Fabrication Attacks Fabrication attacks can be classified into three main categories. Detection is very difficult in all of these three cases. Routing table poisoning Routing protocols maintain tables which hold information regarding routes of the network. In routing table poisoning attacks the malicious nodes generate and send fabricated signaling traffic, or modify legitimate messages from other nodes, in order to create false entries in the tables of the participating nodes. For example, an attacker can send routing updates that do not correspond to actual changes in the topology of the ad hoc network. Routing table poisoning attacks can result in selection of non-optimal routes, creation of routing loops and bottlenecks. Route Cache Poisoning This type of attack falls in the category of passive attacks that can occur especially in DSR [6] due to the promiscuous mode of updating routing tables. This type of situation arises when information stored in routing tables is deleted, altered or injected with false information. A node overhearing any packet may add the routing information contained in that packet’s header to its own route cache, even if that node is not on the path from source to destination. The vulnerability of this system is that an attacker could easily exploit this method of learning routes and poison route caches by broadcast a message with a spoofed IP address to other nodes. When they receive this message, the nodes would add this new route to their cache and would now communicate using the route to reach the malicious node. Rote Error Messages fabrication This attack is very common in AODV and DSR, because when nodes move these two protocols use path maintenance to recover the optimum path. The weakness of this architecture is that whenever a node moves, the closest node sends an error message to the other nodes so as to inform them that a route is no longer accessible. If an attacker can cause a DoS attack by spoofing any node and sending error messages to the all other nodes. As a result malicious node can separate any node quite easily. Eavesdropping Eavesdropping is another kind of attack that usually happens in the mobile ad hoc networks. The goal of eavesdropping is to obtain some confidential information that should be kept secret during the communication. This information may include the location, public key, private key or even passwords of the nodes. Because such data are very important to the security state of the nodes, they should be kept away from the unauthorized access. Secure Ad hoc Routing Protocols Many solutions have been proposed for secure routing in ad hoc networks, in order to offer protection against the attacks discussed earlier. These proposed solutions are either completely new stand-alone protocols, or in some cases incorporations of security mechanisms into existing ones In order to analyze the proposed solutions and how they are still vulnerable to attacks we classified them into two main categories based on asymmetric cryptography and symmetric cryptography. Asymmetric Cryptographic Solution Protocols that use asymmetric cryptography to secure routing in mobile ad hoc networks require the existence of a universally trusted third party. This trusted third party can be either online or offline. The trusted third party issues certificates that bind a node’s public key with a node’s persistent identifier. Authenticated Routing for Ad hoc Networks ARAN falls in this category of secure Ad hoc routing protocols; many of the other protocols presented in other categories that use asymmetric cryptography operate in a similar manner and have similar requirements. Authenticated Routing for Ad hoc Networks ARAN The Authenticated Routing for Ad hoc Networks (ARAN) proposed in is a standalone solution for secure routing in ad hoc networking environments. ARAN use digital certificates and can successfully operate in the managed open scenario where no infrastructure is pre-deployed. The basic mechanism used in ARAN is certification that is achieved through the existence of a trusted certification authority (CA). All nodes are supposed to know their public key from the certification authority and also the public key of server. Prior to entering into the network, each node has to apply for a certificate that is signed by the certificate server. ARAN accomplishes the discovery of routes by a broadcast message from source node which is replied in a unicast manner. This route discovery of the ARAN protocol begins with a node broadcasting to its neighbors a route discovery packet (RDP). The RDP includes the certificate of the initiating node, a nonce, a timestamp and the address of the destination node. Furthermore, the initiating node signs the RDP. Each node validates the signature with the certificate, updates its routing table with the neighbor from which it received the RDP, signs it, and forwards it to its neighbors after removing the certificate and the signature of the previous node (but not the initiator’s signature and certificate). The signature prevents malicious nodes from injecting arbitrary route discovery packets that alter routes or form loops. The destination node eventually receives the RDP and replies with a reply packet (REP). The REP contains the address of the source node, the destination’s certificate, a nonce, and the associated timestamp. The destination node signs the REP before transmitting it. The REP is forwarded back to the initiating node by a process similar to the one described for the route discovery, except that the REP is unicasted along the reverse path. The source node is able to verify that the destination node sent the REP by checking the nonce and the signature. Figure 2 illustrates the process of route discovery in ARAN. All messages are authenticated at each hop from source to destination as well as on the reverse path. Due to heavy computation involved with the certificates, ARAN is vulnerable to many attacks e.g. DOS attacks. In situation when there are no malicious nodes in the network the load involved in the routing process force the legitimate nodes to drop the packets in order to save their resources. Symmetric Cryptography Solutions Symmetric cryptographic solutions rely solely on symmetric cryptography to secure the function of routing in wireless ad hoc networks. The mechanisms utilized is hash functions and hash chains. A one-way hash function is a function that takes an input of arbitrary length and returns an output of fixed length. As hash functions are especially lightweight when compared to other symmetric and asymmetric cryptographic operations, they have been extensively used in the context of securing ad hoc routing.
