From a4a4559881f0345573f511e64326fce6c9efec41 Mon Sep 17 00:00:00 2001
From: Yilun <zyl.skysniper@gmail.com>
Date: Tue, 20 Jul 2021 17:33:35 -0700
Subject: [PATCH] Use random beacon as salt when computing sigchain miner

Signed-off-by: Yilun <zyl.skysniper@gmail.com>
---
 chain/blockvalidator.go |  2 +-
 config/config.go        |  4 ++++
 pb/sigchain.go          | 12 +++++++++---
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/chain/blockvalidator.go b/chain/blockvalidator.go
index 16f250021..2401da39d 100644
--- a/chain/blockvalidator.go
+++ b/chain/blockvalidator.go
@@ -295,7 +295,7 @@ func GetNextBlockSigner(height uint32, timestamp int64) ([]byte, []byte, pb.Winn
 				return nil, nil, 0, err
 			}
 
-			publicKey, chordID, err = sigChain.GetMiner(height)
+			publicKey, chordID, err = sigChain.GetMiner(height, header.UnsignedHeader.RandomBeacon)
 			if err != nil {
 				return nil, nil, 0, err
 			}
diff --git a/config/config.go b/config/config.go
index f8490a456..d21bb6d3f 100644
--- a/config/config.go
+++ b/config/config.go
@@ -220,6 +220,10 @@ var (
 		heights: []uint32{2633000, 0},
 		values:  []int32{10, 0},
 	}
+	SigChainMinerSalt = HeightDependentBool{
+		heights: []uint32{2900000, 0},
+		values:  []bool{true, false},
+	}
 )
 
 var (
diff --git a/pb/sigchain.go b/pb/sigchain.go
index 5fc87bd4c..8c3c48022 100644
--- a/pb/sigchain.go
+++ b/pb/sigchain.go
@@ -201,7 +201,7 @@ func (sc *SigChain) GetSignerIndex(pubkey []byte) (int, error) {
 	return idx, err
 }
 
-func (sc *SigChain) GetMiner(height uint32) ([]byte, []byte, error) {
+func (sc *SigChain) GetMiner(height uint32, randomBeacon []byte) ([]byte, []byte, error) {
 	if !sc.IsComplete() {
 		return nil, nil, errors.New("sigchain is not complete")
 	}
@@ -235,15 +235,21 @@ func (sc *SigChain) GetMiner(height uint32) ([]byte, []byte, error) {
 		return nil, nil, err
 	}
 
+	h := sigHash
+	if config.SigChainMinerSalt.GetValueAtHeight(height) {
+		hs := sha256.Sum256(append(sigHash, randomBeacon...))
+		h = hs[:]
+	}
+
 	x := big.NewInt(0)
-	x.SetBytes(sigHash)
+	x.SetBytes(h)
 	y := big.NewInt(int64(elemLen))
 	newIndex := big.NewInt(0)
 	newIndex.Mod(x, y)
 
 	originalIndex := minerElems[newIndex.Int64()].index
 	if originalIndex == 0 {
-		return sc.SrcPubkey, sc.Elems[0].Id, nil
+		return nil, nil, errors.New("invalid miner index")
 	}
 
 	return sc.Elems[originalIndex-1].NextPubkey, sc.Elems[originalIndex].Id, nil