Transponders have been developed to further enhance the convenience of remote keyless entry (RKE) systems in automotive and access control applications. "Just imagine walking up to your vehicle, arms full of grocery bags and without having to dig for keys or pressing any keyfob buttons, your vehicle detects you 1,5 m away as the authorised driver. The car unlocks the doors automatically, the driver's door opens and the seat and rear-view mirror adjust to your favourite position," says Willem Hijbeek of Tempe Technologies. According to Hijbeek this can be accomplished with the HCS4212 single-chip solution available from Microchip Technology, which is a transponder based on the Keeloq technology, that has become the de-facto standard in vehicle security.
Remote keyless entry (RKE)
The now dated RKE systems transmit the same code from a transmitter to a receiver each time a button is pushed on the keyfob. Would-be thieves that wish to crack/break/decode the transmitted code would simply use either a 'code-grabber' or 'code-scanner'. Assuming it is an RF-based system, the 'code-grabber' would operate on the same radio frequency as the keyfob which it is attempting to duplicate. The 'code-grabber' does this by recording the transmitted codes enabling it to retransmit the recorded codes at a later time. The 'code-grabber' has effectively duplicated the legitimate keyfob/remote transmitter. A 'code-scanner' works on a different principle - it simply broadcasts sequential or random codes at a rapid rate on the same radio frequency as the keyfob it is attempting the crack.
KeeLoq technology
KeeLoq is a patented code-hopping technology providing a means for encrypting data for a unidirectional transmission, where each transmission is unique even if the same keyfob button is pressed. Typical uses are found in command and authentication control applications such as remote keyless entry, garage door openers, car alarms and access control systems. The KeeLoq product range consists of encoders, decoders and a crypto transcoder (a combined encoder and transponder). "Decoding can also be performed in one of Microchip's PIC microcontrollers using KeeLoq software which is available under free licence," adds Hijbeek.
Hijbeek points out that transponders based on Microchip's KeeLoq technology have been designed to enhance convenience for the driver in that it would no longer be necessary to press a button on the keyfob (remote transmitter) to activate or deactivate the vehicle. Instead, the driver simply needs to be in possession of a radio frequency tag (electronic key). The basic operation requires interrogatory RF communications to be established between the RF tag and the vehicle's electronic security controller. By positioning the antennae correctly it is possible to deploy passive-entry systems to lock/unlock the doors or arm/disarm the security system when the driver/key-holder approaches within a couple of metres of the vehicle.
"As with conventional RKE systems, it is mandatory that passive-entry systems offer the user an ultra-high degree of security," says Hijbeek, "and to this end Microchip introduced the Keeloq HCS412 primarily designed for passive entry supporting both the code-hopping RKE and identify friend-or-foe (IFF) modes." The HCS412 incorporates a sensitive passive-entry amplifier as well as a complex low-frequency design, eliminating the need for almost 10 discrete components generally required in similar applications. It further provides the necessary control signals to interface directly to popular FSK and ASK PLLs (phase locked loop). The HCS412 can also function as a batteryless transponder in back-up mode when the battery fails. In this mode, low frequency communication is used in both directions. An anticollision feature allows fast authentication in passive entry for multiple transponders in a field.
Technical features
The HCS412 combines a 32-bit code hopping mechanism generated by a nonlinear encryption algorithm with a programmable 28-bit serial number to identify the transmitter and six status bits to create a 69-bit transmission stream. A programmable 64-bit encoder key and two 64-bit transponder keys are also used. The length of the transmission eliminates the threat of code scanning and the code hopping mechanism makes each transmission unique, rendering code capture and resend ('code grabbing') systems useless. "The device provides features typically required in higher-end security systems, including a longer transmission length of 69 bits and extended 60-bit read-protected seed for secure learning and CRC error detection", says Hijbeek. The encoder key, serial number and configuration data are stored in EEPROM which is not accessible via any external connection, making the HCS412 a very secure device. The HCS412 provides a serial interface for programming the necessary security keys, system parameters and configurations data.
Additional applications include highway toll collection, gas/petrol pump billing and keyboard locks.
For more details contact Willem Hijbeek, Tempe Technologies, (011) 452 0530.
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