package lnwallet import ( "bytes" "crypto/sha256" "errors" "fmt" "net" "sync" "sync/atomic" "github.com/btcsuite/btcd/blockchain" "github.com/btcsuite/btcd/btcec" "github.com/btcsuite/btcd/chaincfg/chainhash" "github.com/btcsuite/btcd/txscript" "github.com/btcsuite/btcd/wire" "github.com/btcsuite/btcutil" "github.com/btcsuite/btcutil/txsort" "github.com/davecgh/go-spew/spew" "github.com/lightningnetwork/lnd/channeldb" "github.com/lightningnetwork/lnd/input" "github.com/lightningnetwork/lnd/keychain" "github.com/lightningnetwork/lnd/lnwallet/chainfee" "github.com/lightningnetwork/lnd/lnwallet/chanfunding" "github.com/lightningnetwork/lnd/lnwallet/chanvalidate" "github.com/lightningnetwork/lnd/lnwire" "github.com/lightningnetwork/lnd/shachain" ) const ( // The size of the buffered queue of requests to the wallet from the // outside word. msgBufferSize = 100 ) // InitFundingReserveMsg is the first message sent to initiate the workflow // required to open a payment channel with a remote peer. The initial required // parameters are configurable across channels. These parameters are to be // chosen depending on the fee climate within the network, and time value of // funds to be locked up within the channel. Upon success a ChannelReservation // will be created in order to track the lifetime of this pending channel. // Outputs selected will be 'locked', making them unavailable, for any other // pending reservations. Therefore, all channels in reservation limbo will be // periodically timed out after an idle period in order to avoid "exhaustion" // attacks. type InitFundingReserveMsg struct { // ChainHash denotes that chain to be used to ultimately open the // target channel. ChainHash *chainhash.Hash // PendingChanID is the pending channel ID for this funding flow as // used in the wire protocol. PendingChanID [32]byte // NodeID is the ID of the remote node we would like to open a channel // with. NodeID *btcec.PublicKey // NodeAddr is the address port that we used to either establish or // accept the connection which led to the negotiation of this funding // workflow. NodeAddr net.Addr // SubtractFees should be set if we intend to spend exactly // LocalFundingAmt when opening the channel, subtracting the fees from // the funding output. This can be used for instance to use all our // remaining funds to open the channel, since it will take fees into // account. SubtractFees bool // LocalFundingAmt is the amount of funds requested from us for this // channel. LocalFundingAmt btcutil.Amount // RemoteFundingAmnt is the amount of funds the remote will contribute // to this channel. RemoteFundingAmt btcutil.Amount // CommitFeePerKw is the starting accepted satoshis/Kw fee for the set // of initial commitment transactions. In order to ensure timely // confirmation, it is recommended that this fee should be generous, // paying some multiple of the accepted base fee rate of the network. CommitFeePerKw chainfee.SatPerKWeight // FundingFeePerKw is the fee rate in sat/kw to use for the initial // funding transaction. FundingFeePerKw chainfee.SatPerKWeight // PushMSat is the number of milli-satoshis that should be pushed over // the responder as part of the initial channel creation. PushMSat lnwire.MilliSatoshi // Flags are the channel flags specified by the initiator in the // open_channel message. Flags lnwire.FundingFlag // MinConfs indicates the minimum number of confirmations that each // output selected to fund the channel should satisfy. MinConfs int32 // CommitType indicates what type of commitment type the channel should // be using, like tweakless or anchors. CommitType CommitmentType // ChanFunder is an optional channel funder that allows the caller to // control exactly how the channel funding is carried out. If not // specified, then the default chanfunding.WalletAssembler will be // used. ChanFunder chanfunding.Assembler // err is a channel in which all errors will be sent across. Will be // nil if this initial set is successful. // // NOTE: In order to avoid deadlocks, this channel MUST be buffered. err chan error // resp is channel in which a ChannelReservation with our contributions // filled in will be sent across this channel in the case of a // successfully reservation initiation. In the case of an error, this // will read a nil pointer. // // NOTE: In order to avoid deadlocks, this channel MUST be buffered. resp chan *ChannelReservation } // fundingReserveCancelMsg is a message reserved for cancelling an existing // channel reservation identified by its reservation ID. Cancelling a reservation // frees its locked outputs up, for inclusion within further reservations. type fundingReserveCancelMsg struct { pendingFundingID uint64 // NOTE: In order to avoid deadlocks, this channel MUST be buffered. err chan error // Buffered } // addContributionMsg represents a message executing the second phase of the // channel reservation workflow. This message carries the counterparty's // "contribution" to the payment channel. In the case that this message is // processed without generating any errors, then channel reservation will then // be able to construct the funding tx, both commitment transactions, and // finally generate signatures for all our inputs to the funding transaction, // and for the remote node's version of the commitment transaction. type addContributionMsg struct { pendingFundingID uint64 // TODO(roasbeef): Should also carry SPV proofs in we're in SPV mode contribution *ChannelContribution // NOTE: In order to avoid deadlocks, this channel MUST be buffered. err chan error } // addSingleContributionMsg represents a message executing the second phase of // a single funder channel reservation workflow. This messages carries the // counterparty's "contribution" to the payment channel. As this message is // sent when on the responding side to a single funder workflow, no further // action apart from storing the provided contribution is carried out. type addSingleContributionMsg struct { pendingFundingID uint64 contribution *ChannelContribution // NOTE: In order to avoid deadlocks, this channel MUST be buffered. err chan error } // addCounterPartySigsMsg represents the final message required to complete, // and 'open' a payment channel. This message carries the counterparty's // signatures for each of their inputs to the funding transaction, and also a // signature allowing us to spend our version of the commitment transaction. // If we're able to verify all the signatures are valid, the funding transaction // will be broadcast to the network. After the funding transaction gains a // configurable number of confirmations, the channel is officially considered // 'open'. type addCounterPartySigsMsg struct { pendingFundingID uint64 // Should be order of sorted inputs that are theirs. Sorting is done // in accordance to BIP-69: // https://github.com/bitcoin/bips/blob/master/bip-0069.mediawiki. theirFundingInputScripts []*input.Script // This should be 1/2 of the signatures needed to successfully spend our // version of the commitment transaction. theirCommitmentSig []byte // This channel is used to return the completed channel after the wallet // has completed all of its stages in the funding process. completeChan chan *channeldb.OpenChannel // NOTE: In order to avoid deadlocks, this channel MUST be buffered. err chan error } // addSingleFunderSigsMsg represents the next-to-last message required to // complete a single-funder channel workflow. Once the initiator is able to // construct the funding transaction, they send both the outpoint and a // signature for our version of the commitment transaction. Once this message // is processed we (the responder) are able to construct both commitment // transactions, signing the remote party's version. type addSingleFunderSigsMsg struct { pendingFundingID uint64 // fundingOutpoint is the outpoint of the completed funding // transaction as assembled by the workflow initiator. fundingOutpoint *wire.OutPoint // theirCommitmentSig are the 1/2 of the signatures needed to // successfully spend our version of the commitment transaction. theirCommitmentSig []byte // This channel is used to return the completed channel after the wallet // has completed all of its stages in the funding process. completeChan chan *channeldb.OpenChannel // NOTE: In order to avoid deadlocks, this channel MUST be buffered. err chan error } // LightningWallet is a domain specific, yet general Bitcoin wallet capable of // executing workflow required to interact with the Lightning Network. It is // domain specific in the sense that it understands all the fancy scripts used // within the Lightning Network, channel lifetimes, etc. However, it embeds a // general purpose Bitcoin wallet within it. Therefore, it is also able to // serve as a regular Bitcoin wallet which uses HD keys. The wallet is highly // concurrent internally. All communication, and requests towards the wallet // are dispatched as messages over channels, ensuring thread safety across all // operations. Interaction has been designed independent of any peer-to-peer // communication protocol, allowing the wallet to be self-contained and // embeddable within future projects interacting with the Lightning Network. // // NOTE: At the moment the wallet requires a btcd full node, as it's dependent // on btcd's websockets notifications as event triggers during the lifetime of a // channel. However, once the chainntnfs package is complete, the wallet will // be compatible with multiple RPC/notification services such as Electrum, // Bitcoin Core + ZeroMQ, etc. Eventually, the wallet won't require a full-node // at all, as SPV support is integrated into btcwallet. type LightningWallet struct { started int32 // To be used atomically. shutdown int32 // To be used atomically. nextFundingID uint64 // To be used atomically. // Cfg is the configuration struct that will be used by the wallet to // access the necessary interfaces and default it needs to carry on its // duties. Cfg Config // WalletController is the core wallet, all non Lightning Network // specific interaction is proxied to the internal wallet. WalletController // SecretKeyRing is the interface we'll use to derive any keys related // to our purpose within the network including: multi-sig keys, node // keys, revocation keys, etc. keychain.SecretKeyRing // This mutex MUST be held when performing coin selection in order to // avoid inadvertently creating multiple funding transaction which // double spend inputs across each other. coinSelectMtx sync.RWMutex // All messages to the wallet are to be sent across this channel. msgChan chan interface{} // Incomplete payment channels are stored in the map below. An intent // to create a payment channel is tracked as a "reservation" within // limbo. Once the final signatures have been exchanged, a reservation // is removed from limbo. Each reservation is tracked by a unique // monotonically integer. All requests concerning the channel MUST // carry a valid, active funding ID. fundingLimbo map[uint64]*ChannelReservation limboMtx sync.RWMutex // lockedOutPoints is a set of the currently locked outpoint. This // information is kept in order to provide an easy way to unlock all // the currently locked outpoints. lockedOutPoints map[wire.OutPoint]struct{} // fundingIntents houses all the "interception" registered by a caller // using the RegisterFundingIntent method. intentMtx sync.RWMutex fundingIntents map[[32]byte]chanfunding.Intent quit chan struct{} wg sync.WaitGroup // TODO(roasbeef): handle wallet lock/unlock } // NewLightningWallet creates/opens and initializes a LightningWallet instance. // If the wallet has never been created (according to the passed dataDir), first-time // setup is executed. func NewLightningWallet(Cfg Config) (*LightningWallet, error) { return &LightningWallet{ Cfg: Cfg, SecretKeyRing: Cfg.SecretKeyRing, WalletController: Cfg.WalletController, msgChan: make(chan interface{}, msgBufferSize), nextFundingID: 0, fundingLimbo: make(map[uint64]*ChannelReservation), lockedOutPoints: make(map[wire.OutPoint]struct{}), fundingIntents: make(map[[32]byte]chanfunding.Intent), quit: make(chan struct{}), }, nil } // Startup establishes a connection to the RPC source, and spins up all // goroutines required to handle incoming messages. func (l *LightningWallet) Startup() error { // Already started? if atomic.AddInt32(&l.started, 1) != 1 { return nil } // Start the underlying wallet controller. if err := l.Start(); err != nil { return err } l.wg.Add(1) // TODO(roasbeef): multiple request handlers? go l.requestHandler() return nil } // Shutdown gracefully stops the wallet, and all active goroutines. func (l *LightningWallet) Shutdown() error { if atomic.AddInt32(&l.shutdown, 1) != 1 { return nil } // Signal the underlying wallet controller to shutdown, waiting until // all active goroutines have been shutdown. if err := l.Stop(); err != nil { return err } close(l.quit) l.wg.Wait() return nil } // LockedOutpoints returns a list of all currently locked outpoint. func (l *LightningWallet) LockedOutpoints() []*wire.OutPoint { outPoints := make([]*wire.OutPoint, 0, len(l.lockedOutPoints)) for outPoint := range l.lockedOutPoints { outPoint := outPoint outPoints = append(outPoints, &outPoint) } return outPoints } // ResetReservations reset the volatile wallet state which tracks all currently // active reservations. func (l *LightningWallet) ResetReservations() { l.nextFundingID = 0 l.fundingLimbo = make(map[uint64]*ChannelReservation) for outpoint := range l.lockedOutPoints { l.UnlockOutpoint(outpoint) } l.lockedOutPoints = make(map[wire.OutPoint]struct{}) } // ActiveReservations returns a slice of all the currently active // (non-canceled) reservations. func (l *LightningWallet) ActiveReservations() []*ChannelReservation { reservations := make([]*ChannelReservation, 0, len(l.fundingLimbo)) for _, reservation := range l.fundingLimbo { reservations = append(reservations, reservation) } return reservations } // requestHandler is the primary goroutine(s) responsible for handling, and // dispatching replies to all messages. func (l *LightningWallet) requestHandler() { out: for { select { case m := <-l.msgChan: switch msg := m.(type) { case *InitFundingReserveMsg: l.handleFundingReserveRequest(msg) case *fundingReserveCancelMsg: l.handleFundingCancelRequest(msg) case *addSingleContributionMsg: l.handleSingleContribution(msg) case *addContributionMsg: l.handleContributionMsg(msg) case *addSingleFunderSigsMsg: l.handleSingleFunderSigs(msg) case *addCounterPartySigsMsg: l.handleFundingCounterPartySigs(msg) } case <-l.quit: // TODO: do some clean up break out } } l.wg.Done() } // InitChannelReservation kicks off the 3-step workflow required to successfully // open a payment channel with a remote node. As part of the funding // reservation, the inputs selected for the funding transaction are 'locked'. // This ensures that multiple channel reservations aren't double spending the // same inputs in the funding transaction. If reservation initialization is // successful, a ChannelReservation containing our completed contribution is // returned. Our contribution contains all the items necessary to allow the // counterparty to build the funding transaction, and both versions of the // commitment transaction. Otherwise, an error occurred and a nil pointer along // with an error are returned. // // Once a ChannelReservation has been obtained, two additional steps must be // processed before a payment channel can be considered 'open'. The second step // validates, and processes the counterparty's channel contribution. The third, // and final step verifies all signatures for the inputs of the funding // transaction, and that the signature we record for our version of the // commitment transaction is valid. func (l *LightningWallet) InitChannelReservation( req *InitFundingReserveMsg) (*ChannelReservation, error) { req.resp = make(chan *ChannelReservation, 1) req.err = make(chan error, 1) select { case l.msgChan <- req: case <-l.quit: return nil, errors.New("wallet shutting down") } return <-req.resp, <-req.err } // RegisterFundingIntent allows a caller to signal to the wallet that if a // pending channel ID of expectedID is found, then it can skip constructing a // new chanfunding.Assembler, and instead use the specified chanfunding.Intent. // As an example, this lets some of the parameters for funding transaction to // be negotiated outside the regular funding protocol. func (l *LightningWallet) RegisterFundingIntent(expectedID [32]byte, shimIntent chanfunding.Intent) error { l.intentMtx.Lock() defer l.intentMtx.Unlock() if _, ok := l.fundingIntents[expectedID]; ok { return fmt.Errorf("pendingChanID(%x) already has intent "+ "registered", expectedID[:]) } l.fundingIntents[expectedID] = shimIntent return nil } // CancelFundingIntent allows a caller to cancel a previously registered // funding intent. If no intent was found, then an error will be returned. func (l *LightningWallet) CancelFundingIntent(pid [32]byte) error { l.intentMtx.Lock() defer l.intentMtx.Unlock() if _, ok := l.fundingIntents[pid]; !ok { return fmt.Errorf("no funding intent found for "+ "pendingChannelID(%x)", pid[:]) } delete(l.fundingIntents, pid) return nil } // handleFundingReserveRequest processes a message intending to create, and // validate a funding reservation request. func (l *LightningWallet) handleFundingReserveRequest(req *InitFundingReserveMsg) { // It isn't possible to create a channel with zero funds committed. if req.LocalFundingAmt+req.RemoteFundingAmt == 0 { err := ErrZeroCapacity() req.err <- err req.resp <- nil return } // If the funding request is for a different chain than the one the // wallet is aware of, then we'll reject the request. if !bytes.Equal(l.Cfg.NetParams.GenesisHash[:], req.ChainHash[:]) { err := ErrChainMismatch( l.Cfg.NetParams.GenesisHash, req.ChainHash, ) req.err <- err req.resp <- nil return } // If no chanFunder was provided, then we'll assume the default // assembler, which is backed by the wallet's internal coin selection. if req.ChanFunder == nil { cfg := chanfunding.WalletConfig{ CoinSource: &CoinSource{l}, CoinSelectLocker: l, CoinLocker: l, Signer: l.Cfg.Signer, DustLimit: DefaultDustLimit(), } req.ChanFunder = chanfunding.NewWalletAssembler(cfg) } localFundingAmt := req.LocalFundingAmt remoteFundingAmt := req.RemoteFundingAmt var ( fundingIntent chanfunding.Intent err error ) // If we've just received an inbound funding request that we have a // registered shim intent to, then we'll obtain the backing intent now. // In this case, we're doing a special funding workflow that allows // more advanced constructions such as channel factories to be // instantiated. l.intentMtx.Lock() fundingIntent, ok := l.fundingIntents[req.PendingChanID] l.intentMtx.Unlock() // Otherwise, this is a normal funding flow, so we'll use the chan // funder in the attached request to provision the inputs/outputs // that'll ultimately be used to construct the funding transaction. if !ok { // Coin selection is done on the basis of sat/kw, so we'll use // the fee rate passed in to perform coin selection. var err error fundingReq := &chanfunding.Request{ RemoteAmt: req.RemoteFundingAmt, LocalAmt: req.LocalFundingAmt, MinConfs: req.MinConfs, SubtractFees: req.SubtractFees, FeeRate: req.FundingFeePerKw, ChangeAddr: func() (btcutil.Address, error) { return l.NewAddress(WitnessPubKey, true) }, } fundingIntent, err = req.ChanFunder.ProvisionChannel( fundingReq, ) if err != nil { req.err <- err req.resp <- nil return } localFundingAmt = fundingIntent.LocalFundingAmt() remoteFundingAmt = fundingIntent.RemoteFundingAmt() } // If this is a shim intent, then it may be attempting to use an // existing set of keys for the funding workflow. In this case, we'll // make a simple wrapper keychain.KeyRing that will proxy certain // derivation calls to future callers. var ( keyRing keychain.KeyRing = l.SecretKeyRing thawHeight uint32 ) if shimIntent, ok := fundingIntent.(*chanfunding.ShimIntent); ok { keyRing = &shimKeyRing{ KeyRing: keyRing, ShimIntent: shimIntent, } // As this was a registered shim intent, we'll obtain the thaw // height of the intent, if present at all. If this is // non-zero, then we'll mark this as the proper channel type. thawHeight = shimIntent.ThawHeight() } // The total channel capacity will be the size of the funding output we // created plus the remote contribution. capacity := localFundingAmt + remoteFundingAmt id := atomic.AddUint64(&l.nextFundingID, 1) reservation, err := NewChannelReservation( capacity, localFundingAmt, req.CommitFeePerKw, l, id, req.PushMSat, l.Cfg.NetParams.GenesisHash, req.Flags, req.CommitType, req.ChanFunder, req.PendingChanID, thawHeight, ) if err != nil { if fundingIntent != nil { fundingIntent.Cancel() } req.err <- err req.resp <- nil return } err = l.initOurContribution( reservation, fundingIntent, req.NodeAddr, req.NodeID, keyRing, ) if err != nil { if fundingIntent != nil { fundingIntent.Cancel() } req.err <- err req.resp <- nil return } // Create a limbo and record entry for this newly pending funding // request. l.limboMtx.Lock() l.fundingLimbo[id] = reservation l.limboMtx.Unlock() // Funding reservation request successfully handled. The funding inputs // will be marked as unavailable until the reservation is either // completed, or canceled. req.resp <- reservation req.err <- nil } // initOurContribution initializes the given ChannelReservation with our coins // and change reserved for the channel, and derives the keys to use for this // channel. func (l *LightningWallet) initOurContribution(reservation *ChannelReservation, fundingIntent chanfunding.Intent, nodeAddr net.Addr, nodeID *btcec.PublicKey, keyRing keychain.KeyRing) error { // Grab the mutex on the ChannelReservation to ensure thread-safety reservation.Lock() defer reservation.Unlock() // At this point, if we have a funding intent, we'll use it to populate // the existing reservation state entries for our coin selection. if fundingIntent != nil { if intent, ok := fundingIntent.(*chanfunding.FullIntent); ok { for _, coin := range intent.InputCoins { reservation.ourContribution.Inputs = append( reservation.ourContribution.Inputs, &wire.TxIn{ PreviousOutPoint: coin.OutPoint, }, ) } reservation.ourContribution.ChangeOutputs = intent.ChangeOutputs } reservation.fundingIntent = fundingIntent } reservation.nodeAddr = nodeAddr reservation.partialState.IdentityPub = nodeID var err error reservation.ourContribution.MultiSigKey, err = keyRing.DeriveNextKey( keychain.KeyFamilyMultiSig, ) if err != nil { return err } reservation.ourContribution.RevocationBasePoint, err = keyRing.DeriveNextKey( keychain.KeyFamilyRevocationBase, ) if err != nil { return err } reservation.ourContribution.HtlcBasePoint, err = keyRing.DeriveNextKey( keychain.KeyFamilyHtlcBase, ) if err != nil { return err } reservation.ourContribution.PaymentBasePoint, err = keyRing.DeriveNextKey( keychain.KeyFamilyPaymentBase, ) if err != nil { return err } reservation.ourContribution.DelayBasePoint, err = keyRing.DeriveNextKey( keychain.KeyFamilyDelayBase, ) if err != nil { return err } // With the above keys created, we'll also need to initialization our // initial revocation tree state. nextRevocationKeyDesc, err := keyRing.DeriveNextKey( keychain.KeyFamilyRevocationRoot, ) if err != nil { return err } revocationRoot, err := l.DerivePrivKey(nextRevocationKeyDesc) if err != nil { return err } // Once we have the root, we can then generate our shachain producer // and from that generate the per-commitment point. revRoot, err := chainhash.NewHash(revocationRoot.Serialize()) if err != nil { return err } producer := shachain.NewRevocationProducer(*revRoot) firstPreimage, err := producer.AtIndex(0) if err != nil { return err } reservation.ourContribution.FirstCommitmentPoint = input.ComputeCommitmentPoint( firstPreimage[:], ) reservation.partialState.RevocationProducer = producer reservation.ourContribution.ChannelConstraints = l.Cfg.DefaultConstraints return nil } // handleFundingReserveCancel cancels an existing channel reservation. As part // of the cancellation, outputs previously selected as inputs for the funding // transaction via coin selection are freed allowing future reservations to // include them. func (l *LightningWallet) handleFundingCancelRequest(req *fundingReserveCancelMsg) { // TODO(roasbeef): holding lock too long l.limboMtx.Lock() defer l.limboMtx.Unlock() pendingReservation, ok := l.fundingLimbo[req.pendingFundingID] if !ok { // TODO(roasbeef): make new error, "unknown funding state" or something req.err <- fmt.Errorf("attempted to cancel non-existent funding state") return } // Grab the mutex on the ChannelReservation to ensure thread-safety pendingReservation.Lock() defer pendingReservation.Unlock() // Mark all previously locked outpoints as useable for future funding // requests. for _, unusedInput := range pendingReservation.ourContribution.Inputs { delete(l.lockedOutPoints, unusedInput.PreviousOutPoint) l.UnlockOutpoint(unusedInput.PreviousOutPoint) } // TODO(roasbeef): is it even worth it to keep track of unused keys? // TODO(roasbeef): Is it possible to mark the unused change also as // available? delete(l.fundingLimbo, req.pendingFundingID) pid := pendingReservation.pendingChanID l.intentMtx.Lock() if intent, ok := l.fundingIntents[pid]; ok { intent.Cancel() delete(l.fundingIntents, pendingReservation.pendingChanID) } l.intentMtx.Unlock() req.err <- nil } // CreateCommitmentTxns is a helper function that creates the initial // commitment transaction for both parties. This function is used during the // initial funding workflow as both sides must generate a signature for the // remote party's commitment transaction, and verify the signature for their // version of the commitment transaction. func CreateCommitmentTxns(localBalance, remoteBalance btcutil.Amount, ourChanCfg, theirChanCfg *channeldb.ChannelConfig, localCommitPoint, remoteCommitPoint *btcec.PublicKey, fundingTxIn wire.TxIn, chanType channeldb.ChannelType) ( *wire.MsgTx, *wire.MsgTx, error) { localCommitmentKeys := DeriveCommitmentKeys( localCommitPoint, true, chanType, ourChanCfg, theirChanCfg, ) remoteCommitmentKeys := DeriveCommitmentKeys( remoteCommitPoint, false, chanType, ourChanCfg, theirChanCfg, ) ourCommitTx, err := CreateCommitTx( chanType, fundingTxIn, localCommitmentKeys, ourChanCfg, theirChanCfg, localBalance, remoteBalance, 0, ) if err != nil { return nil, nil, err } otxn := btcutil.NewTx(ourCommitTx) if err := blockchain.CheckTransactionSanity(otxn); err != nil { return nil, nil, err } theirCommitTx, err := CreateCommitTx( chanType, fundingTxIn, remoteCommitmentKeys, theirChanCfg, ourChanCfg, remoteBalance, localBalance, 0, ) if err != nil { return nil, nil, err } ttxn := btcutil.NewTx(theirCommitTx) if err := blockchain.CheckTransactionSanity(ttxn); err != nil { return nil, nil, err } return ourCommitTx, theirCommitTx, nil } // handleContributionMsg processes the second workflow step for the lifetime of // a channel reservation. Upon completion, the reservation will carry a // completed funding transaction (minus the counterparty's input signatures), // both versions of the commitment transaction, and our signature for their // version of the commitment transaction. func (l *LightningWallet) handleContributionMsg(req *addContributionMsg) { l.limboMtx.Lock() pendingReservation, ok := l.fundingLimbo[req.pendingFundingID] l.limboMtx.Unlock() if !ok { req.err <- fmt.Errorf("attempted to update non-existent funding state") return } // Grab the mutex on the ChannelReservation to ensure thread-safety pendingReservation.Lock() defer pendingReservation.Unlock() // Some temporary variables to cut down on the resolution verbosity. pendingReservation.theirContribution = req.contribution theirContribution := req.contribution ourContribution := pendingReservation.ourContribution var ( chanPoint *wire.OutPoint err error ) // At this point, we can now construct our channel point. Depending on // which type of intent we obtained from our chanfunding.Assembler, // we'll carry out a distinct set of steps. switch fundingIntent := pendingReservation.fundingIntent.(type) { case *chanfunding.ShimIntent: chanPoint, err = fundingIntent.ChanPoint() if err != nil { req.err <- fmt.Errorf("unable to obtain chan point: %v", err) return } pendingReservation.partialState.FundingOutpoint = *chanPoint case *chanfunding.FullIntent: // Now that we know their public key, we can bind theirs as // well as ours to the funding intent. fundingIntent.BindKeys( &pendingReservation.ourContribution.MultiSigKey, theirContribution.MultiSigKey.PubKey, ) // With our keys bound, we can now construct+sign the final // funding transaction and also obtain the chanPoint that // creates the channel. fundingTx, err := fundingIntent.CompileFundingTx( theirContribution.Inputs, theirContribution.ChangeOutputs, ) if err != nil { req.err <- fmt.Errorf("unable to construct funding "+ "tx: %v", err) return } chanPoint, err = fundingIntent.ChanPoint() if err != nil { req.err <- fmt.Errorf("unable to obtain chan "+ "point: %v", err) return } // Finally, we'll populate the relevant information in our // pendingReservation so the rest of the funding flow can // continue as normal. pendingReservation.fundingTx = fundingTx pendingReservation.partialState.FundingOutpoint = *chanPoint pendingReservation.ourFundingInputScripts = make( []*input.Script, 0, len(ourContribution.Inputs), ) for _, txIn := range fundingTx.TxIn { _, err := l.FetchInputInfo(&txIn.PreviousOutPoint) if err != nil { continue } pendingReservation.ourFundingInputScripts = append( pendingReservation.ourFundingInputScripts, &input.Script{ Witness: txIn.Witness, SigScript: txIn.SignatureScript, }, ) } walletLog.Debugf("Funding tx for ChannelPoint(%v) "+ "generated: %v", chanPoint, spew.Sdump(fundingTx)) } // Initialize an empty sha-chain for them, tracking the current pending // revocation hash (we don't yet know the preimage so we can't add it // to the chain). s := shachain.NewRevocationStore() pendingReservation.partialState.RevocationStore = s // Store their current commitment point. We'll need this after the // first state transition in order to verify the authenticity of the // revocation. chanState := pendingReservation.partialState chanState.RemoteCurrentRevocation = theirContribution.FirstCommitmentPoint // Create the txin to our commitment transaction; required to construct // the commitment transactions. fundingTxIn := wire.TxIn{ PreviousOutPoint: *chanPoint, } // With the funding tx complete, create both commitment transactions. localBalance := pendingReservation.partialState.LocalCommitment.LocalBalance.ToSatoshis() remoteBalance := pendingReservation.partialState.LocalCommitment.RemoteBalance.ToSatoshis() ourCommitTx, theirCommitTx, err := CreateCommitmentTxns( localBalance, remoteBalance, ourContribution.ChannelConfig, theirContribution.ChannelConfig, ourContribution.FirstCommitmentPoint, theirContribution.FirstCommitmentPoint, fundingTxIn, pendingReservation.partialState.ChanType, ) if err != nil { req.err <- err return } // With both commitment transactions constructed, generate the state // obfuscator then use it to encode the current state number within // both commitment transactions. var stateObfuscator [StateHintSize]byte if chanState.ChanType.IsSingleFunder() { stateObfuscator = DeriveStateHintObfuscator( ourContribution.PaymentBasePoint.PubKey, theirContribution.PaymentBasePoint.PubKey, ) } else { ourSer := ourContribution.PaymentBasePoint.PubKey.SerializeCompressed() theirSer := theirContribution.PaymentBasePoint.PubKey.SerializeCompressed() switch bytes.Compare(ourSer, theirSer) { case -1: stateObfuscator = DeriveStateHintObfuscator( ourContribution.PaymentBasePoint.PubKey, theirContribution.PaymentBasePoint.PubKey, ) default: stateObfuscator = DeriveStateHintObfuscator( theirContribution.PaymentBasePoint.PubKey, ourContribution.PaymentBasePoint.PubKey, ) } } err = initStateHints(ourCommitTx, theirCommitTx, stateObfuscator) if err != nil { req.err <- err return } // Sort both transactions according to the agreed upon canonical // ordering. This lets us skip sending the entire transaction over, // instead we'll just send signatures. txsort.InPlaceSort(ourCommitTx) txsort.InPlaceSort(theirCommitTx) walletLog.Debugf("Local commit tx for ChannelPoint(%v): %v", chanPoint, spew.Sdump(ourCommitTx)) walletLog.Debugf("Remote commit tx for ChannelPoint(%v): %v", chanPoint, spew.Sdump(theirCommitTx)) // Record newly available information within the open channel state. chanState.FundingOutpoint = *chanPoint chanState.LocalCommitment.CommitTx = ourCommitTx chanState.RemoteCommitment.CommitTx = theirCommitTx // Next, we'll obtain the funding witness script, and the funding // output itself so we can generate a valid signature for the remote // party. fundingIntent := pendingReservation.fundingIntent fundingWitnessScript, fundingOutput, err := fundingIntent.FundingOutput() if err != nil { req.err <- fmt.Errorf("unable to obtain funding output") return } // Generate a signature for their version of the initial commitment // transaction. ourKey := ourContribution.MultiSigKey signDesc := input.SignDescriptor{ WitnessScript: fundingWitnessScript, KeyDesc: ourKey, Output: fundingOutput, HashType: txscript.SigHashAll, SigHashes: txscript.NewTxSigHashes(theirCommitTx), InputIndex: 0, } sigTheirCommit, err := l.Cfg.Signer.SignOutputRaw(theirCommitTx, &signDesc) if err != nil { req.err <- err return } pendingReservation.ourCommitmentSig = sigTheirCommit req.err <- nil } // handleSingleContribution is called as the second step to a single funder // workflow to which we are the responder. It simply saves the remote peer's // contribution to the channel, as solely the remote peer will contribute any // funds to the channel. func (l *LightningWallet) handleSingleContribution(req *addSingleContributionMsg) { l.limboMtx.Lock() pendingReservation, ok := l.fundingLimbo[req.pendingFundingID] l.limboMtx.Unlock() if !ok { req.err <- fmt.Errorf("attempted to update non-existent funding state") return } // Grab the mutex on the channelReservation to ensure thread-safety. pendingReservation.Lock() defer pendingReservation.Unlock() // TODO(roasbeef): verify sanity of remote party's parameters, fail if // disagree // Simply record the counterparty's contribution into the pending // reservation data as they'll be solely funding the channel entirely. pendingReservation.theirContribution = req.contribution theirContribution := pendingReservation.theirContribution chanState := pendingReservation.partialState // Initialize an empty sha-chain for them, tracking the current pending // revocation hash (we don't yet know the preimage so we can't add it // to the chain). remotePreimageStore := shachain.NewRevocationStore() chanState.RevocationStore = remotePreimageStore // Now that we've received their first commitment point, we'll store it // within the channel state so we can sync it to disk once the funding // process is complete. chanState.RemoteCurrentRevocation = theirContribution.FirstCommitmentPoint req.err <- nil return } // verifyFundingInputs attempts to verify all remote inputs to the funding // transaction. func (l *LightningWallet) verifyFundingInputs(fundingTx *wire.MsgTx, remoteInputScripts []*input.Script) error { sigIndex := 0 fundingHashCache := txscript.NewTxSigHashes(fundingTx) inputScripts := remoteInputScripts for i, txin := range fundingTx.TxIn { if len(inputScripts) != 0 && len(txin.Witness) == 0 { // Attach the input scripts so we can verify it below. txin.Witness = inputScripts[sigIndex].Witness txin.SignatureScript = inputScripts[sigIndex].SigScript // Fetch the alleged previous output along with the // pkscript referenced by this input. // // TODO(roasbeef): when dual funder pass actual // height-hint // // TODO(roasbeef): this fails for neutrino always as it // treats the height hint as an exact birthday of the // utxo rather than a lower bound pkScript, err := txscript.ComputePkScript( txin.SignatureScript, txin.Witness, ) if err != nil { return fmt.Errorf("cannot create script: %v", err) } output, err := l.Cfg.ChainIO.GetUtxo( &txin.PreviousOutPoint, pkScript.Script(), 0, l.quit, ) if output == nil { return fmt.Errorf("input to funding tx does "+ "not exist: %v", err) } // Ensure that the witness+sigScript combo is valid. vm, err := txscript.NewEngine( output.PkScript, fundingTx, i, txscript.StandardVerifyFlags, nil, fundingHashCache, output.Value, ) if err != nil { return fmt.Errorf("cannot create script "+ "engine: %s", err) } if err = vm.Execute(); err != nil { return fmt.Errorf("cannot validate "+ "transaction: %s", err) } sigIndex++ } } return nil } // handleFundingCounterPartySigs is the final step in the channel reservation // workflow. During this step, we validate *all* the received signatures for // inputs to the funding transaction. If any of these are invalid, we bail, // and forcibly cancel this funding request. Additionally, we ensure that the // signature we received from the counterparty for our version of the commitment // transaction allows us to spend from the funding output with the addition of // our signature. func (l *LightningWallet) handleFundingCounterPartySigs(msg *addCounterPartySigsMsg) { l.limboMtx.RLock() res, ok := l.fundingLimbo[msg.pendingFundingID] l.limboMtx.RUnlock() if !ok { msg.err <- fmt.Errorf("attempted to update non-existent funding state") return } // Grab the mutex on the ChannelReservation to ensure thread-safety res.Lock() defer res.Unlock() // Now we can complete the funding transaction by adding their // signatures to their inputs. res.theirFundingInputScripts = msg.theirFundingInputScripts inputScripts := msg.theirFundingInputScripts // Only if we have the final funding transaction do we need to verify // the final set of inputs. Otherwise, it may be the case that the // channel was funded via an external wallet. fundingTx := res.fundingTx if res.partialState.ChanType.HasFundingTx() { err := l.verifyFundingInputs(fundingTx, inputScripts) if err != nil { msg.err <- err msg.completeChan <- nil return } } // At this point, we can also record and verify their signature for our // commitment transaction. res.theirCommitmentSig = msg.theirCommitmentSig commitTx := res.partialState.LocalCommitment.CommitTx ourKey := res.ourContribution.MultiSigKey theirKey := res.theirContribution.MultiSigKey // Re-generate both the witnessScript and p2sh output. We sign the // witnessScript script, but include the p2sh output as the subscript // for verification. witnessScript, _, err := input.GenFundingPkScript( ourKey.PubKey.SerializeCompressed(), theirKey.PubKey.SerializeCompressed(), int64(res.partialState.Capacity), ) if err != nil { msg.err <- err msg.completeChan <- nil return } // Next, create the spending scriptSig, and then verify that the script // is complete, allowing us to spend from the funding transaction. channelValue := int64(res.partialState.Capacity) hashCache := txscript.NewTxSigHashes(commitTx) sigHash, err := txscript.CalcWitnessSigHash( witnessScript, hashCache, txscript.SigHashAll, commitTx, 0, channelValue, ) if err != nil { msg.err <- err msg.completeChan <- nil return } // Verify that we've received a valid signature from the remote party // for our version of the commitment transaction. theirCommitSig := msg.theirCommitmentSig sig, err := btcec.ParseSignature(theirCommitSig, btcec.S256()) if err != nil { msg.err <- err msg.completeChan <- nil return } else if !sig.Verify(sigHash, theirKey.PubKey) { msg.err <- fmt.Errorf("counterparty's commitment signature is invalid") msg.completeChan <- nil return } res.partialState.LocalCommitment.CommitSig = theirCommitSig // Funding complete, this entry can be removed from limbo. l.limboMtx.Lock() delete(l.fundingLimbo, res.reservationID) l.limboMtx.Unlock() l.intentMtx.Lock() delete(l.fundingIntents, res.pendingChanID) l.intentMtx.Unlock() // As we're about to broadcast the funding transaction, we'll take note // of the current height for record keeping purposes. // // TODO(roasbeef): this info can also be piped into light client's // basic fee estimation? _, bestHeight, err := l.Cfg.ChainIO.GetBestBlock() if err != nil { msg.err <- err msg.completeChan <- nil return } // As we've completed the funding process, we'll no convert the // contribution structs into their underlying channel config objects to // he stored within the database. res.partialState.LocalChanCfg = res.ourContribution.toChanConfig() res.partialState.RemoteChanCfg = res.theirContribution.toChanConfig() // We'll also record the finalized funding txn, which will allow us to // rebroadcast on startup in case we fail. res.partialState.FundingTxn = fundingTx // Set optional upfront shutdown scripts on the channel state so that they // are persisted. These values may be nil. res.partialState.LocalShutdownScript = res.ourContribution.UpfrontShutdown res.partialState.RemoteShutdownScript = res.theirContribution.UpfrontShutdown // Add the complete funding transaction to the DB, in its open bucket // which will be used for the lifetime of this channel. nodeAddr := res.nodeAddr err = res.partialState.SyncPending(nodeAddr, uint32(bestHeight)) if err != nil { msg.err <- err msg.completeChan <- nil return } msg.completeChan <- res.partialState msg.err <- nil } // handleSingleFunderSigs is called once the remote peer who initiated the // single funder workflow has assembled the funding transaction, and generated // a signature for our version of the commitment transaction. This method // progresses the workflow by generating a signature for the remote peer's // version of the commitment transaction. func (l *LightningWallet) handleSingleFunderSigs(req *addSingleFunderSigsMsg) { l.limboMtx.RLock() pendingReservation, ok := l.fundingLimbo[req.pendingFundingID] l.limboMtx.RUnlock() if !ok { req.err <- fmt.Errorf("attempted to update non-existent funding state") req.completeChan <- nil return } // Grab the mutex on the ChannelReservation to ensure thread-safety pendingReservation.Lock() defer pendingReservation.Unlock() chanState := pendingReservation.partialState chanState.FundingOutpoint = *req.fundingOutpoint fundingTxIn := wire.NewTxIn(req.fundingOutpoint, nil, nil) // Now that we have the funding outpoint, we can generate both versions // of the commitment transaction, and generate a signature for the // remote node's commitment transactions. localBalance := pendingReservation.partialState.LocalCommitment.LocalBalance.ToSatoshis() remoteBalance := pendingReservation.partialState.LocalCommitment.RemoteBalance.ToSatoshis() ourCommitTx, theirCommitTx, err := CreateCommitmentTxns( localBalance, remoteBalance, pendingReservation.ourContribution.ChannelConfig, pendingReservation.theirContribution.ChannelConfig, pendingReservation.ourContribution.FirstCommitmentPoint, pendingReservation.theirContribution.FirstCommitmentPoint, *fundingTxIn, pendingReservation.partialState.ChanType, ) if err != nil { req.err <- err req.completeChan <- nil return } // With both commitment transactions constructed, we can now use the // generator state obfuscator to encode the current state number within // both commitment transactions. stateObfuscator := DeriveStateHintObfuscator( pendingReservation.theirContribution.PaymentBasePoint.PubKey, pendingReservation.ourContribution.PaymentBasePoint.PubKey, ) err = initStateHints(ourCommitTx, theirCommitTx, stateObfuscator) if err != nil { req.err <- err req.completeChan <- nil return } // Sort both transactions according to the agreed upon canonical // ordering. This ensures that both parties sign the same sighash // without further synchronization. txsort.InPlaceSort(ourCommitTx) txsort.InPlaceSort(theirCommitTx) chanState.LocalCommitment.CommitTx = ourCommitTx chanState.RemoteCommitment.CommitTx = theirCommitTx walletLog.Debugf("Local commit tx for ChannelPoint(%v): %v", req.fundingOutpoint, spew.Sdump(ourCommitTx)) walletLog.Debugf("Remote commit tx for ChannelPoint(%v): %v", req.fundingOutpoint, spew.Sdump(theirCommitTx)) channelValue := int64(pendingReservation.partialState.Capacity) hashCache := txscript.NewTxSigHashes(ourCommitTx) theirKey := pendingReservation.theirContribution.MultiSigKey ourKey := pendingReservation.ourContribution.MultiSigKey witnessScript, _, err := input.GenFundingPkScript( ourKey.PubKey.SerializeCompressed(), theirKey.PubKey.SerializeCompressed(), channelValue, ) if err != nil { req.err <- err req.completeChan <- nil return } sigHash, err := txscript.CalcWitnessSigHash( witnessScript, hashCache, txscript.SigHashAll, ourCommitTx, 0, channelValue, ) if err != nil { req.err <- err req.completeChan <- nil return } // Verify that we've received a valid signature from the remote party // for our version of the commitment transaction. sig, err := btcec.ParseSignature(req.theirCommitmentSig, btcec.S256()) if err != nil { req.err <- err req.completeChan <- nil return } if !sig.Verify(sigHash, theirKey.PubKey) { req.err <- fmt.Errorf("counterparty's commitment signature " + "is invalid") req.completeChan <- nil return } chanState.LocalCommitment.CommitSig = req.theirCommitmentSig // With their signature for our version of the commitment transactions // verified, we can now generate a signature for their version, // allowing the funding transaction to be safely broadcast. p2wsh, err := input.WitnessScriptHash(witnessScript) if err != nil { req.err <- err req.completeChan <- nil return } signDesc := input.SignDescriptor{ WitnessScript: witnessScript, KeyDesc: ourKey, Output: &wire.TxOut{ PkScript: p2wsh, Value: channelValue, }, HashType: txscript.SigHashAll, SigHashes: txscript.NewTxSigHashes(theirCommitTx), InputIndex: 0, } sigTheirCommit, err := l.Cfg.Signer.SignOutputRaw(theirCommitTx, &signDesc) if err != nil { req.err <- err req.completeChan <- nil return } pendingReservation.ourCommitmentSig = sigTheirCommit _, bestHeight, err := l.Cfg.ChainIO.GetBestBlock() if err != nil { req.err <- err req.completeChan <- nil return } // Set optional upfront shutdown scripts on the channel state so that they // are persisted. These values may be nil. chanState.LocalShutdownScript = pendingReservation.ourContribution.UpfrontShutdown chanState.RemoteShutdownScript = pendingReservation.theirContribution.UpfrontShutdown // Add the complete funding transaction to the DB, in it's open bucket // which will be used for the lifetime of this channel. chanState.LocalChanCfg = pendingReservation.ourContribution.toChanConfig() chanState.RemoteChanCfg = pendingReservation.theirContribution.toChanConfig() err = chanState.SyncPending(pendingReservation.nodeAddr, uint32(bestHeight)) if err != nil { req.err <- err req.completeChan <- nil return } req.completeChan <- chanState req.err <- nil l.limboMtx.Lock() delete(l.fundingLimbo, req.pendingFundingID) l.limboMtx.Unlock() l.intentMtx.Lock() delete(l.fundingIntents, pendingReservation.pendingChanID) l.intentMtx.Unlock() } // WithCoinSelectLock will execute the passed function closure in a // synchronized manner preventing any coin selection operations from proceeding // while the closure is executing. This can be seen as the ability to execute a // function closure under an exclusive coin selection lock. func (l *LightningWallet) WithCoinSelectLock(f func() error) error { l.coinSelectMtx.Lock() defer l.coinSelectMtx.Unlock() return f() } // DeriveStateHintObfuscator derives the bytes to be used for obfuscating the // state hints from the root to be used for a new channel. The obfuscator is // generated via the following computation: // // * sha256(initiatorKey || responderKey)[26:] // * where both keys are the multi-sig keys of the respective parties // // The first 6 bytes of the resulting hash are used as the state hint. func DeriveStateHintObfuscator(key1, key2 *btcec.PublicKey) [StateHintSize]byte { h := sha256.New() h.Write(key1.SerializeCompressed()) h.Write(key2.SerializeCompressed()) sha := h.Sum(nil) var obfuscator [StateHintSize]byte copy(obfuscator[:], sha[26:]) return obfuscator } // initStateHints properly sets the obfuscated state hints on both commitment // transactions using the passed obfuscator. func initStateHints(commit1, commit2 *wire.MsgTx, obfuscator [StateHintSize]byte) error { if err := SetStateNumHint(commit1, 0, obfuscator); err != nil { return err } if err := SetStateNumHint(commit2, 0, obfuscator); err != nil { return err } return nil } // ValidateChannel will attempt to fully validate a newly mined channel, given // its funding transaction and existing channel state. If this method returns // an error, then the mined channel is invalid, and shouldn't be used. func (l *LightningWallet) ValidateChannel(channelState *channeldb.OpenChannel, fundingTx *wire.MsgTx) error { // First, we'll obtain a fully signed commitment transaction so we can // pass into it on the chanvalidate package for verification. channel, err := NewLightningChannel(l.Cfg.Signer, channelState, nil) if err != nil { return err } signedCommitTx, err := channel.getSignedCommitTx() if err != nil { return err } // We'll also need the multi-sig witness script itself so the // chanvalidate package can check it for correctness against the // funding transaction, and also commitment validity. localKey := channelState.LocalChanCfg.MultiSigKey.PubKey remoteKey := channelState.RemoteChanCfg.MultiSigKey.PubKey witnessScript, err := input.GenMultiSigScript( localKey.SerializeCompressed(), remoteKey.SerializeCompressed(), ) if err != nil { return err } pkScript, err := input.WitnessScriptHash(witnessScript) if err != nil { return err } // Finally, we'll pass in all the necessary context needed to fully // validate that this channel is indeed what we expect, and can be // used. _, err = chanvalidate.Validate(&chanvalidate.Context{ Locator: &chanvalidate.OutPointChanLocator{ ChanPoint: channelState.FundingOutpoint, }, MultiSigPkScript: pkScript, FundingTx: fundingTx, CommitCtx: &chanvalidate.CommitmentContext{ Value: channel.Capacity, FullySignedCommitTx: signedCommitTx, }, }) if err != nil { return err } return nil } // CoinSource is a wrapper around the wallet that implements the // chanfunding.CoinSource interface. type CoinSource struct { wallet *LightningWallet } // NewCoinSource creates a new instance of the CoinSource wrapper struct. func NewCoinSource(w *LightningWallet) *CoinSource { return &CoinSource{wallet: w} } // ListCoins returns all UTXOs from the source that have between // minConfs and maxConfs number of confirmations. func (c *CoinSource) ListCoins(minConfs int32, maxConfs int32) ([]chanfunding.Coin, error) { utxos, err := c.wallet.ListUnspentWitness(minConfs, maxConfs) if err != nil { return nil, err } var coins []chanfunding.Coin for _, utxo := range utxos { coins = append(coins, chanfunding.Coin{ TxOut: wire.TxOut{ Value: int64(utxo.Value), PkScript: utxo.PkScript, }, OutPoint: utxo.OutPoint, }) } return coins, nil } // CoinFromOutPoint attempts to locate details pertaining to a coin based on // its outpoint. If the coin isn't under the control of the backing CoinSource, // then an error should be returned. func (c *CoinSource) CoinFromOutPoint(op wire.OutPoint) (*chanfunding.Coin, error) { inputInfo, err := c.wallet.FetchInputInfo(&op) if err != nil { return nil, err } return &chanfunding.Coin{ TxOut: wire.TxOut{ Value: int64(inputInfo.Value), PkScript: inputInfo.PkScript, }, OutPoint: inputInfo.OutPoint, }, nil } // shimKeyRing is a wrapper struct that's used to provide the proper multi-sig // key for an initiated external funding flow. type shimKeyRing struct { keychain.KeyRing *chanfunding.ShimIntent } // DeriveNextKey intercepts the normal DeriveNextKey call to a keychain.KeyRing // instance, and supplies the multi-sig key specified by the ShimIntent. This // allows us to transparently insert new keys into the existing funding flow, // as these keys may not come from the wallet itself. func (s *shimKeyRing) DeriveNextKey(keyFam keychain.KeyFamily) (keychain.KeyDescriptor, error) { if keyFam != keychain.KeyFamilyMultiSig { return s.KeyRing.DeriveNextKey(keyFam) } fundingKeys, err := s.ShimIntent.MultiSigKeys() if err != nil { return keychain.KeyDescriptor{}, err } return *fundingKeys.LocalKey, nil }