Nonlinear Cryptosystem Based on QC-LDPC Codes for Enhanced Security and Reliability with Low Hardware Complexity and Reduced Key Size

The main issues to be addressed in resource limited devices are security, reliability and hardware complexity. Cryptosystems that combine encryption and error correction in a single step can offer a good solution to meet these issues. In this work, a nonlinear cryptosystem based on structured Low-Density Parity-Check code that offers small key size, low hardware complexity and high security against differential type of attack is proposed. The method adopted to introduce nonlinearity in a cryptosystem plays a key role in deciding the hardware complexity and security of the overall system. The work adopts a method for generating nonlinear function using maximum length Cellular Automata, so that enhanced security can be attained without going for a complex hardware structure. Also a light weight stream cipher is adopted for generating random error vectors for encryption and addition of intentional noise in such a way that the security is increased by a large margin at a low hardware cost. Different permutation matrices are generated for different message blocks for achieving good degrees of freedom with reasonable key size. Analysis shows that the proposed system provides high security with smaller key size and lower hardware complexity when compared with a nonlinear cryptosystem called Error Correction Based Cipher.