A high-radix hardware algorithm for calculating the exponential ME modulo N

In a class of cryptosystems, fast computation of modulo exponentials is essential. The authors present a parallel version of a well-known exponentiation algorithm that halves the worst-case computing time. It is described how a high radix modulo multiplication can be implemented by interleaving a serial-parallel multiplication scheme with an SRT division scheme. The problems associated with high radices are efficiently solved by the use of a redundant representation of intermediate operands. It is shown how the algorithms can be realized as a highly regular VLSI circuit. Simulations indicate that a radix 32 implementation of the algorithms is capable of computing 512-b operand exponentials in 3.2 ms. This is more than five times faster than other known implementations