Tether brings iMessage, SMS, and OTP autofill to Linux for iPhone users

A developer who moved to Linux full-time built Tether to recover the Apple “Continuity” features they missed most: sending and receiving iMessage and SMS, file transfer, clipboard sync, notification mirroring, contact sync, and — the standout — automatic autofill of one-time passcodes arriving by mail or text. The project grew incrementally, starting with clipboard sync (which forced the underlying foundation into place), then file transfer, then OTP handling implemented through WebExtensions for Firefox-based browsers and Thunderbird-based mail clients. That extension approach works well but only covers those specific clients, leaving other mail apps unsupported for now.

The hard part was iMessage and SMS itself. Rather than run a Mac as a proxy — an approach the author tried and found unpleasant even over Tailscale — Tether talks to the iPhone directly. That became feasible after the author found projects like ancs4linux and BlueFerry, plus protocol documentation that explained the Bluetooth-based interface. Because those projects are GPL and Tether is MIT, the author wrote a clean-room C++ implementation, arguing that an interoperability protocol should be usable regardless of a consuming project’s license (floating the idea of a reusable “libtether”). The Bluetooth integration was reportedly painful, requiring extensive edge-case handling.

Security has been a design constraint from the start: communication between the iOS app and the Linux daemon uses mTLS with mutual pairing required before anything is exchanged, and the author says they run regular Claude-assisted (Opus and Fable) bug and security sweeps. Tether is free, MIT-licensed, and open to contributions. Its significance is less about novel technology than about chipping away at Apple’s walled-garden lock-in — giving Linux-plus-iPhone users a self-hosted, local alternative to Continuity without routing messages through a Mac or a cloud service.