In (Appl. Opt. 55, 4720-4728 (2016)) authors demonstrated the vulnerability of Linear Canonical Transform (LCT) based optical encryption system. One of the primary reasons for this is the predictable nature of the security keys (i.e., simulated random keys) used in the encryption process. To alleviate, in this work, we are presenting a Physically Unclonable Function (PUF) for producing a robust encryption key for the digital implementations of any optical encoding systems. We note, a correlation function of the scattered perfect optical vortex (POV) beam is utilized to generate the encryption keys. To the best of our knowledge, this is the first report on properly utilizing a scattered POV for the optical encryption systems. To validate the generated secret keys, the standard Linear Canonical Transform based Double Random Phase Encoding (LCT-DRPE) technique is used. Experimental and simulation result validates the proposed key generation method as an effective alternative to the digital encryption keys.