Air-gapped signing
Air gap
Air-gapped signing means signing transactions on a device that has no cable or wireless connection to a computer, passing the unsigned and signed transaction by memory card or QR code.
The computer writes a PSBT to a memory card or displays it as QR codes. The isolated device reads it, shows the details, signs after confirmation and passes the result back the same way.
The approach removes USB and wireless links as an attack path, which suits long-term cold storage. It does not remove the need to check the destination address on the device screen.
It is slower than signing over a cable, which is usually acceptable for savings that move rarely.
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