Security & Encryption

TetherDroid is built so that your private conversations, calls, notifications, and screen stay yours — visible only on your own paired devices, and to no one in between, including us. This page explains, at a high level, how that works and why we designed it the way we did.

1. The short version
2. End-to-end encryption
3. Why we can't see your content — even in flight
4. Pairing: keys that never leave your devices
5. Why we drive the phone through automation (RCS, not SMS)
6. What stays on your devices

The short version

• Everything TetherDroid moves between your phone and your desktop is encrypted end-to-end with strong, modern cryptography.
• The encryption keys are created directly between your two devices when you pair them, and are never sent to or stored on our servers.
• Our relay servers only ever pass along encrypted, unreadable data. We cannot decrypt it, and neither can anyone who might intercept it in transit.
• We interact with your messages through your phone's secure RCS channel via Google Messages — not by reading or sending raw SMS.

End-to-end encryption

TetherDroid uses end-to-end encryption (E2EE). That means content is encrypted on the device that sends it and can only be decrypted on the other device you paired — the two endpoints. Nothing readable exists anywhere in between.

Under the hood we use AES‑256 in GCM mode, an industry-standard authenticated-encryption algorithm. "Authenticated" means the encryption also protects against tampering: if data were altered in transit, the receiving device would detect it and reject it rather than trust it. Every message, notification, screen frame, audio packet, and control command is encrypted this way before it ever leaves the device.

Why we can't see your content — even in flight

Your two devices don't connect directly to each other; they connect through a lightweight TetherDroid relay so they can find and reach each other from anywhere. But the relay is deliberately built to be blind:

• By the time any data reaches our servers, it is already encrypted with a key only your two devices hold.
• Our relay simply forwards those encrypted bytes from one of your devices to the other. It does not — and cannot — decrypt, inspect, log, or store the content.
• Because we never hold the decryption key, there is nothing on our side that could reveal your messages, calls, notifications, or screen. This isn't a policy promise we ask you to trust — it's a property of the design: we don't have the key.

The same holds for anyone else in the network path between your devices: they'd see only unreadable ciphertext.

Pairing: keys that never leave your devices

When you pair your phone with your desktop, TetherDroid shows a one-time pairing code (as a code and QR) that you confirm on the phone. That out-of-band step is what lets both devices independently derive the same shared encryption key — combining that pairing secret with a per-account secret.

Crucially, the key itself is never transmitted through our servers. It is computed on each device, so the full key exists only on your phone and your desktop. Even during pairing, an observer watching the network never sees the key — only the two endpoints ever possess it.

Why we drive the phone through automation (RCS, not SMS)

TetherDroid interacts with your messages by securely automating Google Messages on your own phone — reading the conversation that's on screen and sending on your behalf — rather than intercepting or re-sending raw SMS the way many "text from your computer" tools do. This is a deliberate security choice:

• RCS is genuinely secure; SMS is not. Modern messaging on Android uses RCS, which supports end-to-end encryption between participants through your phone's own secure handshake. Traditional SMS has no such protection — it's an old protocol with no meaningful encryption, and tools that route your texts as SMS give up that security entirely.
• We use the phone's real, secure channel. By driving Google Messages directly on your device, your messages continue to be sent and received over the same trusted, RCS-secured channel your phone already uses — with its native encryption fully intact. TetherDroid is simply your hands on your own phone, from your desktop.
• Nothing is re-routed through a less-secure path. Your conversations never get downgraded to an insecure transport or funneled through a third-party SMS gateway. The message content stays within your phone's secure messaging pipeline, and the mirror to your desktop is separately protected by TetherDroid's own end-to-end encryption described above.

The result is the best of both: the convenience of texting and calling from your computer, without trading away the security your phone's RCS messaging already gives you.

What stays on your devices

• Encryption keys live only on your phone and desktop — never on our servers.
• Your content (messages, call info, notifications, screen) is only ever decrypted on your paired devices.
• TetherDroid steps back automatically when you're actively using your phone, and you can pause it at any time.

Have a security question or concern? Contact Us.