In our modern society comfort became a standard. This comfort, especially in cars can only be achieved by equipping the car with more electronic devices. Some of the electronic devices must cooperate with each other and thus they require a communication channel, which can be wired or wireless. In these days, it would be hard to sell a new car operating with traditional keys. Almost all modern cars can be locked or unlocked with a Remote Keyless System. A Remote Keyless System consists of a key fob that communicates wirelessly with the car transceiver that is responsible for locking and unlocking the car. However there are several threats for wireless communication channels. This paper describes the possible attacks against a Remote Keyless System and introduces a secure protocol as well as a lightweight Symmetric Encryption Algorithm for a Remote Keyless Entry System applicable in vehicles.