How It Works
Install Sync on all devices you want to share with. You don’t need to create an account to get started.
Step 1 - Add a folder to Sync
When you add a folder to Sync, a set of read-only and read/write keys to the folder are created. These keys can then be shared with other devices.
Step 2 - Share the folder
Keys are shared with other people or device using one of three methods; a clickable HTTPS link representing the key can be sent over email or chat, a QR code can be presented for a mobile device to scan, or one of the keys can be entered directly on another device.
If sharing a folder using an HTTPS link, the key can be protected by requiring sender approval and setting link expiration by time and/or number of uses.
Step 3 - Devices become peers
Once a folder is added to Sync, it immediately tries to discover other devices that have a folder with the same key. Sync easily finds other devices by using multiple methods. It also allows Sync to work on a private network that is not connected to the Internet.
These methods include contacting user-defined IP addresses, looking on the local network, using the distributed hash table (DHT), automatically registering with a Sync-specific BitTorrent tracker, and using a relay server. While devices becoming peers is an automated activity, all of these methods can be enabled/disabled by the user.
Step 4 - Devices determine what to sync
After two or more devices confirm they have the same folder to sync, folder contents are compared between all peers. To do this, peers informs each other of its folder contents. Each device is then able to determine if it needs updates to its folder. Files that need to be transferred are placed in its queue. Sync is then ready to fetch files from its peers.
Step 5 - Files are transferred directly between peers
Each file contained in a Sync folder has an associated torrent and is broken up into small pieces before it is transferred. Using the BitTorrent protocol, this protocol allows devices to receive file pieces from any peer simultaneously. The more devices a folder is shared with, the faster files are transferred. While the speed is not visible to the user, the accelerated speeds will be noticeable.
File pieces are AES-128 encrypted when in transit. They are then decrypted and reassembled when they arrive at the destination.
File pieces take the shortest and fastest path to get from one device to another. Transferring files on a local network is most often fastest, while using the relay server to reach a device halfway around the world is often the slowest. This is different than cloud services, which have to send files through centralized data centers.