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network it is obvious that identity-based encryption
suits ad hoc networks’ needs very well. It is like they
were made for each other. Using identity-based
cryptography for securing ad hoc networks is a
lately preoccupation of researchers. An example can
be found in Oliveira L.B.et al., 2007. A team from
The University of Brazil had successfully
implemented and tested a secure communication
scheme for sensor networks based on Tate pairing
and named TinyTate. The protocol developed
focuses on the needs of resource constrained nodes,
but this does not affect the generality of the
implementation.
What our team proposed was to develop a
simulation environment where the use of identity-
based cryptography in ad hoc networks can be
simulated and tested. The simulation of ad hoc
routing protocols is very easy with the use of
network simulators (like ns2), because ad hoc
routing protocols implementations already exists.
But simulating secure ad hoc networks is not as
easy. This was the motivation of our work that tried
to answer this issue.
2 IDEA
Imagine the scenario of a conference. When a
conference is organized, several discussion topics
are established, and for every one of the themes a
separate room is assigned. People joining the
conference can participate at discussions in all the
rooms. This means that someone can arrive at the
beginning and join discussion topic in room A. After
an half an hour, say he or she gets bored and goes to
room B. Then, after fifteen minutes, decides to go
back to room A. And so on and so forth. A mobile
ad hoc network would be the best solution to assure
the communication between the laptops or the PDAs
of the participants. But how can someone assure
security? What are the characteristics of such a
scenario? First of all, before the actual
communication starts all the participants had arrived
and all had checked in. After the conference began
no one can check in anymore. Second, the security
of communications has to be provided only for the
duration of the conference, witch is a relative small
time (several hours maybe). Third, once a person
was selected for this conference, he of she cannot be
excluded during the conference.
The following security scheme can be proposed
for such scenarios, based on the utilization of
identity-based cryptography. At checking in, every
attendant of the conference is provided with an IP, in
order to access the ad hoc network of the
conference. At the reception there is also the key
generation center. After the IP is assigned to the
participant’s device, it can ask the key generation
center for the public variables needed for identity-
based computations. After it receives them, it can
ask for its private key. The key generation center
computes the participant’s private key based on the
IP assigned to it and returns it. The private key is
exchanged on a secure channel (for example
Bluetooth) and the authentication of the requestor is
made by physical contact. The participant will also
receive a list of all the participants of the conference
and their IP numbers. After all the participants check
in, the key generation center, the only one that can
generate the private keys is shutdown. So the
participants can interchange secure messages based
only on their IPs.
3 IMPLEMENTATION
When implementing all these in ns2, the work was
divided in several steps. The first step was to
determine how this security scheme can be
implemented in ns2. The second step was to find an
identity-based cryptography library that can be use
with ns2 (this means that it had to be written in C or
C++). The next step was the implementation of the
objects involved (the key generation centre, the
communicating nodes) through the implementation
of the five needed algorithms (Boyen X., Martin L.,
2007): initialization of the key generation centre,
generation of the private keys, generation of the
public keys, and encryption of a message and
decryption of a message. The last step was to test the
implementation and to conclude future development
directions.
3.1 Security Scheme Implementation
and Library Utilization
With ns2, ad hoc networks can be simulated using
specific objects that represent the nodes of the
network. For these nodes, among other things, the
name of the ad hoc routing protocol needs to be
specified. Of course, ns2 does not contain an
implementation for all the routing protocols known,
but only for the most important ones like AODV,
DSR, and TORA. To simulate traffic in ns2, an
agent object must be attached to the nodes. The
agent object can act as a source or as a destination
for the communication packets. New agents can be
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