Toward All-Optical Layered Encryption: A Feasibility Analysis of Optical Stream Cipher

Abstract

We study whether the layered encryption and, thus, anonymity of communication can be implemented all-optically, granting ultra-high speed communication and processing. To this end, we evaluate the feasibility of the state-of-the-art all-optical components, including optical linear feedback shift register (oLFSR) and optical XOR (oXOR), for implementing an all-optical stream cipher (oSC). Just like the function of key expansion in today's electronic ciphers, we use pRNGs and oLFSRs to expand short bit sequences of the secret key, thus enabling the transmission and en-/decryption at line rate; oXOR is used for the actual all-optical encryption. Using the principles of information-theoretical entropic security, we evaluate the key uncertainty (entropy and equivocation) and, thus, the computational complexity of various guessing attacks. We also analyze the maximum length of optical key stream and show that oSC can be designed as secure as in today's systems while operating all-optically at higher line rates.