lnd.xprv/keychain/btcwallet.go

289 lines
8.2 KiB
Go

package keychain
import (
"crypto/sha256"
"fmt"
"github.com/roasbeef/btcd/btcec"
"github.com/roasbeef/btcwallet/waddrmgr"
"github.com/roasbeef/btcwallet/wallet"
"github.com/roasbeef/btcwallet/walletdb"
)
var (
// lightningKeyScope is the key scope that will be used within the
// waddrmgr to create an HD chain for deriving all of our required
// keys.
lightningKeyScope = waddrmgr.KeyScope{
Purpose: BIP0043Purpose,
Coin: 0,
}
// lightningAddrSchema is the scope addr schema for all keys that we
// derive. We'll treat them all as p2wkh addresses, as atm we must
// specify a particular type.
lightningAddrSchema = waddrmgr.ScopeAddrSchema{
ExternalAddrType: waddrmgr.WitnessPubKey,
InternalAddrType: waddrmgr.WitnessPubKey,
}
// waddrmgrNamespaceKey is the namespace key that the waddrmgr state is
// stored within the top-level waleltdb buckets of btcwallet.
waddrmgrNamespaceKey = []byte("waddrmgr")
)
// BtcWalletKeyRing is an implementation of both the KeyRing and SecretKeyRing
// interfaces backed by btcwallet's internal root waddrmgr. Internally, we'll
// be using a ScopedKeyManager to do all of our derivations, using the key
// scope and scope addr scehma defined above. Re-using the existing key scope
// construction means that all key derivation will be protected under the root
// seed of the wallet, making each derived key fully deterministic.
type BtcWalletKeyRing struct {
// wallet is a pointer to the active instance of the btcwallet core.
// This is required as we'll need to manually open database
// transactions in order to derive addresses and lookup relevant keys
wallet *wallet.Wallet
// lightningScope is a pointer to the scope that we'll be using as a
// sub key manager to derive all the keys that we require.
lightningScope *waddrmgr.ScopedKeyManager
}
// NewBtcWalletKeyRing creates a new implementation of the
// keychain.SecretKeyRing interface backed by btcwallet.
//
// NOTE: The passed waddrmgr.Manager MUST be unlocked in order for the keychain
// to function.
func NewBtcWalletKeyRing(w *wallet.Wallet) SecretKeyRing {
return &BtcWalletKeyRing{
wallet: w,
}
}
// keyScope attempts to return the key scope that we'll use to derive all of
// our keys. If the scope has already been fetched from the database, then a
// cached version will be returned. Otherwise, we'll fetch it from the database
// and cache it for subsequent accesses.
func (b *BtcWalletKeyRing) keyScope() (*waddrmgr.ScopedKeyManager, error) {
// If the scope has already been populated, then we'll return it
// directly.
if b.lightningScope != nil {
return b.lightningScope, nil
}
// Otherwise, we'll first do a check to ensure that the root manager
// isn't locked, as otherwise we won't be able to *use* the scope.
if b.wallet.Manager.Locked() {
return nil, fmt.Errorf("cannot create BtcWalletKeyRing with " +
"locked waddrmgr.Manager")
}
// If the manager is indeed unlocked, then we'll fetch the scope, cache
// it, and return to the caller.
lnScope, err := b.wallet.Manager.FetchScopedKeyManager(
lightningKeyScope,
)
if err != nil {
return nil, err
}
b.lightningScope = lnScope
return lnScope, nil
}
// createAccountIfNotExists will create the corresponding account for a key
// family if it doesn't already exist in the database.
func (b *BtcWalletKeyRing) createAccountIfNotExists(
addrmgrNs walletdb.ReadWriteBucket, keyFam KeyFamily,
scope *waddrmgr.ScopedKeyManager) error {
// If this is the multi-sig key family, then we can return early as
// this is the default account that's created.
if keyFam == KeyFamilyMultiSig {
return nil
}
// Otherwise, we'll check if the account already exists, if so, we can
// once again bail early.
_, err := scope.AccountName(addrmgrNs, uint32(keyFam))
if err == nil {
return nil
}
// If we reach this point, then the account hasn't yet been created, so
// we'll need to create it before we can proceed.
return scope.NewRawAccount(addrmgrNs, uint32(keyFam))
}
// DeriveNextKey attempts to derive the *next* key within the key family
// (account in BIP43) specified. This method should return the next external
// child within this branch.
//
// NOTE: This is part of the keychain.KeyRing interface.
func (b *BtcWalletKeyRing) DeriveNextKey(keyFam KeyFamily) (KeyDescriptor, error) {
var pubKey *btcec.PublicKey
db := b.wallet.Database()
err := walletdb.Update(db, func(tx walletdb.ReadWriteTx) error {
addrmgrNs := tx.ReadWriteBucket(waddrmgrNamespaceKey)
scope, err := b.keyScope()
if err != nil {
return err
}
// If the account doesn't exist, then we may need to create it
// for the first time in order to derive the keys that we
// require.
err = b.createAccountIfNotExists(addrmgrNs, keyFam, scope)
if err != nil {
return err
}
addrs, err := scope.NextExternalAddresses(
addrmgrNs, uint32(keyFam), 1,
)
if err != nil {
return err
}
pubKey = addrs[0].(waddrmgr.ManagedPubKeyAddress).PubKey()
return nil
})
if err != nil {
return KeyDescriptor{}, err
}
return KeyDescriptor{
PubKey: pubKey,
}, nil
}
// DeriveKey attempts to derive an arbitrary key specified by the passed
// KeyLocator. This may be used in several recovery scenarios, or when manually
// rotating something like our current default node key.
//
// NOTE: This is part of the keychain.KeyRing interface.
func (b *BtcWalletKeyRing) DeriveKey(keyLoc KeyLocator) (KeyDescriptor, error) {
var keyDesc KeyDescriptor
db := b.wallet.Database()
err := walletdb.Update(db, func(tx walletdb.ReadWriteTx) error {
addrmgrNs := tx.ReadWriteBucket(waddrmgrNamespaceKey)
scope, err := b.keyScope()
if err != nil {
return err
}
// If the account doesn't exist, then we may need to create it
// for the first time in order to derive the keys that we
// require.
err = b.createAccountIfNotExists(addrmgrNs, keyLoc.Family, scope)
if err != nil {
return err
}
path := waddrmgr.DerivationPath{
Account: uint32(keyLoc.Family),
Branch: 0,
Index: uint32(keyLoc.Index),
}
addr, err := scope.DeriveFromKeyPath(addrmgrNs, path)
if err != nil {
return err
}
keyDesc.KeyLocator = keyLoc
keyDesc.PubKey = addr.(waddrmgr.ManagedPubKeyAddress).PubKey()
return nil
})
if err != nil {
return keyDesc, err
}
return keyDesc, nil
}
// DerivePrivKey attempts to derive the private key that corresponds to the
// passed key descriptor.
//
// NOTE: This is part of the keychain.SecretKeyRing interface.
func (b *BtcWalletKeyRing) DerivePrivKey(keyDesc KeyDescriptor) (*btcec.PrivateKey, error) {
var key *btcec.PrivateKey
db := b.wallet.Database()
err := walletdb.Update(db, func(tx walletdb.ReadWriteTx) error {
addrmgrNs := tx.ReadWriteBucket(waddrmgrNamespaceKey)
scope, err := b.keyScope()
if err != nil {
return err
}
// If the account doesn't exist, then we may need to create it
// for the first time in order to derive the keys that we
// require.
err = b.createAccountIfNotExists(
addrmgrNs, keyDesc.Family, scope,
)
if err != nil {
return err
}
// Now that we know the account exists, we can safely derive
// the full private key from the given path.
path := waddrmgr.DerivationPath{
Account: uint32(keyDesc.Family),
Branch: 0,
Index: uint32(keyDesc.Index),
}
addr, err := scope.DeriveFromKeyPath(addrmgrNs, path)
if err != nil {
return err
}
key, err = addr.(waddrmgr.ManagedPubKeyAddress).PrivKey()
if err != nil {
return err
}
return nil
})
if err != nil {
return nil, err
}
return key, nil
}
// ScalarMult performs a scalar multiplication (ECDH-like operation) between
// the target key descriptor and remote public key. The output returned will be
// the sha256 of the resulting shared point serialized in compressed format. If
// k is our private key, and P is the public key, we perform the following
// operation:
//
// sx := k*P s := sha256(sx.SerializeCompressed())
//
// NOTE: This is part of the keychain.SecretKeyRing interface.
func (b *BtcWalletKeyRing) ScalarMult(keyDesc KeyDescriptor,
pub *btcec.PublicKey) ([]byte, error) {
privKey, err := b.DerivePrivKey(keyDesc)
if err != nil {
return nil, err
}
s := &btcec.PublicKey{}
x, y := btcec.S256().ScalarMult(pub.X, pub.Y, privKey.D.Bytes())
s.X = x
s.Y = y
h := sha256.Sum256(s.SerializeCompressed())
return h[:], nil
}