// signMultiSigUTXO signs the P2SH UTXO with the given index by constructing a // script containing all given signatures plus the redeem (multi-sig) script. The // redeem script is obtained by looking up the address of the given P2SH pkScript // on the address manager. // The order of the signatures must match that of the public keys in the multi-sig // script as OP_CHECKMULTISIG expects that. // This function must be called with the manager unlocked. func signMultiSigUTXO(mgr *waddrmgr.Manager, tx *wire.MsgTx, idx int, pkScript []byte, sigs []RawSig) error { class, addresses, _, err := txscript.ExtractPkScriptAddrs(pkScript, mgr.ChainParams()) if err != nil { return newError(ErrTxSigning, "unparseable pkScript", err) } if class != txscript.ScriptHashTy { return newError(ErrTxSigning, fmt.Sprintf("pkScript is not P2SH: %s", class), nil) } redeemScript, err := getRedeemScript(mgr, addresses[0].(*btcutil.AddressScriptHash)) if err != nil { return newError(ErrTxSigning, "unable to retrieve redeem script", err) } class, _, nRequired, err := txscript.ExtractPkScriptAddrs(redeemScript, mgr.ChainParams()) if err != nil { return newError(ErrTxSigning, "unparseable redeem script", err) } if class != txscript.MultiSigTy { return newError(ErrTxSigning, fmt.Sprintf("redeem script is not multi-sig: %v", class), nil) } if len(sigs) < nRequired { errStr := fmt.Sprintf("not enough signatures; need %d but got only %d", nRequired, len(sigs)) return newError(ErrTxSigning, errStr, nil) } // Construct the unlocking script. // Start with an OP_0 because of the bug in bitcoind, then add nRequired signatures. unlockingScript := txscript.NewScriptBuilder().AddOp(txscript.OP_FALSE) for _, sig := range sigs[:nRequired] { unlockingScript.AddData(sig) } // Combine the redeem script and the unlocking script to get the actual signature script. sigScript := unlockingScript.AddData(redeemScript) script, err := sigScript.Script() if err != nil { return newError(ErrTxSigning, "error building sigscript", err) } tx.TxIn[idx].SignatureScript = script if err := validateSigScript(tx, idx, pkScript); err != nil { return err } return nil }