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Hideki Imai

Publications and source records attributed to Hideki Imai.

28 records · Page 2Linked to original sources
arXiv2006

Strength of interaction for information distribution

Let us consider two quantum systems: system A and system B. Suppose that a classical information is encoded to quantum states of the system A and we distribute this information to both systems by making them interact with each other. We show that it is impossible to achieve this goal perfectly if the strength of interaction between the quantum systems is smaller than a quantity that is determined by noncommutativity between a Hamiltonian of the system A and the states (density operators) used for the information encoding. It is a consequence of a generalized Winger-Araki-Yanase theorem which enables us to treat conserved quantities other than additive ones.

quant-ph↗
arXiv2006

Wigner-Araki-Yanase theorem on Distinguishability

The presence of an additive conserved quantity imposes a limitation on the measurement process. According to the Wigner-Araki-Yanase theorem, the perfect repeatability and the distinguishability on the apparatus cannot be attained simultaneously. Instead of the repeatability, in this paper, the distinguishability on both systems is examined. We derive a trade-off inequality between the distinguishability of the final states on the system and the one on the apparatus. The inequality shows that the perfect distinguishability of both systems cannot be attained simultaneously.

quant-ph↗
arXiv2006

A Quantum Key Distribution Protocol with Selecting Announced States, Robust against Photon Number Splitting Attacks

We propose a new class of quantum key distribution protocol, that ended up to be robust against photon number splitting attacks in the weak laser pulse implementations. This protocol comprises of BB84 protocol and SARG protocol, especially in aspects of controlling classical sifting procedures of two protocols. The protocol is more secure than both of BB84 protocol and SARG protocol, and the ultimate limit of robustness in the proposed protocol expands as well than both of them.

quant-ph↗
arXiv2005

A Secure Traitor Tracing Scheme against Key Exposure

Copyright protection is a major issue in distributing digital content. On the other hand, improvements to usability are sought by content users. In this paper, we propose a secure {\it traitor tracing scheme against key exposure (TTaKE)} which contains the properties of both a traitor tracing scheme and a forward secure public key cryptosystem. Its structure fits current digital broadcasting systems and it may be useful in preventing traitors from making illegal decoders and in minimizing the damage from accidental key exposure. It can improve usability through these properties.

cs.CR↗
arXiv2004

Non stabilizer Clifford codes with qupits

Clifford codes can be understood as a generalization of stabilizer codes. To show the existence of a true Clifford code which is better than any stabilizer code is a well known open problem in the theory of Clifford codes. One of the main difficulties in solving this problem is that we know only about 110 examples of codes which are Clifford but not stabilizer codes. In this paper, we obtain infinite examples of Clifford codes which are not stabilizer codes. We expect our examples to be useful in the study of Clifford codes.

quant-ph↗
arXiv2003

A Quantum Information Theoretical Model for Quantum Secret Sharing Schemes

In this paper we introduce a quantum information theoretical model for quantum secret sharing schemes. We show that quantum information theory provides a unifying framework for the study of these schemes. We prove that the information theoretical requirements for a class of quantum secret sharing schemes reduce to only one requirement (the recoverability condition) as a consequence of the no-cloning principle. We give also a shorter proof of the fact that the size of the shares in a quantum secret sharing scheme must be at least as large as the secret itself.

quant-ph↗
arXiv2003

How much security does Y-00 protocol provide us ?

New quantum cryptography, often called Y-00 protocol, has much higher performance than the conventional quantum cryptographies. It seems that the conventional quantum cryptographic attacks are inefficient at Y-00 protocol as its security is based on the different grounds from that of the conventional ones. We have, then, tried to cryptoanalyze Y-00 protocol in the view of cryptographic communication system. As a result, it turns out that the security of Y-00 protocol is equivalent to that of classical stream cipher.

quant-ph↗
arXiv2003

Commitment Capacity of Discrete Memoryless Channels

In extension of the bit commitment task and following work initiated by Crepeau and Kilian, we introduce and solve the problem of characterising the optimal rate at which a discrete memoryless channel can be used for bit commitment. It turns out that the answer is very intuitive: it is the maximum equivocation of the channel (after removing trivial redundancy), even when unlimited noiseless bidirectional side communication is allowed. By a well-known reduction, this result provides a lower bound on the channel's capacity for implementing coin tossing, which we conjecture to be an equality. The method of proving this relates the problem to Wyner's wire--tap channel in an amusing way. We also discuss extensions to quantum channels.

cs.CR↗
arXiv2001

Pretty-Simple Password-Authenticated Key-Exchange Protocol

We propose pretty simple password-authenticated key-exchange protocol which is based on the difficulty of solving DDH problem. It has the following advantages: (1) Both $y_1$ and $y_2$ in our protocol are independent and thus they can be pre-computed and can be sent independently. This speeds up the protocol. (2) Clients and servers can use almost the same algorithm. This reduces the implementation costs without accepting replay attacks and abuse of entities as oracles.

cs.CR↗