The scattering system through a highly scattering thin layer only affects the amplitude and phase distribution of incident light wave, but does not lead the total energy to be attenuated. This process can be regarded as a process that light wave is encoded by the scattering medium, which is similar to a double random phase encryption system. In this paper, firstly, it is proved that the distribution characteristics of speckle generated by the light wave carrying the target information through a strongly scattering thin layer are highly similar to the distribution characteristics of cyphertext obtained by the double random phase encryption system encrypting the same plaintext target. Therefore, the scattering system is seen as a double random phase encryption system, and the two random phase keys corresponding to the scattering system are calculated accurately by using the phase recovery algorithm. At the same time, it is proved that these two key boards can successfully reconstruct the original images corresponding to any other speckles obtained by the scattering system. Finally, a cyphertext-only attack method to attack a scattering system through a highly scattering thin layer is used to further prove the equivalence of two key boards and the good results are obtained. Since imaging through a scattering medium is an extremely complicated process, we actually simplify the corresponding process ideally. It should be noted that the equivalent system means that the incident-surface-to-exit-surface of scattering medium is equivalent to the incident-surface-to-exit-surface of DRPE system. However, in the actual process, there are still two diffraction processes: one is the diffraction process from the object to the incident surface and the other is the diffraction process from the output surface to the receiving surface. These two diffraction processes will cause the incident image and the output image of scattering medium to have a certain diffraction effect. We believe that under ideal conditions, due to the equivalence between the thin-layer strong scattering system and the DRPE system, theoretically all pure ciphertext attack methods applicable to the DRPE system can be applied to the speckle recovery of the thin-layer strong scattering system. In the future, it is possible to develop more methods of using system equivalence to crack the scattered light field. We hope this article can provide a new idea for scattering imaging.