<?
// Encrypt Function
function mc_encrypt($encrypt, $mc_key) {
	$iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND);
	$passcrypt = trim(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $mc_key, trim($encrypt), MCRYPT_MODE_ECB, $iv));
	$encode = base64_encode($passcrypt);
	return $encode;
}

// Decrypt Function
function mc_decrypt($decrypt, $mc_key) {
	$decoded = base64_decode($decrypt);
	$iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND);
	$decrypted = trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $mc_key, trim($decoded), MCRYPT_MODE_ECB, $iv));
	return $decrypted;
}
?>

http://www.phpsnaps.com/snaps/view/rijndael-256-bit-encryption-using-mcrypt/

Here are some functions I found on the net that will allow you to easily do encryption / decryption as long as you have the mcrypt extension loaded with PHP.

2 way encryption / decryption in PHP w/ mcrypt

PHP