We revise Montgomery's algorithm such that modular multiplication can be executed two times faster. Each iteration in our algorithm requires only one addition, while that in Montgomery's requires two additions. We then propose a cellular array to implement modular exponentiation for the Rivest-Shamir-Adleman cryptosystem. It has approximately 2n cells, where n is the word length. The cell contains one full-adder and some controlling logic. The time to calculate a modular exponentiation is about 2n/sup 2/ clock cycles. The proposed architecture has a data rate of 100 kb/s for 512-b words and a 100 MHz clock.
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