A circuit for data encryption is provided. The circuit includes an encryption controller configured to randomly generate a frequency parameter defining different timeframes corresponding to different frequencies. The circuit also includes a random-clock-signal generator configured to receive the frequency parameter to synthesize an encryption clock signal based on a base clock signal. The encryption clock signal includes a random combination of different clock frequencies respectively over multiple different timeframes. Additionally, the circuit includes an encryption sub-circuit configured to receive plain data and to encrypt the plain data by a sampling replacement driven by the encryption clock signal to obtain encrypted data.