Vehicles cannot be secured while the in-vehicle network remains insecure. The growing number of attacks reported each year shows that in-vehicle buses are not isolated from the outside world. By exploiting their lack of security, adversaries can gain control over virtually any functionality inside the car. We discuss the most promising approaches for assuring security on the controller area network (CAN) bus after a decade of attacks and security proposals. Most of the proposals are based on cryptographic mechanisms, but some exploit the physical layer or even the physical characteristics of the controllers. The surveyed solutions prove a significant degree of maturity and sophistication, which suggests that the moment for adoption and standardization by the industry has come.