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single.go
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single.go
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package chanbackup
import (
"bytes"
"fmt"
"io"
"net"
"github.com/btcsuite/btcd/btcec/v2"
"github.com/btcsuite/btcd/btcutil"
"github.com/btcsuite/btcd/chaincfg/chainhash"
"github.com/btcsuite/btcd/wire"
"github.com/lightningnetwork/lnd/channeldb"
"github.com/lightningnetwork/lnd/keychain"
"github.com/lightningnetwork/lnd/lnencrypt"
"github.com/lightningnetwork/lnd/lnwire"
)
// SingleBackupVersion denotes the version of the single static channel backup.
// Based on this version, we know how to pack/unpack serialized versions of the
// backup.
type SingleBackupVersion byte
const (
// DefaultSingleVersion is the default version of the single channel
// backup. The serialized version of this static channel backup is
// simply: version || SCB. Where SCB is the known format of the
// version.
DefaultSingleVersion = 0
// TweaklessCommitVersion is the second SCB version. This version
// implicitly denotes that this channel uses the new tweakless commit
// format.
TweaklessCommitVersion = 1
// AnchorsCommitVersion is the third SCB version. This version
// implicitly denotes that this channel uses the new anchor commitment
// format.
AnchorsCommitVersion = 2
// AnchorsZeroFeeHtlcTxCommitVersion is a version that denotes this
// channel is using the zero-fee second-level anchor commitment format.
AnchorsZeroFeeHtlcTxCommitVersion = 3
// ScriptEnforcedLeaseVersion is a version that denotes this channel is
// using the zero-fee second-level anchor commitment format along with
// an additional CLTV requirement of the channel lease maturity on any
// commitment and HTLC outputs that pay directly to the channel
// initiator.
ScriptEnforcedLeaseVersion = 4
// SimpleTaprootVersion is a version that denotes this channel is using
// the musig2 based taproot commitment format.
SimpleTaprootVersion = 5
)
// Single is a static description of an existing channel that can be used for
// the purposes of backing up. The fields in this struct allow a node to
// recover the settled funds within a channel in the case of partial or
// complete data loss. We provide the network address that we last used to
// connect to the peer as well, in case the node stops advertising the IP on
// the network for whatever reason.
//
// TODO(roasbeef): suffix version into struct?
type Single struct {
// Version is the version that should be observed when attempting to
// pack the single backup.
Version SingleBackupVersion
// IsInitiator is true if we were the initiator of the channel, and
// false otherwise. We'll need to know this information in order to
// properly re-derive the state hint information.
IsInitiator bool
// ChainHash is a hash which represents the blockchain that this
// channel will be opened within. This value is typically the genesis
// hash. In the case that the original chain went through a contentious
// hard-fork, then this value will be tweaked using the unique fork
// point on each branch.
ChainHash chainhash.Hash
// FundingOutpoint is the outpoint of the final funding transaction.
// This value uniquely and globally identities the channel within the
// target blockchain as specified by the chain hash parameter.
FundingOutpoint wire.OutPoint
// ShortChannelID encodes the exact location in the chain in which the
// channel was initially confirmed. This includes: the block height,
// transaction index, and the output within the target transaction.
// Channels that were not confirmed at the time of backup creation will
// have the funding TX broadcast height set as their block height in
// the ShortChannelID.
ShortChannelID lnwire.ShortChannelID
// RemoteNodePub is the identity public key of the remote node this
// channel has been established with.
RemoteNodePub *btcec.PublicKey
// Addresses is a list of IP address in which either we were able to
// reach the node over in the past, OR we received an incoming
// authenticated connection for the stored identity public key.
Addresses []net.Addr
// Capacity is the size of the original channel.
Capacity btcutil.Amount
// LocalChanCfg is our local channel configuration. It contains all the
// information we need to re-derive the keys we used within the
// channel. Most importantly, it allows to derive the base public
// that's used to deriving the key used within the non-delayed
// pay-to-self output on the commitment transaction for a node. With
// this information, we can re-derive the private key needed to sweep
// the funds on-chain.
//
// NOTE: Of the items in the ChannelConstraints, we only write the CSV
// delay.
LocalChanCfg channeldb.ChannelConfig
// RemoteChanCfg is the remote channel confirmation. We store this as
// well since we'll need some of their keys to re-derive things like
// the state hint obfuscator which will allow us to recognize the state
// their broadcast on chain.
//
// NOTE: Of the items in the ChannelConstraints, we only write the CSV
// delay.
RemoteChanCfg channeldb.ChannelConfig
// ShaChainRootDesc describes how to derive the private key that was
// used as the shachain root for this channel.
ShaChainRootDesc keychain.KeyDescriptor
// LeaseExpiry represents the absolute expiration as a height of the
// chain of a channel lease that is applied to every output that pays
// directly to the channel initiator in addition to the usual CSV
// requirement.
//
// NOTE: This field will only be present for the following versions:
//
// - ScriptEnforcedLeaseVersion
LeaseExpiry uint32
}
// NewSingle creates a new static channel backup based on an existing open
// channel. We also pass in the set of addresses that we used in the past to
// connect to the channel peer.
func NewSingle(channel *channeldb.OpenChannel,
nodeAddrs []net.Addr) Single {
var shaChainRootDesc keychain.KeyDescriptor
// If the channel has a populated RevocationKeyLocator, then we can
// just store that instead of the public key.
if channel.RevocationKeyLocator.Family == keychain.KeyFamilyRevocationRoot {
shaChainRootDesc = keychain.KeyDescriptor{
KeyLocator: channel.RevocationKeyLocator,
}
} else {
// If the RevocationKeyLocator is not populated, then we'll need
// to obtain a public point for the shachain root and store that.
// This is the legacy scheme.
var b bytes.Buffer
_ = channel.RevocationProducer.Encode(&b) // Can't return an error.
// Once we have the root, we'll make a public key from it, such that
// the backups plaintext don't carry any private information. When
// we go to recover, we'll present this in order to derive the
// private key.
_, shaChainPoint := btcec.PrivKeyFromBytes(b.Bytes())
shaChainRootDesc = keychain.KeyDescriptor{
PubKey: shaChainPoint,
KeyLocator: keychain.KeyLocator{
Family: keychain.KeyFamilyRevocationRoot,
},
}
}
// If a channel is unconfirmed, the block height of the ShortChannelID
// is zero. This will lead to problems when trying to restore that
// channel as the spend notifier would get a height hint of zero.
// To work around that problem, we add the channel broadcast height
// to the channel ID so we can use that as height hint on restore.
chanID := channel.ShortChanID()
if chanID.BlockHeight == 0 {
chanID.BlockHeight = channel.BroadcastHeight()
}
// If this is a zero-conf channel, we'll need to have separate logic
// depending on whether it's confirmed or not. This is because the
// ShortChanID is an alias.
if channel.IsZeroConf() {
// If the channel is confirmed, we'll use the confirmed SCID.
if channel.ZeroConfConfirmed() {
chanID = channel.ZeroConfRealScid()
} else {
// Else if the zero-conf channel is unconfirmed, we'll
// need to use the broadcast height and zero out the
// TxIndex and TxPosition fields. This is so
// openChannelShell works properly.
chanID.BlockHeight = channel.BroadcastHeight()
chanID.TxIndex = 0
chanID.TxPosition = 0
}
}
single := Single{
IsInitiator: channel.IsInitiator,
ChainHash: channel.ChainHash,
FundingOutpoint: channel.FundingOutpoint,
ShortChannelID: chanID,
RemoteNodePub: channel.IdentityPub,
Addresses: nodeAddrs,
Capacity: channel.Capacity,
LocalChanCfg: channel.LocalChanCfg,
RemoteChanCfg: channel.RemoteChanCfg,
ShaChainRootDesc: shaChainRootDesc,
}
switch {
case channel.ChanType.IsTaproot():
single.Version = SimpleTaprootVersion
case channel.ChanType.HasLeaseExpiration():
single.Version = ScriptEnforcedLeaseVersion
single.LeaseExpiry = channel.ThawHeight
case channel.ChanType.ZeroHtlcTxFee():
single.Version = AnchorsZeroFeeHtlcTxCommitVersion
case channel.ChanType.HasAnchors():
single.Version = AnchorsCommitVersion
case channel.ChanType.IsTweakless():
single.Version = TweaklessCommitVersion
default:
single.Version = DefaultSingleVersion
}
return single
}
// Serialize attempts to write out the serialized version of the target
// StaticChannelBackup into the passed io.Writer.
func (s *Single) Serialize(w io.Writer) error {
// Check to ensure that we'll only attempt to serialize a version that
// we're aware of.
switch s.Version {
case DefaultSingleVersion:
case TweaklessCommitVersion:
case AnchorsCommitVersion:
case AnchorsZeroFeeHtlcTxCommitVersion:
case ScriptEnforcedLeaseVersion:
case SimpleTaprootVersion:
default:
return fmt.Errorf("unable to serialize w/ unknown "+
"version: %v", s.Version)
}
// If the sha chain root has specified a public key (which is
// optional), then we'll encode it now.
var shaChainPub [33]byte
if s.ShaChainRootDesc.PubKey != nil {
copy(
shaChainPub[:],
s.ShaChainRootDesc.PubKey.SerializeCompressed(),
)
}
// First we gather the SCB as is into a temporary buffer so we can
// determine the total length. Before we write out the serialized SCB,
// we write the length which allows us to skip any Singles that we
// don't know of when decoding a multi.
var singleBytes bytes.Buffer
if err := lnwire.WriteElements(
&singleBytes,
s.IsInitiator,
s.ChainHash[:],
s.FundingOutpoint,
s.ShortChannelID,
s.RemoteNodePub,
s.Addresses,
s.Capacity,
s.LocalChanCfg.CsvDelay,
// We only need to write out the KeyLocator portion of the
// local channel config.
uint32(s.LocalChanCfg.MultiSigKey.Family),
s.LocalChanCfg.MultiSigKey.Index,
uint32(s.LocalChanCfg.RevocationBasePoint.Family),
s.LocalChanCfg.RevocationBasePoint.Index,
uint32(s.LocalChanCfg.PaymentBasePoint.Family),
s.LocalChanCfg.PaymentBasePoint.Index,
uint32(s.LocalChanCfg.DelayBasePoint.Family),
s.LocalChanCfg.DelayBasePoint.Index,
uint32(s.LocalChanCfg.HtlcBasePoint.Family),
s.LocalChanCfg.HtlcBasePoint.Index,
s.RemoteChanCfg.CsvDelay,
// We only need to write out the raw pubkey for the remote
// channel config.
s.RemoteChanCfg.MultiSigKey.PubKey,
s.RemoteChanCfg.RevocationBasePoint.PubKey,
s.RemoteChanCfg.PaymentBasePoint.PubKey,
s.RemoteChanCfg.DelayBasePoint.PubKey,
s.RemoteChanCfg.HtlcBasePoint.PubKey,
shaChainPub[:],
uint32(s.ShaChainRootDesc.KeyLocator.Family),
s.ShaChainRootDesc.KeyLocator.Index,
); err != nil {
return err
}
if s.Version == ScriptEnforcedLeaseVersion {
err := lnwire.WriteElements(&singleBytes, s.LeaseExpiry)
if err != nil {
return err
}
}
// TODO(yy): remove the type assertion when we finished refactoring db
// into using write buffer.
buf, ok := w.(*bytes.Buffer)
if !ok {
return fmt.Errorf("expect io.Writer to be *bytes.Buffer")
}
return lnwire.WriteElements(
buf,
byte(s.Version),
uint16(len(singleBytes.Bytes())),
singleBytes.Bytes(),
)
}
// PackToWriter is similar to the Serialize method, but takes the operation a
// step further by encryption the raw bytes of the static channel back up. For
// encryption we use the chacah20poly1305 AEAD cipher with a 24 byte nonce and
// 32-byte key size. We use a 24-byte nonce, as we can't ensure that we have a
// global counter to use as a sequence number for nonces, and want to ensure
// that we're able to decrypt these blobs without any additional context. We
// derive the key that we use for encryption via a SHA2 operation of the with
// the golden keychain.KeyFamilyBaseEncryption base encryption key. We then
// take the serialized resulting shared secret point, and hash it using sha256
// to obtain the key that we'll use for encryption. When using the AEAD, we
// pass the nonce as associated data such that we'll be able to package the two
// together for storage. Before writing out the encrypted payload, we prepend
// the nonce to the final blob.
func (s *Single) PackToWriter(w io.Writer, keyRing keychain.KeyRing) error {
// First, we'll serialize the SCB (StaticChannelBackup) into a
// temporary buffer so we can store it in a temporary place before we
// go to encrypt the entire thing.
var rawBytes bytes.Buffer
if err := s.Serialize(&rawBytes); err != nil {
return err
}
// Finally, we'll encrypt the raw serialized SCB (using the nonce as
// associated data), and write out the ciphertext prepend with the
// nonce that we used to the passed io.Reader.
e, err := lnencrypt.KeyRingEncrypter(keyRing)
if err != nil {
return fmt.Errorf("unable to generate encrypt key %w", err)
}
return e.EncryptPayloadToWriter(rawBytes.Bytes(), w)
}
// readLocalKeyDesc reads a KeyDescriptor encoded within an unpacked Single.
// For local KeyDescs, we only write out the KeyLocator information as we can
// re-derive the pubkey from it.
func readLocalKeyDesc(r io.Reader) (keychain.KeyDescriptor, error) {
var keyDesc keychain.KeyDescriptor
var keyFam uint32
if err := lnwire.ReadElements(r, &keyFam); err != nil {
return keyDesc, err
}
keyDesc.Family = keychain.KeyFamily(keyFam)
if err := lnwire.ReadElements(r, &keyDesc.Index); err != nil {
return keyDesc, err
}
return keyDesc, nil
}
// readRemoteKeyDesc reads a remote KeyDescriptor encoded within an unpacked
// Single. For remote KeyDescs, we write out only the PubKey since we don't
// actually have the KeyLocator data.
func readRemoteKeyDesc(r io.Reader) (keychain.KeyDescriptor, error) {
var (
keyDesc keychain.KeyDescriptor
pub [33]byte
)
_, err := io.ReadFull(r, pub[:])
if err != nil {
return keychain.KeyDescriptor{}, err
}
keyDesc.PubKey, err = btcec.ParsePubKey(pub[:])
if err != nil {
return keychain.KeyDescriptor{}, err
}
return keyDesc, nil
}
// Deserialize attempts to read the raw plaintext serialized SCB from the
// passed io.Reader. If the method is successful, then the target
// StaticChannelBackup will be fully populated.
func (s *Single) Deserialize(r io.Reader) error {
// First, we'll need to read the version of this single-back up so we
// can know how to unpack each of the SCB.
var version byte
err := lnwire.ReadElements(r, &version)
if err != nil {
return err
}
s.Version = SingleBackupVersion(version)
switch s.Version {
case DefaultSingleVersion:
case TweaklessCommitVersion:
case AnchorsCommitVersion:
case AnchorsZeroFeeHtlcTxCommitVersion:
case ScriptEnforcedLeaseVersion:
case SimpleTaprootVersion:
default:
return fmt.Errorf("unable to de-serialize w/ unknown "+
"version: %v", s.Version)
}
var length uint16
if err := lnwire.ReadElements(r, &length); err != nil {
return err
}
err = lnwire.ReadElements(
r, &s.IsInitiator, s.ChainHash[:], &s.FundingOutpoint,
&s.ShortChannelID, &s.RemoteNodePub, &s.Addresses, &s.Capacity,
)
if err != nil {
return err
}
err = lnwire.ReadElements(r, &s.LocalChanCfg.CsvDelay)
if err != nil {
return err
}
s.LocalChanCfg.MultiSigKey, err = readLocalKeyDesc(r)
if err != nil {
return err
}
s.LocalChanCfg.RevocationBasePoint, err = readLocalKeyDesc(r)
if err != nil {
return err
}
s.LocalChanCfg.PaymentBasePoint, err = readLocalKeyDesc(r)
if err != nil {
return err
}
s.LocalChanCfg.DelayBasePoint, err = readLocalKeyDesc(r)
if err != nil {
return err
}
s.LocalChanCfg.HtlcBasePoint, err = readLocalKeyDesc(r)
if err != nil {
return err
}
err = lnwire.ReadElements(r, &s.RemoteChanCfg.CsvDelay)
if err != nil {
return err
}
s.RemoteChanCfg.MultiSigKey, err = readRemoteKeyDesc(r)
if err != nil {
return err
}
s.RemoteChanCfg.RevocationBasePoint, err = readRemoteKeyDesc(r)
if err != nil {
return err
}
s.RemoteChanCfg.PaymentBasePoint, err = readRemoteKeyDesc(r)
if err != nil {
return err
}
s.RemoteChanCfg.DelayBasePoint, err = readRemoteKeyDesc(r)
if err != nil {
return err
}
s.RemoteChanCfg.HtlcBasePoint, err = readRemoteKeyDesc(r)
if err != nil {
return err
}
// Finally, we'll parse out the ShaChainRootDesc.
var (
shaChainPub [33]byte
zeroPub [33]byte
)
if err := lnwire.ReadElements(r, shaChainPub[:]); err != nil {
return err
}
// Since this field is optional, we'll check to see if the pubkey has
// been specified or not.
if !bytes.Equal(shaChainPub[:], zeroPub[:]) {
s.ShaChainRootDesc.PubKey, err = btcec.ParsePubKey(
shaChainPub[:],
)
if err != nil {
return err
}
}
var shaKeyFam uint32
if err := lnwire.ReadElements(r, &shaKeyFam); err != nil {
return err
}
s.ShaChainRootDesc.KeyLocator.Family = keychain.KeyFamily(shaKeyFam)
err = lnwire.ReadElements(r, &s.ShaChainRootDesc.KeyLocator.Index)
if err != nil {
return err
}
if s.Version == ScriptEnforcedLeaseVersion {
if err := lnwire.ReadElement(r, &s.LeaseExpiry); err != nil {
return err
}
}
return nil
}
// UnpackFromReader is similar to Deserialize method, but it expects the passed
// io.Reader to contain an encrypt SCB. Refer to the SerializeAndEncrypt method
// for details w.r.t the encryption scheme used. If we're unable to decrypt the
// payload for whatever reason (wrong key, wrong nonce, etc), then this method
// will return an error.
func (s *Single) UnpackFromReader(r io.Reader, keyRing keychain.KeyRing) error {
e, err := lnencrypt.KeyRingEncrypter(keyRing)
if err != nil {
return fmt.Errorf("unable to generate key decrypter %w", err)
}
plaintext, err := e.DecryptPayloadFromReader(r)
if err != nil {
return err
}
// Finally, we'll pack the bytes into a reader to we can deserialize
// the plaintext bytes of the SCB.
backupReader := bytes.NewReader(plaintext)
return s.Deserialize(backupReader)
}
// PackStaticChanBackups accepts a set of existing open channels, and a
// keychain.KeyRing, and returns a map of outpoints to the serialized+encrypted
// static channel backups. The passed keyRing should be backed by the users
// root HD seed in order to ensure full determinism.
func PackStaticChanBackups(backups []Single,
keyRing keychain.KeyRing) (map[wire.OutPoint][]byte, error) {
packedBackups := make(map[wire.OutPoint][]byte)
for _, chanBackup := range backups {
chanPoint := chanBackup.FundingOutpoint
var b bytes.Buffer
err := chanBackup.PackToWriter(&b, keyRing)
if err != nil {
return nil, fmt.Errorf("unable to pack chan backup "+
"for %v: %v", chanPoint, err)
}
packedBackups[chanPoint] = b.Bytes()
}
return packedBackups, nil
}
// PackedSingles represents a series of fully packed SCBs. This may be the
// combination of a series of individual SCBs in order to batch their
// unpacking.
type PackedSingles [][]byte
// Unpack attempts to decrypt the passed set of encrypted SCBs and deserialize
// each one into a new SCB struct. The passed keyRing should be backed by the
// same HD seed as was used to encrypt the set of backups in the first place.
// If we're unable to decrypt any of the back ups, then we'll return an error.
func (p PackedSingles) Unpack(keyRing keychain.KeyRing) ([]Single, error) {
backups := make([]Single, len(p))
for i, encryptedBackup := range p {
var backup Single
backupReader := bytes.NewReader(encryptedBackup)
err := backup.UnpackFromReader(backupReader, keyRing)
if err != nil {
return nil, err
}
backups[i] = backup
}
return backups, nil
}
// TODO(roasbeef): make codec package?