Written for Synergy 3 (v3.7.2), checked 3 October 2026.
When a computer first connects, Synergy 3 shows a code on both screens. Check the codes match, then click Codes match on both computers. That proves you're connecting to your own computer and not something pretending to be it.
Verify a computer
- On the primary computer, a Computer wants to connect message appears. On the other computer, it reads Connect to this computer?.
- Compare the code under Check this code matches on both screens: on both computers.
- If they match, click Codes match on both computers. If they don't, click Codes don't match.
Both computers must accept before they connect. Closing the message counts as not accepting. If several computers are waiting, you'll see how many and they're asked one at a time. To compare the full certificate fingerprints instead, switch on Show fingerprints; the buttons then read Fingerprints match and Fingerprints don't match.
If the codes didn't match, you'll see Not connected. Click Compare again to retry, or check you compared with the right screen.
Other messages you may see
- New certificate from a computer: it presents a different certificate from the one you accepted. That's expected after you reinstall or reset Synergy 3 on it. If you didn't, click the don't-match button.
- Can't verify a computer: it runs an older version of Synergy 3 that can't show a code. Update it, or click Connect without verifying if you trust your network, or Don't connect.
- An older Synergy 3 can't connect: update the named computers to connect securely. Security settings opens the settings below; Keep blocking leaves them disconnected.
Security settings
Go to Security (under Advanced).
- TLS encryption (recommended): encrypts everything sent between your computers. On by default, and shared with all your computers. Available with Synergy 3 Plus, Synergy 3 Max and Synergy Business; on Synergy 3 Lite you'll see Upgrade for TLS.
- Key length: 2048 or 4096 (the default).
- Certificate path: where this computer's certificate is stored.
When TLS encryption is on, two more lists appear. Under This computer:
- Only allow verified computers (recommended): on by default. When this computer is primary, every computer must be verified with a code before it can connect. Turn it off only to let an older version of Synergy 3 connect; any computer on your network could then pose as one of yours.
- Fingerprint: this computer's certificate fingerprint, to compare when you use Show fingerprints.
Under Other computers, each computer you've verified shows as Trusted. Click Forget to remove it; you'll be asked to verify it again next time it connects. A computer you turned down shows Not connected: declined on this computer. with a Compare again button.
For how Synergy 3 encryption works under the hood, see: Security and Architecture Overview