This paper analyzes the security of double random phase encoding in fresnel domain from the viewpoint of cryptoanalysis. We demonstrate the encryption system is vulnerable to chosen-plaintext attack with a prior knowledge of diffraction distance and wavelength. With this attack an opponent can access double random phase keys with the help of the impulse functions as chosen plaintext. The significant feature of proposed attack is that the decryption process is lossless. Numerical simulations show good agreement with theoretical analysis.