Encrypt::hashSessionId() 

\nn\t3::Encrypt()->hashSessionId($sessionId = NULL); 

Get session hash for fe_sessions.ses_id Corresponds to the value that is stored for the fe_typo_user cookie in the database.

In TYPO3 < v10 an unchanged value is returned here. As of TYPO3 v10, the session ID is stored in the cookie fe_typo_user is no longer stored directly in the database, but hashed. See: TYPO3\CMS\Core\Session\Backend\DatabaseSessionBackend->hash().

\nn\t3::Encrypt()->hashSessionId( $sessionIdFromCookie );

Example:

$cookie = $_COOKIE['fe_typo_user'];
$hash = \nn\t3::Encrypt()->hashSessionId( $cookie );
$sessionFromDatabase = \nn\t3::Db()->findOneByValues('fe_sessions', ['ses_id'=>$hash]);

Used by, among others: \nn\t3::FrontendUserAuthentication()->loginBySessionId().

| @return string

public function hashSessionId( $sessionId = null ) {
	$key = sha1(($GLOBALS['TYPO3_CONF_VARS']['SYS']['encryptionKey'] ?? '') . 'core-session-backend');
	return hash_hmac('sha256', $sessionId, $key);
}