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input: restore usage of NUMS key for to_remote output

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In this commit, we restore usage of the NUMS key for the to remote
output, as this allows a remote party to scan the chain in order to find
their remote output that in emergency recovery scenarios.
This commit is contained in:
Olaoluwa Osuntokun 2023-05-23 16:49:26 -07:00
parent 5e921376c4
commit 7f05c765c3
No known key found for this signature in database
GPG Key ID: 3BBD59E99B280306
2 changed files with 47 additions and 18 deletions
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62
input/script_utils.go
View File

@ -3,6 +3,7 @@ package input
import (
"bytes"
"crypto/sha256"
"encoding/hex"
"fmt"
"github.com/btcsuite/btcd/btcec/v2"
@ -23,6 +24,34 @@ var (
SequenceLockTimeSeconds = uint32(1 << 22)
)
// mustParsePubKey parses a hex encoded public key string into a public key and
// panic if parsing fails.
func mustParsePubKey(pubStr string) btcec.PublicKey {
pubBytes, err := hex.DecodeString(pubStr)
if err != nil {
panic(err)
}
pub, err := btcec.ParsePubKey(pubBytes)
if err != nil {
panic(err)
}
return *pub
}
// TaprootNUMSHex is the hex encoded version of the taproot NUMs key.
const TaprootNUMSHex = "02dca094751109d0bd055d03565874e8276dd53e926b44e3bd1bb" +
"6bf4bc130a279"
var (
// TaprootNUMSKey is a NUMS key (nothing up my sleeves number) that has
// no known private key. This was generated using the following script:
// https://github.com/lightninglabs/lightning-node-connect/tree/master/mailbox/numsgen),
// with the seed phrase "Lightning Simple Taproot".
TaprootNUMSKey = mustParsePubKey(TaprootNUMSHex)
)
// Signature is an interface for objects that can populate signatures during
// witness construction.
type Signature interface {
@ -1130,7 +1159,7 @@ func receiverHtlcTapScriptTree(senderHtlcKey, receiverHtlcKey,
// With the two leaves obtained, we'll now make the tapscript tree,
// then obtain the root from that
tapscriptTree := txscript.AssembleTaprootScriptTree(
successTapLeaf, timeoutTapLeaf,
timeoutTapLeaf, successTapLeaf,
)
tapScriptRoot := tapscriptTree.RootNode.TapHash()
@ -1823,7 +1852,7 @@ func NewLocalCommitScriptTree(csvTimeout uint32,
// Now that we have our root, we can arrive at the final output script
// by tweaking the internal key with this root.
toLocalOutputKey := txscript.ComputeTaprootOutputKey(
revokeKey, tapScriptRoot[:],
&TaprootNUMSKey, tapScriptRoot[:],
)
return &CommitScriptTree{
@ -1883,7 +1912,9 @@ func TaprootCommitSpendSuccess(signer Signer, signDesc *SignDescriptor,
).TapHash()
settleIdx := scriptTree.LeafProofIndex[settleTapleafHash]
settleMerkleProof := scriptTree.LeafMerkleProofs[settleIdx]
settleControlBlock := settleMerkleProof.ToControlBlock(revokeKey)
settleControlBlock := settleMerkleProof.ToControlBlock(
&TaprootNUMSKey,
)
// With the control block created, we'll now generate the signature we
// need to authorize the spend.
@ -2142,8 +2173,8 @@ func CommitScriptToRemoteConfirmed(key *btcec.PublicKey) ([]byte, error) {
// NewRemoteCommitScriptTree constructs a new script tree for the remote party
// to sweep their funds after a hard coded 1 block delay.
func NewRemoteCommitScriptTree(numsKey,
remoteKey *btcec.PublicKey) (*CommitScriptTree, error) {
func NewRemoteCommitScriptTree(remoteKey *btcec.PublicKey,
) (*CommitScriptTree, error) {
// First, construct the remote party's tapscript they'll use to sweep their
// outputs.
@ -2166,7 +2197,7 @@ func NewRemoteCommitScriptTree(numsKey,
// Now that we have our root, we can arrive at the final output script
// by tweaking the internal key with this root.
toRemoteOutputKey := txscript.ComputeTaprootOutputKey(
numsKey, tapScriptRoot[:],
&TaprootNUMSKey, tapScriptRoot[:],
)
return &CommitScriptTree{
@ -2179,9 +2210,10 @@ func NewRemoteCommitScriptTree(numsKey,
// TaprootCommitScriptToRemote constructs a taproot witness program for the
// output on the commitment transaction for the remote party. For the top level
// key spend, we'll use the combined funding key (musig2.KeyAgg(k1, k2)), as a
// sort of practical NUMs point (the local party would never sign for this). We
// then commit to a single tapscript leaf that holds the normal CSV 1 delay
// key spend, we'll use a NUMs key to ensure that only the script path can be
// taken. Using a set NUMs key here also means that recovery solutions can scan
// the chain given knowledge of the public key fo the remote party. We then
// commit to a single tapscript leaf that holds the normal CSV 1 delay
// script.
//
// Our single tapleaf will use the following script:
@ -2195,12 +2227,10 @@ func NewRemoteCommitScriptTree(numsKey,
// the stack.
//
// TODO(roasbeef): double check here can't pass additional stack elements?
func TaprootCommitScriptToRemote(combinedFundingKey,
remoteKey *btcec.PublicKey) (*btcec.PublicKey, error) {
func TaprootCommitScriptToRemote(remoteKey *btcec.PublicKey,
) (*btcec.PublicKey, error) {
commitScriptTree, err := NewRemoteCommitScriptTree(
combinedFundingKey, remoteKey,
)
commitScriptTree, err := NewRemoteCommitScriptTree(remoteKey)
if err != nil {
return nil, err
}
@ -2211,7 +2241,7 @@ func TaprootCommitScriptToRemote(combinedFundingKey,
// TaprootCommitRemoteSpend allows the remote party to sweep their output into
// their wallet after an enforced 1 block delay.
func TaprootCommitRemoteSpend(signer Signer, signDesc *SignDescriptor,
sweepTx *wire.MsgTx, numsKey *btcec.PublicKey,
sweepTx *wire.MsgTx,
scriptTree *txscript.IndexedTapScriptTree) (wire.TxWitness, error) {
// First, we'll need to construct a valid control block to execute the
@ -2221,7 +2251,7 @@ func TaprootCommitRemoteSpend(signer Signer, signDesc *SignDescriptor,
).TapHash()
settleIdx := scriptTree.LeafProofIndex[settleTapleafHash]
settleMerkleProof := scriptTree.LeafMerkleProofs[settleIdx]
settleControlBlock := settleMerkleProof.ToControlBlock(numsKey)
settleControlBlock := settleMerkleProof.ToControlBlock(&TaprootNUMSKey)
// With the control block created, we'll now generate the signature we
// need to authorize the spend.

3
input/taproot_test.go
View File

@ -927,7 +927,7 @@ func newTestCommitScriptTree(local bool) (*testCommitScriptTree, error) {
)
} else {
commitScriptTree, err = NewRemoteCommitScriptTree(
revokeKey.PubKey(), selfKey.PubKey(),
selfKey.PubKey(),
)
}
@ -1210,7 +1210,6 @@ func remoteCommitSweepWitGen(sigHash txscript.SigHashType,
return TaprootCommitRemoteSpend(
signer, signDesc, spendTx,
commitScriptTree.revokeKey.PubKey(),
commitScriptTree.TapscriptTree,
)
}