feat: added randao utility module

lib/lambda_ethereum_consensus/state_transition/accessors.ex

@@ -6,6 +6,7 @@ defmodule LambdaEthereumConsensus.StateTransition.Accessors do
   alias LambdaEthereumConsensus.SszEx
   alias LambdaEthereumConsensus.StateTransition.{Cache, Math, Misc, Predicates}
   alias LambdaEthereumConsensus.Utils
+  alias LambdaEthereumConsensus.Utils.Randao
   alias Types.{Attestation, BeaconState, IndexedAttestation, SyncCommittee, Validator}
 
   @max_random_byte 2 ** 8 - 1
@@ -174,15 +175,6 @@ defmodule LambdaEthereumConsensus.StateTransition.Accessors do
     end
   end
 
-  @doc """
-  Return the randao mix at a recent ``epoch``.
-  """
-  @spec get_randao_mix(BeaconState.t(), Types.epoch()) :: Types.bytes32()
-  def get_randao_mix(%BeaconState{randao_mixes: randao_mixes}, epoch) do
-    epochs_per_historical_vector = ChainSpec.get("EPOCHS_PER_HISTORICAL_VECTOR")
-    Enum.fetch!(randao_mixes, rem(epoch, epochs_per_historical_vector))
-  end
-
   @doc """
   Return the combined effective balance of the active validators.
   Note: ``get_total_balance`` returns ``EFFECTIVE_BALANCE_INCREMENT`` Gwei minimum to avoid divisions by zero.
@@ -437,7 +429,7 @@ defmodule LambdaEthereumConsensus.StateTransition.Accessors do
       epoch + ChainSpec.get("EPOCHS_PER_HISTORICAL_VECTOR") -
         ChainSpec.get("MIN_SEED_LOOKAHEAD") - 1
 
-    mix = get_randao_mix(state, future_epoch)
+    mix = Randao.get_randao_mix(state.randao_mixes, future_epoch)
 
     SszEx.hash(domain_type <> Misc.uint64_to_bytes(epoch) <> mix)
   end

lib/lambda_ethereum_consensus/state_transition/epoch_processing.ex

@@ -5,6 +5,7 @@ defmodule LambdaEthereumConsensus.StateTransition.EpochProcessing do
 
   alias LambdaEthereumConsensus.StateTransition.{Accessors, Misc, Mutators, Predicates}
   alias LambdaEthereumConsensus.Utils.BitVector
+  alias LambdaEthereumConsensus.Utils.Randao
   alias Types.{BeaconState, HistoricalSummary, Validator}
 
   @spec process_sync_committee_updates(BeaconState.t()) ::
@@ -91,10 +92,8 @@ defmodule LambdaEthereumConsensus.StateTransition.EpochProcessing do
   def process_randao_mixes_reset(%BeaconState{randao_mixes: randao_mixes} = state) do
     current_epoch = Accessors.get_current_epoch(state)
     next_epoch = current_epoch + 1
-    epochs_per_historical_vector = ChainSpec.get("EPOCHS_PER_HISTORICAL_VECTOR")
-    randao_mix = Accessors.get_randao_mix(state, current_epoch)
-    index = rem(next_epoch, epochs_per_historical_vector)
-    new_randao_mixes = List.replace_at(randao_mixes, index, randao_mix)
+    randao_mix = Randao.get_randao_mix(randao_mixes, current_epoch)
+    new_randao_mixes = Randao.replace_randao_mix(randao_mixes, next_epoch, randao_mix)
     new_state = %BeaconState{state | randao_mixes: new_randao_mixes}
     {:ok, new_state}
   end

lib/lambda_ethereum_consensus/state_transition/operations.ex

@@ -8,6 +8,7 @@ defmodule LambdaEthereumConsensus.StateTransition.Operations do
   alias LambdaEthereumConsensus.Utils
   alias LambdaEthereumConsensus.Utils.BitList
   alias LambdaEthereumConsensus.Utils.BitVector
+  alias LambdaEthereumConsensus.Utils.Randao
 
   alias Types.{
     Attestation,
@@ -228,7 +229,8 @@ defmodule LambdaEthereumConsensus.StateTransition.Operations do
         {:error, "Inconsistency in parent hash"}
 
       # Verify prev_randao
-      payload.prev_randao != Accessors.get_randao_mix(state, Accessors.get_current_epoch(state)) ->
+      payload.prev_randao !=
+          Randao.get_randao_mix(state.randao_mixes, Accessors.get_current_epoch(state)) ->
         {:error, "Prev_randao verification failed"}
 
       # Verify timestamp
@@ -766,18 +768,13 @@ defmodule LambdaEthereumConsensus.StateTransition.Operations do
       signing_root = Misc.compute_signing_root(epoch, Types.Epoch, domain)
 
       if Bls.valid?(proposer.pubkey, signing_root, randao_reveal) do
-        randao_mix = Accessors.get_randao_mix(state, epoch)
+        randao_mix = Randao.get_randao_mix(state.randao_mixes, epoch)
         hash = SszEx.hash(randao_reveal)
 
         # Mix in RANDAO reveal
         mix = :crypto.exor(randao_mix, hash)
 
-        updated_randao_mixes =
-          List.replace_at(
-            state.randao_mixes,
-            rem(epoch, ChainSpec.get("EPOCHS_PER_HISTORICAL_VECTOR")),
-            mix
-          )
+        updated_randao_mixes = Randao.replace_randao_mix(state.randao_mixes, epoch, mix)
 
         {:ok,
          %BeaconState{

lib/types/beacon_chain/beacon_state.ex

@@ -67,7 +67,7 @@ defmodule Types.BeaconState do
           balances: Aja.Vector.t(Types.gwei()),
           # Randomness
           # size EPOCHS_PER_HISTORICAL_VECTOR 65_536
-          randao_mixes: list(Types.bytes32()),
+          randao_mixes: Aja.Vector.t(Types.bytes32()),
           # Slashings
           # Per-epoch sums of slashed effective balances
           # size EPOCHS_PER_SLASHINGS_VECTOR 8192
@@ -110,6 +110,7 @@ defmodule Types.BeaconState do
     map
     |> Map.update!(:validators, &Aja.Vector.to_list/1)
     |> Map.update!(:balances, &Aja.Vector.to_list/1)
+    |> Map.update!(:randao_mixes, &Aja.Vector.to_list/1)
     |> Map.update!(:previous_epoch_participation, &Aja.Vector.to_list/1)
     |> Map.update!(:current_epoch_participation, &Aja.Vector.to_list/1)
     |> Map.update!(:latest_execution_payload_header, &Types.ExecutionPayloadHeader.encode/1)
@@ -119,6 +120,7 @@ defmodule Types.BeaconState do
     map
     |> Map.update!(:validators, &Aja.Vector.new/1)
     |> Map.update!(:balances, &Aja.Vector.new/1)
+    |> Map.update!(:randao_mixes, &Aja.Vector.new/1)
     |> Map.update!(:previous_epoch_participation, &Aja.Vector.new/1)
     |> Map.update!(:current_epoch_participation, &Aja.Vector.new/1)
     |> Map.update!(:latest_execution_payload_header, &Types.ExecutionPayloadHeader.decode/1)

lib/utils/randao.ex

@@ -0,0 +1,25 @@
+defmodule LambdaEthereumConsensus.Utils.Randao do
+  @moduledoc """
+  This module provides utility functions for randao mixes
+  """
+
+  @spec get_randao_mix_index(Types.epoch()) :: Types.epoch()
+  defp get_randao_mix_index(epoch), do: rem(epoch, ChainSpec.get("EPOCHS_PER_HISTORICAL_VECTOR"))
+
+  @doc """
+  Replaces the randao mix with a new one at the given epoch.
+  """
+  @spec replace_randao_mix(Aja.Vector.t(Types.bytes32()), Types.epoch(), Types.bytes32()) ::
+          Aja.Vector.t(Types.bytes32())
+  def replace_randao_mix(randao_mixes, epoch, randao_mix),
+    do: Aja.Vector.replace_at!(randao_mixes, get_randao_mix_index(epoch), randao_mix)
+
+  @doc """
+  Return the randao mix at a recent ``epoch``.
+  """
+  @spec get_randao_mix(Aja.Vector.t(Types.bytes32()), Types.epoch()) :: Types.bytes32()
+  def get_randao_mix(randao_mixes, epoch) do
+    index = get_randao_mix_index(epoch)
+    Aja.Vector.at!(randao_mixes, index)
+  end
+end

test/spec/utils.ex

@@ -8,6 +8,7 @@ defmodule SpecTestUtils do
   @vector_keys [
     "validators",
     "balances",
+    "randao_mixes",
     "previous_epoch_participation",
     "current_epoch_participation"
   ]