Originally, I wrote zpint to help me with my algebric structures homework. For those not familiar with it, it allows you to do computations modulo p the same way you do for ints. Not surprisingly, I found myself using it in my cryptography homework as well. At first I used it for trying to breaking the Hill Cipher. Then for some computations such as using the Chinese Remainder Theorem to solve equations, or to compute RSA values. Last it was for checking if algorithms I wrote were correct.
Usually I prefer to write a script than do all the computations by hand, even if writing the script is more work. Mostly because it is work I enjoy more. This time I had a script ready. I improved it a little bit during the semester, and it is still available. It is certainly not the fastest way to compute, but it is a fast way of doing computations.