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Merge pull request #2515 from cfromknecht/altruist-output-calc

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watchtower/wtpolicy: altruist output calculation
This commit is contained in:
Olaoluwa Osuntokun 2019-02-01 19:58:06 -08:00 committed by GitHub
commit bcc9e30396
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GPG Key ID: 4AEE18F83AFDEB23
4 changed files with 253 additions and 84 deletions
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53
watchtower/lookout/justice_descriptor.go
View File

@ -8,6 +8,7 @@ import (
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcutil/txsort"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/watchtower/blob"
"github.com/lightningnetwork/lnd/watchtower/wtdb"
@ -166,40 +167,41 @@ func (p *JusticeDescriptor) assembleJusticeTxn(txWeight int64,
})
}
// Using the total input amount and the transaction's weight, compute
// the sweep and reward amounts. This corresponds to the amount returned
// to the victim and the amount paid to the tower, respectively. To do
// so, the required transaction fee is subtracted from the total, and
// the remaining amount is divided according to the prenegotiated reward
// rate from the client's session info.
sweepAmt, rewardAmt, err := p.SessionInfo.ComputeSweepOutputs(
totalAmt, txWeight,
// Using the session's policy, compute the outputs that should be added
// to the justice transaction. In the case of an altruist sweep, there
// will be a single output paying back to the victim. Otherwise for a
// reward sweep, there will be two outputs, one of which pays back to
// the victim while the other gives a cut to the tower.
outputs, err := p.SessionInfo.Policy.ComputeJusticeTxOuts(
totalAmt, txWeight, p.JusticeKit.SweepAddress[:],
p.SessionInfo.RewardAddress,
)
if err != nil {
return nil, err
}
// TODO(conner): abort/don't add if outputs are dusty
// Attach the computed txouts to the justice transaction.
justiceTxn.TxOut = outputs
// Add the sweep and reward outputs to the justice transaction.
justiceTxn.AddTxOut(&wire.TxOut{
PkScript: p.JusticeKit.SweepAddress[:],
Value: int64(sweepAmt),
})
justiceTxn.AddTxOut(&wire.TxOut{
PkScript: p.SessionInfo.RewardAddress,
Value: int64(rewardAmt),
})
// TODO(conner): apply and handle BIP69 sort
// Apply a BIP69 sort to the resulting transaction.
txsort.InPlaceSort(justiceTxn)
btx := btcutil.NewTx(justiceTxn)
if err := blockchain.CheckTransactionSanity(btx); err != nil {
return nil, err
}
// Since the transaction inputs could have been reordered as a result of the
// BIP69 sort, create an index mapping each prevout to it's new index.
inputIndex := make(map[wire.OutPoint]int)
for i, txIn := range justiceTxn.TxIn {
inputIndex[txIn.PreviousOutPoint] = i
}
// Attach each of the provided witnesses to the transaction.
for i, input := range inputs {
for _, input := range inputs {
// Lookup the input's new post-sort position.
i := inputIndex[input.outPoint]
justiceTxn.TxIn[i].Witness = input.witness
// Validate the reconstructed witnesses to ensure they are valid
@ -229,9 +231,6 @@ func (p *JusticeDescriptor) CreateJusticeTxn() (*wire.MsgTx, error) {
weightEstimate input.TxWeightEstimator
)
// Add our reward address to the weight estimate.
weightEstimate.AddP2WKHOutput()
// Add the sweep address's contribution, depending on whether it is a
// p2wkh or p2wsh output.
switch len(p.JusticeKit.SweepAddress) {
@ -245,6 +244,12 @@ func (p *JusticeDescriptor) CreateJusticeTxn() (*wire.MsgTx, error) {
return nil, ErrUnknownSweepAddrType
}
// Add our reward address to the weight estimate if the policy's blob
// type specifies a reward output.
if p.SessionInfo.Policy.BlobType.Has(blob.FlagReward) {
weightEstimate.AddP2WKHOutput()
}
// Assemble the breached to-local output from the justice descriptor and
// add it to our weight estimate.
toLocalInput, err := p.commitToLocalInput()

79
watchtower/lookout/justice_descriptor_test.go
View File

@ -12,6 +12,7 @@ import (
"github.com/btcsuite/btcd/txscript"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/btcsuite/btcutil/txsort"
"github.com/davecgh/go-spew/spew"
"github.com/lightningnetwork/lnd/input"
"github.com/lightningnetwork/lnd/keychain"
@ -46,9 +47,39 @@ var (
0x70, 0x4c, 0xff, 0x1e, 0x9c, 0x00, 0x93, 0xbe,
0xe2, 0x2e, 0x68, 0x08, 0x4c, 0xb4, 0x0f, 0x4f,
}
rewardCommitType = blob.TypeFromFlags(
blob.FlagReward, blob.FlagCommitOutputs,
)
altruistCommitType = blob.FlagCommitOutputs.Type()
)
// TestJusticeDescriptor asserts that a JusticeDescriptor is able to produce the
// correct justice transaction for different blob types.
func TestJusticeDescriptor(t *testing.T) {
tests := []struct {
name string
blobType blob.Type
}{
{
name: "reward and commit type",
blobType: rewardCommitType,
},
{
name: "altruist and commit type",
blobType: altruistCommitType,
},
}
for _, test := range tests {
t.Run(test.name, func(t *testing.T) {
testJusticeDescriptor(t, test.blobType)
})
}
}
func testJusticeDescriptor(t *testing.T, blobType blob.Type) {
const (
localAmount = btcutil.Amount(100000)
remoteAmount = btcutil.Amount(200000)
@ -113,31 +144,25 @@ func TestJusticeDescriptor(t *testing.T) {
// Compute the weight estimate for our justice transaction.
var weightEstimate input.TxWeightEstimator
weightEstimate.AddP2WKHOutput()
weightEstimate.AddP2WKHOutput()
weightEstimate.AddWitnessInput(input.ToLocalPenaltyWitnessSize)
weightEstimate.AddWitnessInput(input.P2WKHWitnessSize)
weightEstimate.AddP2WKHOutput()
if blobType.Has(blob.FlagReward) {
weightEstimate.AddP2WKHOutput()
}
txWeight := weightEstimate.Weight()
// Create a session info so that simulate agreement of the sweep
// parameters that should be used in constructing the justice
// transaction.
sessionInfo := &wtdb.SessionInfo{
Policy: wtpolicy.Policy{
policy := wtpolicy.Policy{
BlobType: blobType,
SweepFeeRate: 2000,
RewardRate: 900000,
},
RewardAddress: makeAddrSlice(22),
}
// Given the total input amount and the weight estimate, compute the
// amount that should be swept for the victim and the amount taken as a
// reward by the watchtower.
sweepAmt, rewardAmt, err := sessionInfo.ComputeSweepOutputs(
totalAmount, int64(txWeight),
)
if err != nil {
t.Fatalf("unable to compute sweep outputs: %v", err)
sessionInfo := &wtdb.SessionInfo{
Policy: policy,
RewardAddress: makeAddrSlice(22),
}
// Begin to assemble the justice kit, starting with the sweep address,
@ -170,20 +195,20 @@ func TestJusticeDescriptor(t *testing.T) {
},
},
},
TxOut: []*wire.TxOut{
{
Value: int64(sweepAmt),
PkScript: justiceKit.SweepAddress,
},
{
Value: int64(rewardAmt),
PkScript: sessionInfo.RewardAddress,
},
},
}
outputs, err := policy.ComputeJusticeTxOuts(
totalAmount, int64(txWeight), justiceKit.SweepAddress,
sessionInfo.RewardAddress,
)
if err != nil {
t.Fatalf("unable to compute justice txouts: %v", err)
}
// Attach the txouts and BIP69 sort the resulting transaction.
justiceTxn.TxOut = outputs
txsort.InPlaceSort(justiceTxn)
hashCache := txscript.NewTxSigHashes(justiceTxn)
// Create the sign descriptor used to sign for the to-local input.

31
watchtower/wtdb/session_info.go
View File

@ -3,7 +3,6 @@ package wtdb
import (
"errors"
"github.com/btcsuite/btcutil"
"github.com/lightningnetwork/lnd/watchtower/wtpolicy"
)
@ -35,11 +34,6 @@ var (
// number larger than the session's max number of updates.
ErrSessionConsumed = errors.New("all session updates have been " +
"consumed")
// ErrFeeExceedsInputs signals that the total input value of breaching
// commitment txn is insufficient to cover the fees required to sweep
// it.
ErrFeeExceedsInputs = errors.New("sweep fee exceeds input values")
)
// SessionInfo holds the negotiated session parameters for single session id,
@ -98,31 +92,6 @@ func (s *SessionInfo) AcceptUpdateSequence(seqNum, lastApplied uint16) error {
return nil
}
// ComputeSweepOutputs splits the total funds in a breaching commitment
// transaction between the victim and the tower, according to the sweep fee rate
// and reward rate. The fees are first subtracted from the overall total, before
// splitting the remaining balance amongst the victim and tower.
func (s *SessionInfo) ComputeSweepOutputs(totalAmt btcutil.Amount,
txVSize int64) (btcutil.Amount, btcutil.Amount, error) {
txFee := s.Policy.SweepFeeRate.FeeForWeight(txVSize)
if txFee > totalAmt {
return 0, 0, ErrFeeExceedsInputs
}
totalAmt -= txFee
// Apply the reward rate to the remaining total, specified in millionths
// of the available balance.
rewardRate := btcutil.Amount(s.Policy.RewardRate)
rewardAmt := (totalAmt*rewardRate + 999999) / 1000000
sweepAmt := totalAmt - rewardAmt
// TODO(conner): check dustiness
return sweepAmt, rewardAmt, nil
}
// Match is returned in response to a database query for a breach hints
// contained in a particular block. The match encapsulates all data required to
// properly decrypt a client's encrypted blob, and pursue action on behalf of

170
watchtower/wtpolicy/policy.go
View File

@ -1,13 +1,21 @@
package wtpolicy
import (
"errors"
"fmt"
"github.com/btcsuite/btcd/wire"
"github.com/btcsuite/btcutil"
"github.com/lightningnetwork/lnd/lnwallet"
"github.com/lightningnetwork/lnd/watchtower/blob"
)
const (
// RewardScale is the denominator applied when computing the
// proportional component for a tower's reward output. The current scale
// is in millionths.
RewardScale = 1000000
// DefaultMaxUpdates specifies the number of encrypted blobs a client
// can send to the tower in a single session.
DefaultMaxUpdates = 1024
@ -22,6 +30,21 @@ const (
DefaultSweepFeeRate = 3000
)
var (
// ErrFeeExceedsInputs signals that the total input value of breaching
// commitment txn is insufficient to cover the fees required to sweep
// it.
ErrFeeExceedsInputs = errors.New("sweep fee exceeds input value")
// ErrRewardExceedsInputs signals that the reward given to the tower (in
// addition to the transaction fees) is more than the input amount.
ErrRewardExceedsInputs = errors.New("reward amount exceeds input value")
// ErrCreatesDust signals that the session's policy would create a dust
// output for the victim.
ErrCreatesDust = errors.New("justice transaction creates dust at fee rate")
)
// DefaultPolicy returns a Policy containing the default parameters that can be
// used by clients or servers.
func DefaultPolicy() Policy {
@ -71,3 +94,150 @@ func (p Policy) String() string {
"sweep-fee-rate=%d)", p.BlobType, p.MaxUpdates, p.RewardRate,
p.SweepFeeRate)
}
// ComputeAltruistOutput computes the lone output value of a justice transaction
// that pays no reward to the tower. The value is computed using the weight of
// of the justice transaction and subtracting an amount that satisfies the
// policy's fee rate.
func (p *Policy) ComputeAltruistOutput(totalAmt btcutil.Amount,
txWeight int64) (btcutil.Amount, error) {
txFee := p.SweepFeeRate.FeeForWeight(txWeight)
if txFee > totalAmt {
return 0, ErrFeeExceedsInputs
}
sweepAmt := totalAmt - txFee
// TODO(conner): replace w/ configurable dust limit
dustLimit := lnwallet.DefaultDustLimit()
// Check that the created outputs won't be dusty.
if sweepAmt <= dustLimit {
return 0, ErrCreatesDust
}
return sweepAmt, nil
}
// ComputeRewardOutputs splits the total funds in a breaching commitment
// transaction between the victim and the tower, according to the sweep fee rate
// and reward rate. The reward to he tower is substracted first, before
// splitting the remaining balance amongst the victim and fees.
func (p *Policy) ComputeRewardOutputs(totalAmt btcutil.Amount,
txWeight int64) (btcutil.Amount, btcutil.Amount, error) {
txFee := p.SweepFeeRate.FeeForWeight(txWeight)
if txFee > totalAmt {
return 0, 0, ErrFeeExceedsInputs
}
// Apply the reward rate to the remaining total, specified in millionths
// of the available balance.
rewardAmt := ComputeRewardAmount(totalAmt, p.RewardBase, p.RewardRate)
if rewardAmt+txFee > totalAmt {
return 0, 0, ErrRewardExceedsInputs
}
// The sweep amount for the victim constitutes the remainder of the
// input value.
sweepAmt := totalAmt - rewardAmt - txFee
// TODO(conner): replace w/ configurable dust limit
dustLimit := lnwallet.DefaultDustLimit()
// Check that the created outputs won't be dusty.
if sweepAmt <= dustLimit {
return 0, 0, ErrCreatesDust
}
return sweepAmt, rewardAmt, nil
}
// ComputeRewardAmount computes the amount rewarded to the tower using the
// proportional rate expressed in millionths, e.g. one million is equivalent to
// one hundred percent of the total amount. The amount is rounded up to the
// nearest whole satoshi.
func ComputeRewardAmount(total btcutil.Amount, base, rate uint32) btcutil.Amount {
rewardBase := btcutil.Amount(base)
rewardRate := btcutil.Amount(rate)
// If the base reward exceeds the total, there is no more funds left
// from which to derive the proportional fee. We simply return the base,
// the caller should detect that this exceeds the total amount input.
if rewardBase > total {
return rewardBase
}
// Otherwise, subtract the base from the total and compute the
// proportional reward from the remaining total.
afterBase := total - rewardBase
proportional := (afterBase*rewardRate + RewardScale - 1) / RewardScale
return rewardBase + proportional
}
// ComputeJusticeTxOuts constructs the justice transaction outputs for the given
// policy. If the policy specifies a reward for the tower, there will be two
// outputs paying to the victim and the tower. Otherwise there will be a single
// output sweeping funds back to the victim. The totalAmt should be the sum of
// any inputs used in the transaction. The passed txWeight should include the
// weight of the outputs for the justice transaction, which is dependent on
// whether the justice transaction has a reward. The sweepPkScript should be the
// pkScript of the victim to which funds will be recovered. The rewardPkScript
// is the pkScript of the tower where its reward will be deposited, and will be
// ignored if the blob type does not specify a reward.
func (p *Policy) ComputeJusticeTxOuts(totalAmt btcutil.Amount, txWeight int64,
sweepPkScript, rewardPkScript []byte) ([]*wire.TxOut, error) {
var outputs []*wire.TxOut
// If the policy specifies a reward for the tower, compute a split of
// the funds based on the policy's parameters. Otherwise, we will use an
// the altruist output computation and sweep as much of the funds back
// to the victim as possible.
if p.BlobType.Has(blob.FlagReward) {
// Using the total input amount and the transaction's weight,
// compute the sweep and reward amounts. This corresponds to the
// amount returned to the victim and the amount paid to the
// tower, respectively. To do so, the required transaction fee
// is subtracted from the total, and the remaining amount is
// divided according to the prenegotiated reward rate from the
// client's session info.
sweepAmt, rewardAmt, err := p.ComputeRewardOutputs(
totalAmt, txWeight,
)
if err != nil {
return nil, err
}
// Add the sweep and reward outputs to the list of txouts.
outputs = append(outputs, &wire.TxOut{
PkScript: sweepPkScript,
Value: int64(sweepAmt),
})
outputs = append(outputs, &wire.TxOut{
PkScript: rewardPkScript,
Value: int64(rewardAmt),
})
} else {
// Using the total input amount and the transaction's weight,
// compute the sweep amount, which corresponds to the amount
// returned to the victim. To do so, the required transaction
// fee is subtracted from the total input amount.
sweepAmt, err := p.ComputeAltruistOutput(
totalAmt, txWeight,
)
if err != nil {
return nil, err
}
// Add the sweep output to the list of txouts.
outputs = append(outputs, &wire.TxOut{
PkScript: sweepPkScript,
Value: int64(sweepAmt),
})
}
return outputs, nil
}