Add more details to refund signing result (#675)

We seem to sometimes obtain invalid sigs from Phoenix users.
Having more details should help troubleshoot the issue.

Author: t-bast

phoenix-android/src/main/kotlin/fr/acinq/phoenix/android/settings/channels/SpendFromChannelAddress.kt

@@ -154,7 +154,9 @@ fun SpendFromChannelAddress(
                         ErrorMessage(
                             header = stringResource(id = R.string.spendchanneladdress_error_generic),
                             details = when (state) {
-                                is SpendFromChannelAddressViewState.Error.Generic -> state.cause.localizedMessage
+                                is SpendFromChannelAddressViewState.Error.Generic -> {
+                                    state.cause.localizedMessage
+                                }
                                 is SpendFromChannelAddressViewState.Error.AmountMissing -> {
                                     stringResource(id = R.string.spendchanneladdress_error_amount)
                                 }
@@ -179,9 +181,30 @@ fun SpendFromChannelAddress(
                                 is SpendFromChannelAddressViewState.Error.TransactionMalformed -> {
                                     stringResource(id = R.string.spendchanneladdress_error_tx, state.details)
                                 }
+                                is SpendFromChannelAddressViewState.Error.InvalidSig -> {
+                                    stringResource(R.string.spendchanneladdress_error_invalid_sig)
+                                }
                             },
                             alignment = Alignment.CenterHorizontally
                         )
+                        if (state is SpendFromChannelAddressViewState.Error.InvalidSig) {
+                            val context = LocalContext.current
+                            FilledButton(
+                                text = "Copy error data",
+                                onClick = {
+                                    copyToClipboard(
+                                        context = context,
+                                        data = """
+                                            tx_id=${state.txId}
+                                            funding_script=${state.fundingScript.toHex()}
+                                            public_key=${state.publicKey.toHex()}
+                                            signature=${state.signature.toHex()}
+                                        """.trimIndent(),
+                                        dataLabel = "signature error data"
+                                    )
+                                }
+                            )
+                        }
                     }
 
                     Card {

phoenix-android/src/main/kotlin/fr/acinq/phoenix/android/settings/channels/SpendFromChannelAddressViewModel.kt

@@ -20,9 +20,11 @@ import androidx.compose.runtime.mutableStateOf
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.ViewModelProvider
 import androidx.lifecycle.viewModelScope
+import fr.acinq.bitcoin.ByteVector
 import fr.acinq.bitcoin.ByteVector64
 import fr.acinq.bitcoin.PublicKey
 import fr.acinq.bitcoin.Satoshi
+import fr.acinq.bitcoin.TxId
 import fr.acinq.phoenix.PhoenixBusiness
 import fr.acinq.phoenix.utils.channels.SpendChannelAddressHelper
 import fr.acinq.phoenix.utils.channels.SpendChannelAddressResult
@@ -48,6 +50,7 @@ sealed class SpendFromChannelAddressViewState {
         data class ChannelDataUnhandledVersion(val version: Int) : Error()
         data class PublicKeyMalformed(val details: String) : Error()
         data class TransactionMalformed(val details: String) : Error()
+        data class InvalidSig(val txId: TxId, val publicKey: PublicKey, val fundingScript: ByteVector, val signature: ByteVector64): Error()
     }
 
     val canProcess: Boolean = this !is Processing && this !is SignedTransaction
@@ -120,6 +123,9 @@ class SpendFromChannelAddressViewModel(
                 is SpendChannelAddressResult.Failure.TransactionMalformed -> {
                     state.value = SpendFromChannelAddressViewState.Error.TransactionMalformed(result.details)
                 }
+                is SpendChannelAddressResult.Failure.InvalidSig -> {
+                    state.value = SpendFromChannelAddressViewState.Error.InvalidSig(result.txId, result.publicKey, result.fundingScript, result.signature)
+                }
             }
         }
     }

phoenix-android/src/main/res/values/strings.xml

@@ -331,6 +331,7 @@
     <string name="spendchanneladdress_error_unsigned_tx">Malformed unsigned tx [%1$s]</string>
     <string name="spendchanneladdress_error_remote_funding_pubkey">Malformed remote funding pubkey [%1$s]</string>
     <string name="spendchanneladdress_error_tx">Malformed transaction [%1$s]</string>
+    <string name="spendchanneladdress_error_invalid_sig">Invalid signature</string>
 
     <!-- home: balance section & misc -->
 

phoenix-shared/src/commonMain/kotlin/fr.acinq.phoenix/utils/channels/SpendChannelAddressHelper.kt

@@ -18,10 +18,15 @@ package fr.acinq.phoenix.utils.channels
 
 import fr.acinq.bitcoin.ByteVector
 import fr.acinq.bitcoin.ByteVector64
+import fr.acinq.bitcoin.Crypto
 import fr.acinq.bitcoin.PublicKey
 import fr.acinq.bitcoin.Satoshi
+import fr.acinq.bitcoin.SigHash
+import fr.acinq.bitcoin.SigVersion
 import fr.acinq.bitcoin.Script
 import fr.acinq.bitcoin.Transaction
+import fr.acinq.bitcoin.TxId
+import fr.acinq.bitcoin.byteVector
 import fr.acinq.lightning.channel.states.ChannelStateWithCommitments
 import fr.acinq.lightning.channel.states.PersistedChannelState
 import fr.acinq.lightning.logging.error
@@ -112,8 +117,12 @@ object SpendChannelAddressHelper {
             val fundingScript = Scripts.multiSig2of2(localFundingKey.publicKey(), pubkey)
 
             val sig = Transactions.sign(tx = tx, inputIndex = 0, Script.write(fundingScript), amount, localFundingKey)
-            return SpendChannelAddressResult.Success(localFundingKey.publicKey(), sig)
-
+            val signedData = tx.hashForSigning(0, Script.write(fundingScript), SigHash.SIGHASH_ALL, amount, SigVersion.SIGVERSION_WITNESS_V0)
+            return if (!Crypto.verifySignature(signedData, sig, localFundingKey.publicKey())) {
+                SpendChannelAddressResult.Failure.InvalidSig(tx.txid, localFundingKey.publicKey(), Script.write(fundingScript).byteVector(), sig)
+            } else {
+                SpendChannelAddressResult.Success(tx.txid, localFundingKey.publicKey(), Script.write(fundingScript).byteVector(), sig)
+            }
         } catch (e: Exception) {
             log.error { "error when spending from channel address: ${e.message}" }
             return SpendChannelAddressResult.Failure.Generic(e)
@@ -122,7 +131,7 @@ object SpendChannelAddressHelper {
 }
 
 sealed class SpendChannelAddressResult {
-    data class Success(val publicKey: PublicKey, val signature: ByteVector64) : SpendChannelAddressResult()
+    data class Success(val txId: TxId, val publicKey: PublicKey, val fundingScript: ByteVector, val signature: ByteVector64) : SpendChannelAddressResult()
     sealed class Failure : SpendChannelAddressResult() {
         data class Generic(val error: Throwable) : Failure()
         data object ChannelDataMalformed : Failure()
@@ -131,5 +140,6 @@ sealed class SpendChannelAddressResult {
         data class ChannelDataUnhandledVersion(val version: Int) : Failure()
         data class TransactionMalformed(val details: String) : Failure()
         data class RemoteFundingPubkeyMalformed(val details: String) : Failure()
+        data class InvalidSig(val txId: TxId, val publicKey: PublicKey, val fundingScript: ByteVector, val signature: ByteVector64) : Failure()
     }
 }