RSA Cryptosystem Based on Early Word Based Montgomery Modular Multiplication

RSA is a public key cryptosystem in which encryption and decryption are modular exponentiation functions. Modular exponentiation is achieved by repeated modular multiplications. Montgomery modular multiplication is an efficient algorithm, hence is widely used for RSA public key cryptosystem. Performance of RSA depends on throughput of Montgomery modular multiplication. This paper presents RSA with Early Word based Montgomery modular multiplication. Early word based approach is scalable and Radix 4 Early Word Based Common Multiplicand Montgomery is proposed. RSA cryptosystem is implemented on virtex 5 FPGAs. The processing elements in Early Word based Montgomery use target device resources DSP48E for addition of operands. Two factors: algorithmic approach and use of target device resources have improved the performance of RSA on FPGAs.