A key protecting device is provided. The key protecting device includes a crypto engine, a ROM and a processor. The ROM stores a chip unique key, and is exclusively accessible to the crypto engine. The processor receives a first salt value and a first encrypted key from a non-volatile memory. The crypto engine receives the chip unique key from the ROM, receives the first salt value and the first encrypted key from the processor, and generates a first key according to the first salt value, the chip unique key and the first encrypted key.