Atsushi Waseda

Numerical Evaluation of PPM for Deep-Space Links

We numerically evaluate the deep-space communication performance in a broadband lossy channel of coherent pulse position modulation (PPM) with an on/off receiver, single-symbol square root detection, and Holevo information. We also consider quadrature amplitude modulation (QAM) signals and phase-shift keying signals with dyne-type detections. We show the quantitative gap between these detection strategies in terms of the capacity, particularly in the quantum-limited region where the quantum noise seriously limits the transmission rate. In particular, we find that for an extremely weak signal input power, use of a multilevel PPM system is a good strategy, whereas for an extremely strong signal, use of a multilevel QAM system is recommended.

Quantum detection of wavelength-division-multiplexing optical coherent signals

We numerically evaluate the transmission rates of a single fiber with the wavelength-division-multiplexing (WDM) transmission of coherent signals with conventional homodyne-based (dyne-type) detections and various quantum detection strategies. We reveal the quantitative gap between these detection strategies especially in the quantum-limited region where the quantum noise seriously limits the transmission rate. For an extremely weak signal input power, there is a crucial gap between the capacity limit and the transmission rates of the WDM system with dyne-type detections. We show that this gap is filled by applying a collective square root detection (SRD) only for each channel, not necessary for quantum collective decoding among WDM channels.

Unbreakable distributed storage with quantum key distribution network and password-authenticated secret sharing.

Distributed storage plays an essential role in realizing robust and secure data storage in a network over long periods of time. A distributed storage system consists of a data owner machine, multiple storage servers and channels to link them. In such a system, secret sharing scheme is widely adopted, in which secret data are split into multiple pieces and stored in each server. To reconstruct them, the data owner should gather plural pieces. Shamir’s (k, n)-threshold scheme, in which the data are split into n pieces (shares) for storage and at least k pieces of them must be gathered for reconstruction, furnishes information theoretic security, that is, even if attackers could collect shares of less than the threshold k, they cannot get any information about the data, even with unlimited computing power. Behind this scenario, however, assumed is that data transmission and authentication must be perfectly secure, which is not trivial in practice. Here we propose a totally information theoretically secure distributed storage system based on a user-friendly single-password-authenticated secret sharing scheme and secure transmission using quantum key distribution, and demonstrate it in the Tokyo metropolitan area (≤90 km).

LINCOS: A Storage System Providing Long-Term Integrity, Authenticity, and Confidentiality

The amount of digital data that requires long-term protection of integrity, authenticity, and confidentiality grows rapidly. Examples include electronic health records, genome data, and tax data. In this paper we present the secure storage system LINCOS, which provides protection of integrity, authenticity, and confidentiality in the long-term, i.e., for an indefinite time period. It is the first such system. It uses the long-term integrity scheme COPRIS, which is also presented here and is the first such scheme that does not leak any information about the protected data. COPRIS uses information-theoretic hiding commitments for confidentiality-preserving integrity and authenticity protection. LINCOS uses proactive secret sharing for confidential storage of secret data. We also present implementations of COPRIS and LINCOS. A special feature of our LINCOS implementation is the use of quantum key distribution and one-time pad encryption for information-theoretic private channels within the proactive secret sharing protocol. The technological platform for this is the Tokyo QKD Network, which is one of worlds most advanced networks of its kind. Our experimental evaluation establishes the feasibility of LINCOS and shows that in view of the expected progress in quantum communication technology, LINCOS is a promising solution for protecting very sensitive data in the cloud.

Analyzing Randomized Response Mechanisms Under Differential Privacy

The randomized response technique was first introduced by Warner in 1965 [27] as a technique to survey sensitive questions. Since it is considered to protect the respondent’s privacy, many variants and applications have been proposed in the literature. Unfortunately, the randomized response and its variants have not been well evaluated from the privacy viewpoint historically. In this paper, we evaluate them by using differential privacy. Specifically, we show that some variants have a tradeoff between the privacy and utility, and that the “negative” survey technique obtains negative results.

Numerical evaluation of coherent signals for deep-space links

We numerically evaluate the deep-space communication performance in a broadband lossy channel of coherent pulse position modulation (PPM) with on/off receiver. We also consider quadrature amplitude modulation (QAM) signal and phase-shift keying (PSK) signal with dyne-type detections. We find that for an extremely weak signal input power, multilevel PPM system is good strategy, while for an extremely strong signal, multilevel QAM system is recommended.

POSTER: PRINCESS: A Secure Cloud File Storage System for Managing Data with Hierarchical Levels of Sensitivity

PRINCESS (Proxy Re-encryption with INd-Cca security in an Encrypted file Storage System) is a secure storage system which utilizes special proxy re-encryption technology. With PRINCESS, the files encrypted in accordance with the confidentiality levels can be shared among appointed users while remaining encrypted. In this poster/demo, we show the efficiency of PRINCESS, which can be applied to a Body Area Network information sharing, automobile information sharing, etc. This system facilitates the potential for new services that require privacy data to be shared securely via cloud technology.

Quantum Detection of Wavelength Division Multiplexing Optical Coherent Signals in Lossy Channels

We numerically evaluate the wavelength division multiplexing (WDM) data transmission of coherent phase-shift keying (PSK) and quadrature amplitude modulation (QAM) signals in optical fiber communication and deep-space communication channels with conventional homodyne-based(dyne-type) detections and various quantum detection strategies. We show the quantitative gap between these detection strategies and especially in the quantum-limited region where the quantum noise seriously limits the transmission rate. For an extremely weak signal input power, there is a crucial gap between the capacity limit and the transmission rates of the WDM system with dyne-type detections. We show that this gap is filled by applying a collective square root detection (SRD) only for each channel, not necessary for quantum collective decoding among WDM channels.