diff --git a/transport/internet/kcp/cryptreal.go b/transport/internet/kcp/cryptreal.go
index 391d714e..cd33a6f3 100644
--- a/transport/internet/kcp/cryptreal.go
+++ b/transport/internet/kcp/cryptreal.go
@@ -9,5 +9,5 @@ import (
 
 func NewAEADAESGCMBasedOnSeed(seed string) cipher.AEAD {
 	hashedSeed := sha256.Sum256([]byte(seed))
-	return crypto.NewAesGcm(hashedSeed[:])
+	return crypto.NewAesGcm(hashedSeed[:16])
 }