We have reported a theoretical device design for reversible writing and erasing information encryption using a simple two layered structure, which consists of a MoOx layer and a SiO2 space layer on a silver substrate. The MoOx layer can be switched between two phases, i.e., metallic MoO2 and insulating MoO3. The phase transition of MoOx possesses very complicated processes, which makes it advantageous for information decryption. Generally, in the proposed structure with metallic MoO2, various colors can be generated due to the F-P enhanced absorption at wavelengths where construction interference occurs. However, owing to the low loss of insulating MoO3 in visible region, the absorption is low though out the whole visible region, thus all colors can be erased to white. Therefore, the color image information can be written and erased with our proposed structure by switching MoOx between phases of metallic MoO2 and insulating MoO3. The proposed image encryption device can be acquired easily by masking and coating processes. We believe our results provides a new way in designing encryption devices.