Cipher

Estou tentando implementar este código abaixo mas está dando este erro

Fatal error: Call to undefined function mcrypt_module_open() in suporte/criptografia.php on line 3

 

 . Alguém sabe se é preciso instalar alguma coisa pra rodar ?

 

<?php	/* Open the cipher */	$td = mcrypt_module_open('rijndael-256', '', 'ofb', '');	/* Create the IV and determine the keysize length, used MCRYPT_RAND * on Windows instead */	$iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_DEV_RANDOM);	$ks = mcrypt_enc_get_key_size($td);	/* Create key */	$key = substr(md5('very secret key'), 0, $ks);	/* Intialize encryption */	mcrypt_generic_init($td, $key, $iv);	/* Encrypt data */	$encrypted = mcrypt_generic($td, 'This is very important data');	/* Terminate encryption handler */	mcrypt_generic_deinit($td);	/* Initialize encryption module for decryption */	mcrypt_generic_init($td, $key, $iv);	/* Decrypt encrypted string */	$decrypted = mdecrypt_generic($td, $encrypted);	/* Terminate decryption handle and close module */	mcrypt_generic_deinit($td);	mcrypt_module_close($td);	/* Show string */	echo trim($decrypted) . "\n";?>