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.

Handbook of Applied Cryptography

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.

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Ciphertext-Policy Attribute-Based Encryption

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).

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

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.

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Proofs of Partial Knowledge and Simplified Design of Witness Hiding Protocols

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.

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Attribute-based encryption with non-monotonic access structures

M -alternating paths in n -extendable bipartite graphs

On two equimatchable graph classes

The well-known Chvatal--Erdos theorem states that every graph $G$ of order at least three with $\alpha(G)\le\kappa(G)$ has a Hamiltonian cycle, where $\alpha(G)$ and $\kappa(G)$ are the independenc...

The Existence of a 2-Factor in a Graph Satisfying the Local Chvátal--Erdös Condition

Closure and factor-critical graphs

Let K1,n denote the star on n + 1 vertices; that is, K1,n is the complete bipartite graph having one vertex in the first vertex class of its bipartition and n in the second. The special graph K1,3, called the claw, has received much attention in the literature. In particular, a graph G is said to be claw-free if G possesses no K1,3 as an induced subgraph. A well-known theorem of Sumner and, independently, Las Vergnas says that every connected even claw-free graph contains a perfect matching. (Later, Junger, Pulleyblank, and Reinelt proved that if G is connected, claw-free, and odd, then G must contain a near-perfect matching.) More generally, Sumner proved that if G is K1,n-free, (n - 1)-connected, and even, then G must contain a perfect matching. In this paper, we extend these results in several ways. First, we show that if G is a k-connected K1,n-free graph on p vertices, then def(G) is bounded above by a certain function of k,n, and p, where def(G) is the deficiency of G. (The deficiency of a graph measures how far a maximum matching is from being perfect; that is, def (G) = p - 2ν(G), where ν(G) is the size of any maximum matching in G.) We then provide examples to show that this upper bound is sharp for each value of k and n. We then prove a result that is a type of converse to the above theorem in the following sense. Suppose that H is a connected graph and suppose that there exist constants α and β, 0 ≤ α < 1, such that every k-connected H-free graph G of sufficiently large order satisfies (G) ≤ α|V(G)| + β. Then the excluded subgraph H must be a K1,n, where n is bounded above by a certain function of α and k. © 2005 Wiley Periodicals, Inc. J Graph Theory

Akira Saito

Papers

M -alternating paths in n -extendable bipartite graphs

On two equimatchable graph classes

The Existence of a 2-Factor in a Graph Satisfying the Local Chvátal--Erdös Condition

Closure and factor-critical graphs

Forbidden subgraphs and bounds on the size of a maximum matching