diff --git a/c/openssl/bn.go b/c/openssl/bn.go
index 4a765b1c..225dd324 100644
--- a/c/openssl/bn.go
+++ b/c/openssl/bn.go
@@ -49,8 +49,19 @@ func BN_CTXSecureNew() *BN_CTX
 func (*BN_CTX) Free() {}
 
 // void BN_CTX_start(BN_CTX *ctx);
+//
+// llgo:link (*BN_CTX).Start C.BN_CTX_start
+func (*BN_CTX) Start() {}
+
 // BIGNUM *BN_CTX_get(BN_CTX *ctx);
+//
+// llgo:link (*BN_CTX).Get C.BN_CTX_get
+func (*BN_CTX) Get() *BIGNUM { return nil }
+
 // void BN_CTX_end(BN_CTX *ctx);
+//
+// llgo:link (*BN_CTX).End C.BN_CTX_end
+func (*BN_CTX) End() {}
 
 // -----------------------------------------------------------------------------
 
diff --git a/internal/lib/math/big/int.go b/internal/lib/math/big/int.go
index 02341907..f3ce8724 100644
--- a/internal/lib/math/big/int.go
+++ b/internal/lib/math/big/int.go
@@ -18,6 +18,8 @@ package big
 
 // llgo:skipall
 import (
+	"sync"
+
 	"github.com/goplus/llgo/c/openssl"
 )
 
@@ -35,6 +37,18 @@ func ctxPut(ctx *openssl.BN_CTX) {
 	ctx.Free()
 }
 
+var g_lock = &sync.Mutex{}
+var g_ctx *openssl.BN_CTX
+
+func getCtxInstance() *openssl.BN_CTX {
+	if g_ctx == nil {
+		g_lock.Lock()
+		defer g_lock.Unlock()
+		g_ctx = ctxGet()
+	}
+	return g_ctx
+}
+
 // -----------------------------------------------------------------------------
 
 type Int openssl.BIGNUM
@@ -147,7 +161,9 @@ func (z *Int) Mul(x, y *Int) *Int {
 	a := (*openssl.BIGNUM)(z)
 	xx := (*openssl.BIGNUM)(x)
 	yy := (*openssl.BIGNUM)(y)
-	a.Mul(a, xx, yy, ctxGet())
+	getCtxInstance().Start()
+	defer getCtxInstance().End()
+	a.Mul(a, xx, yy, getCtxInstance())
 	return z
 }