A small GUI to test out plain RSA Get the precompiled version from here: https://github.com/SuspiciousActivity/Random-Java-Stuff/blob/master/RSAGui.jar
This program is built on top of this wikipedia article about RSA: https://en.wikipedia.org/wiki/RSA_(cryptosystem)
It's using http://factordb.com/ for factoring 'n' into 'p' and 'q'.
It's pretty straight forward.
Just enter some numbers. You can press enter on most of the text fields to calculate other fields.
You can copy a hex value in format '0xDEADBEEF' and paste it into a field, it gets converted to decimal automatically.
Enter n = 1337, press enter in n. p and q are fetched from FactorDB, phi is calculated.
Enter e = 65537, press enter in e. d is calculated.
Enter m = 42, press enter in m. The cipher c is calculated. You can also press enter in c to get m.