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stariusstarius
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add package scbforceclose
It provides function SignCloseTx which produces a signed force close transaction from a channel backup and private key material.
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‎scbforceclose/sign_close_tx.go

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package scbforceclose
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import (
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"errors"
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"fmt"
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"github.com/btcsuite/btcd/btcec/v2"
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"github.com/btcsuite/btcd/btcutil"
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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"github.com/btcsuite/btcd/txscript"
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"github.com/btcsuite/btcd/wire"
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"github.com/lightningnetwork/lnd/chanbackup"
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"github.com/lightningnetwork/lnd/channeldb"
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"github.com/lightningnetwork/lnd/fn/v2"
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"github.com/lightningnetwork/lnd/input"
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"github.com/lightningnetwork/lnd/keychain"
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"github.com/lightningnetwork/lnd/lnwallet"
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"github.com/lightningnetwork/lnd/shachain"
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)
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// SignCloseTx produces a signed commit tx from a channel backup.
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func SignCloseTx(s chanbackup.Single, keyRing keychain.KeyRing,
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ecdher keychain.ECDHRing, signer input.Signer) (*wire.MsgTx, error) {
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var errNoInputs = errors.New("channel backup does not have data " +
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"needed to sign force close tx")
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closeTxInputs, err := s.CloseTxInputs.UnwrapOrErr(errNoInputs)
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if err != nil {
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return nil, err
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}
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// Each of the keys in our local channel config only have their
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// locators populated, so we'll re-derive the raw key now.
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localMultiSigKey, err := keyRing.DeriveKey(
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s.LocalChanCfg.MultiSigKey.KeyLocator,
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)
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if err != nil {
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return nil, fmt.Errorf("unable to derive multisig key: %w", err)
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}
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// Determine the value of tapscriptRoot option.
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tapscriptRootOpt := fn.None[chainhash.Hash]()
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if s.Version.HasTapscriptRoot() {
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tapscriptRootOpt = closeTxInputs.TapscriptRoot
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}
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// Create signature descriptor.
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signDesc, err := createSignDesc(
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localMultiSigKey, s.RemoteChanCfg.MultiSigKey.PubKey,
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s.Version, s.Capacity, tapscriptRootOpt,
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)
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if err != nil {
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return nil, fmt.Errorf("failed to create signDesc: %w", err)
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}
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// Build inputs for GetSignedCommitTx.
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inputs := lnwallet.SignedCommitTxInputs{
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CommitTx: closeTxInputs.CommitTx,
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CommitSig: closeTxInputs.CommitSig,
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OurKey: localMultiSigKey,
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TheirKey: s.RemoteChanCfg.MultiSigKey,
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SignDesc: signDesc,
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}
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// Add special fields in case of a taproot channel.
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if s.Version.IsTaproot() {
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producer, err := createTaprootNonceProducer(
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s.ShaChainRootDesc, localMultiSigKey.PubKey, ecdher,
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)
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if err != nil {
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return nil, err
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}
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inputs.Taproot = fn.Some(lnwallet.TaprootSignedCommitTxInputs{
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CommitHeight: closeTxInputs.CommitHeight,
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TaprootNonceProducer: producer,
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TapscriptRoot: tapscriptRootOpt,
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})
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}
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return lnwallet.GetSignedCommitTx(inputs, signer)
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}
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// createSignDesc creates SignDescriptor from local and remote keys,
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// backup version and capacity.
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// See LightningChannel.createSignDesc on how signDesc is produced.
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func createSignDesc(localMultiSigKey keychain.KeyDescriptor,
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remoteKey *btcec.PublicKey, version chanbackup.SingleBackupVersion,
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capacity btcutil.Amount, tapscriptRoot fn.Option[chainhash.Hash]) (
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*input.SignDescriptor, error) {
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var fundingPkScript, multiSigScript []byte
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localKey := localMultiSigKey.PubKey
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var err error
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if version.IsTaproot() {
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fundingPkScript, _, err = input.GenTaprootFundingScript(
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localKey, remoteKey, int64(capacity), tapscriptRoot,
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)
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if err != nil {
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return nil, err
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}
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} else {
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multiSigScript, err = input.GenMultiSigScript(
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localKey.SerializeCompressed(),
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remoteKey.SerializeCompressed(),
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)
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if err != nil {
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return nil, err
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}
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fundingPkScript, err = input.WitnessScriptHash(multiSigScript)
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if err != nil {
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return nil, err
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}
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}
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return &input.SignDescriptor{
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KeyDesc: localMultiSigKey,
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WitnessScript: multiSigScript,
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Output: &wire.TxOut{
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PkScript: fundingPkScript,
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Value: int64(capacity),
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},
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HashType: txscript.SigHashAll,
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PrevOutputFetcher: txscript.NewCannedPrevOutputFetcher(
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fundingPkScript, int64(capacity),
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),
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InputIndex: 0,
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}, nil
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}
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// createTaprootNonceProducer makes taproot nonce producer from a
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// ShaChainRootDesc and our public multisig key.
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func createTaprootNonceProducer(shaChainRootDesc keychain.KeyDescriptor,
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localKey *btcec.PublicKey, ecdher keychain.ECDHRing) (shachain.Producer,
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error) {
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if shaChainRootDesc.PubKey != nil {
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return nil, errors.New("taproot channels always use ECDH, " +
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"but legacy ShaChainRootDesc with pubkey found")
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}
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// This is the scheme in which the shachain root is derived via an ECDH
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// operation on the private key of ShaChainRootDesc and our public
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// multisig key.
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ecdh, err := ecdher.ECDH(shaChainRootDesc, localKey)
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if err != nil {
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return nil, fmt.Errorf("ecdh failed: %w", err)
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}
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// The shachain root that seeds RevocationProducer for this channel.
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revRoot := chainhash.Hash(ecdh)
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revocationProducer := shachain.NewRevocationProducer(revRoot)
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return channeldb.DeriveMusig2Shachain(revocationProducer)
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}

‎scbforceclose/sign_close_tx_test.go

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package scbforceclose
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import (
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"bytes"
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_ "embed"
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"encoding/hex"
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"encoding/json"
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"strings"
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"testing"
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"github.com/btcsuite/btcd/btcutil/hdkeychain"
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"github.com/btcsuite/btcd/chaincfg"
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"github.com/btcsuite/btcd/txscript"
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"github.com/lightninglabs/chantools/lnd"
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"github.com/lightningnetwork/lnd/aezeed"
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"github.com/lightningnetwork/lnd/chanbackup"
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"github.com/lightningnetwork/lnd/input"
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"github.com/stretchr/testify/require"
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)
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//go:embed testdata/channel_backups.json
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var channelBackupsJSON []byte
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// TestSignCloseTx tests that SignCloseTx produces valid transactions.
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func TestSignCloseTx(t *testing.T) {
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// Load prepared channel backups with seeds and passwords.
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type TestCase struct {
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Name string `json:"name"`
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RootKey string `json:"rootkey"`
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Password string `json:"password"`
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Mnemonic string `json:"mnemonic"`
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Single bool `json:"single"`
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ChannelBackup string `json:"channel_backup"`
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PkScript string `json:"pk_script"`
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AmountSats int64 `json:"amount_sats"`
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}
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var testdata struct {
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Cases []TestCase `json:"cases"`
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}
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require.NoError(t, json.Unmarshal(channelBackupsJSON, &testdata))
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chainParams := &chaincfg.RegressionNetParams
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for _, tc := range testdata.Cases {
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t.Run(tc.Name, func(t *testing.T) {
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var extendedKey *hdkeychain.ExtendedKey
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if tc.RootKey != "" {
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// Parse root key.
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var err error
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extendedKey, err = hdkeychain.NewKeyFromString(
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tc.RootKey,
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)
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require.NoError(t, err)
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} else {
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// Generate root key from seed and password.
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words := strings.Split(tc.Mnemonic, " ")
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require.Len(t, words, 24)
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var mnemonic aezeed.Mnemonic
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copy(mnemonic[:], words)
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cipherSeed, err := mnemonic.ToCipherSeed(
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[]byte(tc.Password),
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)
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require.NoError(t, err)
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extendedKey, err = hdkeychain.NewMaster(
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cipherSeed.Entropy[:], chainParams,
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)
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require.NoError(t, err)
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}
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// Make key ring and signer.
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keyRing := &lnd.HDKeyRing{
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ExtendedKey: extendedKey,
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ChainParams: chainParams,
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}
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signer := &lnd.Signer{
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ExtendedKey: extendedKey,
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ChainParams: chainParams,
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}
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musigSessionManager := input.NewMusigSessionManager(
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signer.FetchPrivateKey,
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)
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signer.MusigSessionManager = musigSessionManager
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// Unpack channel.backup.
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backup, err := hex.DecodeString(
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tc.ChannelBackup,
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)
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require.NoError(t, err)
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r := bytes.NewReader(backup)
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var s chanbackup.Single
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if tc.Single {
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err := s.UnpackFromReader(r, keyRing)
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require.NoError(t, err)
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} else {
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var m chanbackup.Multi
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err := m.UnpackFromReader(r, keyRing)
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require.NoError(t, err)
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// Extract a single channel backup from
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// multi backup.
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require.Len(t, m.StaticBackups, 1)
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s = m.StaticBackups[0]
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}
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// Sign force close transaction.
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sweepTx, err := SignCloseTx(
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s, keyRing, signer, signer,
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)
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require.NoError(t, err)
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// Check if the transaction is valid.
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pkScript, err := hex.DecodeString(tc.PkScript)
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require.NoError(t, err)
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fetcher := txscript.NewCannedPrevOutputFetcher(
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pkScript, tc.AmountSats,
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)
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sigHashes := txscript.NewTxSigHashes(sweepTx, fetcher)
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vm, err := txscript.NewEngine(
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pkScript, sweepTx, 0,
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txscript.StandardVerifyFlags,
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nil, sigHashes, tc.AmountSats, fetcher,
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)
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require.NoError(t, err)
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require.NoError(t, vm.Execute())
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})
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}
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}

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