Update confirmation scaling factor post-halving

We were still using values from before the halving. We update those
values and change the scaling factor to a reasonable scaling. This
protects channels against attackers with significant mining power.

eclair-core/src/main/scala/fr/acinq/eclair/channel/Commitments.scala

@@ -141,8 +141,8 @@ object ChannelParams {
       // small amount: not scaled
       defaultMinDepth
     } else {
-      val blockReward = 6.25 // this is true as of ~May 2020, but will be too large after 2024
-      val scalingFactor = 15
+      val blockReward = 3.125 // this will be too large after the halving in 2028
+      val scalingFactor = 10
       val blocksToReachFunding = (((scalingFactor * amount.toBtc.toDouble) / blockReward).ceil + 1).toInt
       defaultMinDepth.max(blocksToReachFunding)
     }

eclair-core/src/test/scala/fr/acinq/eclair/channel/HelpersSpec.scala

@@ -39,13 +39,13 @@ class HelpersSpec extends TestKitBaseClass with AnyFunSuiteLike with ChannelStat
   implicit val log: akka.event.LoggingAdapter = akka.event.NoLogging
 
   test("scale funding tx min depth according to funding amount") {
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(1)) == 4)
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 6, Btc(1)) == 6) // 4 conf would be enough but we use min-depth=6
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(6.25)) == 16) // we use scaling_factor=15 and a fixed block reward of 6.25BTC
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(12.5)) == 31)
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(12.6)) == 32)
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(30)) == 73)
-    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(50)) == 121)
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(1)) == 5)
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 6, Btc(1)) == 6) // 5 conf would be enough but we use min-depth=6
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(3.125)) == 11) // we use scaling_factor=10 and a fixed block reward of 3.125BTC
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(6.25)) == 21)
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(10)) == 33)
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(25)) == 81)
+    assert(ChannelParams.minDepthScaled(defaultMinDepth = 3, Btc(50)) == 161)
   }
 
   test("compute refresh delay") {

eclair-core/src/test/scala/fr/acinq/eclair/channel/states/a/WaitForAcceptChannelStateSpec.scala

@@ -301,7 +301,7 @@ class WaitForAcceptChannelStateSpec extends TestKitBaseClass with FixtureAnyFunS
   test("recv AcceptChannel (large channel)", Tag(LargeChannel)) { f =>
     import f._
     val accept = bob2alice.expectMsgType[AcceptChannel]
-    assert(accept.minimumDepth == 13) // with large channel tag we create a 5BTC channel
+    assert(accept.minimumDepth == 17) // with large channel tag we create a 5BTC channel
     bob2alice.forward(alice, accept)
     awaitCond(alice.stateName == WAIT_FOR_FUNDING_INTERNAL)
     aliceOpenReplyTo.expectNoMessage()

eclair-core/src/test/scala/fr/acinq/eclair/integration/ChannelIntegrationSpec.scala

@@ -554,8 +554,8 @@ class StandardChannelIntegrationSpec extends ChannelIntegrationSpec {
       fundeeState == WAIT_FOR_FUNDING_CONFIRMED && funderState == WAIT_FOR_CHANNEL_READY
     }, max = 30 seconds, interval = 10 seconds)
 
-    // 5 extra blocks make it 13, just the amount of confirmations needed
-    generateBlocks(5)
+    // 10 extra blocks make it 18, which should be enough confirmations
+    generateBlocks(10)
 
     awaitCond({
       fundee.register ! Register.Forward(sender.ref.toTyped[Any], channelId, CMD_GET_CHANNEL_STATE(ActorRef.noSender))