diff --git a/ecdh/sm2ec.go b/ecdh/sm2ec.go
index b6cc3ed8..4c124a0a 100644
--- a/ecdh/sm2ec.go
+++ b/ecdh/sm2ec.go
@@ -51,7 +51,7 @@ func (c *sm2Curve) NewPrivateKey(key []byte) (*PrivateKey, error) {
 	if len(key) != len(c.scalarOrderMinus1) {
 		return nil, errors.New("ecdh: invalid private key size")
 	}
-	if subtle.ConstantTimeAllZero(key) || !isLess(key, c.scalarOrderMinus1) {
+	if subtle.ConstantTimeAllZero(key) == 1 || !isLess(key, c.scalarOrderMinus1) {
 		return nil, errInvalidPrivateKey
 	}
 	return &PrivateKey{
diff --git a/internal/subtle/constant_time.go b/internal/subtle/constant_time.go
index f70ef384..ac5cb22f 100644
--- a/internal/subtle/constant_time.go
+++ b/internal/subtle/constant_time.go
@@ -1,9 +1,9 @@
 package subtle
 
-func ConstantTimeAllZero(bytes []byte) bool {
+func ConstantTimeAllZero(bytes []byte) int {
 	var b uint8
 	for _, v := range bytes {
 		b |= v
 	}
-	return b == 0
+	return int((uint32(b) - 1) >> 31)
 }
diff --git a/internal/subtle/constant_time_test.go b/internal/subtle/constant_time_test.go
index 81346082..e3b4d59f 100644
--- a/internal/subtle/constant_time_test.go
+++ b/internal/subtle/constant_time_test.go
@@ -1,6 +1,9 @@
 package subtle
 
-import "testing"
+import (
+	"fmt"
+	"testing"
+)
 
 func TestConstantTimeAllZero(t *testing.T) {
 	type args struct {
@@ -9,10 +12,10 @@ func TestConstantTimeAllZero(t *testing.T) {
 	tests := []struct {
 		name string
 		args args
-		want bool
+		want int
 	}{
-		{"all zero", args{[]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}, true},
-		{"not all zero", args{[]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 1}}, false},
+		{"all zero", args{[]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}, 1},
+		{"not all zero", args{[]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 1}}, 0},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -22,3 +25,17 @@ func TestConstantTimeAllZero(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkConstantTimeAllZero(b *testing.B) {
+	data := make([]byte, 1<<15)
+	sizes := []int64{1 << 3, 1 << 4, 1 << 5, 1 << 7, 1 << 11, 1 << 13, 1 << 15}
+	for _, size := range sizes {
+		b.Run(fmt.Sprintf("%dBytes", size), func(b *testing.B) {
+			s0 := data[:size]
+			b.SetBytes(int64(size))
+			for i := 0; i < b.N; i++ {
+				ConstantTimeAllZero(s0)
+			}
+		})
+	}
+}
diff --git a/sm2/sm2.go b/sm2/sm2.go
index 15b5a473..526373e4 100644
--- a/sm2/sm2.go
+++ b/sm2/sm2.go
@@ -251,7 +251,7 @@ func encryptSM2EC(c *sm2Curve, pub *ecdsa.PublicKey, random io.Reader, msg []byt
 		}
 		C2Bytes := C2.Bytes()[1:]
 		c2 := sm3.Kdf(C2Bytes, len(msg))
-		if subtle.ConstantTimeAllZero(c2) {
+		if subtle.ConstantTimeAllZero(c2) == 1 {
 			retryCount++
 			if retryCount > maxRetryLimit {
 				return nil, fmt.Errorf("sm2: A5, failed to calculate valid t, tried %v times", retryCount)
@@ -424,7 +424,7 @@ func decryptSM2EC(c *sm2Curve, priv *PrivateKey, ciphertext []byte, opts *Decryp
 	C2Bytes := C2.Bytes()[1:]
 	msgLen := len(c2)
 	msg := sm3.Kdf(C2Bytes, msgLen)
-	if subtle.ConstantTimeAllZero(c2) {
+	if subtle.ConstantTimeAllZero(c2) == 1 {
 		return nil, ErrDecryption
 	}
 
diff --git a/sm2/sm2_legacy.go b/sm2/sm2_legacy.go
index 2cd8a98e..bd1a0bcc 100644
--- a/sm2/sm2_legacy.go
+++ b/sm2/sm2_legacy.go
@@ -260,7 +260,7 @@ func encryptLegacy(random io.Reader, pub *ecdsa.PublicKey, msg []byte, opts *Enc
 
 		//A5, calculate t=KDF(x2||y2, klen)
 		c2 := sm3.Kdf(append(toBytes(curve, x2), toBytes(curve, y2)...), msgLen)
-		if subtle.ConstantTimeAllZero(c2) {
+		if subtle.ConstantTimeAllZero(c2) == 1 {
 			retryCount++
 			if retryCount > maxRetryLimit {
 				return nil, fmt.Errorf("sm2: A5, failed to calculate valid t, tried %v times", retryCount)
@@ -408,7 +408,7 @@ func rawDecrypt(priv *PrivateKey, x1, y1 *big.Int, c2, c3 []byte) ([]byte, error
 	x2, y2 := curve.ScalarMult(x1, y1, priv.D.Bytes())
 	msgLen := len(c2)
 	msg := sm3.Kdf(append(toBytes(curve, x2), toBytes(curve, y2)...), msgLen)
-	if subtle.ConstantTimeAllZero(c2) {
+	if subtle.ConstantTimeAllZero(c2) == 1 {
 		return nil, ErrDecryption
 	}
 
diff --git a/sm9/sm9.go b/sm9/sm9.go
index bd0aaa1e..02c842f4 100644
--- a/sm9/sm9.go
+++ b/sm9/sm9.go
@@ -317,7 +317,7 @@ func WrapKey(rand io.Reader, pub *EncryptMasterPublicKey, uid []byte, hid byte,
 		buffer = append(buffer, uid...)
 
 		key = sm3.Kdf(buffer, kLen)
-		if !subtle.ConstantTimeAllZero(key) {
+		if subtle.ConstantTimeAllZero(key) == 0 {
 			break
 		}
 	}
@@ -403,7 +403,7 @@ func UnwrapKey(priv *EncryptPrivateKey, uid []byte, cipher *bn256.G1, kLen int)
 	buffer = append(buffer, uid...)
 
 	key := sm3.Kdf(buffer, kLen)
-	if subtle.ConstantTimeAllZero(key) {
+	if subtle.ConstantTimeAllZero(key) == 1 {
 		return nil, ErrDecryption
 	}
 	return key, nil