base64 RFC1113 Vanilla ANSI-C Code for a portable stand-alone file encode/decode utility. In 2001, I asked people to 'Help me break it!' Since then, 10+years later, the code remains unbroken and is in wide production use world-wide. It has been ported to all major architectures and been used as a template for ports to different computer and human languages. This is very mature and stable code.
Although this comes from a project that was constrained by export controls and is used in secure systems, it is not security code per-se. I have therefore altered the 'Export Controls' category.