Security challenges in mobile ad hoc networks:a survey <s> ANALYSES AND DISCUSSION <s> A Mobile Ad Hoc Network (MANET) is a self-organizing, infrastructureless, multi-hop network. The wireless and distributed nature of MANETs poses a great challenge to system security designers. Key management is crucial part of security, this issue is even bigger in MANETs. The distribution of encryption keys in an authenticated manner is a difficult task. Because of dynamic nature of MANETs, when a node leaves or joins it need to generate new session key to maintain forward and backward secrecy. In this paper we divide the network into clusters. Cluster head will maintain the group key, it will also update the group key whenever there is a change in the membership And also we provide authentication between communicating nodes both in inter and intra cluster. This paper proposes a new cluster based tree (CBT) algorithm for secure multicast key distribution, in which source node uses Destination Sequenced Distance Vector(DSDV) routing protocol to collects its 1 hop neighbors to form cluster. The simulations are performed using Network simulator, Simulation results shows the demonstration of CBT using DSDV in terms of end to end delay, key delivery ratio and packet drop rate, fault tolerance, communication cost under varying network conditions. <s> BIB001 </s> Security challenges in mobile ad hoc networks:a survey <s> ANALYSES AND DISCUSSION <s> The secrecy throughput of mobile ad hoc networks (MANETs) with malicious nodes is investigated. The MANET consists of n legitimate mobile nodes and m malicious nodes. Transmissions between legitimate nodes are subject to a delay constraint D. A model under passive attack is first studied, in which the malicious nodes are assumed to be eavesdroppers that only listen to transmission without actively injecting signals. An information-theoretic approach for security is applied to achieve secure communication among legitimate nodes in MANETs with transmissions being kept perfectly secure from eavesdroppers. A critical threshold on the number of malicious nodes (m) is identified such that when m = o(√{nD}), i.e., limn→∞m/√{nD} = 0, the optimal secrecy throughput equals that of MANETs without malicious nodes, i.e., the impact of the presence of malicious nodes on the network throughput is negligible; and when m = Ω(√{nD}poly(n)), i.e., limn→∞m/(√{nD}poly(n)) ≥ c for a positive constant c, the optimal secrecy throughput is limited by the number of malicious nodes. A model under active attack is further studied, in which the malicious nodes actively attack the network by transmitting modified packets to the destination nodes. It is shown that to guarantee the same throughput as the model under passive attack, the model under active attack needs to satisfy more stringent condition on the number of malicious nodes. <s> BIB002 </s> Security challenges in mobile ad hoc networks:a survey <s> ANALYSES AND DISCUSSION <s> Ad hoc Network is a self organized autonomous network that consists of mobile nodes which communicate with each other over wireless links .Wireless ad hoc networks are not well protected against the attack of malicious nodes due to security vulnerabilities in the routing protocols. One of the common attacks in MANETs is the Black hole Attack, in which malicious node falsely claiming it to have the fresh and shortest path to the destination and then drops all the receiving packets. If this malicious node work together as a group then the damage will be very serious. This type of attack is known as Cooperative Black Hole attack. We proposed a mechanism to mitigate single black hole attack as well as cooperative black hole attack to discover a safe route to the destination by avoiding attacks. In this paper we proposed an approach for better analysis and improve security of AODV, which is one of the popular routing protocols for MANET. Our scheme is based on AODV protocol which is improved by deploying Advanced DRI table with additional check bit. The Simulation on NS2 is carried out and the proposed scheme has produced results that demonstrate the effectiveness of the mechanism in detection and elimination of the attack and maximizing network performance by reducing the packet dropping ratio in network. <s> BIB003 </s> Security challenges in mobile ad hoc networks:a survey <s> ANALYSES AND DISCUSSION <s> The migration from wired network to wireless network has been a global trend in the past few decades. The mobility and scalability brought by wireless network made it possible in many applications. Among all the contemporary wireless networks, Mobile Ad hoc Network (MANET) is one of the most important and unique applications. MANET is a collection of autonomous nodes or terminals which communicate with each other by forming a multi-hop radio network and maintaining connectivity in a decentralized manner. Due to the nature of unreliable wireless medium data transfer is a major problem in MANET and it lacks security and reliability of data. A Key management is vital part of security. This issue is even bigger in wireless network compared to wired network. The distribution of keys in an authenticated manner is a difficult task in MANET and when a member leaves or joins it need to generate a new key to maintain forward and backward secrecy. In this paper, we propose a Clustering based Group Key Management scheme (CGK) that is a simple, efficient and scalable Group Key management for MANETs and different other schemes are classified. Group members compute the group key in a distributed manner. <s> BIB004
Previous sections discussed incorporating security challenge with other challenges. This section presents an analytics and classification on previous issues. In order to analyse attacks and their behaviour, an analyses in each attack is presented in Table 1 . For each attack five important parameters has been discussed. These parameters are as follows:  Violated Service: Each attack breaks a security service. We presented the most important defeated service in this column.  The Proposed Solutions: Some of the most effective approaches to detect and eliminate malicious nodes.  MANET features which lead to this attack: Each malicious node uses a feature or features of MANET to break the security.  Attack Type: Lots of researches classified attacks in two mainly class that are as follows: Active attack, Passive attack. In passive attacks, malicious node listens to transmissions without any active injection or effect on network BIB002 . While, in active attacks malicious node inject information.  Attack Goal: The most important goal of each attack. Referring to Table 1 , it's understandable that lots of attacks are against availability security service. In availability aimed attacks, malicious nodes inject fault routing information or destroy nodes routing tables in order to defeat availability. Malicious nodes break availability service using passive or active attacks and in different types of attacks. For instance, in worm hole attack malicious node break availability by consuming resources, while in DOS attack, it drops all received packets in order to breach availability. As another point in Table 1 , it is clear that among defeating approaches, sniffing is one of the widely used approach in order to secure MANET. Generally in sniffing approaches, sniffer put itself in promiscuous mode and capture the network traffic. In this way, it can detect misbehaviour of malicious nodes. As another effective defeating approach, we can name encryption and route information. In encryption approaches, packet generator uses a key in order to encrypt packets to avoid malicious nodes from reading or modifying data packets. Whoever, it can discard encrypted packets. Therefore, encryption can't guarantee the availability service. Routing information defeating approach uses route tables or additional control packets to detect malicious nodes. Refers to Table 1 this approach mostly used for active attacks. The reason is that in active attacks, malicious node injects packets or uses other nodes tables to break into the network. Refer to Table 1 , "Distributed network" is the most challengeable feature of MANET. Referring to this feature, in MANET all nodes cooperatively work with each other to configure and maintain network since there is no central control unit. Due to this feature, MANET faced lots of attacks since malicious nodes can pretend themselves as ordinal nodes and take part in network configurations and routing discoveries. There are six different defeating mechanisms as presented in Table 1 . By using defeating approaches all attacks detected and malicious nodes eliminated from the network. Therefore we present analyses in defeating approaches in Table 2 . Each proposed solution uses some of network resources in order to detect an attack. Table 2 presents' five important parameters for security approaches and discussed the effect of each solution in each parameter. In order to analyses the energy consumption of proposed solutions; Table 1 : Analytics on MANET Attacks. Table 2 presents energy consumption of each approach in compare with other approaches. The word 'low' in "Energy consumption" column means referred approach consumes lower energy than other approaches. Other words used in this column are "Normal" and "High" which mean normal and higher energy consumption in compare with other approaches. "Accuracy" column refers to ability of defeating approach to detect single or cooperative malicious nodes. In the case of cooperative attacks, malicious nodes work with each other in order to cover their tracks. Routing information approach generates controller packets and uses them in order to detect malicious nodes. In addition, in some cases nodes must keep additional routing table like DRI table BIB003 . As mentioned, in sniffing approach each node must put itself in promiscuous mode and capture all packets transmitted in its range. This feature of sniffing approach wastes nodes energy. Also it increases process and memory overhead. In the case of cooperative malicious nodes, sniffing is useless as malicious nodes may work with each other to proof them-selves as trustable nodes. Redundancy and dynamic frequency approaches can't detect the malicious nodes. These approaches can only avoid network from an attack. In the case of misbehaviour, these approaches can detect attack, while they are unable to detect the malicious nodes or eliminate them from whole network. In routing information defeating approach, control packets transmission increase processing time of the security approach. In encryption and authentication, key distribution is an important challenge, because of lack of central infrastructure or key distribution centre. Therefore, each malicious node can pretend itself as a trustable node and take part in key distribution. In redundancy defeating approach, destination must buffer packets in order to get packets in sequence or to compare them with each other. In addition, it increases traffic overhead by sending duplicated packets. That cause increasing in congestion, packet lost and energy consumption. In addition of five important parameters, Table 2 presents some limitations on each defeating approaches which are as follows:  Processing time: This limitation refers to time needed for each approach to find malicious nodes and secure network against all malicious nodes. High processing time decreases MANET flexibility. The reason is that, during processing time of security approach routes must be constant and any change in route needs rerouting path, that increases time consumed for security approach. In some cases defeating approach is unable to detect cooperative malicious nodes or it can detect with very high processing time. The reason of increasing processing time is that, the approaches can detect malicious nodes just one by one in different executions.  Key distribution: Due to lack of central management in MANET, key distribution is challengeable in this network. Without key distribution centre, malicious nodes can get access to keys by capturing packets or by Man-In-The-Middle attack. One of the highly used approaches to overcome this challenge is using clusters in order to distribute keys in the network BIB001 BIB004 .  Packet overhead: This limitation refers to additional packets generated by the source node to detect and eliminate malicious nodes. Due to wireless media, high packet overhead in a defeating approach increases congestion, collision and packet lost probability in the network. In addition, it increases the processing time and energy consumption in the nodes.  Frequency knowledge: Referring to this limitation, each node must know the frequency of transmissions. In MANET all nodes are free to join or leave the network, so being aware of all frequencies is highly challengeable. Referring to our discussions and analyses it's understandable that routing information and encryption approaches are the most effective approaches for securing MANET. According to the application one of these two approaches is suggested. In cluster-based MANET using encryption is more effective and in MANET without any cluster using routing information is suggested.