This paper presents the design and implementation of a systolic RSA cryptosystem based on a modified Montgomery’s algorithm and the Chinese Remainder Theorem (CRT) technique. The CRT technique improves the throughput rate up to 4 times in the best case. The processing unit of the systolic array has 100% utilization because of the proposed block interleaving technique for multiplication and square operations in the modular exponentiation algorithm. For 512-bit inputs, the number of clock cycles needed for a modular exponentiation is about 0.13 to 0.24 million. The critical path delay is 6.13ns using a 0.6μm CMOS technology. With a 150 MHz clock, we can achieve an encryption/decryption rate of about 328 to 578 Kb/s.