This document reviews various optical encryption and decryption techniques that use algorithms like Diffie-Hellman, Expanded Diffie-Hellman, RSA, and ERSA. It summarizes 8 research papers that propose different systems: 1) a Virtual Optical Holographic Encryption system using EDH-C algorithm, 2) a VOHE system for underwater communications using ERSA, 3) an optical encryption scheme for multiple images using Fresnel transform, 4) a multi-user encryption system using joint transform correlation, 5) a technique for quasi-noise free digital holographic reconstruction, 6) an angle multiplexing method for image encryption using a phase-only computer-generated hologram, 7)