What's the difference between Standard and Advanced folders?

There is a great difference between Advanced and Standard folders in terms of their architecture. Differences are explained below and combined in a comparison chart at the bottom of the page. 

Standard folders are available in both Free and Pro versions of Sync. Advanced folders are available in Sync Pro and during the 14-day Trial. You can’t create an Advanced folder in Sync Free, however, if a Sync Pro user has shared such a folder with you, you can add it to the free version of the app and sync data according to the permission (RO, R&W, Owner) issued. 

To connect to other devices and sync data between them, Standard folders use randomly generated keys, while Advanced folders are based on public key infrastructure (PKI), which enables users to verify each other's identity with the help of digital certificates. This innovation in Advanced folders has introduced:

Additional security. All connection operations (adding peers, sharing folders, etc) are carried out with the help of X.509 digital certificate.

New functionality and convenience. Such features as My Devices and On-the-fly Permission Changes have become possible due to the new architecture. Besides, since Advanced store certificates of previously dealt-with users, it can tell 'new' and 'old' peers apart. If you have successfully exchanged data with some peer, you may disable approval requirement for that peer while keeping it enabled for new ones.

Standard folders lack some of the new functionality offered by Advanced folders:

- The concept of folder Owner is not applicable to Standard folders. Only Owner can share Advanced folder with others. With Standard folders, peer can share the key it has without any limitations. 
- On-the-fly permission changes are not possible. The share needs to be removed from Sycn and re-added with the new key. 
- No user identity will be reflected in your peer list - only peer details and device names. Besides, if you share a folder with a user who has several devices linked under one certificate, on a Standard folder peer list each device will be displayed as a separate entity.

 
For example, we have an Advanced and a Standard folder added to Sync 2.7.3. Both folders are shared with another person, who has two devices - an Ubuntu and Fedora desktops - linked via My Devices:

If we click on the peer list (peers online) of the Advanced folder:

we'll see this:

Note that even though there are two peers in the main window, Sync is able to 'see' that they both belong to the same user - Alex. Clicking on the listed user entry we can see the individual peer names - "Ubuntu" and "Fedora":

However, if we click on the peer list of the Standard folder:

only the following information on the peers will be displayed:

With a Standard folder, Sync doesn't 'see' that the two peers are actually associated with one user - Alex - and displays them separately.

No other limitations apply, that is, both folder types enjoy high transfer speed, no folder-size limits, Selective Sync, etc.