AES cipher algorithms (FIPS-197). AES uses the Rijndael
algorithm.

Rijndael appears to be consistently a very good performer in
both hardware and software across a wide range of computing
environments regardless of its use in feedback or non-feedback
modes. Its key setup time is excellent, and its key agility is
good. Rijndael's very low memory requirements make it very well
suited for restricted-space environments, in which it also
demonstrates excellent performance. Rijndael's operations are
among the easiest to defend against power and timing attacks.

The AES specifies three key sizes: 128, 192 and 256 bits

See <http://csrc.nist.gov/CryptoToolkit/aes/> for more information.

source code:

crypto/aes_generic.c