Abstract: In this paper we demonstrate that the optical encryption scheme with a reference wave in joint transform correlator (JTC) is vulnerable to the chosenplaintext attack (KPA) from the point of view of cryptanalysis. First of all, we selected a dark image as the plaintext and recorded its joint power spectrum, then we recorded the intensity of the reference wave by keeping the input plane out, thereafter we recorded the intensity of the Fourier transform of the encrypting key by sheltering the reference wave and the plaintext. With the obtained three images, the intruder could retrieve the encryption key with the help of several skillful steps. Consequently, the intruder could further access the plaintext with the retrieved key. The theoretical analysis and a set of numerical simulations were carried out to demonstrate how the secret key of the encryption system could be derived out with our proposed strategy.