Asymmetric optical encryption technique implementing spatially incoherent illumination

Abstract

The majority of optical encryption techniques use not only light intensity distribution, easily registered with photosensors, but also its phase distribution. This provides best encryption strength but requires holographic registration in order to register not only light intensity distribution but also its phase distribution and is accompanied by speckle noise occurring due to coherent illumination. These factors lead to poor decryption quality. Method of optical encryption with spatially incoherent illumination does not have drawbacks inherent to coherent techniques but provides lower security. State of the art encryption techniques implement asymmetric encryption which entails that there is no exchange of encryption keys between the sender and receiver. In case of interception of encrypted messages hacker will not be able to decrypt them. There are several asymmetric optical encryption techniques based on DRPE technique. Typically light phase distribution serves as an open key, while amplitude distribution serves as a secret key. However there are no such techniques implementing spatially-incoherent illumination due to limitation to amplitude only registration. We propose for the first time asymmetric optical encryption technique implementing spatially-incoherent illumination. Procedure is described as follows. User 1 optically encrypts information using key 1 and sends it to user 2. User 2 encrypts received data using key 2 and sends it back to user 1. In order to verify identity of user 2, user 1 checks if received data correspond to certain parameters which are unique to user 2 and serve as an additional secret key. If identity check is passed, user 1 decrypts received data using key 1 and sends it back to user 2. Finally, user 2 decrypts received data using key 2 and obtains information. Results of computer simulations of asymmetric optical encryption implementing spatially incoherent illumination are presented.