Praos: use larger nonce stabilization window starting in Conway

Author: amesgen

ouroboros-consensus-cardano/changelog.d/20240206_174354_alexander.esgen_change_epoch_structure.md

@@ -0,0 +1,8 @@
+### Non-Breaking
+
+- Change the randomness stabilization window for Conway (and future eras) to
+  `4k/f` instead of `3k/f` (one stability window) that was used for Babbage and
+  TPraos-based eras. See erratum 17.3 in the Shelley ledger specs for context.
+
+  Note that this is a backwards-incompatible change for all existing chains
+  containing (at least one full epoch worth of) Conway blocks.

ouroboros-consensus-cardano/src/ouroboros-consensus-cardano/Ouroboros/Consensus/Cardano/Node.hs

@@ -730,7 +730,13 @@ protocolInfoCardano paramsCardano
         praosMaxMajorPV = maxMajorProtVer,
         praosMaxLovelaceSupply = SL.sgMaxLovelaceSupply genesisShelley,
         praosNetworkId = SL.sgNetworkId genesisShelley,
-        praosSystemStart = SystemStart $ SL.sgSystemStart genesisShelley
+        praosSystemStart = SystemStart $ SL.sgSystemStart genesisShelley,
+        praosRandomnessStabilisationWindow =
+          -- This value is used for all Praos eras /except/ Babbage, see
+          -- 'partialConsensusConfigBabbage'.
+          SL.computeRandomnessStabilisationWindow
+            (SL.sgSecurityParam genesisShelley)
+            (SL.mkActiveSlotCoeff $ SL.sgActiveSlotsCoeff genesisShelley)
       }
 
     PraosParams { praosSlotsPerKESPeriod, praosMaxKESEvo } = praosParams
@@ -827,7 +833,17 @@ protocolInfoCardano paramsCardano
 
     partialConsensusConfigBabbage ::
          PartialConsensusConfig (BlockProtocol (ShelleyBlock (Praos c) (BabbageEra c)))
-    partialConsensusConfigBabbage = praosParams
+    partialConsensusConfigBabbage = praosParams {
+          -- For Praos in Babbage (just as in all TPraos eras) we use the
+          -- smaller (3k/f vs 4k/f slots) stability window here for
+          -- backwards-compatibility. See erratum 17.3 in the Shelley ledger
+          -- specs for context.
+          praosRandomnessStabilisationWindow =
+            SL.computeStabilityWindow
+              (SL.sgSecurityParam genesisShelley)
+              (SL.mkActiveSlotCoeff $ SL.sgActiveSlotsCoeff genesisShelley)
+        }
+
 
     partialLedgerConfigBabbage :: PartialLedgerConfig (ShelleyBlock (Praos c) (BabbageEra c))
     partialLedgerConfigBabbage =

ouroboros-consensus-protocol/changelog.d/20240206_174209_alexander.esgen_change_epoch_structure.md

@@ -0,0 +1,5 @@
+### Breaking
+
+- Add `praosRandomnessStabilisationWindow` to `PraosParams`, allowing to
+  configure in which slot the epoch nonce is snapshotted (which can now vary
+  between different eras).

ouroboros-consensus-protocol/src/ouroboros-consensus-protocol/Ouroboros/Consensus/Protocol/Praos.hs

@@ -45,7 +45,6 @@ import           Cardano.Ledger.Keys (KeyHash, KeyRole (BlockIssuer),
 import qualified Cardano.Ledger.Keys as SL
 import           Cardano.Ledger.PoolDistr
                      (IndividualPoolStake (IndividualPoolStake))
-import           Cardano.Ledger.Shelley.API (computeStabilityWindow)
 import qualified Cardano.Ledger.Shelley.API as SL
 import           Cardano.Ledger.Slot (Duration (Duration), (+*))
 import           Cardano.Protocol.TPraos.BHeader (BoundedNatural (bvValue),
@@ -183,29 +182,35 @@ forgePraosFields
 -- | Praos parameters that are node independent
 data PraosParams = PraosParams
   { -- | See 'Globals.slotsPerKESPeriod'.
-    praosSlotsPerKESPeriod :: !Word64,
+    praosSlotsPerKESPeriod             :: !Word64,
     -- | Active slots coefficient. This parameter represents the proportion
     -- of slots in which blocks should be issued. This can be interpreted as
     -- the probability that a party holding all the stake will be elected as
     -- leader for a given slot.
-    praosLeaderF           :: !SL.ActiveSlotCoeff,
+    praosLeaderF                       :: !SL.ActiveSlotCoeff,
     -- | See 'Globals.securityParameter'.
-    praosSecurityParam     :: !SecurityParam,
+    praosSecurityParam                 :: !SecurityParam,
     -- | Maximum number of KES iterations, see 'Globals.maxKESEvo'.
-    praosMaxKESEvo         :: !Word64,
+    praosMaxKESEvo                     :: !Word64,
     -- | Quorum for update system votes and MIR certificates, see
     -- 'Globals.quorum'.
-    praosQuorum            :: !Word64,
+    praosQuorum                        :: !Word64,
     -- | All blocks invalid after this protocol version, see
     -- 'Globals.maxMajorPV'.
-    praosMaxMajorPV        :: !MaxMajorProtVer,
+    praosMaxMajorPV                    :: !MaxMajorProtVer,
     -- | Maximum number of lovelace in the system, see
     -- 'Globals.maxLovelaceSupply'.
-    praosMaxLovelaceSupply :: !Word64,
+    praosMaxLovelaceSupply             :: !Word64,
     -- | Testnet or mainnet?
-    praosNetworkId         :: !SL.Network,
+    praosNetworkId                     :: !SL.Network,
     -- | The system start, as projected from the chain's genesis block.
-    praosSystemStart       :: !SystemStart
+    praosSystemStart                   :: !SystemStart,
+    -- | The number of slots before the start of an epoch where the
+    -- corresponding epoch nonce is snapshotted. This has to be at least one
+    -- stability window such that the nonce is stable at the beginning of the
+    -- epoch. Ouroboros Genesis requires this to be even larger, see
+    -- 'SL.computeRandomnessStabilisationWindow'.
+    praosRandomnessStabilisationWindow :: !Word64
   }
   deriving (Generic, NoThunks)
 
@@ -462,7 +467,7 @@ instance PraosCrypto c => ConsensusProtocol (Praos c) where
   -- - Update the operational certificate counter.
   reupdateChainDepState
     _cfg@( PraosConfig
-             PraosParams {praosSecurityParam, praosLeaderF}
+             PraosParams {praosRandomnessStabilisationWindow}
              ei
            )
     b
@@ -473,7 +478,7 @@ instance PraosCrypto c => ConsensusProtocol (Praos c) where
           praosStateLabNonce = prevHashToNonce (Views.hvPrevHash b),
           praosStateEvolvingNonce = newEvolvingNonce,
           praosStateCandidateNonce =
-            if slot +* Duration stabilityWindow < firstSlotNextEpoch
+            if slot +* Duration praosRandomnessStabilisationWindow < firstSlotNextEpoch
               then newEvolvingNonce
               else praosStateCandidateNonce cs,
           praosStateOCertCounters =
@@ -489,8 +494,6 @@ instance PraosCrypto c => ConsensusProtocol (Praos c) where
           let nextEpoch = EpochNo $ currentEpochNo + 1
           epochInfoFirst epochInfoWithErr nextEpoch
         cs = tickedPraosStateChainDepState tcs
-        stabilityWindow =
-          computeStabilityWindow (maxRollbacks praosSecurityParam) praosLeaderF
         eta = vrfNonceValue (Proxy @c) $ Views.hvVrfRes b
         newEvolvingNonce = praosStateEvolvingNonce cs ⭒ eta
         OCert _ n _ _ = Views.hvOCert b