Encryption and verifying your computers

Written for Synergy 3 (v3.8.4) and Synergy 1 (v1.22.3), checked 20 October 2026.

Synergy 3 and Synergy 1 encrypt your keyboard, mouse and copy and paste with TLS as they travel between your computers. The first time two computers connect, both ask you to check that you're connecting to your own computer and not something pretending to be it: Synergy 3 shows a code on both screens, and Synergy 1 shows each computer's fingerprint. The steps differ, so each product has its own section:

• Synergy 3
• Synergy 1

Synergy 3

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

1. On the primary computer, a Computer wants to connect message appears. On the other computer, it reads Connect to this computer?.
2. Compare the code under Check this code matches on both screens: on both computers.
3. 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 (advanced): both screens then show the same pair of fingerprints, one for each computer, and the buttons read Screens match and Screens 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.

On a work computer, your administrator may have chosen which computers can connect. You then aren't asked: only the computers they approved connect, and Other computers in the security settings reads Chosen by your administrator.

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 regenerate its certificate, give it your own certificate, change the key length or reset Synergy 3 on it. If you didn't, click Codes don't match.
• 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 your keyboard, mouse and copy and paste between your computers. On by default, and shared with all your computers. Available with Synergy Business, Synergy 3 Plus and Synergy 3 Max; on Synergy 3 Lite you'll see Upgrade for TLS.

When TLS encryption is on, more settings appear:

• Key length: 2048 or 4096 (the default). Changing it gives each computer a new certificate, so you'll compare codes again.
• Certificate: the certificate this computer uses, which Synergy 3 makes for you. To use your own, click Use your own certificate and choose a PEM file holding both the certificate and its private key (an RSA key of at least 2048 bits, with no password); Use a generated certificate switches back. To make a new one, click Regenerate certificate, then Regenerate certificate again to confirm. Either way, your other computers ask you to check a new code.

Below them are two lists. 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 (advanced).

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, and one that runs an older version shows Not connected: runs an older version of Synergy 3.

Synergy 1

Synergy 1 encrypts the connection between your computers with TLS when Enable TLS Encryption is ticked. It's on by default and needs a Synergy Business or Synergy 1 Pro license; with a Basic license, Synergy 1 turns it off when it starts. To encrypt the connection without it, see: Setting up an SSH connection with Synergy 1

Turn encryption on

1. On each computer, open Edit > Preferences (on macOS, Preferences is in the Synergy menu).
2. Click the Network tab.
3. Tick Enable TLS Encryption.
4. Click Save.

Do this on every computer. Once the computers are connected, hover over the green shield in the status bar: it reads Encryption Enabled, after the TLS version in use. If it reads Encryption Disabled, TLS is off on that computer.

Trust another computer the first time it connects

The first time a client connects to a server, Synergy 1 asks you to check that each is talking to the right computer:

• On the client, Connecting to a new server asks Do you want to connect to the server?
• On the server, when Require client certificates is ticked, New client connecting asks Trust client and allow connection?

Both windows show the Server Fingerprint and the Client Fingerprint side by side. Compare them with the other computer's own fingerprint before you click Yes: on that computer, click the fingerprint button in the status bar (View local fingerprint) to open Local Fingerprints. Click Show hash in either window to compare the fingerprint as text rather than as a picture. Only click Yes if they match. Clicking No on a client stops it connecting.

Once you've clicked Yes, Synergy 1 remembers the other computer and doesn't ask again, unless that computer gets a new certificate: after Regenerate certificate or a change of Key length, a reinstall that removed its settings, or Help > Clear settings. Then compare the new fingerprints the same way.

On a work computer, your administrator may have chosen which computers can connect. You then aren't asked: a computer that isn't approved is refused with Computer not approved, which shows that computer's fingerprint for you to give your administrator.

Encryption settings

All on the Network tab of Preferences:

Forget a trusted computer

Quit Synergy 1, then delete trusted-servers (on a client) or trusted-clients (on a server) from the tls folder. Synergy 1 asks you to trust each computer again on the next connection. Where the tls folder is:

• Windows: C:\ProgramData\Synergy\tls
• macOS: ~/Library/Synergy/tls, or /Library/Synergy/tls when settings are kept for all users
• Linux: ~/.config/Synergy/tls, or /etc/Synergy/tls when settings are kept for all users

More about security

For how Synergy 1 and Synergy 3 encryption works under the hood, see: Security and Architecture Overview

For security teams, the wider picture: Business & Enterprise Hardening Guide