Roberto Di Pietro
This article is presented by:
Dipartimento di Matematica
Universitµa di Roma Tre
Rome, Italy
Luigi Vincenzo Mancini
Dipartimento di Informatica
Universitµa di Roma \La Sapienza"
Rome, Italy
Giorgio Zanin
Dipartimento di Informatica
Universitµa di Roma \La Sapienza"
Rome, Italy
Efficient and Adaptive Threshold Signaturesfor Ad hoc networks
Abstract
In this paper, we propose a secure, °exible, robust and fully distributed signature service, for ad hoc groups. In order to provide the service, we use a new threshold scheme, that allows to share a secret key among the current group members. The novelty of the scheme is in that it easily and e±ciently enables dynamic increase of the threshold, according to the needs of the group, so that the service provides both adaptiveness to the level of threat the ad hoc group is subject to, and availability. We prove the correctness of the protocol and evaluate its e±ciency. The changes to the threshold are performed by using a protocol that is e±cient in terms of in- teractions among nodes and per-node required resources, resulting suitable even for resource-constrained settings. Finally, the same proposed scheme allows to detect nodes that attempt to disrupt the service, providing invalid contributions to the distributed signature service.
Introduction and Background
Mobile Ad Hoc Networks (MANETs) are inherently self-organized, large-scale and fault-tolerant networks, made of miniature wireless devices such as PDAs, cellular phones, Pocket PCs. They generally exhibit dynamic membership and topology, i.e. nodes can join and leave the network, as well as fail, over time. In particular, their size may change drastically in a short time period. MANETs, as in common ad hoc groups, can be characterized by a not-hierarchical struc- ture, such that their nodes are autonomous peers. Due to their ability to provide a wide range of services, their use can be appealing for both military and civilian applications. Further, they are expected to be employed for pro- viding pervasive services, playing a crucial role in any aspect of everyday life, impacting the way people work, and interact with each other, and the way business, education, entertainment, and health-care are operating, depicting the vision of anytime ubiquitous computing. However, MANETs introduce new security challenges, compared to tradi- tional wired or cellular wireless networks, due to: dynamic topology, produced by mobility and change in the number and distribution of active nodes in the network; severe resource constraints, that call for power-e±cient protocols; absence of a trusted infrastructure; necessity for group oriented distributed services and protocols. These challenges have stimulated considerable re- search interest in recent years, because ad hoc networks cannot be adopted widespread, without adequate security. In particular, features such as decen- tralized operation and dynamic membership, bring a bulk of challenges from the perspective of security, such as member authentication, access control, secure group communication, and secure routing to cite a few. In this paper, we present a distributed signature scheme for ad hoc net- works, that improves over current solutions. Basically, a signature Sig(m) of a message m is an encryption of m using a secret key sk, that is Sig(m) = [m]sk. In practice, any signature scheme is generally applied to hashed values of mes- sages, rather than to the messages themselves; the hashed values are computed by using a strong hash function, such as SHA-1. Here, for ease of presentation, we assume that m is an already such hashed value. The signature needs to be veri¯able by using a public key pk, that is, for any valid signature Sig(m), it is required that [Sig(m)]pk = m holds. In order to distribute a signature service, two tools are necessary: one for generating the <sk; pk> pair, and one for distributing, among a set of distinct individuals, the ability to sign messages under sk. In the following, we assume the MANET to have associated an RSA key pair <sk; pk>. Current solutions, for distributing the signing ability to a group of individuals, are based on standard threshold schemes, in which sk is divided into a given number of shares that are distributed to as many cosigners.
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