pool/clmscript/script.go

package clmscript

import (
	"bytes"
	"crypto/sha256"

	"github.com/btcsuite/btcd/btcec"
	"github.com/btcsuite/btcd/txscript"
	"github.com/btcsuite/btcd/wire"
	"github.com/lightningnetwork/lnd/input"
	"github.com/lightningnetwork/lnd/keychain"
)

const (
	// AccountKeyFamily is the key family used to derive keys which will be
	// used in the 2 of 2 multi-sig construction of a CLM account.
	//
	// TODO(wilmer): decide on actual value.
	AccountKeyFamily keychain.KeyFamily = 220
)

// TraderKeyTweak computes the tweak based on the current per-batch key and
// shared secret that should be applied to an account's trader key. The tweak is
// computed as the following:
//
//	tweak = sha256(batchKey || secret || traderKey)
func TraderKeyTweak(batchKey *btcec.PublicKey, secret [32]byte,
	traderKey *btcec.PublicKey) []byte {

	h := sha256.New()
	_, _ = h.Write(batchKey.SerializeCompressed())
	_, _ = h.Write(secret[:])
	_, _ = h.Write(traderKey.SerializeCompressed())
	return h.Sum(nil)
}

// AccountScript returns the witness script of an account on-chain.
//
// <trader_key> OP_CHECKSIGVERIFY
// <auctioneer_key> OP_CHECKSIG OP_IFDUP OP_NOTIF
//	<account_expiry> OP_CHECKLOCKTIMEVERIFY
// OP_ENDIF
func AccountScript(expiry uint32, traderKey, auctioneerKey,
	batchKey *btcec.PublicKey, secret [32]byte) ([]byte, error) {

	traderKeyTweak := TraderKeyTweak(batchKey, secret, traderKey)
	tweakedTraderKey := input.TweakPubKeyWithTweak(traderKey, traderKeyTweak)
	tweakedAuctioneerKey := input.TweakPubKey(auctioneerKey, tweakedTraderKey)

	builder := txscript.NewScriptBuilder()

	builder.AddData(tweakedTraderKey.SerializeCompressed())
	builder.AddOp(txscript.OP_CHECKSIGVERIFY)

	builder.AddData(tweakedAuctioneerKey.SerializeCompressed())
	builder.AddOp(txscript.OP_CHECKSIG)

	builder.AddOp(txscript.OP_IFDUP)
	builder.AddOp(txscript.OP_NOTIF)
	builder.AddInt64(int64(expiry))
	builder.AddOp(txscript.OP_CHECKLOCKTIMEVERIFY)
	builder.AddOp(txscript.OP_ENDIF)

	script, err := builder.Script()
	if err != nil {
		return nil, err
	}
	return input.WitnessScriptHash(script)
}

// IncrementKey increments the given key by the backing curve's base point.
func IncrementKey(key *btcec.PublicKey) *btcec.PublicKey {
	curveParams := key.Curve.Params()
	newX, newY := key.Curve.Add(key.X, key.Y, curveParams.Gx, curveParams.Gy)
	return &btcec.PublicKey{
		X:     newX,
		Y:     newY,
		Curve: btcec.S256(),
	}
}

// LocateOutputScript determines whether a transaction includes an output with a
// specific script. If it does, the output index is returned.
func LocateOutputScript(tx *wire.MsgTx, script []byte) (uint32, bool) {
	for i, txOut := range tx.TxOut {
		if !bytes.Equal(txOut.PkScript, script) {
			continue
		}
		return uint32(i), true
	}
	return 0, false
}