From c927b786cf28cf824c4d612fe3af785538a8dc58 Mon Sep 17 00:00:00 2001
From: Karolis Petrauskas <karolis.petrauskas@ext.iota.org>
Date: Wed, 20 Sep 2023 10:16:02 +0300
Subject: [PATCH] Make fee destination less predictable and avoid using
 go-specific randomness.

---
 .../cons/bp/aggregated_batch_proposals.go     |  8 ++++----
 packages/chain/cons/bp/batch_proposal_set.go  | 19 +++++++++++++------
 packages/chain/cons/cons.go                   |  2 +-
 3 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/packages/chain/cons/bp/aggregated_batch_proposals.go b/packages/chain/cons/bp/aggregated_batch_proposals.go
index 3cc242d54c..3f5a557804 100644
--- a/packages/chain/cons/bp/aggregated_batch_proposals.go
+++ b/packages/chain/cons/bp/aggregated_batch_proposals.go
@@ -18,11 +18,11 @@ import (
 // Here we store just an aggregated info.
 type AggregatedBatchProposals struct {
 	shouldBeSkipped        bool
+	batchProposalSet       batchProposalSet
 	decidedIndexProposals  map[gpa.NodeID][]int
 	decidedBaseAliasOutput *isc.AliasOutputWithID
 	decidedRequestRefs     []*isc.RequestRef
 	aggregatedTime         time.Time
-	validatorFeeTarget     isc.AgentID
 }
 
 func AggregateBatchProposals(inputs map[gpa.NodeID][]byte, nodeIDs []gpa.NodeID, f int, log *logger.Logger) *AggregatedBatchProposals {
@@ -51,11 +51,11 @@ func AggregateBatchProposals(inputs map[gpa.NodeID][]byte, nodeIDs []gpa.NodeID,
 	aggregatedTime := bps.aggregatedTime(f)
 	decidedBaseAliasOutput := bps.decidedBaseAliasOutput(f)
 	abp := &AggregatedBatchProposals{
+		batchProposalSet:       bps,
 		decidedIndexProposals:  bps.decidedDSSIndexProposals(),
 		decidedBaseAliasOutput: decidedBaseAliasOutput,
 		decidedRequestRefs:     bps.decidedRequestRefs(f, decidedBaseAliasOutput),
 		aggregatedTime:         aggregatedTime,
-		validatorFeeTarget:     bps.selectedFeeDestination(aggregatedTime),
 	}
 	if abp.decidedBaseAliasOutput == nil || len(abp.decidedRequestRefs) == 0 || abp.aggregatedTime.IsZero() {
 		log.Debugf(
@@ -92,11 +92,11 @@ func (abp *AggregatedBatchProposals) AggregatedTime() time.Time {
 	return abp.aggregatedTime
 }
 
-func (abp *AggregatedBatchProposals) ValidatorFeeTarget() isc.AgentID {
+func (abp *AggregatedBatchProposals) ValidatorFeeTarget(randomness hashing.HashValue) isc.AgentID {
 	if abp.shouldBeSkipped {
 		panic("trying to use aggregated proposal marked to be skipped")
 	}
-	return abp.validatorFeeTarget
+	return abp.batchProposalSet.selectedFeeDestination(abp.aggregatedTime, randomness)
 }
 
 func (abp *AggregatedBatchProposals) DecidedRequestRefs() []*isc.RequestRef {
diff --git a/packages/chain/cons/bp/batch_proposal_set.go b/packages/chain/cons/bp/batch_proposal_set.go
index 7b64c1fb20..3b641dc7c1 100644
--- a/packages/chain/cons/bp/batch_proposal_set.go
+++ b/packages/chain/cons/bp/batch_proposal_set.go
@@ -5,6 +5,7 @@ package bp
 
 import (
 	"bytes"
+	"encoding/binary"
 	"sort"
 	"time"
 
@@ -13,7 +14,6 @@ import (
 	"github.com/iotaledger/wasp/packages/gpa"
 	"github.com/iotaledger/wasp/packages/hashing"
 	"github.com/iotaledger/wasp/packages/isc"
-	"github.com/iotaledger/wasp/packages/util"
 )
 
 type batchProposalSet map[gpa.NodeID]*BatchProposal
@@ -113,7 +113,7 @@ func (bps batchProposalSet) aggregatedTime(f int) time.Time {
 	return ts[proposalCount-f-1] // Max(|acsProposals|-F Lowest) ~= 66 percentile.
 }
 
-func (bps batchProposalSet) selectedProposal(aggregatedTime time.Time) gpa.NodeID {
+func (bps batchProposalSet) selectedProposal(aggregatedTime time.Time, randomness hashing.HashValue) gpa.NodeID {
 	peers := make([]gpa.NodeID, 0, len(bps))
 	for nid := range bps {
 		peers = append(peers, nid)
@@ -121,11 +121,18 @@ func (bps batchProposalSet) selectedProposal(aggregatedTime time.Time) gpa.NodeI
 	slices.SortFunc(peers, func(a gpa.NodeID, b gpa.NodeID) int {
 		return bytes.Compare(a[:], b[:])
 	})
-	rnd := util.NewPseudoRand(aggregatedTime.UnixNano())
-	return peers[rnd.Intn(len(bps))]
+	uint64Bytes := make([]byte, 8)
+	binary.BigEndian.PutUint64(uint64Bytes, uint64(aggregatedTime.UnixNano()))
+	hashed := hashing.HashDataBlake2b(
+		uint64Bytes,
+		randomness[:],
+	)
+	randomUint := binary.BigEndian.Uint64(hashed[:])
+	randomPos := int(randomUint % uint64(len(bps)))
+	return peers[randomPos]
 }
 
-func (bps batchProposalSet) selectedFeeDestination(aggregatedTime time.Time) isc.AgentID {
-	bp := bps[bps.selectedProposal(aggregatedTime)]
+func (bps batchProposalSet) selectedFeeDestination(aggregatedTime time.Time, randomness hashing.HashValue) isc.AgentID {
+	bp := bps[bps.selectedProposal(aggregatedTime, randomness)]
 	return bp.validatorFeeDestination
 }
diff --git a/packages/chain/cons/cons.go b/packages/chain/cons/cons.go
index 564c3a7410..2ce980a900 100644
--- a/packages/chain/cons/cons.go
+++ b/packages/chain/cons/cons.go
@@ -559,7 +559,7 @@ func (c *consImpl) uponVMInputsReceived(aggregatedProposals *bp.AggregatedBatchP
 		Requests:             aggregatedProposals.OrderedRequests(requests, *randomness),
 		TimeAssumption:       aggregatedProposals.AggregatedTime(),
 		Entropy:              *randomness,
-		ValidatorFeeTarget:   aggregatedProposals.ValidatorFeeTarget(),
+		ValidatorFeeTarget:   aggregatedProposals.ValidatorFeeTarget(*randomness),
 		EstimateGasMode:      false,
 		EnableGasBurnLogging: false,
 		Log:                  c.log.Named("VM"),