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Merge pull request #182 from lightning-signer/bip32-zeros

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Correct BIP-32 derivation issue
This commit is contained in:
Olaoluwa Osuntokun 2020-11-03 16:44:01 -08:00 committed by GitHub
commit a21f014935
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
5 changed files with 157 additions and 28 deletions
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4
hdkeychain/bench_test.go
View file

@ -26,7 +26,7 @@ func BenchmarkDeriveHardened(b *testing.B) {
b.StartTimer()
for i := 0; i < b.N; i++ {
masterKey.Child(hdkeychain.HardenedKeyStart)
masterKey.Derive(hdkeychain.HardenedKeyStart)
}
}
@ -41,7 +41,7 @@ func BenchmarkDeriveNormal(b *testing.B) {
b.StartTimer()
for i := 0; i < b.N; i++ {
masterKey.Child(0)
masterKey.Derive(0)
}
}

8
hdkeychain/doc.go
View file

@ -39,14 +39,14 @@ create a random seed for use with the NewMaster function.
Deriving Children
Once you have created a tree root (or have deserialized an extended key as
discussed later), the child extended keys can be derived by using the Child
function. The Child function supports deriving both normal (non-hardened) and
discussed later), the child extended keys can be derived by using the Derive
function. The Derive function supports deriving both normal (non-hardened) and
hardened child extended keys. In order to derive a hardened extended key, use
the HardenedKeyStart constant + the hardened key number as the index to the
Child function. This provides the ability to cascade the keys into a tree and
Derive function. This provides the ability to cascade the keys into a tree and
hence generate the hierarchical deterministic key chains.
Normal vs Hardened Child Extended Keys
Normal vs Hardened Derived Extended Keys
A private extended key can be used to derive both hardened and non-hardened
(normal) child private and public extended keys. A public extended key can only

10
hdkeychain/example_test.go
View file

@ -71,7 +71,7 @@ func Example_defaultWalletLayout() {
// Derive the extended key for account 0. This gives the path:
// m/0H
acct0, err := masterKey.Child(hdkeychain.HardenedKeyStart + 0)
acct0, err := masterKey.Derive(hdkeychain.HardenedKeyStart + 0)
if err != nil {
fmt.Println(err)
return
@ -80,7 +80,7 @@ func Example_defaultWalletLayout() {
// Derive the extended key for the account 0 external chain. This
// gives the path:
// m/0H/0
acct0Ext, err := acct0.Child(0)
acct0Ext, err := acct0.Derive(0)
if err != nil {
fmt.Println(err)
return
@ -89,7 +89,7 @@ func Example_defaultWalletLayout() {
// Derive the extended key for the account 0 internal chain. This gives
// the path:
// m/0H/1
acct0Int, err := acct0.Child(1)
acct0Int, err := acct0.Derive(1)
if err != nil {
fmt.Println(err)
return
@ -101,7 +101,7 @@ func Example_defaultWalletLayout() {
// Derive the 10th extended key for the account 0 external chain. This
// gives the path:
// m/0H/0/10
acct0Ext10, err := acct0Ext.Child(10)
acct0Ext10, err := acct0Ext.Derive(10)
if err != nil {
fmt.Println(err)
return
@ -110,7 +110,7 @@ func Example_defaultWalletLayout() {
// Derive the 1st extended key for the account 0 internal chain. This
// gives the path:
// m/0H/1/0
acct0Int0, err := acct0Int.Child(0)
acct0Int0, err := acct0Int.Derive(0)
if err != nil {
fmt.Println(err)
return

88
hdkeychain/extendedkey.go
View file

@ -120,7 +120,7 @@ type ExtendedKey struct {
// fields. No error checking is performed here as it's only intended to be a
// convenience method used to create a populated struct. This function should
// only be used by applications that need to create custom ExtendedKeys. All
// other applications should just use NewMaster, Child, or Neuter.
// other applications should just use NewMaster, Derive, or Neuter.
func NewExtendedKey(version, key, chainCode, parentFP []byte, depth uint8,
childNum uint32, isPrivate bool) *ExtendedKey {
@ -198,8 +198,15 @@ func (k *ExtendedKey) ChainCode() []byte {
return append([]byte{}, k.chainCode...)
}
// Child returns a derived child extended key at the given index. When this
// extended key is a private extended key (as determined by the IsPrivate
// Derive returns a derived child extended key at the given index.
//
// IMPORTANT: if you were previously using the Child method, this method is incompatible.
// The Child method had a BIP-32 standard compatibility issue. You have to check whether
// any hardened derivations in your derivation path are affected by this issue, via the
// IsAffectedByIssue172 method and migrate the wallet if so. This method does conform
// to the standard. If you need the old behavior, use DeriveNonStandard.
//
// When this extended key is a private extended key (as determined by the IsPrivate
// function), a private extended key will be derived. Otherwise, the derived
// extended key will be also be a public extended key.
//
@ -219,7 +226,7 @@ func (k *ExtendedKey) ChainCode() []byte {
// index does not derive to a usable child. The ErrInvalidChild error will be
// returned if this should occur, and the caller is expected to ignore the
// invalid child and simply increment to the next index.
func (k *ExtendedKey) Child(i uint32) (*ExtendedKey, error) {
func (k *ExtendedKey) Derive(i uint32) (*ExtendedKey, error) {
// Prevent derivation of children beyond the max allowed depth.
if k.depth == maxUint8 {
return nil, ErrDeriveBeyondMaxDepth
@ -254,7 +261,9 @@ func (k *ExtendedKey) Child(i uint32) (*ExtendedKey, error) {
// When the child is a hardened child, the key is known to be a
// private key due to the above early return. Pad it with a
// leading zero as required by [BIP32] for deriving the child.
copy(data[1:], k.key)
// Additionally, right align it if it's shorter than 32 bytes.
offset := 33 - len(k.key)
copy(data[offset:], k.key)
} else {
// Case #2 or #3.
// This is either a public or private extended key, but in
@ -342,6 +351,75 @@ func (k *ExtendedKey) Child(i uint32) (*ExtendedKey, error) {
k.depth+1, i, isPrivate), nil
}
// Returns true if this key was affected by the BIP-32 issue in the Child
// method (since renamed to DeriveNonStandard).
func (k *ExtendedKey) IsAffectedByIssue172() bool {
return len(k.key) < 32
}
// Deprecated: This is a non-standard derivation that is affected by issue #172.
// 1-of-256 hardened derivations will be wrong. See note in the Derive method
// and IsAffectedByIssue172.
func (k *ExtendedKey) DeriveNonStandard(i uint32) (*ExtendedKey, error) {
if k.depth == maxUint8 {
return nil, ErrDeriveBeyondMaxDepth
}
isChildHardened := i >= HardenedKeyStart
if !k.isPrivate && isChildHardened {
return nil, ErrDeriveHardFromPublic
}
keyLen := 33
data := make([]byte, keyLen+4)
if isChildHardened {
copy(data[1:], k.key)
} else {
copy(data, k.pubKeyBytes())
}
binary.BigEndian.PutUint32(data[keyLen:], i)
hmac512 := hmac.New(sha512.New, k.chainCode)
hmac512.Write(data)
ilr := hmac512.Sum(nil)
il := ilr[:len(ilr)/2]
childChainCode := ilr[len(ilr)/2:]
ilNum := new(big.Int).SetBytes(il)
if ilNum.Cmp(btcec.S256().N) >= 0 || ilNum.Sign() == 0 {
return nil, ErrInvalidChild
}
var isPrivate bool
var childKey []byte
if k.isPrivate {
keyNum := new(big.Int).SetBytes(k.key)
ilNum.Add(ilNum, keyNum)
ilNum.Mod(ilNum, btcec.S256().N)
childKey = ilNum.Bytes()
isPrivate = true
} else {
ilx, ily := btcec.S256().ScalarBaseMult(il)
if ilx.Sign() == 0 || ily.Sign() == 0 {
return nil, ErrInvalidChild
}
pubKey, err := btcec.ParsePubKey(k.key, btcec.S256())
if err != nil {
return nil, err
}
childX, childY := btcec.S256().Add(ilx, ily, pubKey.X, pubKey.Y)
pk := btcec.PublicKey{Curve: btcec.S256(), X: childX, Y: childY}
childKey = pk.SerializeCompressed()
}
parentFP := btcutil.Hash160(k.pubKeyBytes())[:4]
return NewExtendedKey(k.version, childKey, childChainCode, parentFP,
k.depth+1, i, isPrivate), nil
}
// ChildNum returns the index at which the child extended key was derived.
//
// Extended keys with ChildNum value between 0 and 2^31-1 are normal child

75
hdkeychain/extendedkey_test.go
View file

@ -10,6 +10,7 @@ package hdkeychain
import (
"bytes"
"encoding/binary"
"encoding/hex"
"errors"
"math"
@ -224,7 +225,7 @@ tests:
for _, childNum := range test.path {
var err error
extKey, err = extKey.Child(childNum)
extKey, err = extKey.Derive(childNum)
if err != nil {
t.Errorf("err: %v", err)
continue tests
@ -381,7 +382,7 @@ tests:
for _, childNum := range test.path {
var err error
extKey, err = extKey.Child(childNum)
extKey, err = extKey.Derive(childNum)
if err != nil {
t.Errorf("err: %v", err)
continue tests
@ -390,7 +391,7 @@ tests:
privStr := extKey.String()
if privStr != test.wantPriv {
t.Errorf("Child #%d (%s): mismatched serialized "+
t.Errorf("Derive #%d (%s): mismatched serialized "+
"private extended key -- got: %s, want: %s", i,
test.name, privStr, test.wantPriv)
continue
@ -500,7 +501,7 @@ tests:
for _, childNum := range test.path {
var err error
extKey, err = extKey.Child(childNum)
extKey, err = extKey.Derive(childNum)
if err != nil {
t.Errorf("err: %v", err)
continue tests
@ -509,7 +510,7 @@ tests:
pubStr := extKey.String()
if pubStr != test.wantPub {
t.Errorf("Child #%d (%s): mismatched serialized "+
t.Errorf("Derive #%d (%s): mismatched serialized "+
"public extended key -- got: %s, want: %s", i,
test.name, pubStr, test.wantPub)
continue
@ -850,9 +851,9 @@ func TestErrors(t *testing.T) {
}
// Deriving a hardened child extended key should fail from a public key.
_, err = pubKey.Child(HardenedKeyStart)
_, err = pubKey.Derive(HardenedKeyStart)
if err != ErrDeriveHardFromPublic {
t.Fatalf("Child: mismatched error -- got: %v, want: %v",
t.Fatalf("Derive: mismatched error -- got: %v, want: %v",
err, ErrDeriveHardFromPublic)
}
@ -1072,20 +1073,20 @@ func TestMaximumDepth(t *testing.T) {
t.Fatalf("extendedkey depth %d should match expected value %d",
extKey.Depth(), i)
}
newKey, err := extKey.Child(1)
newKey, err := extKey.Derive(1)
if err != nil {
t.Fatalf("Child: unexpected error: %v", err)
t.Fatalf("Derive: unexpected error: %v", err)
}
extKey = newKey
}
noKey, err := extKey.Child(1)
noKey, err := extKey.Derive(1)
if err != ErrDeriveBeyondMaxDepth {
t.Fatalf("Child: mismatched error: want %v, got %v",
t.Fatalf("Derive: mismatched error: want %v, got %v",
ErrDeriveBeyondMaxDepth, err)
}
if noKey != nil {
t.Fatal("Child: deriving 256th key should not succeed")
t.Fatal("Derive: deriving 256th key should not succeed")
}
}
@ -1156,3 +1157,53 @@ func TestCloneWithVersion(t *testing.T) {
}
}
}
// TestLeadingZero ensures that deriving children from keys with a leading zero byte is done according
// to the BIP-32 standard and that the legacy method generates a backwards-compatible result.
func TestLeadingZero(t *testing.T) {
// The 400th seed results in a m/0' public key with a leading zero, allowing us to test
// the desired behavior.
ii := 399
seed := make([]byte, 32)
binary.BigEndian.PutUint32(seed[28:], uint32(ii))
masterKey, err := NewMaster(seed, &chaincfg.MainNetParams)
if err != nil {
t.Fatalf("hdkeychain.NewMaster failed: %v", err)
}
child0, err := masterKey.Derive(0 + HardenedKeyStart)
if err != nil {
t.Fatalf("masterKey.Derive failed: %v", err)
}
if !child0.IsAffectedByIssue172() {
t.Fatal("expected child0 to be affected by issue 172")
}
child1, err := child0.Derive(0 + HardenedKeyStart)
if err != nil {
t.Fatalf("child0.Derive failed: %v", err)
}
if child1.IsAffectedByIssue172() {
t.Fatal("did not expect child1 to be affected by issue 172")
}
child1nonstandard, err := child0.DeriveNonStandard(0 + HardenedKeyStart)
if err != nil {
t.Fatalf("child0.DeriveNonStandard failed: %v", err)
}
// This is the correct result based on BIP32
if hex.EncodeToString(child1.key) != "a9b6b30a5b90b56ed48728c73af1d8a7ef1e9cc372ec21afcc1d9bdf269b0988" {
t.Error("incorrect standard BIP32 derivation")
}
if hex.EncodeToString(child1nonstandard.key) != "ea46d8f58eb863a2d371a938396af8b0babe85c01920f59a8044412e70e837ee" {
t.Error("incorrect btcutil backwards compatible BIP32-like derivation")
}
if !child0.IsAffectedByIssue172() {
t.Error("child 0 should be affected by issue 172")
}
if child1.IsAffectedByIssue172() {
t.Error("child 1 should not be affected by issue 172")
}
}