In this paper, RSA cryptosystem was implemented on an FPGA as resistant against Differential Power Analysis attacks. There are hardware and algorithmic countermeasures against power analysis attacks. This is the first FPGA realization of an algorithmic countermeasure which makes RSA resistant to power analysis attacks. Modular exponentiation is realized with Montgomery Modular Multiplication. The Montgomery modular multiplier has been realized with carry save adders. Carry save representation has been used throughout the RSA encryption algorithm. The protected implementation resulted in 66,66 MHz of clock frequency, 84,42 Kb/s of throughput, and 6,06 ms of total exponentiation time and occupied an area of 10986 slices with the use of the built-in block SelectRAM structure inside XCV1000E.