Sign PSBT

This section explains how to sign PSBT (Partially Signed Bitcoin Transactions) with Cosmostation Extension.

PSBT signing is commonly used for advanced Bitcoin workflows, including:

• multi-step transaction flows (prepare → sign → finalize/broadcast)
• custody-separated signing (dApp constructs PSBT, wallet signs)

Cosmostation’s Bitcoin provider supports both:

• signPsbt(psbtHex) for a single PSBT
• signPsbts(psbtsHexes) for multiple PSBTs in one flow

Note: The provider expects PSBT input as a hex string. Internally, Cosmostation normalizes the PSBT hex (e.g., formatting / prefix handling) before sending it to the wallet signing layer.

SDK Integration (Tomo Wallet SDK)

If you are using Tomo Wallet SDK, PSBT signing is performed through the SDK-exposed bitcoinProvider, which implements the BTCProvider interface.

Sign a Single PSBT

// psbtHex: string (hex-encoded PSBT)
const signedPsbt = await bitcoinProvider.signPsbt(psbtHex);
 
console.log('Signed PSBT:', signedPsbt);

Sign Multiple PSBTs

// psbtsHexes: string[] (array of hex-encoded PSBTs)
const signedPsbts = await bitcoinProvider.signPsbts(psbtsHexes);
 
console.log('Signed PSBTs:', signedPsbts);

Use batch signing when your flow requires multiple related signatures (for example, separate PSBTs for different stages or different inputs).

Vanilla JavaScript

If you are not using the SDK, you can call the injected provider directly.

Access Provider

const bitcoin = () => {
  if ('cosmostation' in window) return window.cosmostation.bitcoin;
  window.open('https://cosmostation.io/wallet/#extension');
};
 
const provider = bitcoin();

Sign a Single PSBT

await provider.connectWallet();
 
try {
  const signedPsbt = await provider.signPsbt(psbtHex);
  console.log('Signed PSBT:', signedPsbt);
} catch (e: any) {
  if (e?.code === 4001) {
    console.log('User rejected the request');
  } else {
    console.error(e);
  }
}

Sign Multiple PSBTs

await provider.connectWallet();
 
try {
  const signedPsbts = await provider.signPsbts(psbtsHexes);
  console.log('Signed PSBTs:', signedPsbts);
} catch (e: any) {
  if (e?.code === 4001) {
    console.log('User rejected the request');
  } else {
    console.error(e);
  }
}

Input Requirements

• psbtHex must be a valid PSBT hex string
• For batch signing, every entry in psbtsHexes must be a valid PSBT hex string
• The wallet will reject malformed PSBTs or unsupported signing requests

What the wallet returns

The exact output type depends on your provider’s implementation, but conceptually:

• For signPsbt, you receive the signed PSBT result
• For signPsbts, you receive an array of signed PSBTs, preserving the input order

In most dApps, the next step after signing is one of:

• finalize the PSBT into a raw transaction using your Bitcoin library/tooling
• broadcast the final transaction using your own backend or via pushTx(txHex)

Notes and Best Practices

• Always call connectWallet() before signing
• If your PSBT flow depends on a specific network (mainnet/testnet/signet), check getNetwork() first and guide the user accordingly

Creating PSBTs (Before Signing)

Cosmostation Extension does not construct PSBTs. Your dApp is responsible for creating a valid PSBT before passing it to the wallet for signing.

For PSBT construction, input selection, and transaction assembly, refer to the official bitcoinjs-lib documentation:

• bitcoinjs-lib (GitHub) (opens in a new tab)
• PSBT guide (opens in a new tab)
• API reference (opens in a new tab)

Typical PSBT creation flow with bitcoinjs-lib:

1. Initialize a Psbt instance with the correct network
2. Add inputs (UTXOs, scripts, witnesses)
3. Add outputs (recipient addresses, change)
4. Export PSBT as hex (psbt.toHex())
5. Pass the PSBT hex to signPsbt or signPsbts

Ensure that:

• Inputs belong to the connected wallet
• The PSBT matches the active Bitcoin network
• Required fields for signing (e.g. witnessUtxo) are properly set

Reference: Tomo SDK + Demo

• Tomo Docs – Sign PSBT (opens in a new tab)