## 4 Overview of the Proposed Solution  
The goal of this work is to enhance the security of key generation and key distribution. We propose key generation in an ultimate secured processing environment provided by a secured development environment with an alternate and highly secured communication protocol by means of an optical communications technique. With this method, the exchange of keys is done by an optical means of communication, where the LED transmits, and the camera captures and records it. The idea is to modulate the information in a way that is complicated to be detected, and the information can be decoded only by processing the appropriate signals of the video camera.  
Figure 5 illustrates the basic idea of the optical-based communication approach. The source computer generates the encrypted key. The key is translated to optical signals, where \"1\" means the LED is \"on\" and \"0\" means it is off. The LED projector keeps projecting optical signals to the camera, which is embedded in a mobile device. The camera captures the transmitted optical signals and records it as a video movie. For authentication and accuracy, the video movie is signed by a standard electronic signature. For an enhanced security level, the signed video is encrypted by an asymmetric cryptography used just for key wrapping encryption and transmitted via VPN to the target mobile device. At the target, the transmitted key is unwrapped and projected to the target camera, which decodes it and sends the key bit string to the target computer, and thus the key reaches the target computer. Then, the target computer decrypts the encrypted messages. To enhance the security, we can consider the possibility of moving the mobile device itself toward the target computer and skipping the need to transmit the video between the two mobile devices, which may be considered less secure.  
Figure 6 illustrates the entire flow. The source computer, in Step 1, generates the encryption key. In Step 2, it converts the encrypted key into an optical code, which then is projected by its attached LED projector to the mobile camera that is embedded in the sender's mobile device as a sequence of LED images. In Step 3, the source camera accepts the LED images, and the mobile device transmits the accepted video to the target mobile device. In Step 4, the receiver camera projects the received LED images to the optical receiver at the target computer. Then, the images are copied to the secured environment of the same computer, which, in Step 5, translates the images into a bit string, representing the encryption key. Subsequently in Step 6, the decryption process is applied to obtain the original key. Then, the key is forwarded to the regular environment for further processing.  
Figure 5: High level secured key transmission system.  
Figure 7 depicts the transmission protocol and messaging flow between the mobile device and the computer.  
The proposed solution of transmitting video signals instead of transmitting the original bare bit string of the key adds computational processing complexity that is equal to the standard image processing complexity. The volume of transmitting video/images is larger in magnitude from a common encrypted bit stream. However, considering the limited key length and the advances in transmission capacity and speed, it is still justified is comparison to the security level it adds.  
Looking at the proposed transmission route, most of it uses standard communication lines and is considered as protected from a potential adversary. However, the optical transition stage is still at risk, as optical signals can be captured from remote using appropriate technologies. To avoid it, we request the optical-signal transmission to be a short distance from the projector and within a non-transparent cover.  
Figure 6: Encryption key generation and optical-based transmission flow.  
Figure 7: Optical-based provisioning message flow protocol.