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Immobilization
General description
Combating the increasing number of car thefts, since the 1990s insurance companies have required that new cars be fitted with an immobilizer system. Amongst these, systems using a contactless data carrier (transponder) embedded in the car key have proven to be very effective in theft protection.
Background information
More than 100 million transponders from NXP Semiconductors are currently protecting vehicles worldwide. Embedded in the car key, the transponders communicate via a radio frequency link with the engine management electronics, without requiring a battery. These immobilizers prevent the engine starting without authorization, even making it impossible to short-circuit the system. Authorization is given at the same time as the driver turns the key in the ignition.
Since 1994, when the first immobilizers were introduced onto the market, the security level has increased from read/only to read/write (code hopping) to solutions which use encrypted data transmission. And the latest systems use challenge response and mutual authentication algorithms designed to prevent transponders being duplicated.
Products
Read only transponders such as the
PCF7931 provide a fixed authorization code. However,
a significantly higher security level can be achieved by providing a re-writeable memory area, such as with
the PCF7930. This enables code hopping algorithms to
be implemented, which change the code in the transponder every time the engine is started.
Using a challenge-response concept, a security transponder (SECT) and the car both process a random number (challenge) generated by the car. Access is only granted if the results (response) are the same. Any attempt to monitor the RF transmission between the transponder and car will only reveal a string of random numbers. The authentication code (secret key) - stored both in the transponder and car - is never transmitted, making it impossible to deduce the authentication code from data flow between the transponder and car. Our PCF7935 security transponder meets these requirements.
The PCF7936 (HITAG2) takes this a step further. It employs a mutual-authentication technique where both the security transponder (PCF7936) and the car exchange encrypted passwords which are verified at each side. The transponder and car both encrypt the transmitted passwords, avoiding deduction of set passwords from the data flow. Again, any attempt to monitor the RF transmission between the transponder and car, will only reveal a string of random numbers. In any case, the authentication code (secret key) - stored in both the transponder and car - is never transmitted.
Immobilizer systems will only work with a properly matching basestation. NXP Semiconductors' Advanced Basestation IC (ABIC), PCF7991, is a highly integrated mixed signal device requiring only a few external passive components for a complete basestation. It features an adaptive sampling time (AST) algorithm, the standard for handling inaccurately tuned basestation antennas.
Customer Benefits
- Effective anti-theft system
- No switches are required for authorization
- Increased motorist convenience
- Fast authentication times