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input: script modifications [temp]
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@Roasbeef
Roasbeef committed Jan 25, 2023
1 parent ec9d3db commit 1d1ab0b
Showing 1 changed file with 46 additions and 31 deletions.
77 changes: 46 additions & 31 deletions input/script_utils.go
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Original file line number Diff line number Diff line change
Expand Up @@ -521,7 +521,7 @@ func SenderHTLCTapLeafSuccess(receiverHtlcKey *btcec.PublicKey,
builder.AddInt64(32)
builder.AddOp(txscript.OP_EQUALVERIFY)

// Check that the specified pre-images matches what we hard code into
// Check that the specified pre-image matches what we hard code into
// the script.
builder.AddOp(txscript.OP_HASH160)
builder.AddData(Ripemd160H(paymentHash))
Expand Down Expand Up @@ -637,9 +637,21 @@ func SenderHTLCScriptTaproot(senderHtlcKey, receiverHtlcKey,
)
}

// maybeAppendSighashType appends a sighash type to the end of a signature if
// the sighash type isn't sighash default.
func maybeAppendSighash(sig Signature, sigHash txscript.SigHashType) []byte {
sigBytes := sig.Serialize()
if sigHash != txscript.SigHashDefault {
return sigBytes
}

return append(sigBytes, byte(sigHash))
}

// SenderHTLCScriptTaprootRedeem creates a valid witness needed to redeem a
// sender taproot HTLC with the pre-image. The returned witness is valid and
// includes the control block required to spend the output.
// includes the control block required to spend the output. This is the offered
// HTLC claimed by the remote party.
func SenderHTLCScriptTaprootRedeem(signer Signer, signDesc *SignDescriptor,
sweepTx *wire.MsgTx, preimage []byte, revokeKey *btcec.PublicKey,
tapscriptTree *txscript.IndexedTapScriptTree) (wire.TxWitness, error) {
Expand All @@ -659,12 +671,12 @@ func SenderHTLCScriptTaprootRedeem(signer Signer, signDesc *SignDescriptor,
successControlBlock := successMerkleProof.ToControlBlock(revokeKey)

// The final witness stack is:
// <receiver sig> <preimage> <timeout_script> <control_block>
// <receiver sig> <preimage> <success_script> <control_block>
witnessStack := make(wire.TxWitness, 4)
witnessStack[0] = append(sweepSig.Serialize(), byte(signDesc.HashType))
witnessStack[0] = maybeAppendSighash(sweepSig, signDesc.HashType)
witnessStack[1] = preimage
witnessStack[2] = signDesc.WitnessScript
witnessStack[4], err = successControlBlock.ToBytes()
witnessStack[3], err = successControlBlock.ToBytes()
if err != nil {
return nil, err
}
Expand All @@ -673,8 +685,9 @@ func SenderHTLCScriptTaprootRedeem(signer Signer, signDesc *SignDescriptor,
}

// SenderHTLCScriptTaprootTimeout creates a valid witness needed to timeout an
// HTLC on the sender's commitment transaction. The returned witness is valid and
// includes the control block required to spend the output.
// HTLC on the sender's commitment transaction. The returned witness is valid
// and includes the control block required to spend the output. This is a
// timeout of the offered HTLC by the sender.
func SenderHTLCScriptTaprootTimeout(receiverSig Signature,
receiverSigHash txscript.SigHashType, signer Signer,
signDesc *SignDescriptor, htlcTimeoutTx *wire.MsgTx,
Expand All @@ -698,8 +711,8 @@ func SenderHTLCScriptTaprootTimeout(receiverSig Signature,
// The final witness stack is:
// <receiver sig> <local sig> <timeout_script> <control_block>
witnessStack := make(wire.TxWitness, 4)
witnessStack[0] = append(receiverSig.Serialize(), byte(receiverSigHash))
witnessStack[1] = append(sweepSig.Serialize(), byte(signDesc.HashType))
witnessStack[0] = maybeAppendSighash(receiverSig, receiverSigHash)
witnessStack[1] = maybeAppendSighash(sweepSig, signDesc.HashType)
witnessStack[2] = signDesc.WitnessScript
witnessStack[3], err = timeoutControlBlock.ToBytes()
if err != nil {
Expand All @@ -723,7 +736,7 @@ func SenderHTLCScriptTaprootRevoke(signer Signer, signDesc *SignDescriptor,
// The witness stack in this case is pretty simple: we only need to
// specify the signature generated.
witnessStack := make(wire.TxWitness, 1)
witnessStack[0] = append(sweepSig.Serialize(), byte(signDesc.HashType))
witnessStack[0] = maybeAppendSighash(sweepSig, signDesc.HashType)

return witnessStack, nil
}
Expand Down Expand Up @@ -1004,17 +1017,17 @@ func ReceiverHtlcSpendTimeout(signer Signer, signDesc *SignDescriptor,
// path of the sender HTLC. This is a small script that allows the sender
// timeout the HTLC after expiry:
//
// <remote_htlcpubkey> OP_CHECKSIG
// <sender_htlcpubkey> OP_CHECKSIG
// OP_CHECKSEQUENCEVERIFY
// <cltv_expiry> OP_CHECKLOCKTIMEVERIFY OP_DROP
func ReceiverHtlcTapLeafTimeout(receiverHtlcKey *btcec.PublicKey,
func ReceiverHtlcTapLeafTimeout(senderHtlcKey *btcec.PublicKey,
cltvExpiry uint32) (txscript.TapLeaf, error) {

builder := txscript.NewScriptBuilder()

// The first part of the script will verify a signature from the
// receiver authorizing the spend.
builder.AddData(schnorr.SerializePubKey(receiverHtlcKey))
// sender authorizing the spend (the timeout).
builder.AddData(schnorr.SerializePubKey(senderHtlcKey))
builder.AddOp(txscript.OP_CHECKSIG)
builder.AddOp(txscript.OP_CHECKSEQUENCEVERIFY)

Expand Down Expand Up @@ -1051,17 +1064,17 @@ func ReceiverHtlcTapLeafSuccess(receiverHtlcKey *btcec.PublicKey,
builder.AddInt64(32)
builder.AddOp(txscript.OP_EQUALVERIFY)

// Check that the specified pre-images matches what we hard code into
// Check that the specified pre-image matches what we hard code into
// the script.
builder.AddOp(txscript.OP_HASH160)
builder.AddData(Ripemd160H(paymentHash))
builder.AddOp(txscript.OP_EQUALVERIFY)

// Verify the "2-of-2" multi-sig that requires both parties to sign
// off.
builder.AddData(schnorr.SerializePubKey(senderHtlcKey))
builder.AddOp(txscript.OP_CHECKSIGVERIFY)
builder.AddData(schnorr.SerializePubKey(receiverHtlcKey))
builder.AddOp(txscript.OP_CHECKSIGVERIFY)
builder.AddData(schnorr.SerializePubKey(senderHtlcKey))
builder.AddOp(txscript.OP_CHECKSIG)

successLeafScript, err := builder.Script()
Expand Down Expand Up @@ -1115,10 +1128,11 @@ func receiverHtlcTapScriptTree(senderHtlcKey, receiverHtlcKey,
}, nil
}

// ReceiverHTLCScriptTaproot cosntructs the taproot witness program (schnor
// ReceiverHTLCScriptTaproot constructs the taproot witness program (schnor
// key) for an outgoing HTLC on the receiver's version of the commitment
// transaction. This method returns the top level tweaked public key that
// commits to both the script paths.
// commits to both the script paths. From the PoV fo teh receiver, this is an
// accepted HTLC.
//
// The returned key commits to a tapscript tree with two possible paths:
//
Expand All @@ -1134,10 +1148,10 @@ func receiverHtlcTapScriptTree(senderHtlcKey, receiverHtlcKey,
// <remote_htlcpubkey> OP_CHECKSIG
//
// The timeout path can be be spent with a witness of:
// - <sender sig>
// - <sender sig> <timeout_script> <control_block>
//
// The success path can be spent with a witness of:
// - <sender sig> <receiver sig> <preimage> <sucess_script> <control_block>
// - <sender sig> <receiver sig> <preimage> <success_script> <control_block>
//
// The top level keyspend key is the revocation key, which allows a defender to
// unilaterally spend the created output. Both the final output key as well as
Expand Down Expand Up @@ -1196,8 +1210,9 @@ func ReceiverHTLCScriptTaprootRedeem(senderSig Signature,
return witnessStack, nil
}

// ReceiverHtlcTapLeafTimeout creates a valid witness needed to timeout an HTLC
// on the receiver's commitment transaction after the timeout has elapsed
// ReceiverHTLCScriptTaprootTimeout creates a valid witness needed to timeout
// an HTLC on the receiver's commitment transaction after the timeout has
// elapsed.
func ReceiverHTLCScriptTaprootTimeout(signer Signer, signDesc *SignDescriptor,
sweepTx *wire.MsgTx, cltvExpiry int32, revokeKey *btcec.PublicKey,
tapscriptTree *txscript.IndexedTapScriptTree) (wire.TxWitness, error) {
Expand Down Expand Up @@ -1226,19 +1241,19 @@ func ReceiverHTLCScriptTaprootTimeout(signer Signer, signDesc *SignDescriptor,

// In addition to the signature and the witness/leaf script, we also
// need to make a control block proof using the tapscript tree.
successTapLeafHash := txscript.NewBaseTapLeaf(
timeoutTapLeafHash := txscript.NewBaseTapLeaf(
signDesc.WitnessScript,
).TapHash()
successIdx := tapscriptTree.LeafProofIndex[successTapLeafHash]
successMerkleProof := tapscriptTree.LeafMerkleProofs[successIdx]
successControlBlock := successMerkleProof.ToControlBlock(revokeKey)
timeoutIdx := tapscriptTree.LeafProofIndex[timeoutTapLeafHash]
timeoutMerkleProof := tapscriptTree.LeafMerkleProofs[timeoutIdx]
timeoutControlBlock := timeoutMerkleProof.ToControlBlock(revokeKey)

// The final witness is pretty simple, we just need to present a valid
// signature for the script, and then provide the control block.
witnessStack := make(wire.TxWitness, 3)
witnessStack[0] = append(sweepSig.Serialize(), byte(signDesc.HashType))
witnessStack[1] = signDesc.WitnessScript
witnessStack[2], err = successControlBlock.ToBytes()
witnessStack[2], err = timeoutControlBlock.ToBytes()
if err != nil {
return nil, err
}
Expand Down Expand Up @@ -1462,9 +1477,9 @@ func TaprootHtlcSpendSuccess(signer Signer, signDesc *SignDescriptor,
//
// <success sig> <success script> <control_block>
witnessStack := make(wire.TxWitness, 3)
witnessStack[1] = append(sweepSig.Serialize(), byte(signDesc.HashType))
witnessStack[2] = signDesc.WitnessScript
witnessStack[3], err = redeemControlBlock.ToBytes()
witnessStack[0] = append(sweepSig.Serialize(), byte(signDesc.HashType))
witnessStack[1] = signDesc.WitnessScript
witnessStack[2], err = redeemControlBlock.ToBytes()
if err != nil {
return nil, err
}
Expand Down

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