A Scalable Architecture for RSA Cryptography on Large FPGAs

The RSA algorithm is the standard for public-key cryptography today, with Montgomery multiplication the most common mechanism of implementation due to modulo operations using a bitwise shift in place of a division operation. Several Montgomery designs have been proposed for ASIC and FPGA implementation based on limited resource availability to satisfy the computational burden. FPGAs are now available that have large configurable logic resources in addition to dedicated high-speed ALU logic for operations such as multiplication. This paper describes an improvement to a limited resource Montgomery multiplier design, the MWR2MM algorithm proposed by Tenca and Koc, which is suitable for implementation on large FPGAs. The design can be scaled to utilize available FPGA multipliers, CLB logic and frequencies of operation. Implementation and design choices are discussed for an RSA core based on this design, and a comparison against the OpenSSL open source cryptographic library is given. Our results show a 1024-bit RSA core on a 100MHz Virtex2 Pro 100 FPGA platform to be 3.13x faster than an equivalent software implementation on a 2.8 GHz Intel Xeon PC workstation.