In this study, a new MAC based on OMAC is implemented in Arduino Uno. In addition, a function to update the common key based on pseudo-random numbers is additionally implemented. A re-verification function of the MAC value on the receiving ECU is also implemented. Similarly, these features have been implemented for the Raspberry Pi. Communication with Arduino is possible. The time taken to calculate the MAC and the time required to update the key are measured for the Arduino and Raspberry Pi, respectively. As a result, both of the OMAC processing time and the key update time in both of the microcomputers satisfied a time constraints.