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watchtower/lookout/justice_descriptor: anchor justice txn

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This commit modifies the JusticeDescriptor to support creation of
justice transactions spending from anchor commitments. Rather than the
unencumbered p2wkh scripts from before, the tower will now use the
to-remote-confirmed that includes the additional CSV delay of 1. This
also requires setting the sequence number appropriately on the to-remote
input.
This commit is contained in:
Conner Fromknecht 2020-09-15 12:44:00 -04:00
parent cfbde5d2ce
commit d440cc4024
No known key found for this signature in database
GPG Key ID: E7D737B67FA592C7
2 changed files with 105 additions and 26 deletions
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51
watchtower/lookout/justice_descriptor.go
View File

@ -48,6 +48,7 @@ type breachedInput struct {
txOut *wire.TxOut
outPoint wire.OutPoint
witness [][]byte
sequence uint32
}
// commitToLocalInput extracts the information required to spend the commit
@ -104,20 +105,35 @@ func (p *JusticeDescriptor) commitToRemoteInput() (*breachedInput, error) {
return nil, err
}
// Since the to-remote witness script should just be a regular p2wkh
// output, we'll parse it to retrieve the public key.
toRemotePubKey, err := btcec.ParsePubKey(toRemoteScript, btcec.S256())
if err != nil {
return nil, err
}
// Compute the witness script hash from the to-remote pubkey, which will
// be used to locate the input on the breach commitment transaction.
toRemoteScriptHash, err := input.CommitScriptUnencumbered(
toRemotePubKey,
var (
toRemoteScriptHash []byte
toRemoteSequence uint32
)
if err != nil {
return nil, err
if p.JusticeKit.BlobType.IsAnchorChannel() {
toRemoteScriptHash, err = input.WitnessScriptHash(
toRemoteScript,
)
if err != nil {
return nil, err
}
toRemoteSequence = 1
} else {
// Since the to-remote witness script should just be a regular p2wkh
// output, we'll parse it to retrieve the public key.
toRemotePubKey, err := btcec.ParsePubKey(toRemoteScript, btcec.S256())
if err != nil {
return nil, err
}
// Compute the witness script hash from the to-remote pubkey, which will
// be used to locate the input on the breach commitment transaction.
toRemoteScriptHash, err = input.CommitScriptUnencumbered(
toRemotePubKey,
)
if err != nil {
return nil, err
}
}
// Locate the to-remote output on the breaching commitment transaction.
@ -146,6 +162,7 @@ func (p *JusticeDescriptor) commitToRemoteInput() (*breachedInput, error) {
txOut: toRemoteTxOut,
outPoint: toRemoteOutPoint,
witness: buildWitness(witnessStack, toRemoteScript),
sequence: toRemoteSequence,
}, nil
}
@ -164,6 +181,7 @@ func (p *JusticeDescriptor) assembleJusticeTxn(txWeight int64,
totalAmt += btcutil.Amount(input.txOut.Value)
justiceTxn.AddTxIn(&wire.TxIn{
PreviousOutPoint: input.outPoint,
Sequence: input.sequence,
})
}
@ -279,8 +297,13 @@ func (p *JusticeDescriptor) CreateJusticeTxn() (*wire.MsgTx, error) {
if err != nil {
return nil, err
}
weightEstimate.AddWitnessInput(input.P2WKHWitnessSize)
sweepInputs = append(sweepInputs, toRemoteInput)
if p.JusticeKit.BlobType.IsAnchorChannel() {
weightEstimate.AddWitnessInput(input.ToRemoteConfirmedWitnessSize)
} else {
weightEstimate.AddWitnessInput(input.P2WKHWitnessSize)
}
}
// TODO(conner): sweep htlc outputs

80
watchtower/lookout/justice_descriptor_test.go
View File

@ -50,6 +50,8 @@ var (
)
altruistCommitType = blob.FlagCommitOutputs.Type()
altruistAnchorCommitType = blob.TypeAltruistAnchorCommit
)
// TestJusticeDescriptor asserts that a JusticeDescriptor is able to produce the
@ -67,6 +69,10 @@ func TestJusticeDescriptor(t *testing.T) {
name: "altruist and commit type",
blobType: altruistCommitType,
},
{
name: "altruist anchor commit type",
blobType: altruistAnchorCommitType,
},
}
for _, test := range tests {
@ -77,6 +83,8 @@ func TestJusticeDescriptor(t *testing.T) {
}
func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
isAnchorChannel := blobType.IsAnchorChannel()
const (
localAmount = btcutil.Amount(100000)
remoteAmount = btcutil.Amount(200000)
@ -111,9 +119,54 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
toLocalScriptHash, err := input.WitnessScriptHash(toLocalScript)
require.Nil(t, err)
// Compute the to-remote witness script hash.
toRemoteScriptHash, err := input.CommitScriptUnencumbered(toRemotePK)
require.Nil(t, err)
// Compute the to-remote redeem script, witness script hash, and
// sequence numbers.
//
// NOTE: This is pretty subtle.
//
// The actual redeem script for a p2wkh output is just the pubkey, but
// the witness sighash calculation injects the classic p2kh script:
// OP_DUP OP_HASH160 <pubkey-hash160> OP_EQUALVERIFY OP_CHECKSIG. When
// signing for p2wkh we don't pass the raw pubkey as the witness script
// to the sign descriptor (since that's also not a valid script).
// Instead we give it the _pkscript_ of the form OP_0 <pubkey-hash160>
// from which pubkey-hash160 is extracted during sighash calculation.
//
// On the other hand, signing for the anchor p2wsh to-remote outputs
// requires the sign descriptor to contain the redeem script ver batim.
// This difference in behavior forces us to use a distinct
// toRemoteSigningScript to handle both cases.
var (
toRemoteSequence uint32
toRemoteRedeemScript []byte
toRemoteScriptHash []byte
toRemoteSigningScript []byte
)
if isAnchorChannel {
toRemoteSequence = 1
toRemoteRedeemScript, err = input.CommitScriptToRemoteConfirmed(
toRemotePK,
)
require.Nil(t, err)
toRemoteScriptHash, err = input.WitnessScriptHash(
toRemoteRedeemScript,
)
require.Nil(t, err)
// As it should be.
toRemoteSigningScript = toRemoteRedeemScript
} else {
toRemoteRedeemScript = toRemotePK.SerializeCompressed()
toRemoteScriptHash, err = input.CommitScriptUnencumbered(
toRemotePK,
)
require.Nil(t, err)
// NOTE: This is the _pkscript_.
toRemoteSigningScript = toRemoteScriptHash
}
// Construct the breaching commitment txn, containing the to-local and
// to-remote outputs. We don't need any inputs for this test.
@ -142,7 +195,11 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
// create signatures using the original weight estimate.
weightEstimate.AddWitnessInput(input.ToLocalPenaltyWitnessSize - 1)
weightEstimate.AddWitnessInput(input.P2WKHWitnessSize)
if isAnchorChannel {
weightEstimate.AddWitnessInput(input.ToRemoteConfirmedWitnessSize)
} else {
weightEstimate.AddWitnessInput(input.P2WKHWitnessSize)
}
weightEstimate.AddP2WKHOutput()
if blobType.Has(blob.FlagReward) {
weightEstimate.AddP2WKHOutput()
@ -167,6 +224,7 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
// Begin to assemble the justice kit, starting with the sweep address,
// pubkeys, and csv delay.
justiceKit := &blob.JusticeKit{
BlobType: blobType,
SweepAddress: makeAddrSlice(22),
CSVDelay: csvDelay,
}
@ -192,6 +250,7 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
Hash: breachTxID,
Index: 1,
},
Sequence: toRemoteSequence,
},
},
}
@ -226,7 +285,7 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
KeyLocator: toRemoteKeyLoc,
PubKey: toRemotePK,
},
WitnessScript: toRemoteScriptHash,
WitnessScript: toRemoteSigningScript,
Output: breachTxn.TxOut[1],
SigHashes: hashCache,
InputIndex: 1,
@ -245,18 +304,15 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
// Compute the witness for the to-remote input. The first element is a
// DER-encoded signature under the to-remote pubkey. The sighash flag is
// also present, so we trim it.
toRemoteWitness, err := input.CommitSpendNoDelay(
signer, toRemoteSignDesc, justiceTxn, false,
)
toRemoteSigRaw, err := signer.SignOutputRaw(justiceTxn, toRemoteSignDesc)
require.Nil(t, err)
toRemoteSigRaw := toRemoteWitness[0][:len(toRemoteWitness[0])-1]
// Convert the DER to-local sig into a fixed-size signature.
toLocalSig, err := lnwire.NewSigFromSignature(toLocalSigRaw)
require.Nil(t, err)
// Convert the DER to-remote sig into a fixed-size signature.
toRemoteSig, err := lnwire.NewSigFromRawSignature(toRemoteSigRaw)
toRemoteSig, err := lnwire.NewSigFromSignature(toRemoteSigRaw)
require.Nil(t, err)
// Complete our justice kit by copying the signatures into the payload.
@ -301,9 +357,9 @@ func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
// Construct the test's to-remote witness.
justiceTxn.TxIn[1].Witness = make([][]byte, 2)
justiceTxn.TxIn[1].Witness[0] = append(toRemoteSigRaw,
justiceTxn.TxIn[1].Witness[0] = append(toRemoteSigRaw.Serialize(),
byte(txscript.SigHashAll))
justiceTxn.TxIn[1].Witness[1] = toRemotePK.SerializeCompressed()
justiceTxn.TxIn[1].Witness[1] = toRemoteRedeemScript
// Assert that the watchtower derives the same justice txn.
require.Equal(t, justiceTxn, wtJusticeTxn)