SRDP: Secure route discovery for dynamic source routing in MANETs

Abstract

Routing is a critical function in multi-hop mobile ad hoc networks (MANETs). A number of MANET-oriented routing protocols have been proposed, of which DSR is widely considered both the simplest and the most effective. At the same time, security in MANETs – especially, routing security – presents a number of new and interesting challenges. Many security techniques geared for MANETs have been developed, among which Ariadne is the flagship protocol for securing DSR.

The focus of this work is on securing the route discovery process in DSR. Our goal is to explore a range of suitable cryptographic techniques with varying flavors of security, efficiency and robustness. The Ariadne approach (with TESLA), while very efficient, assumes loose time synchronization among MANET nodes and does not offer non-repudiation. If the former is not possible or the latter is desired, an alternative approach is necessary. To this end, we construct a secure route discovery protocol (SRDP) which allows the source to securely discover an authenticated route to the destination using either aggregated message authentication codes (MACs) or multi-signatures. Several concrete techniques are presented and their efficiency and security are compared and evaluated.

Introduction

Multi-hop mobile ad hoc networks (MANETs) have been studied extensively in recent years and a large body of relevant research has been accumulated, especially pertaining to routing security.

One of the key MANET characteristics – absence of fixed infrastructure – makes it difficult to re-use results from more traditional wired networks. In particular, popular IP routing protocols (used both in the internet and in private intranets) are not suitable for MANETs, due mostly to node mobility. Consequently, a lot of effort has gone into developing MANET-geared routing protocols. Most of these protocols have, for various reasons, remained on paper, only a few have been implemented and even fewer have made into real MANETs.

Since the focus of this paper is on security, rather than routing, we do not review the relevant routing literature. Suffice it to say, that the most popular MANET routing protocol is also one of the conceptually simplest, dynamic source routing (DSR), developed by Johnson and Maltz. The centerpiece of DSR is the route discovery (RD) protocol which uses flooding to discover routes on-demand. (See Section 2 below for a detailed description.) On-demand routing protocols have been demonstrated to perform better with significantly lower overheads than periodic (or proactive) routing protocols in many situations [2], [3], [4], since they are able to react quickly to the many changes that may occur in node connectivity, yet are able to reduce routing overhead in periods or areas of the network in which changes are less frequent.

Like most network protocols, MANET routing protocols (including DSR) are often designed for non-adversarial networks and thus forgo security features. This follows the traditional model of first designing a protocol and later (sometimes much later) retrofitting it with security features. Being a popular protocol, DSR has received a lot of attention from the security community. The state-of-the-art of MANET routing security is represented by Ariadne [13] which is a DSR-specific security mechanism based on the earlier TESLA protocol [8]. Ariadne’s security is based on message authentication codes (MACs) and loose time synchronization among nodes is required; the latter feature is inherited from TESLA.

The motivation for the work presented in this paper is very similar to Ariadne’s. Our goal is to efficiently secure the route discovery process in DSR.¹ However, in doing so, we aim to address the needs of MANETs where either (or both) stronger security is necessary or loose time synchronization is not possible. Protocol efficiency is also one of our goals, especially, the minimization of communication (bandwidth) overhead. This contrasts with Ariadne which focuses more on lowering computation costs.

With the above goals in mind, we develop secure route discovery protocol (SRDP). It is a generic protocol which works with a range of cryptographic primitives, some based on aggregated MACs and others – on digital signatures amenable to aggregation. (Aggregation is essential as it allows us to compress authentication tags thus saving bandwidth and reduces verification costs.) We explore five cryptographic techniques and evaluate/analyze their respective security features and efficiency features. One of the interesting aspects of our work is the novel application of aggregated signature and multi-signature schemes.

Viewed from the higher-level perspective, SRDP enhances the functionality of DSR with the feature we term route integrity. Informally, this means that all nodes in a putative route agree on the exact sequence (order) of nodes traversed in that route. Moreover, the source is able to ascertain that all intermediate nodes vouch for the integrity of the same route. (See Section 4 for further details.) However, route integrity does not imply viability of the discovered route, since an adversarial node that behaves honestly during route discovery may behave in an arbitrarily malicious manner during subsequent forwarding of data packets.

SRDP is a provably secure routing protocol. Especially, we prove that the generic SRDP scheme based on signatures is secure in a mathematical framework proposed by Acs et al. in [1]. Instead, we add more assumptions and modify the attacker model s.t. the assumptions and the model are fit to the framework. The security goal achieved in the framework is minimal in the sense that it guarantees only that the route list is an existent path. The framework does not detect if the adversary changes the route or modifies it as long as the route is plausible. Still, it is useful in that the security model helps the route discovery protocol find any existing path.

Organization: the remainder of this paper is organized as follows: Section 2 summarizes the basic operation of DSR. Then, Section 3 presents our network assumption, attack model and defines necessary security properties. Section 4, describes SRDP and several cryptographic techniques. Then, Section 5 explains the mathematical framework and proves the security of SRDP in the framework. SRDP’s efficiency is discussed in Section 6. Finally, Section 7 overviews relevant prior work.