A storage device includes a nonvolatile memory device, and a controller that receives a write command, data, and a signature associated with the data from an external device, generates a first hash value from the data, generates a second hash value from the signature, generates an output hash value based on the first hash value and the second hash, and detects whether the data received from the external device are previously written in the nonvolatile memory device, by using the output hash value.