Check block proof-of-work

When a tx is confirmed, we check the proof-of-work of the block in which it was published as well as the following blocks.
For each block, we check that their hash is below the difficulty they advertise, and that this difficulty is below a configured threshold.

Author: sstone

eclair-core/src/main/scala/fr/acinq/eclair/NodeParams.scala

@@ -17,8 +17,9 @@
 package fr.acinq.eclair
 
 import com.typesafe.config.{Config, ConfigFactory, ConfigValueType}
+import fr.acinq.bitcoin.UInt256
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
-import fr.acinq.bitcoin.scalacompat.{Block, ByteVector32, Crypto, Satoshi}
+import fr.acinq.bitcoin.scalacompat.{Block, ByteVector32, Crypto, Satoshi, computeP2WpkhAddress}
 import fr.acinq.eclair.Setup.Seeds
 import fr.acinq.eclair.blockchain.fee._
 import fr.acinq.eclair.channel.ChannelFlags
@@ -36,6 +37,7 @@ import fr.acinq.eclair.router.PathFindingExperimentConf
 import fr.acinq.eclair.router.Router.{MultiPartParams, PathFindingConf, RouterConf, SearchBoundaries}
 import fr.acinq.eclair.tor.Socks5ProxyParams
 import fr.acinq.eclair.wire.protocol.{Color, EncodingType, NodeAddress}
+import fr.acinq.secp256k1.Hex
 import grizzled.slf4j.Logging
 import scodec.bits.ByteVector
 
@@ -82,7 +84,8 @@ case class NodeParams(nodeKeyManager: NodeKeyManager,
                       blockchainWatchdogThreshold: Int,
                       blockchainWatchdogSources: Seq[String],
                       onionMessageConfig: OnionMessageConfig,
-                      purgeInvoicesInterval: Option[FiniteDuration]) {
+                      purgeInvoicesInterval: Option[FiniteDuration],
+                      minBlockDifficulty_opt: Option[UInt256]) {
   val privateKey: Crypto.PrivateKey = nodeKeyManager.nodeKey.privateKey
 
   val nodeId: PublicKey = nodeKeyManager.nodeId
@@ -401,6 +404,10 @@ object NodeParams extends Logging {
       None
     }
 
+    val minBlockDifficulty_opt = if (config.hasPath("minimum-block-difficulty"))
+      Some(new UInt256(Hex.decode(config.getString("minimum-block-difficulty"))))
+    else None
+
     NodeParams(
       nodeKeyManager = nodeKeyManager,
       channelKeyManager = channelKeyManager,
@@ -511,7 +518,8 @@ object NodeParams extends Logging {
         relayPolicy = onionMessageRelayPolicy,
         timeout = FiniteDuration(config.getDuration("onion-messages.reply-timeout").getSeconds, TimeUnit.SECONDS),
       ),
-      purgeInvoicesInterval = purgeInvoicesInterval
+      purgeInvoicesInterval = purgeInvoicesInterval,
+      minBlockDifficulty_opt = minBlockDifficulty_opt
     )
   }
 }

eclair-core/src/main/scala/fr/acinq/eclair/blockchain/bitcoind/ZmqWatcher.scala

@@ -405,7 +405,7 @@ private class ZmqWatcher(nodeParams: NodeParams, blockHeight: AtomicLong, client
     // matter because this only happens once, when the watched transaction has reached min_depth
     client.getTxConfirmations(w.txId).flatMap {
       case Some(confirmations) if confirmations >= w.minDepth =>
-        client.checkTxConfirmations(w.txId, confirmations).flatMap { isValid =>
+        client.checkTxConfirmations(w.txId, confirmations, this.nodeParams.minBlockDifficulty_opt).flatMap { isValid =>
           require(isValid, s"invalid confirmation proof for ${w.txId}")
           client.getTransaction(w.txId).flatMap { tx =>
             client.getTransactionShortId(w.txId).map {
@@ -421,25 +421,4 @@ private class ZmqWatcher(nodeParams: NodeParams, blockHeight: AtomicLong, client
       case _ => Future.successful((): Unit)
     }
   }
-
-  def checkConfirmedOld(w: WatchConfirmed[_ <: WatchConfirmedTriggered]): Future[Unit] = {
-    log.debug("checking confirmations of txid={}", w.txId)
-    // NB: this is very inefficient since internally we call `getrawtransaction` three times, but it doesn't really
-    // matter because this only happens once, when the watched transaction has reached min_depth
-    client.getTxConfirmations(w.txId).flatMap {
-      case Some(confirmations) if confirmations >= w.minDepth =>
-        client.getTransaction(w.txId).flatMap { tx =>
-          client.getTransactionShortId(w.txId).map {
-            case (height, index) => w match {
-              case w: WatchFundingConfirmed => context.self ! TriggerEvent(w.replyTo, w, WatchFundingConfirmedTriggered(height, index, tx))
-              case w: WatchFundingDeeplyBuried => context.self ! TriggerEvent(w.replyTo, w, WatchFundingDeeplyBuriedTriggered(height, index, tx))
-              case w: WatchTxConfirmed => context.self ! TriggerEvent(w.replyTo, w, WatchTxConfirmedTriggered(height, index, tx))
-              case w: WatchParentTxConfirmed => context.self ! TriggerEvent(w.replyTo, w, WatchParentTxConfirmedTriggered(height, index, tx))
-            }
-          }
-        }
-      case _ => Future.successful((): Unit)
-    }
-  }
-
 }

eclair-core/src/main/scala/fr/acinq/eclair/blockchain/bitcoind/rpc/BitcoinCoreClient.scala

@@ -18,7 +18,7 @@ package fr.acinq.eclair.blockchain.bitcoind.rpc
 
 import fr.acinq.bitcoin.scalacompat.Crypto.PublicKey
 import fr.acinq.bitcoin.scalacompat._
-import fr.acinq.bitcoin.{Bech32, Block, BlockHeader}
+import fr.acinq.bitcoin.{Bech32, Block, BlockHeader, UInt256}
 import fr.acinq.eclair.ShortChannelId.coordinates
 import fr.acinq.eclair.blockchain.OnChainWallet
 import fr.acinq.eclair.blockchain.OnChainWallet.{MakeFundingTxResponse, OnChainBalance}
@@ -92,15 +92,33 @@ class BitcoinCoreClient(val rpcClient: BitcoinJsonRPCClient) extends OnChainWall
       })
   }
 
-  def checkTxConfirmations(txid: ByteVector32, confirmations: Int)(implicit ec: ExecutionContext): Future[Boolean] = {
+  /**
+   *
+   * @param txid transactions id
+   * @param confirmations number of confirmations
+   * @param difficultyTarget maximum difficulty threshold
+   * @return true of transaction `txid` was confirmed at least `confirmations` times
+   */
+  def checkTxConfirmations(txid: ByteVector32, confirmations: Int, difficultyTarget_opt: Option[UInt256])(implicit ec: ExecutionContext): Future[Boolean] = {
     import KotlinUtils._
 
     def validate(headerInfos: List[BlockHeaderInfo]): Boolean = {
+      // check that headers are chained together
       for (i <- 0 until headerInfos.size - 1) {
         if(!headerInfos(i).nextBlockHash.contains(kmp2scala(headerInfos(i + 1).header.hash))) return false
         if (headerInfos(i + 1).header.hashPreviousBlock != headerInfos(i).header.hash) return false
       }
-      true
+      // and check that headers include a valid proof of work
+      // this checks that hash(header) is smaller than the header's difficulty
+      // and that the header's difficulty is smaller than the provided target
+      difficultyTarget_opt.foreach(difficultyTarget => {
+        headerInfos.forall(h => {
+          val decoded = UInt256.decodeCompact(h.header.bits)
+          // check that header difficulty is not negative, does not overflow and is below our target
+          !decoded.getSecond && !decoded.getThird && decoded.getFirst.compareTo(difficultyTarget) <= 0
+        })
+      })
+      headerInfos.forall(h => BlockHeader.checkProofOfWork(h.header))
     }
 
     for {

eclair-core/src/test/scala/fr/acinq/eclair/TestConstants.scala

@@ -202,6 +202,7 @@ object TestConstants {
         timeout = 1 minute
       ),
       purgeInvoicesInterval = None,
+      minBlockDifficulty_opt = None
     )
 
     def channelParams: LocalParams = Peer.makeChannelParams(
@@ -343,7 +344,8 @@ object TestConstants {
         relayPolicy = RelayAll,
         timeout = 1 minute
       ),
-      purgeInvoicesInterval = None
+      purgeInvoicesInterval = None,
+      minBlockDifficulty_opt = None
     )
 
     def channelParams: LocalParams = Peer.makeChannelParams(

eclair-core/src/test/scala/fr/acinq/eclair/blockchain/bitcoind/BitcoinCoreClientSpec.scala

@@ -862,14 +862,14 @@ class BitcoinCoreClientSpec extends TestKitBaseClass with BitcoindService with A
     bitcoinClient.getTxConfirmations(tx1.txid).pipeTo(sender.ref)
     sender.expectMsg(Some(0))
 
-    bitcoinClient.checkTxConfirmations(tx1.txid, 1).pipeTo(sender.ref)
+    bitcoinClient.checkTxConfirmations(tx1.txid, 1, None).pipeTo(sender.ref)
     sender.expectMsgType[Failure]
 
     generateBlocks(3)
     bitcoinClient.getTxConfirmations(tx1.txid).pipeTo(sender.ref)
     sender.expectMsg(Some(3))
 
-    bitcoinClient.checkTxConfirmations(tx1.txid, 3).pipeTo(sender.ref)
+    bitcoinClient.checkTxConfirmations(tx1.txid, 3, None).pipeTo(sender.ref)
     assert(sender.expectMsgType[Boolean])
   }
 
@@ -890,14 +890,14 @@ class BitcoinCoreClientSpec extends TestKitBaseClass with BitcoindService with A
     bitcoinClient.getTxConfirmations(tx1.txid).pipeTo(sender.ref)
     sender.expectMsg(Some(0))
 
-    bitcoinClient.checkTxConfirmations(tx1.txid, 1).pipeTo(sender.ref)
+    bitcoinClient.checkTxConfirmations(tx1.txid, 1, None).pipeTo(sender.ref)
     sender.expectMsgType[Failure]
 
     generateBlocks(3)
     bitcoinClient.getTxConfirmations(tx1.txid).pipeTo(sender.ref)
     sender.expectMsg(Some(3))
 
-    bitcoinClient.checkTxConfirmations(tx1.txid, 3).pipeTo(sender.ref)
+    bitcoinClient.checkTxConfirmations(tx1.txid, 3, None).pipeTo(sender.ref)
     val failure = sender.expectMsgType[Failure]
     assert(failure.cause.getMessage.contains(s"cannot find inclusion proof for ${tx1.txid}"))
   }