  With the ever increasing volume of information over wireless medium, security
has assumed an important dimension. The security of transmitted data over a
wireless channel aims at protecting the data from unauthorized intrusion.
Wireless network security is achieved using cryptographic primitives. Some
properties that give encryption mechanism their cryptographic strength also
make them very sensitive to channel error as well. Therefore, security for data
transmission over wireless channel results in throughput loss. Trade-off
between security and throughput is always a major concern in wireless networks.
In this paper, a Link Adaptive Encryption scheme is evaluated that adapts to
channel variations and enhances the security level of WLANs without making any
compromise with the network performance. Numerical results obtained through
simulation are compared with the fixed block length encryption technique in two
different modes of operation- Electronic Code Book (ECB) & Cipher Block
Chaining (CBC). Optimal block length is also computed, which is assumed to be
the effective strength of the cipher. It has been observed that security
attained with link adaptive scheme operating in ECB mode of cipher is a better
solution for security and throughput trade-off. However, it is found that if
computational security is a major concern, link adaptive scheme in CBC mode
should be preferred.
