Air-Gapped Signing

Air-gapped signing keeps a signing device permanently disconnected from any network: the unsigned transaction is carried to it by QR code, microSD card or camera, signed offline, and the signed result is carried back to an online device for broadcast. Because no USB, Bluetooth or internet link exists, remote malware has no channel to reach the keys, which is why the approach is used for long-term cold storage and institutional treasuries. It is slower and more error-prone than plugging in a device, and it does not protect against a tampered device, a leaked recovery phrase, or a user approving a malicious transaction shown on screen. Verify what the device displays every time.