public function setData($data)
{
if (!Sjcl::isValid($data)) {
throw new Exception('Invalid data.', 61);
}
$this->_data->data = $data;
// We just want a small hash to avoid collisions:
// Half-MD5 (64 bits) will do the trick
$this->setId(substr(hash('md5', $data), 0, 16));
}