$db_pass is the encrypted/unencrypted password, and the other values can be found on the 
/var/www/ispcp/gui/include/ispcp-db-keys.php file of the corresponding server.
Code:
function decrypt_db_password ($db_pass, $ispcp_db_pass_key, $ispcp_db_pass_iv) {
        if ($db_pass == '')
                return '';
        if (extension_loaded('mcrypt') || @dl('mcrypt.' . PHP_SHLIB_SUFFIX)) {
                $text = @base64_decode($db_pass . "\n");
                // Open the cipher
                $td = @mcrypt_module_open ('blowfish', '', 'cbc', '');
                // Create key
                $key = $ispcp_db_pass_key;
                // Create the IV and determine the keysize length
                $iv = $ispcp_db_pass_iv;
                // Intialize encryption
                @mcrypt_generic_init ($td, $key, $iv);
                // Decrypt encrypted string
                $decrypted = @mdecrypt_generic ($td, $text);
                @mcrypt_module_close ($td);
                // Show string
                return trim($decrypted);
        } else {
                system_message("ERROR: The php-extension 'mcrypt' not loaded!");
                die();
        }
}
 
Code:
function encrypt_db_password($db_pass, $ispcp_db_pass_key, $ispcp_db_pass_iv){
        if (extension_loaded('mcrypt') || @dl('mcrypt.' . PHP_SHLIB_SUFFIX)) {
                $td = @mcrypt_module_open (MCRYPT_BLOWFISH, '', 'cbc', '');
                // Create key
                $key = $ispcp_db_pass_key;
                // Create the IV and determine the keysize length
                $iv = $ispcp_db_pass_iv;
                //compatibility with used perl pads
                $block_size=@mcrypt_enc_get_block_size($td);
                $strlen=strlen($db_pass);
                $pads=$block_size-$strlen % $block_size;
                for ($i=0; $i<$pads;$i++){
                        $db_pass.=" ";
                }
                // Intialize encryption
                @mcrypt_generic_init ($td, $key, $iv);
                //Encrypt string
                $encrypted = @mcrypt_generic ($td, $db_pass);
                @mcrypt_generic_deinit($td);
                @mcrypt_module_close($td);
                $text = @base64_encode("$encrypted");
                $text=trim($text);
                return $text;
        } else {
                //system_message("ERROR: The php-extension 'mcrypt' not loaded!");
                die("ERROR: The php-extension 'mcrypt' not loaded!");
        }
}