Space/time trade-offs for higher radix modular multiplication using repeated addition

The value of using a higher radix for modular multiplication in the context of RSA is investigated. The main conclusion is that for algorithms which perform the multiplication via repeated addition, there is, broadly speaking, a direct trade-off between space and time provided by change of radix. Thus chip area utilized is roughly proportional to speed. However, initially, as the radix is increased from 2, there is a short-lived increase in speed greater than the extra area used.