The Key is the identifier that connects different devices together and allows them to sync files across devices. We automatically generate random Keys to ensure their uniqueness. Since each Key is 20 bytes or more long, it is virtually impossible that other people can see your synced files and download them without it.
After a folder is added to Resilio Sync, the Key is stored in Resilio Sync folder and can be accessed by clicking on a folder context menu and selecting 'preferences'.
There are several types of Keys:
- Full Access Key
- Read-Only Key for one-way sync
- One-time secrets (both full access and read-only).
API users have an additional option to generate folder backup Key with encrypted peer support.
Encryption secrets are read-only and make sync data encrypted on the receiver’s side (peers can sync files, but cannot see their content or modify them). Such secrets are useful when syncing to an un-trusted location.
How does the key work?
Sync calculates the unique byte sequence from the key (folder ID) and asks Tracker server (if allowed to) or LAN (also, if allowed to) if there are any peers with the same folder ID. If communication done over Tracker, the Tracker server will let the peer know the IPs of other peers with same folder ID so they can connect directly. If comms done in LAN - well, then peers will discover each other using multicast packets.
After peers found each other, they use the key to establish a session encryption key which will be used to encrypt the traffic between them.
Please see more information on Keys here.