Security Issues In Mobile Ad Hoc Networks Computer Science Essay

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Mobile ad hoc networks are one of the fastest growing areas of research .MANET stands for Mobile Ad Hoc Network. Mobile ad hoc network is an autonomous system of mobile nodes connected by wireless links. Each node operates not only as an end system, but also as a router to forward packets. The nodes are free to move about and organize themselves into a network. These nodes change position frequently. They are an attractive technology for many applications, such as rescue and tactical operations, due to the flexibility provided by their dynamic infrastructure. Because MANETS are mobile, they use wireless connections to connect to various networks. To accommodate the changing topology special routing algorithms are needed. However, this flexibility comes at a price and introduces new security threats. There is no single protocol that fits all networks perfectly. The protocols have to be chosen according to network characteristics, such as density, size and the mobility of the nodes. In MANET, the nodes also function as routers that discover and maintain routes to other nodes in the network. Establishing an optimal and efficient route between the communicating parties is the primary concern of the routing protocols of MANET. Any attack in routing phase may disrupt the overall communication and the entire network can be paralyzed. Thus, security in network layer plays an important role in the security of the whole network. A number of attacks in MANETs have been identified and studied in security research. In this paper we attempt to analyze threats faced by the ad hoc network environment and provide a classification of the various security mechanisms.

Keywords

Ad hoc networks, security attacks, secure routing.

1. INTRODUCTION

Ad-hoc networks are a new paradigm of wireless communication for mobile hosts. There is no fixed infrastructure such as base stations for mobile switching. Nodes within each other's radio range communicate directly via wireless links while those which are far apart rely on other nodes to relay messages. Node mobility causes frequent changes in topology. The wireless nature of communication and lack of any security infrastructure raises several security problems [1] [2]. Basically, routing protocols can be broadly classified into two types as (a) Table Driven Protocols or Proactive Protocols and (b) On-Demand Protocols or Reactive Protocols.

Table Driven or Proactive Protocols: In Table Driven routing protocols each node maintains one or more tables containing routing information to every other node in the network. All nodes keep on updating these tables to maintain latest view of the network. Some of the existing table driven or proactive protocols are: DSDV [6], [19], DBF [7], GSR [24], WRP [23] and ZRP [28], [13].

On Demand or Reactive Protocols: In these protocols, routes are created as and when required. When a transmission occurs from source to destination, it invokes the route discovery procedure. The route remains valid till destination is achieved or until the route is no longer needed. Some of the existing on demand routing protocols are: DSR [8], [9], AODV [4], [5] and TORA [26], [27].

Any routing protocol must encapsulate an essential set of security mechanisms. These are mechanisms that help prevent, detect, and respond to security attacks. There are five major security goals that need to be addressed in order to maintain a reliable and secure ad-hoc network environment. They are mainly:

Confidentiality: Protection of any information from being exposed to unintended entities.

Availability: Services should be available whenever required. There should be an assurance of survivability despite a Denial of Service (DOS) attack.

Authentication: Assurance that an entity of concern or the origin of a communication is what it claims to be or from.

Integrity: Message being transmitted is never altered.

Non-repudiation: Ensures that sending and receiving parties can never deny ever sending or receiving the message.

All the above security mechanisms must be implemented in any ad-hoc networks so as to ensure the security of the transmissions along that network. Contemporary Routing Protocols for ad-hoc networks cope well with dynamically changing topology but are not designed to accommodate defense against malicious attackers. No single standard protocol captures the common security threats and provides the guidelines to a secure routing scheme. Routers exchange network topology, informally, in order to establish routes between nodes and other networks which act as another potential target for malicious attackers.

Most of the security measures surrounding ad-hoc networks in general and their routing solutions are, as yet, incomplete and mostly inefficient. Hence we propose a security framework that is integrated into the routing protocols in the design phase itself as a viable solution to satiate the security needs of the ad hoc networks.

2. VULNERABILITIES OF MANETs

2.1. Wireless Links: First of all, the use of wireless links makes the network susceptible to attacks such as eavesdropping and active interference. Unlike wired networks, attackers do not need physical access to network to carry out these attacks.

2.2 Dynamic Topology: MANET nodes can leave and join the network, and move independently. As a result the network topology can change frequently. It is hard to differentiate normal behavior of the network from anomaly/malicious behavior in this dynamic environment.

2.3 Cooperativeness: Routing algorithms for MANETs usually assume that nodes are cooperative and non malicious. As a result, a malicious attacker can easily become an important routing agent and disrupt network operations by disobeying the protocol specifications.

2.4 Lack of a Clear Line of Defense: MANETs do not have a clear line of defense; attacks can come from all directions [27]. The boundary that separates the inside network from the outside world is not very clear on MANETs. For example, there is no well defined place where we can deploy our traffic monitoring, and access control mechanisms.

2.5 Limited Resources: Resource constraints are a further vulnerability. There can be a variety of devices on MANETs, ranging from laptops to handheld devices such as PDAs and mobile phones. These will generally have different computing and storage capacities that can be the focus of new attacks.

3. TYPES OF ATTACKS FACED BY

ROUTING PROTOCOLS

The attacks prevalent on ad-hoc routing protocols can be broadly classified into passive and active attacks.

A Passive Attack does not disrupt the operation of the protocol, but tries to discover valuable information by listening to traffic. Passive attacks basically involve obtaining vital routing information by sniffing about the network. Such attacks are usually difficult to detect and hence, defending against such attacks is complicated. Even if it is not possible to identify the exact location of a node, one may be able to discover information about the network topology, using these attacks.

An Active Attack, however, injects arbitrary packets and tries to disrupt the operation of the protocol in order to limit availability, gain authentication, or attract packets destined to other nodes. The goal is basically to attract all packets to the attacker for analysis or to disable the network. Such attacks can be detected and the nodes can be identified.

Passive Attacks

Snooping, eavesdropping, traffic analysis, monitoring

Active Attacks

Wormhole, black hole, gray hole, information disclosure, resource consumption, routing attacks

The attacks can also be classified into two categories, namely external attacks and internal attacks. External attacks are those, launched by the adversaries that do not belong to the network. Such attacks can be prevented by using powerful encryption techniques and firewalls. Internal attacks are launched by the compromised nodes within the network. This node tries to collect security information and can access the protected rights of the network. Since the compromised node is an authorized one in the network, it is very difficult to identify the internal attacks.

3.1 Attacks based on modification

3.1.1. This is the simplest way for a malicious node to disturb the operations of an ad-hoc network. The only task the malicious node needs to perform, is to announce better routes (to reach other nodes or just a specific one) than the ones presently existing. This kind of attack is based on the modification of the metric value for a route or by altering control message fields. There are 3 ways in which this can be achieved:

3.1.2. Redirection by Changing the Route Sequence Number When deciding upon the best / optimum path to take through a network, the node always relies on a metric of values, such as hop count delays etc. The smaller that value, the more optimum the path. Hence, a simple way to attack a network is to change this value with a smaller number than the last "better" value.

3.1.3. Redirection by Altering the Hop Count This attack is more specific to the AODV protocol wherein the optimum path is chosen by the hop count metric. A malicious node can disturb the network by announcing the smallest hop count value to reach the compromised node. In general, an attacker would use a value zero to ensure to the smallest hop count.

3.1.4. Denial of Service by Altering Routing Information Consider, in a bus topology, a scenario wherein a node A wants to communicate with node E. At node A the routing path in the header would be A-B-C-D-E. If B is a compromised node, it can alter this routing detail to A-B-C-E. But since there exists no direct route from C to E, C will drop the packet. Thus, A will never be able to access any service / information from E.

Impersonation Attacks

More generally known as 'spoofing', since the malicious node hides its' IP and or MAC address and uses that of another node. Since current ad-hoc routing protocols like AODV and DSR do not authenticate source IP address, a malicious node can launch many attacks by using spoofing. Take for example a situation where in an attacker creates loops in the network to isolate a node from the remainder of the network. To do this, the attacker needs to spoof the IP address of the node he wants to isolate from the network and then announce new route to the others nodes. By doing this, he can easily modify the network topology as he wants.

Attack by Fabrication of Information

There are basically 3 sub categories for fabrication attacks. In any of the 3 cases, detection is very difficult.

3.4. Falsification of Rote Error Messages This attack is very prominent in AODV and DSR, because these two protocols use path maintenance to recover the optimum path when nodes move. 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. Thus, the malicious node can isolate any node quite easily.

Corrupting Routing State - Route Cache Poisoning: A passive attack that can occur especially in DSR due to the promiscuous mode of updating routing tables which is employed. This occurs 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.

Routing table overflow attack: Consider ad-hoc network is using a "proactive" protocol i.e. an algorithm which tries to find routing information even before it is needed. This creates vulnerabilities since the attacker can attempt to create routes to non-existent nodes. If enough routes are created, new routes can no longer be added due to an overwhelming pressure on the protocol.

After considering all the above plausible attacks we can draw a conclusion that we need to have a routing protocol that establishes routes without being susceptible to false information from any malicious node.

3.4. Insider Attacks

Dr. Peng Ning and Kun Sun provide a comprehensive analysis of the insider attacks against MANET routing protocols in [24]. They identified the misuse goals an inside attacker may desire to achieve and further classify the misuses of the AODV protocol into two categories namely atomic misuses and compound misuses.

3.4.1. Misuse goals

Route Disruption (RD): Breaking down an existing route or preventing a new route from being established.

Route Invasion (RI): Inside attacker adds itself between two endpoints of a communication channel.

Node Isolation (NI): Preventing a node from communicating with any other node.

Resource Consumption (RC): Consuming network bandwidth or storage space.

3.4. Rushing Attacks

[22] Presents the rushing attack, a new attack that results in denial-of-service when used against all previous on-demand ad hoc network routing protocols. For example, DSR, AODV, and secure protocols based on them, such as Ariadne [11], ARAN [10], and SAODV [3], are unable to discover routes longer than two hops when subject to this attack.

In general terms, an attacker that can forward ROUTE REQUESTs more quickly than legitimate nodes can do so, can increase the probability that routes that include the attacker will be discovered rather than other valid routes. This attack is also particularly damaging because it can be performed by a relatively weak attacker.

CLASSIFICATION OF TECHNIQUES

USED TO SECURE AD-HOC NETWORKS

In order to provide solutions to the security issues involved in ad-hoc networks, we must elaborate on the two of the most commonly used approaches in use today:

4.1. Prevention

Prevention dictates solutions that are designed such that malicious nodes are thwarted from actively initiating attacks. Prevention mechanisms require encryption techniques to provide authentication, confidentiality, integrity and non-repudiation of routing information. Among the existing preventive approaches, some proposals use symmetric algorithms, some use asymmetric algorithms, while the others use one-way hashing, each having different trade-offs and goals.

4.2. Detection and Reaction

Prevention mechanisms, by themselves cannot ensure complete cooperation among nodes in the network. Detection on the other hand specifics solutions that attempt to identify clues of any malicious activity in the network and take punitive actions against such nodes. A node may misbehave by agreeing to forward packets and then failing to do so, because it is overloaded, selfish or malicious. An overloaded node lacks the CPU cycles, buffer space or available network bandwidth to forward packets. A selfish node [18] is unwilling to spend battery life, CPU cycles or available network bandwidth to forward packets not of direct interest to it, even though it expects others to forward packets on its behalf. A malicious node [14] launches a denial of service attack by dropping packets. All protocols defined in this category detect and react to such misbehavior.

Using this as the basis the following are the broad classifications:

4.2.1. Prevention using asymmetric cryptography using symmetric cryptography using one-way hash chains

4.2.2. Detection and Reaction

4.2.1.1. Prevention using asymmetric cryptography

Asymmetric cryptographic techniques specify the underlined basic methodology of operation for protocols under this category. A secure wired networks or a similar network is required to distribute public keys or digital certificates in the ad-hoc network. Mathematically speaking a network with n nodes would require n public keys stored in the network. SAODV [3] (an extension to AODV routing protocol) and ARAN [10] are two of the protocols defined in this category.

4.2.1.2. Prevention using symmetric cryptography

Symmetric cryptographic techniques are used to avoid attacks on routing protocols in this section. We assume that symmetric keys are pre-negotiated via a secured wired connection. Taking a mathematical approach we see that a network with 'n' nodes would require n * (n + 1) / 2 pair wise keys stored in the network. SAR [11] and SRP [12] [16] [15] are the two protocols that belong to this category.

Prevention using one-way hash chains

This category defines a one-way hash chain to prevent attacks on routing protocols. They protect modification of routing information such as metric, sequence number and source route. SEAD [13] and Ariadne [11] fall into this category.

2.0 Detection and Reaction

Detection on the other hand specifics solutions that attempt to identify clues of any malicious activity in the network and take punitive actions against such nodes. [12] All protocols in this category are designed such that they are able to detect malicious activates and react to the threat as needed. Byzantine [8], CONFIDANT [12], DSR, CORE [9] and a protocol that uses Watchdog [10] and Path rater are the few protocols specified in this section.

DESCRIPTION OF THE

CLASSIFICATION

Prevention using Asymmetri Cryptography Secure Ad-hoc On-demand Distance Vector

Routing Protocol (SAODV) [3]

SAODV adds security to the famous AODV protocol. Its basic functionality lies in securing the ADOV protocol by authenticating the non-mutable fields of the routing message using digital signatures. It also provides an end-to-end authentication and node-to-node verification of these messages. The underlined process is relatively simple. The source node digitally signs the route request packet (RREQ) and broadcasts it to its neighbors. When an intermediate node receives a RREQ message, it first verifies the signature before creating or updating a reverse route to its predecessor. It then stores or updates the route only if the signature is verified. A similar procedure is followed for the route reply packet (RREP). As an optimization, intermediate nodes can reply with RREP messages, if they have a "fresh enough" route to the destination. Since the intermediate node will have to digitally sign the RREP message as if it came from the destination, it uses the double signature extension described in this protocol.

The only mutable field in SAODV messages is the hop-count value. In order to prevent wormhole attacks this protocol computes a hash of the hop count field.

5.1.1. Prevention using Asymmetric Cryptography: Authenticated Routing for Ad-hoc Networks (ARAN) [10]

ARAN is an on-demand routing protocol that makes use of cryptographic certificates to offer routing security. Its main usage is seen in managed-open environments. It consists of a preliminary certification process followed by a route instantiation process that guarantees end-to-end authentication. This protocol requires the use of a trusted certificate server T, whose public key is known to all the nodes in the network. End-to-end authentication is achieved by the source by having it verify that the intended destination was reached. In this process, the source trusts the destination to choose the return path. The source begins route instantiation by broadcasting a Route Discovery Packet (RDP) that is digitally signed by the source. Following this, every intermediate node verifies the integrity of the packet received by verifying the signature. The first intermediate node appends its own signature encapsulated over the signed packet that it received from the source. All subsequent intermediate nodes remove the signature of their predecessors, verify it and then append their signature to the packet. The RDP packet contains a nonce and timestamp to prevent replay attacks and to detect looping. Similarly, each node along the reverse path (destination to source) signs the REP and appends its own certificate before forwarding the REP to the next hop.

Although hashing the hop-count value prevents malicious nodes in advertising shorter routes in SAODV, it does not prevent nodes from advertising longer routes. Nodes can forward routing messages by applying the hash function multiple times making the route appear longer than it is.

One of the main issues with the ARAN protocol is the requirement of a certificate server, which means that the integrity of that server is vital. This is by however, only a design issue and as it is intended for securing communication over a managed-open environment it shouldn't be considered a big issue. Both the protocols in this category do not address wormhole attacks. While ARAN provides both node-to-node and end-to-end authentication, it does not have any significant gain over SAODV (that uses only end-to-end authentication) in terms of security.

5.1.2.Prevention using Symmetri Cryptography: Security-Aware ad hoc Routing (SAR) [11]

SAR is an attempt to use traditional shared symmetric key encryption in order to provide a higher level of security in ad-hoc networks. SAR can basically extend any of the current ad-hoc routing protocols without any major issues.

The SAR protocol makes use of trust levels (security attributes assigned to nodes) to make informed, secure routing decision. Although current routing protocols discover the shortest path between two nodes, SAR can discover a path with desired security attributes (E.g. a path through nodes with a particular shared key). The different trust levels are implemented using shared symmetric keys. In order for a node to forward or receive a packet it first has to decrypt it and therefore it needs the required key. Every node sending a packet decides what trust level to use for the transfer and thereby decides the trust level required by every node that will forward the packet to its final destination.

SAR is indeed secure in the way that it does ensure that only nodes having the required trust level will read and reroute the packets being sent. Unfortunately, SAR still leaves a lot of security issues uncovered and still open for attacks such as:

Nothing is done to prevent intervention of a possibly malicious node from being used for routing, as long as they have the required key

If a malicious node somehow retrieves the required key the protocol has no further security measure to prevent against the attacker from bringing the entire network to a standstill.

There is excessive encryption and decryption required at each hop. Since we are dealing with mobile environments the extra processing leading to increased power consumption can be a problem.

SAR is intended for the managed-open environment as it requires some sort of key distribution system in order to distribute the trust level keys to the correct devices.

5.1.3. Prevention using Symmetric Cryptography: Secure Routing Protocol (SRP). [12]

Secure Routing Protocol, SRP, is another protocol extension that can be applied to any of the most commonly used protocols today. The basic idea of SRP is to set up a security association (SA) between the source and the destination node.[16] An SA is a secret-key scheme used to preserve integrity in the routing information. The SA is usually set up by negotiating a shared key based on the other party's public key, and after that the key can be used to encrypt and decrypt the messages. The routing path is always sent along with the packets, unencrypted though (since none of the intermediate nodes have knowledge of the shared key).

The above features are achieved with low computational cost and bit overhead. In addition, the protocol is practically immune to IP spoofing and implements partial caching without compromising security in the network. More than one RREQ packet reaches the destination through different routes. The destination calculates a MAC covering the RREP contents and then returns the packet to the source over the reverse route accumulated in the respective RREQ packet. The destination responds to one or more route request packets to provide the source with an as diverse topology picture as possible.

5.2 Prevention using One-Way Hash Chains: SEAD [13]

The main objective of the protocol is to avoid any malicious node from falsely advertising a better route or tamper the sequence number in the packet that it received from the source. They basically implement features to protect modification of routing information such as metric, sequence number and source route.

SEAD uses a one-way hash chains for authenticating the metric and the sequence number. Each node creates a one-way hash chain and uses the elements in groups of 'm' (given m as the diameter of the network) for each sequence number. Each node uses a specific single next element from its hash chain in each routing update that it sends about itself (metric 0). The upper bound of the network is denoted by (m-1).

An entry is authenticated by using the sequence number in that entry to determine a contiguous group of m elements from that destination node's hash chain, one element of which must be used to authenticate that routing update. The one-way nature of hash chains prevents any node from advertising a route with a greater sequence number than the source's sequence number.

To avoid routing loops the source of each routing update message must be authenticated. This protocol requires pair wise shared secret keys or broadcast authentication such as TESLA, HORS or TIK to authenticate neighbors.

5.2.1. Prevention using One-Way Hash Chains: Ariadne [11]

The ARIADNE protocol relies only on highly efficient symmetric cryptography. The protocol primarily discusses the use of a broadcast authentication protocol namely TESLA, because of its efficiency and requires low synchronization time rather than the high key setup overhead of using pair-wise shared keys. Other authentication protocols such as BiBa are / can also be used for this purpose.

This proposal is an on-demand routing protocol. The design of Ariadne can be viewed as a 3 step process:

Authentication of RREQ by target:

To convince the target of the legitimacy of each field in a RREQ, the initiator includes a MAC computed with a shared key over a timestamp.

Mechanisms for authenticating data in RREQ and RREP:

The scheme allows the initiator to authenticate each individual node in the node list of the RREP. The target can authenticate each node in the node list of the RREQ, so that it will return RREP only along paths that contain legitimate nodes. 3 alternative techniques are available to achieve the node list authentication. These are the TESLA protocol, Digital Signatures and standard MAC. Out of these TESLA is the most widely used due to its inexpensive requirements?

The working of TESLA is very straightforward. Whenever an intermediate node receives a RREQ message, it appends a MAC into the message, the key for which is released in a future time set by the source. The target buffers the RREP until intermediates nodes can release the corresponding TESLA keys. The TESLA security condition is verified at the target, and the target includes a MAC in the reply to certify that the security condition was met.

Per-hop hashing technique

A one-way hash function is used to avoid a node from being removed from the node list in the RREQ message. The source initializes the hash chain to a MAC with a key shared between the source and target. When an intermediate node receives the request, it appends its identifier to the hash chain and rehashes it. The target verifies each hop of the path by comparing the received hash and the computed hash of the MAC. To change or remove a previous hop, the attacker must be able to invert the one-way hash function, which has been proved computationally infeasible

The failing of this protocol, similar to that seen in the SAODV, is that although hashing the hop-count value prevents malicious nodes in advertising shorter routes, it does not prevent nodes from advertising longer routes. Also it can be seen that since this idea is based on a routing protocol with periodic updates, it has a high overhead. Thus it is not suitable to be deployed in resource-constrained mobile ad hoc networks. Since Ariadne assumes clock synchronization between participating nodes, thus there exists a high complexity in obtaining such precise clock synchronization.

Prevention using Asymmetric

Cryptography

Secure Link State Routing Protocol (SLSP) - The main operational requirement of SLSP is the existence of an asymmetric key pair for every network interface of a node. Participating nodes are identified by the IP addresses of their interfaces. The specific mechanism for the certification of public keys is not addressed by the protocol, as previously proposed key management solutions are assumed to be in operation. Furthermore, SLSP limits its scope to secure only the process of topology discovery; parties that participate in it and decide to misbehave during data transmission are not detected or penalized. SLSP can be logically divided into three components: public key distribution, neighbor discovery, and link state updates. To avoid the need for a central key management server, nodes broadcast their public key certificates within their zone using signed public key distribution (PKD) packets. Receiving nodes are then able to verify subsequent SLSP packets from the source node. Link state information is also broadcast periodically using the Neighbor Lookup Protocol (NLP), an internal part of SLSP. NLP hello messages are also signed and include the sending node's MAC address and IP address for the current network interface. This allows a node's neighbors to maintain a mapping of MAC and IP addresses. By generating notification messages, NLP can inform SLSP when suspicious discrepancies are observed, such as two different IP addresses having the same MAC, or a node trying to claim the MAC of the current node, etc. Such notifications are used to inform SLSP to discard the suspicious packets. Link state update (LSU) packets are identified by the IP address of the initiating node and include a 32-bit sequence number for providing updates [37]. The hop count included in the packet is authenticated using hash chains, as we have previously seen in the SAODV and other protocols. The authentication of the hash chain itself is performed through the anchor that is included in the digitally signed part of an LSU message. Nodes that receive an LSU verify the attached signature using a public key they have previously cached in the pubic key distribution phase of the protocol. The hops traversed field of the LSU is set to hashed hops traversed, the TTL is decremented, and finally the packet is broadcast again. To protect against denial of service attacks, SLSP nodes maintain a priority ranking of their neighboring nodes based on the rate of control traffic they have observed. High priority is given to nodes that generate LSU packets with the lowest rate. This functionality enables the neighbors of malicious nodes that flood control packets at very high rates to limit the effectiveness of the attack. SLSP provides a proactive secure link state routing solution for ad hoc networks. By securing the neighbor discovery process and using NLP as a method to detect discrepancies between IP and MAC addresses, SLSP offers protection against individual malicious nodes. As mentioned by the authors, SLSP is vulnerable to colluding attackers that fabricate non-existing links between themselves and flood this information to their neighboring nodes.

5.3. Detection and Reaction:

For Byzantine Failures [8]

[8] Describes an on demand routing protocol that incorporates detection mechanism into its algorithm and attempts to survive under an adversarial network failures which include modification/fabrication of packets, dropping packets, among others, caused by selfish or malicious nodes, collectively known as Byzantine failures.

A general working schema follows:

Each node maintains reliability metrics based on the past history in the link weight management phase. During the route discovery phase, faulty paths (higher weights) are avoided by choosing alternate available paths. The Byzantine fault detection algorithm presented is an 'adaptive probing technique' that detects a malicious link after log n faults have occurred, where n is the length of the path. In the absence of malicious nodes, the algorithm has very little overheads for the authentication of RREQ. However is there does exist some malicious links, they will trigger the fault detection technique, which involves overheads in terms of the encryption needed, and can detect the faulty link after log n faults.

Performance

Parameters

Type

ARAN

Reactive

ARIADNE

Reactive

SAODV

Reactive

SAR

Reactive

SEAD

Proactive

SLSP

Proactive

SRP

Reactive

Encryption

Algorithm

MANET

Protocol

Asymmetric

AODV/DSR

Symmetric

DSR

Asymmetric

AODV

Symmetric/

Asymmetric

AODV

Symmetric

DSDV

Asymmetric

ZHLS

Symmetric

DSR/ZRP

Synchronization

No

Yes

No

No

Yes

No

No

Central trust

authority

CA required

KDC required

CA required

CA/KDC

required

CA

required

CA/KDC

required

CA required

Authentication

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Confidentiality

Yes

No

No

Yes

No

No

No

Integrity

Yes

Yes

Yes

Yes

No

No

Yes

Nonrepudication

Yes

No

Yes

Yes

No

No

Yes

Antispoofing

Yes

Yes

Yes

Yes

No

Yes

Yes

DoS attacks

No

Yes

No

No

Yes

Yes

yes

Anmymity

No

No

No

No

No

Yes

Yes

Detection and Reaction:

CORE [9] suggests a generic mechanism to enforce node cooperation based on a collaborative monitoring technique. It can be integrated with any network and application layer function that can include packet forwarding, route discovery, network management, location management, among others. It proposes a reputation based detection framework to tackle selfish behavior of nodes. All the services available from the network, such as forwarding, are treated as functions and reputation is calculated for each such function.

CORE defines three types of reputations, subjective, indirect and functional. Each node maintains a watchdog component and a reputation table for every function with entries for other nodes in the network. Subjective reputation is based on the observed behavior of the neighboring nodes. Indirect reputation is calculated from information from other nodes. Functional reputation is a global value obtained by assigning different weights to different functions. Based on these factors, a persistent non-cooperative behavior by any node will lead to its exclusion from the network.

Detection and Reaction

Confidant [12]Confidant attempts to detect and isolate misbehaving nodes (or nodes with grudges) in an ad-hoc network, thus making it unattractive to deny cooperation and participation. Trust relationships and routing decisions are made based on experienced, observed, or reported routing and forwarding behavior of other nodes. The protocol has been described using Dynamic Source Routing (DSR) in the network layer.

Each node consists of 4 basic components:

The Monitor: watches its neighbors for any malicious behavior. If such behavior is detected, the reputation system is invoked.

The Reputation System: manages a table consisting of entries for each node and its ratings. Ratings are changed that assigns different weights to the type of behavior detected.according to a rate function

The Trust Manager: responsible for calculating trust levels of nodes and dealing with all incoming and outgoing alarm messages.

The Path Manager: manages all path information, i.e. adds, deletes or updates paths according to the feedback it receives from the reputation system

Detection and Reaction: Protocol Using Watchdog and Pathrater [10]

This proposal describes two techniques that improve throughput of an ad-hoc network in the presence of nodes that agree to forward packets but fail to do so do to some malicious activity. To mitigate this problem, the protocol proposes categorizing nodes based on their dynamically measured behavior. A watchdog is used to identify all misbehaving nodes while the part rater avoids routing packets through these nodes. These act as upgrades / plug-ins and hence can be applied to existing protocols with minimal changes to the underlying routing algorithm.

Approaches to thwart selfishness:

[13] addresses the problem of service availability in mobile ad-hoc WANs. A secure mechanism is studied to stimulate end users to keep their devices turned on, to refrain from overloading the network, and to thwart tampering aimed at converting the device into a ``selfish`` one. The mechanism is based on the application of a tamper resistant security module in each device and cryptographic protection of messages.

ID Techniques

WATCHDOG/

Pathrater

CONFIDANT

CORE

Ex Watchdag

OCEAN

Cooperative IDS

Obervation

Self to neighbor

yes

yes

yes

yes

yes

yes

neighbor to neighbor

no

yes

no

no

yes

yes

Misbehavior Detection

Malicious-routing

no

yes

no

yes

No

yes

Malicious-packet

forwarding

yes

yes

no

yes

No

yes

Selfish-routing

no

yes

yes

No

yes

yes

Selfish-packet forwarding

yes

yes

yes

Yes

yes

yes

Punishment

no

yes

yes

no

yes

n/a

Avoid misbehaving in rout finding

yes

yes

no

yes

yes

n/a

Architecture

Distributed and coopertive

Stand alone

Hierachical

Position aided routing

protocols

Position aided routing protocols can offer a significant performance increase over traditional ad hoc routing protocols. These routing protocols use geographical information to make forwarding decisions, resulting in a significant reduction in the number of routing messages. [20] Presents methods of protecting position information in MANET routing protocols, and ways to use the position information to enhance performance and security of MANET routing protocols. "Secure Position Aided Ad hoc Routing" (SPAAR), [20] is a routing protocol designed to use protected position information to improve security, efficiency, and performance in MANET routing.

SPAAR[20] uses position information to improve performance and security, while keeping position information protected from unauthorized nodes. For MANET routing protocols to achieve a high level of security, we allow nodes to only accept routing messages from one-hop neighbors. In SPAAR, with the aid of position information, a node may verify its one-hop neighbors before including them in the routing protocol. SPAAR requires that each device can determine its own location. GPS receivers are relatively inexpensive and lightweight, so it is reasonable to assume that all devices in our network are equipped with one.

7. Conclusions

Mobile ad-hoc networks have properties that increase their vulnerability to attacks. Unreliable wireless links are vulnerable to jamming and by their inherent broadcast nature facilitate eavesdropping. Constraints in bandwidth, computing power, and battery power in mobile devices can lead to application-specific trade-offs between security and resource consumption of the device. Mobility/Dynamics make it hard to detect behavior anomalies such as advertising bogus routes, because routes in this environment change frequently. Self-organization is a key property of ad-hoc networks. They cannot rely on central authorities and infrastructures, e.g. for key management. Latency is inherently increased in wireless multi-hop networks, rendering message exchange for security more expensive. Multiple paths are likely to be available. This property offers an advantage over infrastructure-based local area networks that can be exploited by diversity coding.Besides authentication, confidentiality, integrity, availability, access control, and non repudiation being harder to enforce because of the properties of mobile ad-hoc networks, there are also additional requirements such as location confidentiality, cooperation fairness and the absence of traffic diversion.

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