// receiverHtlcSpendRedeem constructs a valid witness allowing the receiver of
// an HTLC to redeem the conditional payment in the event that their commitment
// transaction is broadcast. Since this is a pay out to the receiving party as
// an output on their commitment transaction, a relative time delay is required
// before the output can be spent.
func receiverHtlcSpendRedeem(commitScript []byte, outputAmt btcutil.Amount,
reciverKey *btcec.PrivateKey, sweepTx *wire.MsgTx,
paymentPreimage []byte, relativeTimeout uint32) (wire.TxWitness, error) {
// In order to properly spend the transaction, we need to set the
// sequence number. We do this by convering the relative block delay
// into a sequence number value able to be interpeted by
// OP_CHECKSEQUENCEVERIFY.
sweepTx.TxIn[0].Sequence = lockTimeToSequence(false, relativeTimeout)
// Additionally, OP_CSV requires that the version of the transaction
// spending a pkscript with OP_CSV within it *must* be >= 2.
sweepTx.Version = 2
hashCache := txscript.NewTxSigHashes(sweepTx)
sweepSig, err := txscript.RawTxInWitnessSignature(
sweepTx, hashCache, 0, int64(outputAmt), commitScript,
txscript.SigHashAll, reciverKey)
if err != nil {
return nil, err
}
// Place a one as the first item in the evaluated witness stack to
// force script execution to the HTLC redemption clause.
witnessStack := wire.TxWitness(make([][]byte, 4))
witnessStack[0] = sweepSig
witnessStack[1] = paymentPreimage
witnessStack[2] = []byte{1}
witnessStack[3] = commitScript
return witnessStack, nil
}
// htlcSpendTimeout constructs a valid witness allowing the sender of an HTLC
// to recover the pending funds after an absolute, then relative locktime
// period.
func senderHtlcSpendTimeout(commitScript []byte, outputAmt btcutil.Amount,
senderKey *btcec.PrivateKey, sweepTx *wire.MsgTx,
absoluteTimeout, relativeTimeout uint32) (wire.TxWitness, error) {
// Since the HTLC output has an absolute timeout before we're permitted
// to sweep the output, we need to set the locktime of this sweepign
// transaction to that aboslute value in order to pass Script
// verification.
sweepTx.LockTime = absoluteTimeout
// Additionally, we're required to wait a relative period of time
// before we can sweep the output in order to allow the other party to
// contest our claim of validity to this version of the commitment
// transaction.
sweepTx.TxIn[0].Sequence = lockTimeToSequence(false, relativeTimeout)
// Finally, OP_CSV requires that the version of the transaction
// spending a pkscript with OP_CSV within it *must* be >= 2.
sweepTx.Version = 2
hashCache := txscript.NewTxSigHashes(sweepTx)
sweepSig, err := txscript.RawTxInWitnessSignature(
sweepTx, hashCache, 0, int64(outputAmt), commitScript,
txscript.SigHashAll, senderKey)
if err != nil {
return nil, err
}
// We place a zero as the first item of the evaluated witness stack in
// order to force Script execution to the HTLC timeout clause.
witnessStack := wire.TxWitness(make([][]byte, 3))
witnessStack[0] = sweepSig
witnessStack[1] = []byte{0}
witnessStack[2] = commitScript
return witnessStack, nil
}