Rot13 is a simple substitution cypher that is used as a simple, but easy to break, obfuscation technique. For example it is used in some email or online forums to hide punchlines to jokes or answers to quizzes. It is similar in operation to the base-64 algorithm used to hide user names and passwords from the casual observer in the HTTP basic authentication scheme. Like all substitution cyphers, it is easy to break (even easier if you know or can guess that it's been used). But it is a nice example that can serve as a introductory example for most programming languages. It also has the interesting property of symmetry: the encrypted text can be passed though the same process to return the plain text.
This category's articles describe programs that perform the Rot13 cypher. There is a site that list many hundreds of implementations of this example (but please don't copy content from them).hijackerhijacker