This library was the first implementation of ed25519 in Java, and I highly recommend you don't use this for anything serious. It uses BigInteger for everything and is therefore extremely slow (takes 5 seconds to sign a message) and is also not secure against side-channel or timing attacks.
Instead, you should use the updated version by str4d which is not only much faster, but also more secure than this code.
Consider this code to be legacy.
Ed25519 ported to Java
This class was ported from the Python Ed25519 reference implementation, located at http://ed25519.cr.yp.to/python/ed25519.py
It is not meant to be a proper OOP Java class, but rather a (mostly) direct translation from the Python code.
Compile and run test.java, and compare the output to validtest.txt - if it matches, you have a working Ed25519 library.
This code is released to the public domain and can be used for any purpose.