[Coco] Color Computer RSA

[Don Barber]

Hi folks, wanted to share my latest project that I've just published.

I've written an RSA implementation for the Color Computer. It will 
handle up to 2048-bit keys. Its written in assembly, and I've made all 
the code I developed open source and placed it on github here:

https://github.com/barberd/cocorsa

A disk image is also available on that site.

I needed to implement several multi-precision-byte algorithms, including:
Modular Exponentiation
Prime testing using Miller-Rabin
GCD with Euler's method
Multiplication with Karatsuba

I also implemented some filesytem/file-handling routines, and a screen 
output routine that will wrap text nicely. Hopefully by making all these 
open source, I can also help future CoCo programmers.

I taught myself basic on my coco3 when I was 9 and always told myself 
that I'd learn to program it with 'machine language' one day. I also 
dusted off a lot of those mathematical algorithm skills from my computer 
science undergrad days to create this. So while an RSA implementation 
for the CoCo may not be that useful on a day-to-day basis, I'm still 
quite proud of this effort. Hopefully others can appreciate.

Thanks to all the list members who have helped me along the way; one may 
recall me pointing out the bug in Leventhal's 6809 subroutines books, my 
(dumb) question about stack corruption, my question about disk routines, 
or my question about determining coco1/2 versus 3.

Thanks again,

Don