Allow empty proofFac, roll back rejectSample for compatibility

common/hash_utils.go

@@ -7,25 +7,12 @@
 package common
 
 import (
-	"crypto/sha256"
 	"math/big"
 )
 
 // RejectionSample implements the rejection sampling logic for converting a
 // SHA512/256 hash to a value between 0-q
 func RejectionSample(q *big.Int, eHash *big.Int) *big.Int { // e' = eHash
-	auxiliary := new(big.Int).Set(eHash)
-	e := new(big.Int).Set(q)
-	qBytesLen := len(q.Bytes())
-	if qBytesLen > 32 {
-		panic("invalid q size")
-	}
-	one := new(big.Int).SetInt64(1)
-	for e.Cmp(q) != -1 {
-		eHashAdded := auxiliary.Add(auxiliary, one)
-		eHashReSample := sha256.Sum256(eHashAdded.Bytes())
-		// sample qBytesLen bytes
-		e = new(big.Int).SetBytes(eHashReSample[:qBytesLen])
-	}
+	e := eHash.Mod(eHash, q)
 	return e
 }

ecdsa/keygen/messages.go

@@ -128,8 +128,9 @@ func NewKGRound2Message1(
 
 func (m *KGRound2Message1) ValidateBasic() bool {
 	return m != nil &&
-		common.NonEmptyBytes(m.GetShare()) &&
-		common.NonEmptyMultiBytes(m.GetFacProof(), facproof.ProofFacBytesParts)
+		common.NonEmptyBytes(m.GetShare())
+	// This is commented for backward compatibility, which msg has no proof
+	// && common.NonEmptyMultiBytes(m.GetFacProof(), facproof.ProofFacBytesParts)
 }
 
 func (m *KGRound2Message1) UnmarshalShare() *big.Int {