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How Keyless Entry Works in Your Car

How Keyless Entry Works in Your Car

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The majority of the cars produced in the last fifteen years have had some option for keyless entry, and it’s becoming more popular all the time. But how exactly do these remote keys work? And how does it know to only open the doors on your car?

The Basics

Inside the key is a short range radio transmitter which works up to about twenty meters away. At its core the system is similar to the one used to open many garage doors or for electronic locks. The transmitter in the key sends a signal with a code. If the code matches the code at the receiver, then the receiver activates the mechanism, such as opening the garage door or disengaging the electronic lock.

Active Keys

Active remote entry keys have been around since the 1990s. When you press a button, a transmission is sent with a code and a command matching the button, such as unlocking the doors. The transmission spreads out in all directions, which is why your key can be pointed any direction to unlock the car. In order to make sure that no other cars are unlocked, the transmitter and receiver are linked to have corresponding codes. The receiver will only follow the command if it comes with the right code.

Passive Keys

Also known as smart keys, these more recent additions to the keyless entry lineup can authorize commands without having to press a single button. The core of these is an array of low frequency (LF) antennas  spread out around the car, usually around four to six antennas. These produce a magnetic field around the car. The key fob itself normally stays in a sleep mode that keeps an extremely low power LF detector active. When the LF field around the car is detected, the key fob switches on and begins transmitting the code. The multiple antennas pick up that transmission, and can use the varying signal strengthens to locate exactly where the key fob is, such as next to the door or in the driver’s seat.

Security & Encryption

Security is an extremely important concern for keyless entry. There are millions of key fobs out there, and it’s vital that they can’t open any other car. Additionally, the security needs to be strong enough that someone can’t easily receive the transmission from the key, duplicate it, and gain access to the car.

That complicated security is handled with heavy-duty encryption. Each car manufacturer has its own method for encrypting their keys, but most modern ones use an encryption key with 128-bit encryption. That means that the code key is 128 characters long, or about 339 decillion combinations. To give you an idea of large that number is, a decillion 1 with 33 zeroes. A trillion is 10 with 12 zeroes.

If that weren’t difficult enough, the encryption is done on a changing or rolling basis. The receiver and transmitter are synced with a program that near-randomly generates a new key every time. This rolling and changing encryption is key to defeating efforts to hacking into keyless entry systems.


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