Ad Hoc Networks : Technologies and Protocols - University of ...

118 Multicasting in Ad Hoc Networks
by the network layer will be a change in effective throughput (bandwidth) and
delay.
4.6.4 Secure Multicasting
Security is an essential requirement in MANET environment. Its importance
is amplified in group communications because of the involvement of more number
of nodes. However, research in this area is still in the very beginning stage.
Multicast in MANETs shares the same security issues as Internet multicast: receiver/source
access control, group key management, multicast fingerprinting
and secure multicast routing. The open group membership model makes joining
a lightweight operation which can be conducted at any node. Besides, any host
can send traffic to any multicast group, which the network tries to deliver to all
group members. These properties, though the very spirit of multicast service
provisioning, make the multicast service prone to the theft of service and/or
denial of service attacks. Receiver and source access control is thus needed. If
there is need to ensure the service is restricted to an authorized group of hosts,
group data encryption with group key management is further needed as well. To
prevent attacks towards the routing process, secure mechanisms is a necessity
to group communication protocols.
Ad hoc networks have created a lot more additional challenges for implementation
of the required security services beyond those that wireless communications
encounter created when compared to wireline networks. The wireless
broadcast media is more prone to both passive and active attacks. The MAC
layer solutions to group key management and source authentication proposed
for wireline networks need to be modified/enhanced to be able to adopted to
wireless environment. Compared to other wireless communications such as
cellular networks, ad hoc networks require even more sophisticated, efficient,
and light-weighted security mechanisms in order to achieve the same security
goals. These extra challenges are caused by, again, the dynamic characteristics
of MANETs. First, MANETs lack trusted centralized infrastructure,
which is often required in previous security proposals for wireline networks.
Threshold-based and/or quorum-based approaches have been investigated toward
addressing this problem. Second, the wireless links between nodes in
a MANET is formed and torn down in an ad hoc fashion, which results in
ephemeral relationships between nodes. The ephemeral relationships make it
more difficult to build trust based on direct reciprocity. Third, proposed ad hoc
multicast routing schemes are quite different from those for wireline networks.
Additionally, MANET multicast has new group models such as geocasting. For
some applications, especially in hostile environments such as battlefield communications,
individual mobile nodes can be captured and compromised. As a
result, the entire ad hoc network may be severely threatened. Finally, as always,