At 10:34 AM 5/30/03 -0700, Bill Frantz wrote:

I think your best bet for an 8 bit CPU will be an assembly language routine.

Likely so. For those interested, I found this article, which does in fact use enhanced (it has a multiplier) Z80 assembly, included in the article: http://www.ddj.com/documents/s=1030/ddj9309e/9309e.htm The Z80180 and Big-number Arithmetic Squeezing 512-bit operations out of 8-bit microcontrollers Burton S. Kaliski, Jr. For instance, in one recent project, our challenge was to implement 512-bit RSA private-key operations in less than 10 seconds on Zilog's 8-bit Z80180 microcontroller running at 10 million cycles/second. .............. The folks at cyphercalc.com have a cyphermath8 library, albeit commercial. See http://cyphercalc.com/math/features.htm They give this performance data for the Rabbit CPU (see http://cyphercalc.com/math/performance.htm) 780 milliseconds for a modular exponentiation with a 128-bit base, 40-bit exponent, and 128-bit odd modulus. Exponent ones density: 50%. Target: Rabbit Semiconductor RCM2020, running at 18.4Mhz. Compiled under Dynamic C, version 6.03, with assembly optimizations in effect. [no affiliation] .............. Smartcard vendors tend to include a modexp co-processor.