.

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