This paper addresses the security service infrastructure included in the Controller Area Network (CAN standard), proposing the incorporation of the confidentiality service for that kind of network. Regarding security currently CAN only supports a special kind of service, namely safety, of data transfers for error detection, signalling, and self checking. Nevertheless, as CAN has become more diverse, complex and integrated into other kind of networks, it must provide higher security services, such as confidentiality, quite specially for its bus which is the most attack-prone point on CAN. Taking into account, on one hand, the security services defined by ISO and, on the other hand, the security services defined by CAN, this paper proposes to incorporate the confidentiality service to CAN based on RC4, which is a lightweight symmetric stream cipher algorithm. The paper presents then the clock cycles required for encrypting different data sizes of the CAN frame in the 87C196CB, which is a microcontroller with integrated CAN 2.0 serial interface.