280 research outputs found

    計算コストの小さい準最適な不正検知可能秘密分散法

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    A cheating detectable secret sharing scheme is a secret sharing scheme that can detect forged shares in reconstructing a secret. For example, if we store shares in cloud storage, there is a possibility of it being forged. If the administrators of cloud storage are malicious, it is easy for them to forge a share. Therefore, cheating detectable secretsharing schemes have attracted attention, and many efficient schemes have been proposed. However, most existing schemes are not suitable for implementation. The reasons are as follows. First, the computational cost ofthe schemes is very high. Second, the required finite field for implementation depends on the secret. Finally, the schemes do not support secrets that are bit strings.In this paper, we propose a cheating detectable secret sharing scheme suitable for implementation. However, we assume that cheaters do not know the secret. The basicidea is a bit-decomposing technique. The bit length of the proposed scheme is an optimum. Moreover, the proposed scheme is applicable to any linear secret sharing schemes

    Efficient Threshold Secret Sharing Schemes Secure against Rushing Cheaters

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    In this paper, we consider three very important issues namely detection, identification and robustness of kk-out-of-nn secret sharing schemes against rushing cheaters who are allowed to submit (possibly forged) shares {\em after} observing shares of the honest users in the reconstruction phase. Towards this we present five different schemes. Among these, first we present two kk-out-of-nn secret sharing schemes, the first one being capable of detecting (k1)/3(k-1)/3 cheaters such that Vi=S/ϵ3|V_i|=|S|/\epsilon^3 and the second one being capable of detecting n1n-1 cheaters such that Vi=S/ϵk+1|V_i|=|S|/\epsilon^{k+1}, where SS denotes the set of all possible secrets, ϵ\epsilon denotes the successful cheating probability of cheaters and ViV_i denotes set all possible shares. Next we present two kk-out-of-nn secret sharing schemes, the first one being capable of identifying (k1)/3(k-1)/3 rushing cheaters with share size Vi|V_i| that satisfies Vi=S/ϵk|V_i|=|S|/\epsilon^k. This is the first scheme whose size of shares does not grow linearly with nn but only with kk, where nn is the number of participants. For the second one, in the setting of public cheater identification, we present an efficient optimal cheater resilient kk-out-of-nn secret sharing scheme against rushing cheaters having the share size Vi=(nt)n+2tS/ϵn+2t|V_i|= (n-t)^{n+2t}|S|/\epsilon^{n+2t}. The proposed scheme achieves {\em flexibility} in the sense that the security level (i.e. the cheater(s) success probability) is independent of the secret size. Finally, we design an efficient (k,δ)(k, \delta) robust secret sharing secure against rushing adversary with optimal cheater resiliency. Each of the five proposed schemes has the smallest share size having the mentioned properties among the existing schemes in the respective fields

    Artificial-noise-aided message authentication codes with information-theoretic security

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    Data Processing over Concealed Data

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    研究成果の概要 (和文) : 情報を秘匿したまま情報処理を行う秘匿演算方式に関しては,多項目間の相関を計算するクロス集計方式,生体認証方式,および検索を暗号化したまま実現する方式を提案した.複数のユーザが自分の入力を秘匿したままで関数の計算を行うマルチパーティ計算に関しては,マルチパーティ計算において不正を防止するための基礎技術となる不正を検知,あるいは不正者を特定することが可能な秘密分散法の提案を行った.また,関数計算時にユーザ間の通信が不要となる非対話型マルチパーティ計算やd乗算可能な秘密分散に関して,理論的限界の証明や効率の良い方式の提案を行った.研究成果の概要 (英文) : With respect to secure computation over encrypted data that enables us to process encrypted data without decrypting them, we constructed protocols for cross tabulation, biometric authentication, and keyword search. With respect to secure multiparty computation (MPC) that enables multiple users to compute function without revealing inputs possessed by users, we constructed efficient cheating detectable secret sharing and cheater identifiable secret sharing which are used as building blocks to construct MPC. Moreover, we study MPC which does not require user interaction during protocol execution. Namely, we proved theoretical limitation about such protocols, and give efficient construction for them

    Artificial-Noise-Aided Message Authentication Codes With Information-Theoretic Security

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    Cryptography in a quantum world

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    Ideal quantum protocols in the non-ideal physical world

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    The development of quantum protocols from conception to experimental realizations is one of the main sources of the stimulating exchange between fundamental and experimental research characteristic to quantum information processing. In this thesis we contribute to the development of two recent quantum protocols, Universal Blind Quantum Computation (UBQC) and Quantum Digital Signatures (QDS). UBQC allows a client to delegate a quantum computation to a more powerful quantum server while keeping the input and computation private. We analyse the resilience of the privacy of UBQC under imperfections. Then, we introduce approximate blindness quantifying any compromise to privacy, and propose a protocol which enables arbitrary levels of security despite imperfections. Subsequently, we investigate the adaptability of UBQC to alternative implementations with practical advantages. QDS allow a party to send a message to other parties which cannot be forged, modified or repudiated. We analyse the security properties of a first proof-of-principle experiment of QDS, implemented in an optical system. We estimate the security failure probabilities of our system as a function of protocol parameters, under all but the most general types of attacks. Additionally, we develop new techniques for analysing transformations between symmetric sets of states, utilized not only in the security proofs of QDS but in other applications as well
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