研究者業績
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  2. 澁谷 智治

澁谷 智治

Shibuya Tomoharu

基本情報

所属
上智大学 理工学部情報理工学科 教授
(兼任)理工学部長
学位
博士（工学）(1999年4月 東京工業大学)
研究者番号
20262280
J-GLOBAL ID
200901097688266540
researchmap会員ID
1000181747
外部リンク

主に以下のような研究を行っています。

・安心・安全な分散コンピューティングに関する研究

・無限個のシェアを生成可能な秘密分散法に関する研究

・各種暗号方式・情報セキュリティに関する研究

研究キーワード

 7

研究分野

 9

受賞

 5

論文

 63
  • T. Shibuya, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E86A(4) 928-939 2003年4月  
    A parity check matrix for a binary linear code defines a bipartite graph (Tanner graph) which is isomorphic to a subgraph of a factor graph which explains a mechanism of the iterative decoding based on the sum-product algorithm. It is known that this decoding algorithm well approximates MAP decoding, but degradation of the approximation becomes serious when there exist cycles of short length, especially length 4, in Tanner graph. In this paper, based on the generating idempotents, we propose some methods to design parity check matrices for cyclic codes which define Tanner graphs with no cycles of length 4. We also show numerically error performance of cyclic codes by the iterative decoding implemented on factor graphs derived from the proposed parity check matrices.
  • K Kasai, T. Shibuya, K Sakaniwa
    2003 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY - PROCEEDINGS 121-121 2003年  査読有り
    We construct new families of low-density parity-check (LDPC) code ensembles which are sub-ensembles of conventional irregular LDPC code ensembles and develop density evolution for those new ensembles. Further, we find an ensemble which has a better threshold than that of its super ensemble.
  • T. Shibuya, K Sakaniwa
    2003 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY - PROCEEDINGS 148-148 2003年  査読有り
    In this paper, we empirically show the effectiveness of double-loop algorithm based on the concave-convex procedure in decoding linear codes.
  • T. Shibuya, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E84A(12) 3138-3145 2001年12月  
    A lower bound for the generalized Hamming weight of linear codes is proposed. The proposed bound is a generalization of the bound we previously presented and gives good estimate for generalized Hamming weight of Reed-Muller, some one point algebraic geometry, and arbitrary cyclic codes, Moreover the proposed bound contains the BCH bound as its special case. The relation between the proposed bound and conventional bounds is also investigated.
  • T. Shibuya, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E84A(2) 647-652 2001年2月  
    In this paper, we propose a lower hound for the minimum distance of [n, k] linear codes which are specified by generator matrices whose rows are k vectors of a given sequence of n. linearly independent vectors over a finite field. The Feng-Rao bound and the order bound give the lower bounds for the minimum distance of the dual codes of the codes considered in this paper. We show that the proposed bound gives the true minimum distance for Reed-Solomon and Reed-Muller codes and exceeds the Goppa bound for some L-type algebraic geometry codes.
  • T. Shibuya, K Sakaniwa
    2000 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY, PROCEEDINGS 169-169 2000年  査読有り
    We propose a lower bound for the minimum distance of [n, k] linear codes which are specified by generator matrices whose rows are k vectors of a given sequence of n linearly independent vectors over a finite field. Note that the Feng-Rao and the order bounds give lower bounds for the minimum distance of the dual codes.
  • T Shibuya, R Hasegawa, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E82A(6) 1090-1101 1999年6月  
    In this paper, we introduce a lower bound for the generalized Hamming weights, which is applicable to arbitrary linear code, in terms of the notion of well-behaving. We also show that any [n, k] linear code C over a finite field F is the t-th rank MDS for t such that g(C) + 1 less than or equal to t less than or equal to k where g(C) is easily calculated from the basis of F-n so chosen that whose first n - k elements generate C-perpendicular to Finally, we apply our result to Reed-Solomon, Reed-Muller and algebraic geometry codes on C-ab, and determine g(C) for each code.
  • T Shibuya, J Mizutani, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E81A(10) 1979-1989 1998年10月  
    In this paper, we give lower bounds for the generalize Hamming weights of linear codes constructed on affine algebraic varieties. By introducing a Dumber g*, which is determined by a given affine variety, we show that when the order t of generalized Hamming weights is greater than g*, the proposed lower bound agrees with their true generalize Hamming weights. Moreover. if we use the notion of well-behaving, we can obtain a more precise bound. Finally, we compare the proposed bound and the conventional one for algebraic geometric code on the curve C-ab.
  • T. Shibuya, K Sakaniwa
    1998 IEEE INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY - PROCEEDINGS 96-96 1998年  査読有り
    A lower bound for generalized Hamming weights of linear codes is introduced by using the notion of well-behaving. A sufficient condition for t-th rank MDS codes is also given.
  • T Shibuya, R Matsumoto, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E80A(11) 2058-2065 1997年11月  
    In this paper, we present a lower bound for the dimension of subfield subcodes of residue Goppa codes on the curve Cab. which exceeds the lower bound given by Stichtenoth when the number of check symbols is not small. We also give an illustrative example which shows that the proposed bound for the dimension of certain residue Goppa code exceeds the true dimension of a BCH code with the same code length and designed distance.
  • T Shibuya, R Matsumoto, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E80A(5) 876-880 1997年5月  
    In this paper. we give a new lower bound for the dimension of subfield subcodes. This bound improves the lower bound given by Stichtenoth. A BCH code and a subfield subcode of algebraic geometric code on a hyper elliptic curve are discussed as special cases.
  • T. Shibuya, J Mizutani, K Sakaniwa
    APPLIED ALGEBRA, ALGEBRAIC ALGORITHMS AND ERROR-CORRECTING CODES 1255(1255) 311-320 1997年  
    As a generalization of conventional algebraic geometric codes, codes constructed on affine algebraic sets were proposed by S. Miura. He has also shown that if a monomial order and a Grobner basis are given for the code on an affine algebraic set, a lower bound for the minimum distance is obtained as a generalization of Feng-Rao designed distance. In this paper, we investigate their generalized Hamming weights. We first provide a lower bound for generalized Hamming weights by using the monomial order structure of the Grobner basis employed. Secondary, by introducing a number g*, which is also determined by the monomial order structure of the Grobner basis, we show that when the order mu of generalized Hamming weights is greater than g*, the proposed lower bound agrees with the true generalized Hamming weights.
  • T. Shibuya, H Jinushi, S Miura, K Sakaniwa
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E79A(6) 928-937 1996年6月  
    In this paper, we show that the conventional BCH codes can be better than the AG codes when the number of check symbols is relatively small. More precisely, we consider an AG code on C-ab whose number of check symbols is less than min {g + a, n - g}, where n and g denote the code length and the genus of the curve, respectively. It is shown that there always exists an extended BCH code, (i) which has the same designed distance as the Feng-Rao designed distance of the AG code and the code length and the rate greater than those of the AG code, or (ii) which has the same number of check symbols as that of the AG code, the designed distance not less than that of the AG code and the code length longer than that of the AG code.

MISC

 44
  • 須藤 尊, 渋谷 智治
    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 116(395) 231-236 2017年1月19日  
  • Shibuya Tomoharu, Sudo Takeru
    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 116(33) 115-120 2016年5月19日  
  • Shibuya Tomoharu, Sudo Takeru
    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 116(34) 115-120 2016年5月19日  
  • 神林 雄也, 渋谷 智治
    電子情報通信学会技術研究報告 : 信学技報 112(461) 113-118 2013年3月7日  
    Rank Modulation符号は,フラッシュメモリを構成する各セルの電荷量の大小関係のみを用いて情報を表現する記録符号である.また,Compressed Encoding,はpush up操作を行うことによってメモリの状態遷移を実現するRnak Modulation符号化の一種である.本研究では,Compressed Encodingにおいて記憶容量増大とブロック消去の発生頻度低減を実現する1手法として知られる,遷移グラフの支配集合に基づく符号構成について検討した.この結果,支配集合を構成する新たなアルゴリズムを提案し,さらに,このアルゴリズムが極小支配集合を生成するための十分条件について明らかにしている.また,メモリを構成するセル数が5のときの,極小支配集合を具体的に構成している.
  • Ihara Hiroyuki, Shibuya Tomoharu
    電子情報通信学会技術研究報告. IT, 情報理論 112(124) 85-89 2012年7月12日  
    Spatially coupled (SC) low-density parity-check (LDPC) codes are denned by bipartite graphs that are obtained by assembling prototype graphs. The combination and connection of prototype graphs are designated by specifying some parameters, and Kudekar et al. showed that BP threshold of the ensemble of SC LDPC codes agrees with MAP threshold of the ensemble of regular LDPC codes when those parameters are grown up so that the code length tends to infinity. When we design SC LDPC codes with practical code length, however, it is not clear how to set those parameters to enhance the performance of SC LDPC codes. In this paper, we provide the result of numerical experiments that suggest the dependence of error performance of SC LDPC codes over BEC on their design parameters.
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書籍等出版物

 6
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講演・口頭発表等

 14
  • Daisuke Hibino, Tomoharu Shibuya
    Technical Committee Meeting on Information Theory 2023年3月15日
  • Taiyu Kamiyama, Yuta Ugaya, Keisuke Kodaira, Tomoharu Shibuya
    2018 The International Symposium on Information Theory and Its Applications 2018年10月28日 Engineering Sciences Society, IEICE
    conventional secret sharing, password protected secret sharing (PPSS) was invented. Recently, Nakahara et al. improved Ogata's multiple-use PPSS (mPPSS), which protects multiple data by one password, by employing secure computation known as CSEC70 method in the user authentication. In this paper, we propose an attack on Nakahara's mPPSS that presumes on a security hall in the adoption of CSEC70 method. Then, we show that the proposed attack enables an administrator of any server of the system to disclose the password of an arbitrary user in Nakahara's mPPSS.
  • Tomoharu Shibuya
    Japan-Singapore Workshop on Coding and Information Theory 2018年3月4日 School of Physical & Mathematical Sciences, Nanyang Technological University
    In this talk, a group theoretic representation suitable for the rank-modulation (RM) scheme over the multi-cell ranking developed by En Gad et al. is presented. By introducing an action of the group of all permutation matrices on the set of all permutations, the scheme is clearly reformulated. Moreover, we introduce the concept of r-dominating sets over the multi-cell ranking, which is a generalization of conventional dominating sets, in the design of rank-modulation rewriting codes. The concept together with the presented group theoretic representation helps to yield an explicit formula of an upper bound on the size of the set of messages that can be stored in the memory by using RM rewriting codes over multi-cell ranking. We also note that this bound enables us to consider the trade-off between the size of the storable message set and the rewriting cost more closely.
  • 須藤 尊, 渋谷 智治
    電子情報通信学会情報理論研究会 2017年1月20日 電子情報通信学会
  • Tomoharu Shibuya, Takeru Sudo
    Conference of Technical Committee on Information Theory 2016年5月20日 IEICE
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所属学協会

 4

共同研究・競争的資金等の研究課題

 13
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社会貢献活動

 13
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