diff --git a/backend/mpc-system/pkg/tss/signing.go b/backend/mpc-system/pkg/tss/signing.go
index 4d37ed2f..b22a7156 100644
--- a/backend/mpc-system/pkg/tss/signing.go
+++ b/backend/mpc-system/pkg/tss/signing.go
@@ -66,6 +66,9 @@ type SigningSession struct {
 	msgHandler  MessageHandler
 	mu          sync.Mutex
 	started     bool
+	// keygenIndexToSortedIndex maps keygen party index to sorted array index
+	// This is needed because TSS messages use keygen index, but tssPartyIDs is sorted
+	keygenIndexToSortedIndex map[int]int
 }
 
 // NewSigningSession creates a new signing session
@@ -112,6 +115,22 @@ func NewSigningSession(
 	// Sort party IDs
 	sortedPartyIDs := tss.SortPartyIDs(tssPartyIDs)
 
+	// Build mapping from keygen index to sorted array index
+	// The sorted array is ordered by big.Int key (PartyIndex+1)
+	keygenIndexToSortedIndex := make(map[int]int)
+	for sortedIdx, partyID := range sortedPartyIDs {
+		// Find the original keygen index for this party
+		for _, p := range allParties {
+			if p.PartyID == partyID.Id {
+				keygenIndexToSortedIndex[p.PartyIndex] = sortedIdx
+				break
+			}
+		}
+	}
+
+	fmt.Printf("[TSS-SIGN] Built keygen index to sorted index mapping: %v party_id=%s\n",
+		keygenIndexToSortedIndex, selfParty.PartyID)
+
 	// Create peer context and parameters
 	// IMPORTANT: Use TotalParties from keygen, not len(sortedPartyIDs) which is current signers
 	// For 2-of-3: threshold=2, TotalParties=3, but only 2 parties might participate in signing
@@ -122,18 +141,19 @@ func NewSigningSession(
 	msgHash := new(big.Int).SetBytes(messageHash)
 
 	return &SigningSession{
-		config:      config,
-		selfParty:   selfParty,
-		allParties:  allParties,
-		messageHash: msgHash,
-		saveData:    &saveData,
-		tssPartyIDs: sortedPartyIDs,
-		selfTSSID:   selfTSSID,
-		params:      params,
-		outCh:       make(chan tss.Message, config.TotalSigners*10),
-		endCh:       make(chan *common.SignatureData, 1),
-		errCh:       make(chan error, 1),
-		msgHandler:  msgHandler,
+		config:                   config,
+		selfParty:                selfParty,
+		allParties:               allParties,
+		messageHash:              msgHash,
+		saveData:                 &saveData,
+		tssPartyIDs:              sortedPartyIDs,
+		selfTSSID:                selfTSSID,
+		params:                   params,
+		outCh:                    make(chan tss.Message, config.TotalSigners*10),
+		endCh:                    make(chan *common.SignatureData, 1),
+		errCh:                    make(chan error, 1),
+		msgHandler:               msgHandler,
+		keygenIndexToSortedIndex: keygenIndexToSortedIndex,
 	}, nil
 }
 
@@ -232,18 +252,31 @@ func (s *SigningSession) handleIncomingMessages(ctx context.Context) {
 				return
 			}
 
-			fmt.Printf("[TSS-SIGN] received incoming message party_id=%s from_index=%d is_broadcast=%v msg_len=%d\n",
+			fmt.Printf("[TSS-SIGN] received incoming message party_id=%s from_keygen_index=%d is_broadcast=%v msg_len=%d\n",
 				s.selfParty.PartyID, msg.FromPartyIndex, msg.IsBroadcast, len(msg.MsgBytes))
 
-			// Check if FromPartyIndex is valid
-			if msg.FromPartyIndex < 0 || msg.FromPartyIndex >= len(s.tssPartyIDs) {
-				fmt.Printf("[TSS-SIGN] ERROR: invalid FromPartyIndex=%d, len(tssPartyIDs)=%d party_id=%s\n",
-					msg.FromPartyIndex, len(s.tssPartyIDs), s.selfParty.PartyID)
+			// Map keygen index to sorted array index
+			// msg.FromPartyIndex is the original keygen party index (e.g., 0, 1, 2)
+			// We need the sorted array index (e.g., 0, 1 for a 2-party signing session)
+			sortedIndex, exists := s.keygenIndexToSortedIndex[msg.FromPartyIndex]
+			if !exists {
+				fmt.Printf("[TSS-SIGN] ERROR: unknown keygen index=%d, mapping=%v party_id=%s\n",
+					msg.FromPartyIndex, s.keygenIndexToSortedIndex, s.selfParty.PartyID)
 				continue
 			}
 
-			// Parse the message
-			parsedMsg, err := tss.ParseWireMessage(msg.MsgBytes, s.tssPartyIDs[msg.FromPartyIndex], msg.IsBroadcast)
+			fmt.Printf("[TSS-SIGN] mapped keygen_index=%d to sorted_index=%d party_id=%s\n",
+				msg.FromPartyIndex, sortedIndex, s.selfParty.PartyID)
+
+			// Check if sorted index is valid
+			if sortedIndex < 0 || sortedIndex >= len(s.tssPartyIDs) {
+				fmt.Printf("[TSS-SIGN] ERROR: invalid sortedIndex=%d, len(tssPartyIDs)=%d party_id=%s\n",
+					sortedIndex, len(s.tssPartyIDs), s.selfParty.PartyID)
+				continue
+			}
+
+			// Parse the message using the sorted index
+			parsedMsg, err := tss.ParseWireMessage(msg.MsgBytes, s.tssPartyIDs[sortedIndex], msg.IsBroadcast)
 			if err != nil {
 				fmt.Printf("[TSS-SIGN] ERROR: failed to parse wire message party_id=%s from_index=%d error=%v\n",
 					s.selfParty.PartyID, msg.FromPartyIndex, err)