How to sign PSBT transactions in UniSat? (Batch Signing)

Understanding PSBT in UniSat Wallet

1. PSBT stands for Partially Signed Bitcoin Transaction, a standardized format enabling multi-signature and air-gapped signing workflows across Bitcoin wallets.

2. UniSat supports PSBT natively through its browser extension and mobile interface, allowing users to construct, review, and finalize transactions without exposing private keys.

3. The wallet parses raw PSBT data, displays inputs, outputs, fees, and script details before requesting user confirmation.

4. Signing occurs locally inside the browser environment using cryptographic libraries compiled to WebAssembly, ensuring no private key leaves the device.

5. UniSat validates BIP-174 compliance during import, rejecting malformed or tampered PSBTs with clear error messages.

Preparing for Batch Signing

1. Users must enable “Advanced Mode” in UniSat Settings to unlock batch PSBT functionality.

2. Multiple PSBT files can be imported simultaneously via drag-and-drop or file selection—supported formats include .psbt, .txt, and base64-encoded strings.

3. Each transaction is scanned for compatibility: Taproot inputs require Schnorr signatures; legacy P2PKH requires ECDSA; P2SH-P2WPKH requires nested witness verification.

4. UniSat cross-checks UTXO status against its internal indexer and external full node fallbacks to prevent double-spends or dust output errors.

5. Fee estimation uses dynamic mempool analysis, adjusting per input weight and output count to maintain optimal inclusion probability.

Executing Batch Signing Workflow

1. After importing multiple PSBTs, UniSat renders a consolidated preview screen listing all transactions with total fee, cumulative size, and estimated confirmation time.

2. Users may toggle individual transactions on or off before signing—disabled items remain unprocessed but stay loaded for later activation.

3. Signing initiates only after explicit user approval; a hardware wallet prompt appears if Ledger or Coldcard is connected and configured.

4. UniSat applies deterministic signature order based on input derivation paths, preserving compatibility with multisig coordinators like Sparrow or Specter Desktop.

5. Once signed, each PSBT is reassembled with new witness data and exported as separate base64 strings or downloadable .psbt files.

Verification and Broadcast Options

1. Signed PSBTs display a green checkmark icon next to each item indicating successful signature attachment and internal consistency validation.

2. Users can click any transaction to view raw hex, decoded inputs/outputs, sighash type, and final weight units before broadcast.

3. UniSat integrates with multiple public broadcast endpoints including Mempool.space, Blockstream Green, and its own relay node with fallback routing.

4. If broadcast fails due to policy violations (e.g., non-standard scripts or excessive sigops), detailed rejection reasons are shown alongside suggested corrections.

5. A local copy of every signed PSBT remains accessible under “History > Signed Transactions”, searchable by timestamp or txid prefix.

Frequently Asked Questions

Q: Can I batch sign PSBTs containing both Taproot and legacy inputs?Yes. UniSat processes each input independently according to its scriptPubKey type and applies the correct signing algorithm without requiring uniformity across the batch.

Q: Does UniSat store my private keys when signing PSBTs?No. Private keys never leave the secure context of your browser or device memory. All cryptographic operations occur locally using WebCrypto API or WASM-based secp256k1 implementations.

Q: Why does one PSBT in my batch show “Invalid Input” while others succeed?This usually indicates an outdated UTXO state, mismatched derivation path, or unsupported descriptor format. UniSat flags such cases individually rather than halting the entire batch.

Q: Is there a limit to how many PSBTs I can sign at once?The practical limit depends on device RAM and browser constraints. UniSat enforces a default cap of 20 PSBTs per batch to ensure stable rendering and signing performance.