Security

ClipPair moves what you copy between your own computers. This page explains, in plain terms, how that is protected and where the protection stops.

The short version

• Your clipboard never leaves your network. Copies go straight from one of your computers to another. They never pass through a server, ours or anyone else's.
• Every connection is encrypted end to end, and both computers prove who they are before anything is sent.
• Only computers that know your six pairing words can connect.
• ClipPair only talks to computers on your local network.
• Updates are signed. ClipPair checks the signature before it installs anything.
• License checks never include your clipboard. They send your license key and a public key, nothing else from your computer.

Your pairing words

• ClipPair picks six words at random from a list of 1,296. That is about 4.7 quintillion possible combinations.
• The words are turned into an encryption key with Argon2id, a function that is deliberately slow and memory-hungry, so guessing words is expensive.
• The words and that key are kept in your computer's secure credential store: Windows Credential Manager or the macOS Keychain. The words are never written to a file or a log. If the credential store is unavailable, the key (not the words) is kept in a file only your user account can read.
• Treat the words like a password. Anyone who has them can add a computer to your group. Use the words ClipPair generates; don't make up your own.

How your computers connect

• Connections use the Noise protocol framework (Noise_XXpsk3, with X25519, ChaCha20-Poly1305 and BLAKE2s), the same framework WireGuard is built on.
• Each computer has its own private key, created the first time ClipPair runs and kept in the credential store.
• The first time two computers connect, each one remembers the other's key. If a computer it already knows later shows up with a different key, ClipPair refuses the connection.
• Your pairing words are needed on every connection, not just the first one.
• By default ClipPair only connects to private network addresses (your home or office network), never the open internet.
• Devices on your network that aren't paired can't crash ClipPair, fill your disk with log lines, or disconnect your computers.
• If your Wi-Fi blocks automatic discovery, ClipPair remembers your computers' addresses and also looks for them on the local network. Only computers with your words can connect.

What someone on your network can see

They can see that ClipPair is running, your computers' names and addresses, and when and how much data moves between them. They can also see a group identifier that shows which computers are paired with each other, and can link those computers across networks. They can't see what you copy.

What stays on your computer

• Your clipboard: only the current copy, in memory.
• Clipboard history: off unless you turn it on. When on, it keeps text only, encrypted on that computer.
• In the credential store: the computer's private key, your pairing words and key, and your license key.
• In the settings folder: your settings, your signed license token, the public keys of computers this one has connected to, and logs. Logs never contain keys or pairing words.

Updates

• ClipPair checks for updates at launch and about once a day. Turn this off in Settings with Check for updates automatically. The check sends no license key and no device ID.
• Every update comes with a description signed with ClipPair's update key. ClipPair checks the signature, the file size and the file's checksum before installing.
• Windows: Windows Installer does the install and rolls back if it fails.
• Mac: the new version must also pass Apple's code-signing and notarization checks and come from the same developer. If it doesn't start correctly, ClipPair rolls back to the previous version.
• Updates install when you choose Install update…, or by themselves if you turn on Install updates automatically (off by default).

Your license

• When you activate, ClipPair sends your license key, that computer's public key and the ClipPair version, over HTTPS.
• About once a week, a licensed computer renews in the background, sending only the license key and its public key. A renewal lasts 3 weeks, so a licensed computer that can't reach the internet keeps syncing for up to 3 weeks, then pauses until it can renew.
• Computers that joined with your words send nothing to the license server. They sync on a licensed computer's renewal, so the same 3-week limit applies to them if that computer stops renewing.
• Never sent: clipboard content, pairing words, computer names or history.
• Keep your computer's clock correct; the license depends on the date.
• The Privacy policy lists exactly what the license server stores.

Where the protection stops

• Anyone with your pairing words can join your group. Groups in the Devices window control what gets shared, but they don't keep out a computer that has your words.
• ClipPair can't protect a computer that is already compromised. Malware running on one of your computers can read that computer's clipboard and keys.
• Offline guessing is expensive, not impossible. Someone who records your network traffic could try to guess your words offline. The huge number of combinations and the slow key function make that impractical, which is why the words must be random.

If something goes wrong

• A computer is lost or stolen, or someone may have your words: on each of your other computers, choose Forget pairing… in Settings, then pair them again. That creates new words; the old ones stop working.
• ClipPair warns that a computer's key changed: don't reset it unless you know why it changed, for example you reinstalled that computer.
• Found a security problem? Email support@clippair.app. We reply within 24 hours.