Akira Saito

Bio: Akira Saito is an academic researcher from Nihon University. The author has contributed to research in topics: Bound graph & Graph power. The author has an hindex of 20, co-authored 150 publications receiving 2220 citations. Previous affiliations of Akira Saito include University UCINF & University of Tokyo.

Secret sharing scheme realizing general access structure

Abstract: As a method of sharing a secret, e.g., a secret key, Shamir's (k, n) threshold method is well known. However, Shamir's method has a problem in that general access structures cannot be realized. This paper shows that by providing the trustees with several information data concerning the distributed information of the (k, n) threshold method, any access structure can be realized. the update with the change of the secret trustees and the relation to the threshold graph are also discussed.

Toughness and the existence of k‐factors

Abstract: A connected graph G is called t-tough if t · w(G - S) ⩽ |S| for any subset S of V(G) with w(G - S) > 1, where w(G - S) is the number of connected components of G - S. We prove that every k-tough graph has a k-factor if k|G| is even and |G| ⩾ k + 1. This result, first conjectured by Chvatal, is sharp in the following sense: For any positive integer k and for any positive real number e, there exists a (k - e)-tough graph G with k|G| even and |G| ⩾ k + 1 which has no k-factor.

Multiple assignment scheme for sharing secret

Abstract: In a secret sharing scheme, a datumd is broken into shadows which are shared by a set of trustees. The family {P?⊆P:P? can reconstructd} is called the access structure of the scheme. A (k, n)-threshold scheme is a secret sharing scheme having the access structure {P?⊆P: |P?|?k}. In this paper, by observing a simple set-theoretic property of an access structure, we propose its mathematical definition. Then we verify the definition by proving that every family satisfying the definition is realized by assigning two more shadows of a threshold scheme to trustees.

Effects of pulsatile CPB on interleukin-8 and endothelin-1 levels.

Abstract: Studies on pulsatile and nonpulsatile perfusion have long been performed. However, investigators have not reached a conclusion on which is more effective. In the present study, pulsatile cardiopulmonary bypass (CPB) was investigated in terms of the effects on cytokines, endothelin, catecholamine, and pulmonary and renal functions. Twenty-four patients who underwent coronary artery bypass grafting were divided into a pulsatile CPB group and a nonpulsatile CPB group. Parameters examined were hemodynamics, interleukin-8 (IL-8), endothelin-1 (ET-1), epinephrine, norepinephrine, lactate, arterial ketone body ratio, urine volume, blood urea nitrogen, creatinine, renin activity, angiotensin-II, lactate dehydrogenase, plasma-free hemoglobin, tracheal intubation time, and respiratory index. The IL-8 at 0.5, 3, and 6 h after CPB, and ET-1 at 3, 6, 9, and 18 h after CPB were significantly lower in the pulsatile group. Both epinephrine and norepinephrine were significantly lower in the pulsatile group. The respiratory index was significantly higher in the pulsatile group. In the present study, inhibitory effects on cytokine activity, edema in pulmonary alveoli, and endothelial damage were shown in addition to the favorable effects on catecholamine level, renal function, and peripheral circulation that have already been documented.

Handbook of Applied Cryptography

Abstract: From the Publisher: A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols; more than 200 tables and figures; more than 1,000 numbered definitions, facts, examples, notes, and remarks; and over 1,250 significant references, including brief comments on each paper.

Ciphertext-Policy Attribute-Based Encryption

Abstract: In several distributed systems a user should only be able to access data if a user posses a certain set of credentials or attributes. Currently, the only method for enforcing such policies is to employ a trusted server to store the data and mediate access control. However, if any server storing the data is compromised, then the confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call ciphertext-policy attribute-based encryption. By using our techniques encrypted data can be kept confidential even if the storage server is untrusted; moreover, our methods are secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's keys; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, our methods are conceptually closer to traditional access control methods such as role-based access control (RBAC). In addition, we provide an implementation of our system and give performance measurements.

Attribute-based encryption for fine-grained access control of encrypted data

Abstract: As more sensitive data is shared and stored by third-party sites on the Internet, there will be a need to encrypt data stored at these sites. One drawback of encrypting data, is that it can be selectively shared only at a coarse-grained level (i.e., giving another party your private key). We develop a new cryptosystem for fine-grained sharing of encrypted data that we call Key-Policy Attribute-Based Encryption (KP-ABE). In our cryptosystem, ciphertexts are labeled with sets of attributes and private keys are associated with access structures that control which ciphertexts a user is able to decrypt. We demonstrate the applicability of our construction to sharing of audit-log information and broadcast encryption. Our construction supports delegation of private keys which subsumesHierarchical Identity-Based Encryption (HIBE).

Proofs of Partial Knowledge and Simplified Design of Witness Hiding Protocols

Abstract: Suppose we are given a proof of knowledge P in which a prover demonstrates that he knows a solution to a given problem instance. Suppose also that we have a secret sharing scheme S on n participants. Then under certain assumptions on P and S, we show how to transform P into a witness indistinguishable protocol, in which the prover demonstrates knowledge of the solution to some subset of n problem instances out of a collection of subsets denned by S. For example, using a threshold scheme, the prover can show that he knows at least d out of n solutions without revealing which d instances are involved. If the instances axe independently generated, we get a witness hiding protocol, even if P did not have this property. Our results can be used to efficiently implement general forms of group oriented identification and signatures. Our transformation produces a protocol with the same number of rounds as P and communication complexity n times that of P. Our results use no unproven complexity assumptions.

Attribute-based encryption with non-monotonic access structures

Abstract: We construct an Attribute-Based Encryption (ABE) scheme that allows a user's private key to be expressed in terms of any access formula over attributes. Previous ABE schemes were limited to expressing only monotonic access structures. We provide a proof of security for our scheme based on the Decisional Bilinear Diffie-Hellman (BDH) assumption. Furthermore, the performance of our new scheme compares favorably with existing, less-expressive schemes.