Immobiliser Introduction – Part 3

  1. Standard Security Architectures using RFID

There are several different security systems on the market which use RFID transponders, each with its own benefits.


Fixed Code Systems.

The most widely used on the market, these systems rely on the unique identification codes stored in the transponders within a vehicle. A controller learns this codes and when the key is placed in the car’s lock cylinder, the code within the transponder is analyzed and compared to the codes the controller has stored within its memory.


Depending on the type of transponder, security of this type of system varies. One type of transponder is a “write-once” unit that is purchased unprogrammed. Readers/writers that are commercially available read the transponder’s code and program the new unit. In doing this, the fixed code has been perfectly copied and is undistinguishable from its source. Another type of system, True Read Only, are factory programmed and cannot be copied. While it is technically possible to emulate the data using radio, the design knowledge and effort required is tremendous.


Rolling Code Systems

These systems are not entirely different from the fixed code system. Their main characteristic is the time limit on the key’s secret code. This time window is generally one ignition cycle to the next. The transponder, of the read/write variety, is reprogrammed with a new secret. The key code is constantly changing, but this method still falls under the umbrella of static authentication.


Sometimes transponders fail or are inadvertently reprogrammed while away from the vehicle. In these cases, a failsafe is built into the system which ensures their reliability. If the need arises, a transponder can be resynchronized so the driver can still use their vehicle. These procedures are critically important for security systems such as these.


Password Protected Transponders.

These types of transponders give an easy path to mutual authentication. Operating like many password protected systems and accounts, the transponder within the vehicle will deny a key access to its information if an incorrect password is provided. The length of a password does a lot for its security and can be customized to give higher or lower security.


Like all passwords, if the transponder is available to a thief, it can be guessed. But the amount of time that could take is anywhere from a minute to many years.


Total transaction time for password protected systems can be less than ideal for many drivers, especially when the implementation of the system requires new hardware. This element makes this system impractical for many.


Combined Rolling Code/Password Systems

These systems use read/write transponders that are password protected. Timing and resynchronization, among other critical issues, are applicable and give this method a much higher level of security than a simple password protected transponder.


Crypto Transponders

These second-generation transponders, developed by Texas Instruments, find their basis in the half-duplex RFID technology of TIRIS TM. They are compatible with all standard RF interfaces within this product line.


System Overview

This crypto device, a Digital Signature Transponder (DST), utilizes the challenge/response system. The transceiver in the vehicle sends the key a 40-bit number at random. It uses Pulse Width Modulation (PWM) to send the challenge. In the key, the transponder shifts the code to a challenge register. For a brief period, the transceiver provides energy and its encryption logic generates a 24-bit response.



Before receiving a response, the vehicle’s security system calculates its expected answer by using the same algorithm and encryption key. Once the transponder answers, the system compares the expected answer and the given one. If the two match perfectly, then the security system is satisfied and the data is sent to the engine’s computer. If time is short, then the challenge and response can be generated beforehand and stored.


This system’s advantages should be evident:

  • The authentication process is dynamic as the response can be different each time it is used, dependingon the challenge.
  • The transponder cannot be copied
  • The encryption key is never communicated once the initialization of the transponder has occurred.
  • The encryption key cannot be released
  • If needed, the encryption key can be permanently changed or locked.


The power consumption of a transponder is important. They are elaborate micro systems intended to perform using very little power. Less than 1mA is consumed during a typical energy transfer allowing a capacitor to charge over long distances very quickly. Even during encryption, the standard of power consumption for a transponder is below 16mA, making its maximum read range comparable to average Read Only systems.

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Immobiliser Introduction – Part 2

  1. Immobilizer System Overview

Four main components make up the key-based immobilizer unit. The transponder is the heart of the system. Battery-free, the transponder can be equipped with several different functionalities best suited to a vehicle’s specific needs. It sends data as a modulated RF signal. The transceiver and antenna coil provide the power for the transponder to function, generating and radiating a high frequency magnetic field. The signal, once demodulated by the transceiver, is sent to the controller, the final component, for data processing.


Two distinct RFID systems can be found on the market, set apart by their method of transmitting energy.


  • Full Duplex Systems.

In this system, the unit sends data similar to a telephone, in that the transponder can send and receive data and energy simultaneously. This is often accomplished using load modulation.


  • Half Duplex Systems.

In this method, the energy and data are sent one after the other, as done with walkie-talkies. The transponder stores the energy collected from the transceiver and sends the data once the energy is fully produced.


While these two systems obviously impact the physical design of the system, one is not superior to the other when it comes to automotive security.


  1. Cryptographic Background

When working with cryptographic immobilization, there are two tasks that the system must be able to perform: identification and authentication. The security system must be able to identify the driver and prove his identity. Cryptography provides multiple means of acquiring this information.



Authentication is achieved through the sharing of a secret. This method is incredibly common in other areas, such as passwords for email or social media accounts, or a PIN number for a debit card. This secret must be utilized as a method of proving one’s identity. In many areas, this method of authentication makes sense since keyboards and number pads are common place. The implementation of such hardware would be cumbersome and unwelcome by many motorists. This method also provides the least amount of security.



Unique biological characteristics offer a high level of security. Vehicles that require fingerprint, retinal, face, or voice scans in order to operate would make vehicles all but impossible to steal. The practicality of this method is very low, however, as hardware and technical complications are unacceptable for automotive use. Renting or borrowing cars in an emergency would also become infinitely more complicated, if not impossible.



Possession is the most prevalent method of authentication currently used in automobiles. In its simplest form, the driver possesses a key or remote that achieves authentication. While its security does not equal that of biometrics, higher security can be attained if the key contains a transponder device or a similar electronic tag that must match a tag within the vehicle in order to authenticate.


In each of these systems, authentication methods are limited in that they verify the identity of the key in order to proceed, but the key does not perform any checks in return. A mutual authentication process would allow the key to preform authentication of its communication partner in return, providing a much tighter security system for the vehicle.


Security of the vehicle can be improved even further by implementing a simple symmetrical algorithm referred to as a challenge/response protocol. The security system housed in the automobile verifies the identity of the key by communicating a challenge or question. The key would send its response, an answer to the question. A mutual secret must be known and shared by each component for a correct answer to be given. This concept has a number of advantages that increase security. During day-to-day use, the secret is not released and the responses needed to complete the exchange would vary for each use.

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Immobiliser Introduction – Part 1


Vehicular security needs are constantly changing. From the invention of the immobilizer system and on, security needs continue to increase. Radio Frequency Identification (RFID) technology is a widely used anti-theft system in vehicles. Its unique features offer solid security and cost less than many other technologies on the market.

This article reviews how the first and second generation of immobilizer systems functioned and compares varying levels of security. It then gives an overview of the newest technology: crypto transponders.


  1. Introduction

The immobilizer system was invented by Edward Birkenbuel and St. George Evans and patented in 1919. It was not until the 1990s, however, when a worldwide increase in car theft, made insurance companies take action. Many insurers in Germany began pushing for the installation of these systems and by 1998, it was mandatory in all new automobile designs. In other countries also, government agencies began facing the problem of vehicle theft and enforcing stricter laws on security.


In a very short time, the automotive industry produced many systems to help secure vehicles against thieves. Laws and methods varied internationally. Remote keyless entry was popular in the United States and France while Germany implemented far more transparent systems. With the RFID’s unique features, and its preexisting prevalence in the industry, small battery-free transponders were frequently used. These small tools set up high security for vehicles and a low cost.


OEM immobilizers quickly became the most prevalent. Statistical analysis from Germany companies confirmed the overwhelming success of this system. Vehicle thefts were down 90% when compared to cars without the immobilizers. Given its success, almost all European markets used this immobilizer on all new models of automobile beginning early in 1995.


No matter the level of technology or the statistical success of any security system, however, criminals don’t remain stagnant. With the resources and capabilities to study security systems, they can quickly learn to bypass and outsmart them. Therefore, security companies must remain vigilant and constantly rework the build of automotive security, staying ahead of the criminals. Key-based immobilizers have varying levels of security, but the new crypto-transponder surpasses them all, offering the highest level of security of any RFID device…