The invention discloses a digital signature system. The digital signature system comprises an electronic device and a data storage device. The electronic device generates a specific data by executing a specific operation, and performs a calculation operation on the specific data via a hash algorithm to generate a hash data. The data storage device comprises a controller, a plurality of flash memories, and a data transmission interface. The electronic device transmits the hash data to the data storage device via the transmission interface. The controller comprises a firmware. The firmware reads an unclonable function, and generates a private key according to the unclonable function, and encrypts the hash data by the private key to obtain a digital signature. The data storage device transmits the digital signature to the electronic device via the transmission interface.