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Set remote dust limit lower bound (#294)
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We are slowly dropping support for non-segwit outputs, as proposed in
lightning/bolts#894

We can thus safely allow dust limits all the way down to 354 satoshis.

In very rare cases where dust_limit_satoshis is negotiated to a low value,
our peer may generate closing txs that will not correctly relay on the
bitcoin network due to dust relay policies.

When that happens, we detect it and force-close instead of completing the
mutual close flow.
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@t-bast
t-bast authored Oct 20, 2021
1 parent aa0aac1 commit fc6fab4
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Showing 5 changed files with 73 additions and 16 deletions.
6 changes: 4 additions & 2 deletions src/commonMain/kotlin/fr/acinq/lightning/channel/Channel.kt
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Expand Up @@ -3011,8 +3011,10 @@ object Channel {

// We may need to rely on our peer's commit tx in certain cases (backup/restore) so we must ensure their transactions
// can propagate through the bitcoin network (assuming bitcoin core nodes with default policies).
// A minimal spend of a p2wsh output is 110 bytes and bitcoin core's dust-relay-fee is 3000 sat/kb, which amounts to 330 sat.
val MIN_DUST_LIMIT = 330.sat
// The various dust limits enforced by the bitcoin network are summarized here:
// https://github.com/lightningnetwork/lightning-rfc/blob/master/03-transactions.md#dust-limits
// A dust limit of 354 sat ensures all segwit outputs will relay with default relay policies.
val MIN_DUST_LIMIT = 354.sat

// we won't exchange more than this many signatures when negotiating the closing fee
const val MAX_NEGOTIATION_ITERATIONS = 20
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1 change: 1 addition & 0 deletions src/commonMain/kotlin/fr/acinq/lightning/channel/ChannelException.kt
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Expand Up @@ -48,6 +48,7 @@ data class InvalidCommitmentSignature (override val channelId: Byte
data class InvalidHtlcSignature (override val channelId: ByteVector32, val tx: Transaction) : ChannelException(channelId, "invalid htlc signature: tx=$tx")
data class InvalidCloseSignature (override val channelId: ByteVector32, val tx: Transaction) : ChannelException(channelId, "invalid close signature: tx=$tx")
data class InvalidCloseFee (override val channelId: ByteVector32, val fee: Satoshi) : ChannelException(channelId, "invalid close fee: fee_satoshis=$fee")
data class InvalidCloseAmountBelowDust (override val channelId: ByteVector32, val tx: Transaction) : ChannelException(channelId, "invalid closing tx: some outputs are below dust: tx=$tx")
data class HtlcSigCountMismatch (override val channelId: ByteVector32, val expected: Int, val actual: Int) : ChannelException(channelId, "htlc sig count mismatch: expected=$expected actual: $actual")
data class ForcedLocalCommit (override val channelId: ByteVector32) : ChannelException(channelId, "forced local commit")
data class UnexpectedHtlcId (override val channelId: ByteVector32, val expected: Long, val actual: Long) : ChannelException(channelId, "unexpected htlc id: expected=$expected actual=$actual")
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30 changes: 26 additions & 4 deletions src/commonMain/kotlin/fr/acinq/lightning/channel/Helpers.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -451,10 +451,32 @@ object Helpers {
remoteClosingSig: ByteVector64
): Either<ChannelException, ClosingTx> {
val (closingTx, closingSigned) = makeClosingTx(keyManager, commitments, localScriptPubkey, remoteScriptPubkey, remoteClosingFee)
val signedClosingTx = Transactions.addSigs(closingTx, commitments.localParams.channelKeys.fundingPubKey, commitments.remoteParams.fundingPubKey, closingSigned.signature, remoteClosingSig)
return when (Transactions.checkSpendable(signedClosingTx)) {
is Try.Success -> Either.Right(signedClosingTx)
is Try.Failure -> Either.Left(InvalidCloseSignature(commitments.channelId, signedClosingTx.tx))
return if (checkClosingDustAmounts(closingTx)) {
val signedClosingTx = Transactions.addSigs(closingTx, commitments.localParams.channelKeys.fundingPubKey, commitments.remoteParams.fundingPubKey, closingSigned.signature, remoteClosingSig)
when (Transactions.checkSpendable(signedClosingTx)) {
is Try.Success -> Either.Right(signedClosingTx)
is Try.Failure -> Either.Left(InvalidCloseSignature(commitments.channelId, signedClosingTx.tx))
}
} else {
Either.Left(InvalidCloseAmountBelowDust(commitments.channelId, closingTx.tx))
}
}

/**
* Check that all closing outputs are above bitcoin's dust limit for their script type, otherwise there is a risk
* that the closing transaction will not be relayed to miners' mempool and will not confirm.
* The various dust limits are detailed in https://github.com/lightningnetwork/lightning-rfc/blob/master/03-transactions.md#dust-limits
*/
fun checkClosingDustAmounts(closingTx: ClosingTx): Boolean {
return closingTx.tx.txOut.all { txOut ->
val publicKeyScript = txOut.publicKeyScript.toByteArray()
when {
Script.isPay2pkh(publicKeyScript) -> txOut.amount >= 546.sat
Script.isPay2sh(publicKeyScript) -> txOut.amount >= 540.sat
Script.isPay2wpkh(publicKeyScript) -> txOut.amount >= 294.sat
Script.isPay2wsh(publicKeyScript) -> txOut.amount >= 330.sat
else -> false
}
}
}

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48 changes: 40 additions & 8 deletions src/commonTest/kotlin/fr/acinq/lightning/channel/HelpersTestsCommon.kt
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Expand Up @@ -4,10 +4,16 @@ import fr.acinq.bitcoin.*
import fr.acinq.bitcoin.Bitcoin.computeP2PkhAddress
import fr.acinq.bitcoin.Bitcoin.computeP2ShOfP2WpkhAddress
import fr.acinq.bitcoin.Bitcoin.computeP2WpkhAddress
import fr.acinq.lightning.Lightning.randomKey
import fr.acinq.lightning.channel.Helpers.Closing.checkClosingDustAmounts
import fr.acinq.lightning.tests.utils.LightningTestSuite
import fr.acinq.lightning.transactions.Transactions
import fr.acinq.lightning.utils.sat
import fr.acinq.secp256k1.Hex
import kotlin.test.Test
import kotlin.test.assertEquals
import kotlin.test.assertFalse
import kotlin.test.assertTrue

class HelpersTestsCommon : LightningTestSuite() {

Expand All @@ -30,14 +36,14 @@ class HelpersTestsCommon : LightningTestSuite() {
}

listOf(
Triple("0014d0b19277b0f76c9512f26d77573fd31a8fd15fc7", Block.TestnetGenesisBlock.hash, "tb1q6zceyaas7akf2yhjd4m4w07nr28azh78gw79kk"),
Triple("00203287047df2aa7aade3f394790a9c9d6f9235943f48a012e8a9f2c3300ca4f2d1", Block.TestnetGenesisBlock.hash, "tb1qx2rsgl0j4fa2mclnj3us48yad7frt9plfzsp969f7tpnqr9y7tgsyprxej"),
Triple("76a914b17deefe2feab87fef7221cf806bb8ca61f00fa188ac", Block.TestnetGenesisBlock.hash, "mwhSm2SHhRhd19KZyaQLgJyAtCLnkbzWbf"),
Triple("a914d3cf9d04f4ecc36df8207b300e46bc6775fc84c087", Block.TestnetGenesisBlock.hash, "2NCZBGzKadAnLv1ijAqhrKavMuqvxqu18yY"),
Triple("00145cb882efd643b7d63ae133e4d5e88e10bd5a20d7", Block.LivenetGenesisBlock.hash, "bc1qtjug9m7kgwmavwhpx0jdt6ywzz745gxhxwyn8u"),
Triple("00208c2865c87ffd33fc5d698c7df9cf2d0fb39d93103c637a06dea32c848ebc3e1d", Block.LivenetGenesisBlock.hash, "bc1q3s5xtjrll5elchtf337lnnedp7eemycs833h5pk75vkgfr4u8cws3ytg02"),
Triple("76a914536ffa992491508dca0354e52f32a3a7a679a53a88ac", Block.LivenetGenesisBlock.hash, "18cBEMRxXHqzWWCxZNtU91F5sbUNKhL5PX"),
Triple("a91481b9ac6a59b53927da7277b5ad5460d781b365d987", Block.LivenetGenesisBlock.hash, "3DWwX7NYjnav66qygrm4mBCpiByjammaWy"),
Triple("0014d0b19277b0f76c9512f26d77573fd31a8fd15fc7", Block.TestnetGenesisBlock.hash, "tb1q6zceyaas7akf2yhjd4m4w07nr28azh78gw79kk"),
Triple("00203287047df2aa7aade3f394790a9c9d6f9235943f48a012e8a9f2c3300ca4f2d1", Block.TestnetGenesisBlock.hash, "tb1qx2rsgl0j4fa2mclnj3us48yad7frt9plfzsp969f7tpnqr9y7tgsyprxej"),
Triple("76a914b17deefe2feab87fef7221cf806bb8ca61f00fa188ac", Block.TestnetGenesisBlock.hash, "mwhSm2SHhRhd19KZyaQLgJyAtCLnkbzWbf"),
Triple("a914d3cf9d04f4ecc36df8207b300e46bc6775fc84c087", Block.TestnetGenesisBlock.hash, "2NCZBGzKadAnLv1ijAqhrKavMuqvxqu18yY"),
Triple("00145cb882efd643b7d63ae133e4d5e88e10bd5a20d7", Block.LivenetGenesisBlock.hash, "bc1qtjug9m7kgwmavwhpx0jdt6ywzz745gxhxwyn8u"),
Triple("00208c2865c87ffd33fc5d698c7df9cf2d0fb39d93103c637a06dea32c848ebc3e1d", Block.LivenetGenesisBlock.hash, "bc1q3s5xtjrll5elchtf337lnnedp7eemycs833h5pk75vkgfr4u8cws3ytg02"),
Triple("76a914536ffa992491508dca0354e52f32a3a7a679a53a88ac", Block.LivenetGenesisBlock.hash, "18cBEMRxXHqzWWCxZNtU91F5sbUNKhL5PX"),
Triple("a91481b9ac6a59b53927da7277b5ad5460d781b365d987", Block.LivenetGenesisBlock.hash, "3DWwX7NYjnav66qygrm4mBCpiByjammaWy"),
).forEach {
assertEquals(
Helpers.Closing.btcAddressFromScriptPubKey(
Expand All @@ -48,4 +54,30 @@ class HelpersTestsCommon : LightningTestSuite() {
)
}
}

@Test
fun `check closing tx amounts above dust`() {
val p2pkhBelowDust = listOf(TxOut(545.sat, Script.pay2pkh(randomKey().publicKey())))
val p2shBelowDust = listOf(TxOut(539.sat, Script.pay2sh(Hex.decode("0000000000000000000000000000000000000000"))))
val p2wpkhBelowDust = listOf(TxOut(293.sat, Script.pay2wpkh(randomKey().publicKey())))
val p2wshBelowDust = listOf(TxOut(329.sat, Script.pay2wsh(Hex.decode("0000000000000000000000000000000000000000"))))
val allOutputsAboveDust = listOf(
TxOut(546.sat, Script.pay2pkh(randomKey().publicKey())),
TxOut(540.sat, Script.pay2sh(Hex.decode("0000000000000000000000000000000000000000"))),
TxOut(294.sat, Script.pay2wpkh(randomKey().publicKey())),
TxOut(330.sat, Script.pay2wsh(Hex.decode("0000000000000000000000000000000000000000"))),
)

fun toClosingTx(txOut: List<TxOut>): Transactions.TransactionWithInputInfo.ClosingTx {
val input = Transactions.InputInfo(OutPoint(ByteVector32.Zeroes, 0), TxOut(1000.sat, listOf()), listOf())
return Transactions.TransactionWithInputInfo.ClosingTx(input, Transaction(2, listOf(), txOut, 0), null)
}

assertTrue(checkClosingDustAmounts(toClosingTx(allOutputsAboveDust)))
assertFalse(checkClosingDustAmounts(toClosingTx(p2pkhBelowDust)))
assertFalse(checkClosingDustAmounts(toClosingTx(p2shBelowDust)))
assertFalse(checkClosingDustAmounts(toClosingTx(p2wpkhBelowDust)))
assertFalse(checkClosingDustAmounts(toClosingTx(p2wshBelowDust)))
}

}
4 changes: 2 additions & 2 deletions src/commonTest/kotlin/fr/acinq/lightning/channel/states/WaitForAcceptChannelTestsCommon.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -41,8 +41,8 @@ class WaitForAcceptChannelTestsCommon : LightningTestSuite() {
@Test
fun `recv AcceptChannel (dust limit too low)`() {
val (alice, _, accept) = init()
// we don't want their dust limit to be below 330
val lowDustLimitSatoshis = 329.sat
// we don't want their dust limit to be below 354
val lowDustLimitSatoshis = 353.sat
// but we only enforce it on mainnet
val aliceMainnet = alice.copy(staticParams = alice.staticParams.copy(nodeParams = alice.staticParams.nodeParams.copy(chainHash = Block.LivenetGenesisBlock.hash)))
val (alice1, actions1) = aliceMainnet.process(ChannelEvent.MessageReceived(accept.copy(dustLimitSatoshis = lowDustLimitSatoshis)))
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