Obtaining Non-repudiable Proof of Active Attacks in DSR Kulasekaran A. Sivakumar, Mahalingam Ramkumar Department of Computer Science and Engineering Mississippi State University. Abstract—Many secure MANET routing protocols have been proposed in the literature which employ non repudiable crypto- graphic authentication. However, they have not been explicitly designed to provide non repudiable proof of active attacks (NPAA). For example, Ariadne with digital signatures (ADS) is a secure extension of DSR which requires every node forwarding a route request to append a digital signature. Such signatures are carried forward all the way to the destination node to facilitate the destination to detect active attacks. However, ADS is not well- suited for providing NPAA due to the need for accused nodes to provide affirmative defense. We propose a secure DSR based protocol, APALLS, designed explicitly to provide NPAA. Apart from the eliminating the need for affirmative defense, another advantage of APALLS is that it does not require digital signatures to be carried over. I. I NTRODUCTION Routing protocols for mobile ad hoc networks (MANET) are rules to be followed by every node to co-operatively discover optimal paths and route packets between end-points (source and destination nodes). The presence of nodes that do not adhere to the rules, either deliberately, or due to malfunctioning, can have a deleterious effect on other nodes. The types of attacks that can be inflicted by misbehaving nodes can be broadly classified into passive and active attacks. Passive attacks may involve non-participation or selective (selfish) participation. Active attacks involve illegal modifi- cations to routing packets. Secure MANET routing protocols include explicit measures to address such attacks. Cryptographic authentication is necessary to address both forms of attacks. Mechanisms for addressing passive attacks require monitoring of neighbors; for this purpose, a node pro- cessing a packet needs to know who sent that packet - which is made possible through a cryptographic authentication token accompanying the packet. Strategies for addressing active attacks typically require verification of multiple cryptographic tokens created by multiple of nodes. Specific authentication strategies required to detect active attacks are however intricately tied to the nature of the underlying routing protocol. In this paper we restrict ourselves to the dynamic source routing (DSR) protocol. In DSR paths between a pair of nodes (source and destination) is established by flooding a route request (RREQ) packet originating from the source, in response to which the destination, or a node which is aware of a path to the destination, invokes a route- response (RREP) packet indicating the path between the end- points. The focus of this paper is on issues in obtaining non repudiable proof of active attacks on the dynamic source routing (DSR) protocol [1]. A. Contributions Arguably, the most effective deterrent for active attacks is an ability to obtain non repudiable proof of active attacks (NPAA), which could lead to revocation of the attacker from the network. An obvious prerequisite for NPAA is the use of a non repudiable cryptographic authentication strategy, like digital signatures. This is not withstanding some unfortunate side effects of employing digital signatures, like substantial computational and bandwidth overhead for battery operated mobile devices, and increased susceptibility to simple denial of service (DoS) attacks. Specifically, compared to message authentication codes based on symmetric secrets, digital sig- natures impose 2 orders of magnitude higher computational burden. By sending random bits in place of signatures attackers can force receiving nodes to suffer the overhead for verifying the signature. The primary contribution of this paper is an efficient pro- tocol, APALLS - Ariadne with pairwise authentication and link-layer signatures - for NPAA in DSR. We argue that some of the pitfalls of Ariadne with digital signatures (ADS) include 1) the need for accused nodes to provide affirmative de- fense 1 , due to which nodes could be accidentally penal- ized; and 2) the need for carrying over digital signatures (and public key certificates required to verify signatures) appended by every node in the path till the end of the path (the destination node). In APALLS, link-layer (one-hop) signatures are not carried forward. Nevertheless, a signed packet from a node includes all the contextual information required to determine if a node did (or did not) engage in an active attack. Consequently, APALLS eliminates the need for accused nodes to provide additional affirmative defenses, while simultaneously reducing overhead. The rest of this paper is organized as follows. In Section II is i) an overview of DSR, ii) the open-managed network model [7] for MANETs, and iii) key distribution schemes for facilitating cryptographic authentication. In Section III we begin with an overview of Ariadne [2], a popular secure extension of DSR. In particular, we 1 As we shall see later in this paper a falsely accused node will require to store and provide a per-hop hash reported by an upstream node to demonstrate that it did not engage in an active attack.