Due to the IT development, RFID/USN became very familiar means of communication. However, because of increased number, security, and size constraints of nodes, it is insufficient to implement a variety of services. To solve these problems, this paper suggests RI-RSA, which is an appropriate asymmetric cryptographic system for RFID/USN environment. The proposed RI-RSA cryptographic system is easy to implement. To increase the processing speed, RI-RSA was suggested by subdividing the multiplication section into two-dimensional, where bottleneck phenomena occurs, and it was implemented in the hardware chip level. The simulation result verified that it caused 6% of circuit reduction, and for the processing speed, RI-RSA was 30% faster compare to the existing RSA.