Air-Gapped Signing

Air-gapped signing is the practice of signing Bitcoin transactions on a device that has no network connection of any kind, no USB data link, Wi-Fi, Bluetooth, or cellular. Instead, the unsigned transaction is carried to the signer across an air gap using QR codes, a microSD card, or NFC, signed there, and carried back out the same way. Because the signing device is never reachable over any network, remote attackers have no channel to it even while it holds your keys.

PSBT makes it interoperable

The data passed across the gap is a Partially Signed Bitcoin Transaction, standardized in BIP174. A PSBT carries the unsigned transaction plus everything the offline signer needs to verify amounts and fees and apply its signature, without access to the live UTXO set. Any BIP174-compliant coordinator can hand a PSBT to any compliant signer, so air-gapped workflows are portable across wallets and devices rather than locked to one brand.

Verify on the trusted screen

The security of an air gap collapses if you sign blindly. The signer displays the destination, amount, and fee on its own screen, and you confirm those match what you intended before approving. This defends against malware on the online coordinator that might swap an address. The air gap stops remote key extraction; on-device verification stops you from signing a tampered transaction.

The unsigned transaction is usually drafted in a Watch-Only Wallet; D-Central covers the full standard in our guide to Partially Signed Bitcoin Transactions.