Yoshifumi Manabe

k -Arbiter: a safe and general scheme for h -out of- k mutual exclusion

Abstract Mutual exclusion is a well-known problem that arises when multiple processes compete, in an uncoordinated way, for the acquisition of shared resources over a distributed system. In particular, k -mutual exclusion allows at most k processes to get one unit of the same resource simultaneously. These paradigms do not cover all the cases in which resource accesses must be serialized over a distributed system. There exist cases (e.g. the bandwidth of communication lines) where the amount of shared resource might differ from request to request (for example, audio and video communications). In this paper, we formalize this problem as the h-out of-k mutual exclusion problem , in which each request concerns some number h (1 ⩽ h ⩽ k ) of units of shared resource and no unit is allocated to multiple processes at the same time. Former simple and k -mutual algorithms cannot be used to solve this problem. We present a general scheme for a quorum-based h-out of-k mutual exclusion algorithm that relies on a collection of quorums called k-arbiter . Several examples of k -arbiters are discussed, two particular classes of k -arbiters are investigated and a metric to evaluate the resiliency with respect to failures of k -arbiters is also given.

Global conditions in debugging distributed programs

Abstract This paper describes algorithms for a distributed program debugger based on a replay technique. Halting at breakpoints and selective tracing are its fundamental features. In distributed systems, a given breakpoint or trace condition does not uniquely define the global state at which to halt or trace, because of the asynchrony of processes and communications. This paper therefore proposes the “first” global state Inf(P) to be the best global state at which to halt or trace, for a given condition P. Two kinds of global conditions related to plural processes, Conjunctive Predicates and Disjunctive Predicates, are considered. The authors present an algorithm that halts processes at Inf(P) for a given Conjunctive Predicate P. It is also shown that, for a Disjunctive Predicate P, it is impossible to halt at Inf(P), but possible to halt at some state which satisfies P. An algorithm is also provided for selective tracing when a Conjunctive or Disjunctive Predicate selection condition is given.

A Feasibility Decision Algorithm for Rate Monotonic andDeadline Monotonic Scheduling

Rate monotonic and deadline monotonic scheduling are commonly used for periodic real-time task systems. This paper discusses a feasibility decision for a given real-time task system when the system is scheduled by rate monotonic and deadline monotonic scheduling. The time complexity of existing feasibility decision algorithms depends on both the number of tasks and maximum periods or deadlines when the periods and deadlines are integers. This paper presents a new necessary and sufficient condition for a given task system to be feasible and proposes a new feasibility decision algorithm based on that condition. The time complexity of this algorithm depends solely on the number of tasks. This condition can also be applied as a sufficient condition for a task system using priority inheritance protocols to be feasible with rate monotonic and deadline monotonic scheduling.

A quorum-based extended group mutual exclusion algorithm without unnecessary blocking

This paper presents a quorum-based distributed algorithm for the extended group mutual exclusion problem. In the group mutual exclusion problem, multiple processes can enter a critical section simultaneously if they belong to the same group. Processes in different groups cannot enter a critical section at the same time. In the extended group mutual exclusion, each process is a member of multiple groups at the same time. Each process can select which group it belongs at making a request. The algorithm for the group mutual exclusion cannot be applied for this extended problem, since there can be a case that two processes are prevented from entering a critical section simultaneously even when they are capable of doing so. We call the above situation unnecessary blocking. We present a quorum-based algorithm that prevents unnecessary blocking and show its correctness proof.

Fault-tolerant routings in a k-connected network

Abstract Consider a communications network G with a fixed bidirectional routing ϱ in which node and edge faults F might occur. The diameter D( R(G, ϱ) F of the surviving route graph could be one of the fault-tolerant measurements. This paper shows the following results for a K -connected graph G = ( V , E ): (1) If |V| ⩾ 2 K 2 , then there is a routing ϱ 1 such that if |F| K , then D(R (G, ϱ 1 ) F )⩽3 . (2)If |V|⩾ K 2 and K ≠ 2 and 4, then there is a ϱ 2 such that if |F| K , then D(R (G, ϱ 2 ) F ) ⩽5 .

An Efficient Anonymous Credential System

This paper presents an efficient anonymous credential system that includes two variants. One is a system that lacks a credential revoking protocol, but provides perfect anonymity-unlinkability and computational unforgeability under the strong Diffie-Hellman assumption. It is more efficient than existing credential systems with no revocation. The other is a system that provides revocation as well as computational anonymity-unlinkability and unforgeability under the strong Diffie-Hellman and decision linear Diffie-Hellman assumptions. This system provides two types of revocation simultaneously: one is to blacklist a user who acted wrong so that he can no longer use his credential, and the other is identifying a user who acted wrong from his usage of credential. Both systems are provably secure under the above-mentioned assumptions in the standard model.

Constant-Round Black-Box Construction of Composable Multi-Party Computation Protocol

We present the first general MPC protocol that satisfies the following: (1) the construction is black-box, (2) the protocol is universally composable in the plain model, and (3) the number of rounds is constant. The security of our protocol is proven in angel-based UC security under the assumption of the existence of one-way functions that are secure against sub-exponential-time adversaries and constant-round semi-honest oblivious transfer protocols that are secure against quasi-polynomial-time adversaries. We obtain the MPC protocol by constructing a constant-round CCA-secure commitment scheme in a black-box way under the assumption of the existence of one-way functions that are secure against sub-exponential-time adversaries. To justify the use of such a sub-exponential hardness assumption in obtaining our constant-round CCA-secure commitment scheme, we show that if black-box reductions are used, there does not exist any constant-round CCA-secure commitment scheme under any falsifiable polynomial-time hardness assumptions.

An optimistic fair exchange protocol and its security in the universal composability framework

Fair exchange protocols allow both or neither of two parties to obtain the others items, and this property is essential in e-commerce. In this paper, we construct an optimistic fair exchange protocol that is applicable to any digital signature by prescribing three forms of signatures, namely presignature, post-signature and notarised signature. We set an expiration date for presignature, and thus realise the timely termination of the protocol. Next, we define an ideal functionality of fair exchange protocols in the universal composability framework. Then, we construct an optimistic fair exchange protocol based on the above protocol, and prove its security in the universal composability framework.

A universally composable secure channel based on the KEM-DEM framework

For ISO standards on public-key encryption, Shoup introduced the framework of KEM (Key Encapsulation Mechanism), and DEM (Data Encapsulation Mechanism), for formalizing and realizing one-directional hybrid encryption; KEM is a formalization of asymmetric encryption specified for key distribution, and DEM is a formalization of symmetric encryption. This paper investigates a more general hybrid protocol, secure channel, using KEM and DEM, such that KEM is used for distribution of a session key and DEM, along with the session key, is used for multiple bi-directional encrypted transactions in a session. This paper shows that KEM semantically secure against adaptively chosen ciphertext attacks (IND-CCA2) and DEM semantically secure against adaptively chosen plaintext/ciphertext attacks (IND-P2-C2) along with secure signatures and ideal certification authority are sufficient to realize a universally composable (UC) secure channel. To obtain the main result, this paper also shows several equivalence results: UC KEM, IND-CCA2 KEM and NM-CCA2 (non-malleable against CCA2) KEM are equivalent, and UC DEM, IND-P2-C2 DEM and NM-P2-C2 DEM are equivalent.

(h, k)-arbiters for h-out of-k mutual exclusion problem

h-out of-k mutual exclusion is a generalization of 1-mutual exclusion problem, where there are k limits of shared resources and each process requests h(1/spl les/h/spl les/k) units at the same time. Though the k-arbiter has been shown to be a quorum-based solution to this problem, quorums in the k-arbiter are much larger than these in the 1-coterie for 1-mutual exclusion. Thus, the algorithm based on the k-arbiter needs many messages. This paper defines two (h, k)-arbiters for h-out of-k mutual exclusion: a uniform (h, k)-arbiter and a (k+1)-cube (h, k)-arbiter. The quorums in each (h, k)-arbiter are not larger than the ones in the corresponding k-arbiter; consequently using the (h, k)-arbiters is more efficient than using the k-arbiters. Uniform (h, k)-arbiter is an optimal generalization of the majority coterie for 1-mutual exclusion. (k+1)-cube (h, k)-arbiter is a quasi-optimal generalization of square grid coterie for 1-mutual exclusion.