lnd.xprv/keychain/btcwallet.go
Olaoluwa Osuntokun ad25ae1a07
keychain: ensure we properly set the KeyLocator for keys from DeriveNextKey
In this commit, we fix a slight bug in the existing implementation of
DeriveNextKey for btcwallet. Before this commit, we would only set the
public key, and not also the derivation path. It's important that we
also set the path information, as in the near future we'll be using the
KeyDescriptors returned from this method to create static channel back
ups. With these static backups, the key alone may be insufficient to
re-derive the private key as we may need to fallback to brute forcing in
order to re-derive the key as it's possible we add new key families in
the future.
2018-08-14 19:11:40 -07:00

324 lines
9.2 KiB
Go

package keychain
import (
"crypto/sha256"
"fmt"
"github.com/btcsuite/btcd/btcec"
"github.com/btcsuite/btcwallet/waddrmgr"
"github.com/btcsuite/btcwallet/wallet"
"github.com/btcsuite/btcwallet/walletdb"
)
const (
// CoinTypeBitcoin specifies the BIP44 coin type for Bitcoin key
// derivation.
CoinTypeBitcoin uint32 = 0
// CoinTypeTestnet specifies the BIP44 coin type for all testnet key
// derivation.
CoinTypeTestnet = 1
// CoinTypeLitecoin specifies the BIP44 coin type for Litecoin key
// derivation.
CoinTypeLitecoin = 2
)
var (
// 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
// chainKeyScope defines the purpose and coin type to be used when generating
// keys for this keyring.
chainKeyScope waddrmgr.KeyScope
// 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, coinType uint32) SecretKeyRing {
// Construct the key scope that will be used within the waddrmgr to
// create an HD chain for deriving all of our required keys. A different
// scope is used for each specific coin type.
chainKeyScope := waddrmgr.KeyScope{
Purpose: BIP0043Purpose,
Coin: coinType,
}
return &BtcWalletKeyRing{
wallet: w,
chainKeyScope: chainKeyScope,
}
}
// 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.IsLocked() {
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(b.chainKeyScope)
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
keyLoc KeyLocator
)
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
}
// Extract the first address, ensuring that it is of the proper
// interface type, otherwise we can't manipulate it below.
addr, ok := addrs[0].(waddrmgr.ManagedPubKeyAddress)
if !ok {
return fmt.Errorf("address is not a managed pubkey " +
"addr")
}
pubKey = addr.PubKey()
_, pathInfo, _ := addr.DerivationInfo()
keyLoc = KeyLocator{
Family: keyFam,
Index: pathInfo.Index,
}
return nil
})
if err != nil {
return KeyDescriptor{}, err
}
return KeyDescriptor{
PubKey: pubKey,
KeyLocator: keyLoc,
}, 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
}