Abstract: The rapid globalization of the digital ecosystem has elevated information security to a critical concern in modern society. Optical encryption offers an effective approach for enhancing information protection; however, existing optical encryption strategies are unable to reliably recover encrypted information following free-space transmission. To address this challenge, we propose a novel protocol named the optical coherence engineering encryption protocol (OCE-Encryption Protocol). By jointly manipulating the optical coherence structure and introducing astigmatic phase modulation, the protocol generates a spectral intensity ciphertext capable of secure free-space transmission. At the receiver, the original information can be accurately reconstructed by measuring the optical coherence structure of the received ciphertext and applying the correct decryption key. Furthermore, the proposed protocol demonstrates strong resilience to transmission channel disturbances. We hope that optical coherence engineering can expand the functional boundaries of existing optical encryption protocols and provide a pathway toward next-generation secure optical communication systems.