Experimental demonstrations of Y-00 cipher for high capacity and secure optical fiber communications

Quantum Enigma Cipher is an epoch-making concept in the cryptography that may break the Shannon limit of the cryptography. Yuen-2000 (Y-00) protocol is a first generation toward the Quantum Enigma Cipher that overcomes the Shannon limit in cryptography relying on macroscopic quantum effects. Current Y-00 cipher is an encryption scheme where noise masking blocks an eavesdropper’s reading of the physical ciphertext consisting of the mathematical structure. No such masking effect is realized only by using the mathematical encryption, because mathematical ciphertexts are composed of binary signals, “0” or “1” or deterministic symbols, and they are correctly discriminated. Y-00 cipher is one of the candidates to provide high transmission performance and a provable security simultaneously in the real world. In our present, Y-00 cipher, mathematical cipher and physical phenomena are combined. It features multi-level signaling by mathematical cipher and noise masking to hide the ciphertext in the quantum noise and other channel noise. In the paper, transmission performance of Y-00 cipher is experimentally investigated. A running test for 60 days of Y-00 cipher transceiver at 2.5 Gbit/s is demonstrated. In addition, a trial of a current direct modulation scheme using 4096 signal levels for realizing a compact Y-00 transceiver is demonstrated. Furthermore, a wavelength-division multiplexing transmission of Y-00 cipher is experimentally demonstrated, and 100-Gbit/s Y-00 cipher transmission is successfully transmitted over 120 km.