A random code generator includes an address Y decoder, an address X decoder, a PUF entropy pool, a processing circuit and an entropy key storage circuit. The address Y decoder includes plural Y control lines. The address Y decoder selectively activates the plural Y control lines according to a first address Y signal. The address X decoder includes plural X control lines. The address X decoder selectively activates the plural X control lines according to a first address X signal. The PUF entropy pool generates an output data according to the activated Y control lines and the activated X control lines. When the random code generator is in a normal working state, the processing circuit processes the output data into a random code according to at least one entropy key from the entropy key storage circuit.