| abstract |
A remote control access system uses a transmitter and a receiver. The transmitter generates an encrypted identification code which the receiver decrypts and grants access to the system if the decrypted code matches an identification code stored in the receiver. The encryption occurs by taking a 40 bit identification code and forming 5 bytes (8 bytes each). The 5 bytes are logic exclusive OR'd to form a 5 byte wide encrypted code. Decryption occurs by performing the opposite exclusive OR operation on the 5 byte wide encrypted code to convert it back to the 5 byte identification code. The 4 most significant bytes of the decrypted code are compared against the 4 most significant bytes of the previous stored decrypted code in the receiver. If the comparison yields a zero, this means the least significant byte will be within 28 or 256 of each other and access will be granted. |