Position-Based Routing Protocols for Ad Hoc Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 63

only for end-to-end communication, but also for hop-to-hop communications [ 31 ].
SPAAR has a centralized trust and so suffers from the compromised server problem
and the single point of failure.

4.3.15 AODPR

Mobile Ad Hoc networks are susceptible to malicious traffic analysis and many
attacks due to the infrastructure-less, dynamic, and broadcast nature of radio trans-
missions. One of these attacks is the target-oriented attack which is determining a
target node and conducting an intensive attack against it. In [ 20 ] Anonymous
On-Demand Position-based Routing in Mobile Ad Hoc Networks (AODPR) was
proposed while keeping these two problems in mind. It keeps routing nodes
anonymous, thereby preventing possible traffic analysis. A time-variant Temporary
IDentifier (Temp ID) is computed from time and position of a node and used for
keeping the node anonymous. Moreover, AODPR uses the concept of Virtual Home
Regions (VHR) which is a geographical region around a fixed center. In this
scheme each node stays in one of the VHRs and nodes within a VHR obtain their
own geographic position through GPS and report their position information to the
Position Servers (PS). PSs are trusted Ad Hoc nodes distributed in the network.
The PS keeps the position information of the nodes securely. When a node joins the
network, it makes its registration to the PS and gets a common key and a pair of
public and private keys from the PS [ 20 ].
When a node wants to get position information of other nodes, it first authenti-
cates itself to the PS and sends a signed position request, and then PS provides it
with the required position information, Public Key of the destination and other
needed information. The source, before sending the route request, estimates Temp
NH, which is initially the minimum number of hops which the route request packet
travels to find a route from the source to the destination.
Each intermediate node (Forwarder) updates Temp NH, Temp NH = Temp NH - 1,
and compares the updated Temp NH with the minimum number of hops which
route request packet travels to find a route from this node to the destination (h¢). If
h¢ is less than or equal to Temp NH, then forwarder forwards the packet to its radio
region and keeps the route information, else it discards the packets. Both h¢ and NH
are calculated depending on the distance from the node to the destination and the
radius of the maximum radio range coverage of each node. At the last phase of the
route discovery procedure, the destination replies with a route-reply message,
signed with its private key and sends this message on the reverse path.
Analysis in [ 20 ] shows that AODPR ensures the anonymity of route as well as
nodes, the robustness against the target-oriented attack and several others, and it is
applicable to any node density in a Network [ 20 ]. However, many fields such as NH
and destination position taken from PSs are encrypted using the Common key (CK);
if this key is compromised a large percentage of the communication in the whole
network will be compromised. Moreover, AODPR suffers from two problems