The author considers the case where double-precision modular multiplications need to be performed by a device containing a custom IC that provides for a single-precision modular multiplication. The method presented is obviously extended to multiplying (k*n)-bit operands using an n-bit modular multiplier, for the case where k is a power of 2. Whereas multiprecision modular multiplication is simply executed using an available single-precision modular multiplier which provides external division services, the existence of these services is not assumed in the process presented, as the operation carried by the available modular multiplier is not necessarily based on proper division. The process is controlled by a standard CPU which also performs some simple calculations.
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