Transaction Signing

Sending Bitcoin from a Sigvault wallet is a multi-step process: build the transaction, collect the required signatures, finalize, and broadcast. The steps vary depending on the wallet type and number of signers.

Transaction Lifecycle

Every transaction follows this lifecycle:

Draft → Pending Signatures → Signed → Broadcast

1. Draft — The transaction is built with inputs, outputs, and fees
2. Pending Signatures — Waiting for the required devices to sign
3. Signed — All required signatures collected, transaction finalized
4. Broadcast — Sent to the Bitcoin network

Building a Transaction

From the wallet detail page:

1. Click Send
2. Enter the destination address and amount
3. For taproot vaults, select the spending condition to use
4. Review the transaction details:
   • Inputs (UTXOs being spent)
   • Outputs (destination + change)
   • Fee rate and total fee
5. Confirm to create the transaction draft

Sigvault builds a PSBT (Partially Signed Bitcoin Transaction) — a standard format that allows signatures to be added incrementally.

Signing

Single Signature / Hot Wallet

1. The PSBT is sent to the signing device (hardware wallet or system key)
2. For hardware wallets: the desktop app relays the PSBT to your device, which displays the transaction for verification
3. Approve on the device
4. One signature completes the transaction

Multisig Wallet

1. The PSBT is created and shared with all required signers
2. Each signer connects their hardware wallet through the desktop app
3. Each device signs independently — signers don’t need to be online simultaneously
4. Sigvault tracks signature progress (e.g., “1 of 2 signatures collected”)
5. Once the threshold is met, the transaction is finalized

Taproot Vault

1. Choose which spending condition to use
2. The PSBT is built targeting the selected spending path
3. If the condition has a time lock, it must have expired for the transaction to be valid
4. Collect signatures from the devices assigned to that condition
5. The transaction is finalized with the appropriate Taproot witness data

PSBT Format

Sigvault uses the PSBT standard (BIP-174) throughout the signing process. PSBTs allow:

• Incremental signing — Different devices can sign at different times
• Hardware wallet compatibility — All major hardware wallets support PSBT
• Verification — Each signer can independently verify transaction details
• Offline signing — PSBTs can be transported via QR code or file for air-gapped devices

Signing Ceremony

For wallets requiring multiple signatures, Sigvault manages a signing ceremony:

1. A signing ceremony is created when the transaction draft is submitted
2. Signature requests are generated for each required device
3. As each device signs, the signature is verified and added to the PSBT
4. The ceremony tracks progress and notifies when the threshold is reached
5. Once complete, the transaction is automatically finalized

Finalizing and Broadcasting

After all required signatures are collected:

1. Finalization — The PSBT is converted into a complete, signed Bitcoin transaction
2. Broadcasting — The transaction is sent to the Bitcoin network via the connected node
3. Confirmation — The transaction appears in the wallet’s history as pending until confirmed in a block

Verifying Transactions

Before approving a transaction on your hardware wallet, always verify:

• Destination address — Matches what you entered in the web app
• Amount — Correct value being sent
• Fee — Reasonable for current network conditions
• Change — Returns to your wallet

Hardware wallets display these details on their screen, independent of the Sigvault web interface.

Fee Management

Transaction fees are calculated based on:

• Fee rate — Satoshis per virtual byte (sat/vB)
• Transaction size — Depends on the number of inputs, outputs, and script complexity
• UTXO selection — Sigvault selects UTXOs to minimize fees while meeting the target amount

You can review the fee before approving the transaction.