Low Complex Crypto Based Channel Coding

A novel method to combine encryption and channel coding in such a way as to get increased security without any additional complexity is presented in this paper. A secure communication system usually consists of an encryption block followed by the channel coder. The encryption block here is a Shrinking generator which is a Linear Feedback Shift Register (LFSR) based stream cipher system. The channel coding technique used is Turbo codes or Low Density Parity Check Codes (LDPC) that performs very well and provides results near Shannon´s Limit. Controlled randomness using Pseudo Random Bit Sequence (PRBS) generator is incorporated during encoding of these codes to provide additional level of security in the system without any additional complexity. To achieve optimum decoding, soft decision decoding algorithms are used rather than hard decisions. Bit Error Rate (BER) performance of the proposed channel coders with keyed randomness is well analyzed for intended and un-intended users. Security of the system is analyzed by mounting Improved Linear Consistency Attack and the results show that a significant increase in security is achieved in a stream cipher based secure communication system without any additional increase in complexity by introducing security in channel coding.