Bus system

The invention provides a bus system. In the bus system, a memory element is electrically connected to a master control element via a serial peripheral device interface bus. A plurality of slave elements are electrically connected to the master element via an enhanced sequence peripheral device interface bus. Each slave element is provided with a pin, and the plurality of pins of the plurality of slave elements are electrically connected together through a control line. After a program code from the memory element is obtained via the master control element, a first slave element of the plurality of slave elements decrypts the program code according to a first security code, and transmits the program code decrypted by the first security code to the plurality of slave elements via the control line. And decrypting the program code decrypted by the first security code in the plurality of slave elements according to a decryption order. According to the method, the firmware cracking complexity can be increased, and