Security Aspects in Mobile Ad Hoc Networks

Mobile Ad hoc networks (MANETs) are a new paradigm of wireless network, offering unrestricted mobility without any underlying infrastructure  such as base station or mobile switching centers. Basically ad hoc network is a collection of nodes communicating with each other by forming a  multi-hop network. In a mobile ad hoc network, it is much more vulnerable to attacks than a wired network due to its limited physical security, dynamically changing network topology, energy constrained operations and lack of centralized administration. Since all the nodes in the network collaborate to forward the data, the wireless channel is prone to active and passive attacks by malicious nodes, such as Denial of Service (DoS), eavesdropping, spoofing, etc. The intent of this paper is to investigate the security goal, security challenges and different types of active and passive attacks on MANETs.

1.INTRODUCTION

With the proliferation of cheaper, small and more powerful mobile devices, mobile ad hoc networks (MANETs) have become one of the fastest growing areas of research. A Mobile ad hoc network is a system of wireless mobile nodes with routing capabilities – the union of which form an arbitrary graph. Any group of them are capable of  forming  an autonomous network that require no infrastructure and is capable of  organizing  itself into arbitrary changeable topologies. Such a network may operate in a stand-alone fashion, or may be connected to the larger Internet[Figure1,2]. The definition, which  is given by the Internet Engineering Task Force (IETF).Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural or human-induced disasters, military conflicts, emergency medical situations etc. Unlike traditional mobile wireless  networks, Ad hoc networks dont rely on  any fixed infrastructure(base stations, access points). This flexibility makes them attractive technology for many applications such as rescue and tactical operations, disaste recovery operations and educational applications where we can setup virtual class or conferences.

Figure1: Infrastructure based

The following are the advantages of MANETs:-

• They provide access to information and services regardless of geographic position.
• These networks can be set up at any place and time.
• These  networks  work  without  any  pre-existing infrastructure.

Figure2: Infrastructure  less

Security has become a primary concern in order to provide protected communication between nodes in a potentially hostile environment. In a mobile ad hoc network, it is much more vulnerable to attacks than a wired network due to its limited physical security, volatile network topologies, power-constrained operations, and lack of centralized monitoring and management point.

2. APPLICATIONS OF MANETS :

With  the  increase  of  portable  devices  as  well  as  progress  in wireless  communication,  ad  hoc  networking  is  gaining importance  with  the  increasing  number  of  widespread application.

2.1.MANET Applications Military

Ad hoc networking would allow the military to take advantage of commonplace network technology to maintain an information network between the soldiers, vehicles, and military information head quarters. Consider a scenario as shown in figur-3, is deployed over a battlefield . The ad hoc network formed by the air vehicle in the sky can provide a backbone for land based platforms to communicate when they are out of direct range,or when obstacles prevent direct communication. The ad hoc network therefore extends down to the land based forces and allows communication across the  battlefield. Voice and video, as well as sensing and data applications can be supported.

Figure 3: Military Applications

2.2.MANET Applications Disaster Relief

In cases of disasters, the existing infrastructure is often damaged or destroyed. Natural disasters e.g. lead to the loss of electricity and Internet connectivity, as described in Figure 4. Emergency rescue operations must take place where non-existing or damaged communications  infrastructure and rapid deployment of a communication network is needed. An ad hoc network can be used used in emergency/rescue operations for disaster relief efforts, e.g. in fire, flood, or earthquake, to overcome the problems incurred by missing infrastructure, helping to better cope with the consequences of such calamities. Mobile units  carry networking equipment to support routing operations.Information is relayed from one rescue team member to another over a small handheld. Other commercial scenarios include e.g. ship-to-ship ad hoc mobile communication, law enforcement etc.

Figure 4: Disaster Relief Applications

3.CHALLENGES  IN SECURING THE MANETs:

MANETs  are  much  more  vulnerable  to  attack  than  wired network. This is because of following reasons:

3.1  Absence of Infrastructure

Ad hoc networks operate independently of any infrastructure, which  makes inapplicable any classical solutions based on certification authorities and on line servers.

3.2 Limited physical security

Mobile wireless networks are  generally more prone to physical security threats than a fixed-cable nets.  The  increased possibility  of  eavesdropping,  spoofing, and  denial-of-service attacks should be carefully considered. Existing link  security techniques  are often  applied within wireless networks  to  reduce security threat.

3.3 Restricted power Supply

Due  to mobility  of  nodes  in  the  ad  hoc  network,    nodes will rely on battery as their power supply method,  the  problem that may  be  caused by  restricted  power  supply  is  denial-of-service attacks and selfish manner.

 3.4 Dynamically changing network topology

Nodes  are  free  to move  arbitrarily. The  network  topology may change  randomly  and have no  restriction on  their distance  from other  nodes. As a  result  of  this  random  movement, the whole topology is changing in  an unpredictable manner, which  in  turn gives  rise to both  directional as  well  as  unidirectional  links between the nodes as shown in figure 5.

Figure 5: changing network topology

3.5 Lack of Centralized monitoring

Absence  of  any  centralized monitoring makes  the  detection  of attacks a very difficult problem because it is not easy to monitor the  traffic  in  a  highly  and  large  scale  ad  hoc  network .  It  is rather common in the ad hoc network that benign failures such as transmission impairments and packet dropping.

4. SECURITY GOALS IN ADHOC NETWORKS

The goals of security mechanism of MANETs are similar to that of other networks. Security is a great issue in network especially in MANETs where  security  attacks  can  affect  the nodes  limited resources and consume  them or waste the time before rote chain broke.  Security  is  a  vectored  term of multi  systems, procedures and  functions  that  works  together  to  reach  certain  level  of security attributes[6].

Figure 6: Types of Security Goals

4.1 Availability

The main  goal  of  availability  is  to node will be  available  to  its users  when  expected,  i.e.  survivability  of  network  services despite denial of service attack. For example, on the physical and media access control layers, an adversary could employ jamming to  interfere  with  communication  on  physical  channel  while  on network layer it could disrupt the routing protocol and continuity of services of  the network. Again,  in higher  levels, an adversary  could  bring  down  high-level  services  such  as  key management service, authentication service .

4.2 Confidentiality

The goal of confidentiality is to  keeping information secret from unauthorized user or nodes. In other words, ensures payload data and header information is never disclosed to unauthorized nodes. The standard approach for keeping information confidential is to encrypt  the  data with  a  secret key  that only  intended  receivers posses, hence achieving confidentiality.

4.3 Integrity

The  goal  of  integrity  is  to guarantee the message  being  transmitted  is never corrupted. Integrity guarantees the identity of the messages when they are transmitted. Integrity can be compromised mainly in two ways .

Malicious altering:– A message can be  removed, replayed or revised by an adversary with malicious goal.

Accidental altering:- if  the  message  is  lost  or  its content  is  changed due  to  some benign  failures, which may be transmission  errors  in  communication  or  hardware  errors  such as hard disk failure.

4.4 Authentication

The goal of authentication is too able to identify a node with which it is communicating and to prevent  impersonation. In infrastructure-based wireless network, it is possible to implement a central authority at a point such as base station or access point. But in MANETs, no central administration so it is difficult to authenticate an entity.

4.5 Non repudiation

The main  goal  of  non  repudiation  is  sender of  a message cannot  deny  having  sent  the  message.  This  is  useful when  for detection  and  isolation  of  compromised  nodes.  When  node  P receives an erroneous message from Q, non repudiation allows P to access Q using  this message and  to convince other nodes that Q is compromised.

4.6 Authorization

Authorization  is  a  process  in  which  an  entity  is  issued  a credential, which  specifies  the privileges and permissions  it has and cannot be falsified, by the certificate authority. Authorization is  generally  used  to  assign  different  access  rights  to  different level of users.

5.SECURITY ATTACKS  ON  MANET

Malicious  and  selfish  nodes  are  the  ones  that  fabricate  attacks  against  physical,  data  link,  network,  and  application-layer functionality [Fig-7]. Current  routing protocols are exposed to two types of attacks

1.Active attacks

In a active attack, information is inserted to the network and  thus  the network operation or some nodes may be harmed. Through which  the misbehaving  node  has  to  bear  some  energy costs in order to perform some  harmful operation, and Nodes that perform active attacks with the aim of damaging other nodes by causing network outage are considered to be malicious.

2.Passive attacks

In  a  passive  attack,  a malicious  node  either  ignores operations  supposed  to  be  accomplished  by  it. That mainly consists of  lack of cooperation with  the purpose of energy saving Nodes that perform passive attacks with the aim of saving battery  life  for  their own communications are considered to  be  selfish.  Selfish  nodes  can  severely  degrade  network performances and eventually partition the network .

Figure 7: Classification of Attacks

5.1.Denial  of  service  (Data  link  Layer  Attach):

In  this  attack malicious  node  floods  irrelevant  data  to  consume  network bandwidth  or  to  consume  the  resources  (e.g.  power,  storage capacity  or  computation  resource)  of  a  particular  node.  With fixed  infrastructure  networks,  we  can  control  denial  of  service attack  by using  Round Robin Scheduling, but with mobile  ad hoc  networks,  this  approach  has  to  be  extended  to  adapt  to  the lack  of  infrastructure,  which  requires  the  identification  of neighbor  nodes  by  using  cryptographic  tools,  and  cost  is  very high.

For  example,  consider  the  following  Fig.  8. Assume  a  shortest path exists from X to Z and R and Z cannot hear each other, that nodes Q and R cannot hear each other, and that Y is a malicious node attempting a denial of service attack. Suppose X wishes to communicate with Z  and  that X has an unexpired  route  to Z  in its route cache. Transmits a data packet toward Z with the source route X  –> P  –> Q  –> Y  –> R  –>  S  –> Z  contained  in  the packets  header. When  Y  receives  the  packet,  it  can  alter  the source  route  in  the packets header, such as deleting S  from  the source  route. Consequently, when R  receives  the altered packet, it attempts to forward the packet to Z. Since Z cannot hear R, the transmission is unsuccessful.

Figure 8: Denial of service attack

5.2.Tunneling /Wormhole(Network layer attack):

Tunneling  attack  is  also  called wormhole  attack.  In  a  tunneling attack,  an  attacker  receives  packets  at  one  point  in  the network,  tunnels  them  to  another  point  in  the  network, and then replays them into the network from that point. It is called  tunneling  attack  because  the  colluding  malicious nodes  are  linked  through  a  private  network  connection which is invisible at higher layers [Fig-9].

Figure 9: Wormhole Attack

 5.3.Sybil  attack :

Malicious nodes in a network may not only impersonate one node, they could assume the identity of several nodes, by doing so undermining(destroy) the redundancy(repeating) of many routing protocols.    This  attack  is  called  the  Sybil  attack.  Sybil attack tries to degrade the integrity of data, security and resource utilization  that  the  distributed  algorithm  attempts  to  achieve. Sybil attack can be performed for storage, routing mechanism, air resource  allocation  and  misbehavior  detection.  Basically,  any peer-to-peer  network  (especially  wireless  adhoc  networks)  is vulnerable to Sybil attack.

Figure 10: Sybil Attack

Table : Security Solutions for MANETs.

Layer	Attacks	Solution
Application Layer	Repudiation,  data corruption	Detecting and preventing virus, worms, malicious codes and application abuses by use of Firewalls, IDS.
Transport Layer	Session  hijacking, SYN Flooding	Authentication and securing end-to-end or point-to-point communication use of public cryptography(SSL, TLS, PCT) etc.
Network Layer	Routing  protocol attacks  (e.g. DSR, AODV etc.),Wormhole, blackhole, Byzantine, flooding,  resource consumption, location disclosure attacks	Protecting the ad hoc routing and forwarding protocols
Data Link Layer	Traffic  analysis, monitoring, disruption  MAC (802.11),  WEP weakness etc.	Protecting the wireless MAC protocol and providing link layer security support.
Physical Layer	Eavesdropping, Jamming, Interceptions.	Preventing signal jamming denial-of-service attacks by using Spread Spectrum Mechanism.

6. CONCLUSION

Importance of MANET cannot be denied as the world of  computing is getting portable and compact. Mobile ad hoc Network have the ability to setup networks on the fly in a harsh environment where it may not possible to deploy a traditional  network  infrastructure. Security is not a single layer issue but a multilayered issue. Due  to  mobility  and  open media nature,  the mobile ad hoc networks are much more prone to all  kinds  of  security  risks,  such  as  information  disclosure, intrusion,  or  even  denial  of  service.  As  a  result,  the  security needs in the mobile ad hoc networks are much higher than those in  the  traditional  wires  networks.  It requires a multi fence security solution that provides complete security spanning over the entire protocol  stack. The Security research area is still open as many of the  provided solutions are designed keeping a limited size scenario and limited kind of attacks and vulnerabilities. MANET are the future networks.because they are practically versatile ,easy to use,inexpensive and can instantly updates and reconfigures itself. In this  post we  have highlighted the  some  typical  vulnerability  which are  caused by characteristics  of  mobile  ad hoc  networks  such as  dynamic topology,  limited resources  (e.g.  bandwidth,  power),  lack of  central managements points. And finally we discussed active and passive security attacks on each layer and their solutions.