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Quantum Communications and Quantum Imaging

Experimental investigation of security parameter of Y-00 quantum stream cipher transceiver with randomization technique: part II

Fumio Futami, Ken Tanizawa, Kentaro Kato, Osamu Hirota

Published Sep 18, 2018• 6 citations
Publisher

Abstract

As a security parameter of Y-00 quantum stream cipher, a guessing probability by an eavesdropper for a secret key of legitimate users is discussed. Assuming that Eve employs the direct detection and Gaussian intensity distribution of each intensity level of Y-00 cipher signals are same, an analytic solution of probability of correct guessing of the secret key in a case of the ciphertext-only attack is derived. The solution is applied to experimentally measure the probabilities of our Y-00 quantum stream cipher transceiver. A very low probability of the Y-00 cipher transceiver is experimentally confirmed.

DOI
10.1117/12.2320820

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Kentaro Kato, Osamu Hirota

In a series of articles concerned with quantum stream cipher by Y-00 protocol on this conference, we have claimed that the quantum stream cipher has a pretty good security against several concrete attacks. On the other hand, it has been pointed out that one can improve the security level by using various additional randomization techniques. In this paper, we will show some concrete randomization techniques for quantum stream cipher. First we will sketch the framework of the deliberate signal randomization (DSR) that is realized by randomizing the signals deliberately with true-random numbers or with pseud-random numbers generated by a secret key. Secondly, we will consider about the deliberate error randomization (DER) by using concrete models. It will be shown that these randomization techniques enhance the security level of the quantum stream cipher.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Aug 31, 2006•8 citations
As a security parameter of Y-00 quantum stream cipher, a guessing probability by an eavesdropper for a secret key of legitimate users is discussed. Assuming that Eve employs the direct detection and Gaussian intensity distribution of each intensity level of Y-00 cipher signals are same, an analytic solution of probability of correct guessing of the secret key in a case of the ciphertext-only attack is derived. The solution is applied to experimentally measure the probabilities of our Y-00 quantum stream cipher transceiver. A very low probability of the Y-00 cipher transceiver is experimentally confirmed.
A power distribution of optical signals as the ciphertext of Y-00 quantum stream cipher transceivers should be uniform, even when the bit sequence of plaintext is a non-uniform sequence. For examining the uniformity, we experimentally measure powers of optical signals with 4096 intensity levels and calculate the ratio of signal numbers over and under the average power. The ratios for various kinds of bit sequences are 0.5 with measurement error of 1%, which is an evidence of the uniformity of the power distribution. In addition, the effectiveness of a randomization technique of overlapping selection keying for enhancing the security against the known plaintext attack is experimentally observed.
For protecting physical layer of optical fiber communication systems, quantum stream cipher called Y-00 and Alpha-Eta is promising. So far, we demonstrated secure and high speed optical fiber communication experiments using Y-00 quantum stream cipher. Our theoretical research revealed that the randomization techniques could enhance the security performance. In this work, we fabricated a novel Y-00 transceiver for GbE where the randomization technique was implemented. The transceiver employed the optical intensity modulated Y-00 quantum stream cipher with intensity levels of 4096. An appropriately designed irregular mapping as the randomization technique was experimentally demonstrated. The transceiver was successfully applied to secure optical fiber transmission of GbE signals.
The Internet plays an essential role in modern societies and in the amount of sensitive data transported over the optical networks that shows its' importance has increased drastically. Therefore, it is critical to develop data protection schemes for optical fiber communications to provide user security. The Y-00 quantum-noise randomized stream cipher that employs extremely high-order modulation and restricts an attacker's interception of ciphertext is a practical candidate for providing data protection. In this article, we introduce the operation principle of the Y-00 cipher with respect to data encryption and decryption. The Y-00 cipher combines the mathematical encryption of multi-level signaling and physical randomness, and provides a high level of security to the physical layer of optical communications and a high communication performance. We also present the noise masking phenomenon of the Y-00 cipher with intensity modulation (IM). This noise masking is generated by shot noise, i.e., quantum noise and additive noise such as amplified spontaneous emission noise. The noise masking phenomenon fails an attacker's interception of the ciphertext. The secrecy of the IM Y-00 cipher is also discussed, and an approximate analytical solution is introduced for evaluating the probability of the attackers accurately guessing the ciphertext. Finally, the secrecy of a 1,000-km transmission system is experimentally demonstrated with the Y-00 cipher transceiver at data rate of 1.5-Gb/s using the derived analytical solution to deduce the high secrecy of the entire transmission system.
This paper considers two issues on the quantum stream cipher by Yuen-2000 (Y-00) protocol. In the fist part of this paper we investigate the optimal modulation scheme for the basic model of the quantum stream cipher by Y-00 protocol, and in the remaining part we study the deliberate signal randomization. For the problem on the optimal modulation scheme, several modulation schemes are investigated for the cipher text-only attacks and the known plaintext attack under the error probability criterion and the information criterion to find the preferable modulation scheme. As a result, it will be shown that the phase shift keying signal yields the best performance among the modulation schemes investigated in our consideration by numerical simulations. After that, the roperty of the randomization technique called the deliberate signal randomization is considered for the cipher text-only attacks and the known plaintext attack in the information criterion. From this, it will be shown by numerical simulations that the amount of leakage of information from the legitimate user to the eavesdropper is reduced by the deliberate signal randomization. At the last section we will mention about the implementation issues of the deliberate signal randomization, taking account of the numerical results.
Although quantum key distribution is regarded as promising secure communication, security of Y00 protocol proposed by Yuen in 2000 for the affinity to conventional optical communication is not well-understood yet; its security has been evaluated only by the eavesdropper’s error probabilities of detecting individual signals or masking size, the number of hidden signal levels under quantum and classical noise. Our study is the first challenge of evaluating the guessing probabilities on shared secret keys for pseudorandom number generators in a simplified Y00 communication system based on quantum multiple hypotheses testing theory. The result is that even unlimitedly long known-plaintext attack only lets the eavesdropper guess the shared secret keys of limited lengths with a probability strictly <1. This study will give some insights for detailed future works on this quantum communication protocol.
In a series of articles concerned with quantum stream cipher by Y-00 protocol on this conference, we have claimed that the quantum stream cipher has a pretty good security against several concrete attacks. On the other hand, it has been pointed out that one can improve the security level by using various additional randomization techniques. In this paper, we will show some concrete randomization techniques for quantum stream cipher. First we will sketch the framework of the deliberate signal randomization (DSR) that is realized by randomizing the signals deliberately with true-random numbers or with pseud-random numbers generated by a secret key. Secondly, we will consider about the deliberate error randomization (DER) by using concrete models. It will be shown that these randomization techniques enhance the security level of the quantum stream cipher.