Rijndael is the name of an encryption/decryption algorithm that won a competition to be the Advanced Encryption Standard (AES) of the US National Institute of Science and Technology (NIST). That means that it is approved for US Government use but is also supposed to be good for use by anyone.
The name Rijndael was made up by its inventors, Joan Daemon and Vincent Rijmen of Belgium, out of their own names. It is pronounced approximately ``rain-del''.
Rijndael is an efficient algorithm that uses a shared secret
key (as opposed to a public key). It has versions in several
strengths; here we'll discuss the strongest version, with a
256-bit key. Full information can be found at
http://csrc.nist.gov/CryptoToolkit/aes/rijndael/ .