Cipher protection circuit to protect data in ROM

The cipher protection circuit to protect data inside ROM includes initial value generator, shift buffer, operation circuit, adder and latch circuit. The initial value generator produces two initial values within mutually repellent regions; the shift buffer stores the said initial values temporaily and loads the ROM selectively to alter its content; the operation circuit processes the content in the shift buffer and returns the result to the shift buffer for shifting; the adder adds the data in the ROM and the data in the shift buffer with the same length to obtain a ciphered data; and the latch circuit latches the adder is special case to maintain its fixed high or low level.