04-08-2012, 10:30 AM
Security of Ad Hoc Networks and Threshold Cryptography
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Abstract
A Mobile Ad hoc Network (MANET) is a system of
wireless mobile nodes that dynamically self-organize
in arbitrary and temporary network topologies
allowing people and devices to inter-network without
any preexisting communication infrastructure. Taking
into account its nature and challenges and security
issues, we briefly discuss current security solutions,
particularly Threshold Cryptography (TC). Already TC
is being sought in computer networks to provide
security in terms of availability, confidentiality, and
secure key or data distribution. So we investigate to
find out what makes it difficult to implement TC in ad
hoc networks. To find answers to these questions, we
discuss our RSA-based Threshold Cryptography (RSATC)
implementation.
Introduction
Mobile Ad hoc Network (MANET) is emerging as
an important area for new developments in the field of
wireless communication. The premise of forming a
MANET is to provide wireless communication
between heterogeneous devices, anytime and anywhere,
with least or no infiastructure [1], [2], [3], [4]. These
devices, for instance cell phones, laptops, palmtops
remote systems, etc. carry out communication with
other nodes that come in their radio range of
connectivity. Each participating node provide services
such as message forwarding, providing routing
infornation, authentication, etc. to form a network with
other nodes spread over an area.
Current security solutions in MANET
Secure routing
Routing of packets form a basis of the MANET
where intermediate nodes route the data from the
source to the destination. Assumption is that encryption
keys have already been established between the
communicating nodes [2]. The efficient packet routing
is one of the crucial functionalities required in an ad
hoc network [2]. It includes monitoring network traffic,
prioritizing the sending of the data packets,
authenticating the packets from legitimate nodes, and
keeping track of updated routes [3]. Thus, as the
message is broadcasted, each node carries out above
mentioned functions to thwart various attacks based on
the routing protocol.
Secure data forwarding
Secure routing is the pre-requisite for implementing
secure data forwarding [2]. The motivation is to
securely forward data in MANETs in the presence of
malicious nodes- after the route between the source and
target is discovered. There are various schemes
proposed for secure data forwarding such as data
forwarding based on neighbor's rating, implementing
currency system in network for packet exchange, and
redundantly dividing and routing message over
multiple network routes.
For example, Secure Message Transmission (SMT)
is a secure data forwarding scheme in which first the
active paths are discovered between two nodes using
secure routing protocol. Based on N active paths, the
message is divided into N different parts such that any
Mparts can be used to recover this message. These N
partial messages are then routed on the recognized
paths. The destination can recover a message when M
or more partial messages are received. Thus, this
scheme ensures that the message reaches the
destination even if a few packets are dropped in transit.
Threshold cryptography
Threshold cryptography (TC) involves sharing of a
key by multiple individuals called shareholders
engaged in encryption or decryption. The objective is
to have distributed architecture in a hostile
environment. Other than sharing keys or working in
distributed manner, TC can be implemented to
redundantly split the message into n pieces such that
with t or more pieces the original message can be
recovered. This ensures secure message transmission
between two nodes over n multiple paths.
Conclusions
In the RSA-TC implementation, we have proved
that knowledge of qj(N) is must for sharing keys. It is
clearly demonstrated here, that irrespective of key size
and for known qbkN) at the sender, the success rate
increases as t is increased from n/2 to n. Further, 100%
success rate can be achieved with n-out-of-n RSA-TC
scheme. As in regular RSA, RSA-TC implementation
confirmed that the signature generation and signature
verification time increases exponentially when key
sizes are doubled. In this paper, it is established that the
combining and verifying time is less than t times partial
signature generation time. Rather than sharing keys, we
have suggested an alternative of splitting the message
at the sender to achieve 100% success rate without
knowledge of 0(N).