Hi Tom , You should contact Microchip and get the license and sign a non disclosure agreement that will enable you to get the algorithm and the software with the encryption key you will use. Cherry Tomas Kapostas on 09/04/99 12:15:24 Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: (bcc: Nachum Tchernichovski/Visonic Ltd.) Subject: Keeloq trouble HI! I want to build my own car security system, based on PIC16C84 & code hopping encoder/decoder HCS301/HCS500 from Microchip. I bought HCS301, HCS500 The problem, which I have is that i must programm this devices before I use these . I am able to programm HCS301,HCS500. In the HCS500 (decoder) I must programm config byte, manufacturer's code. - this is not problem... In the HCS301 I must program encryption key, sync, serial No., some config byte... Te problem is the encryption key - it is "calculated" from manufacture's key & serial No. - I don't know, how.. :-(((( Does somebody know, how must I create this encryption key or can somebody calculate for me the encryption key??? Thanx, Tom.