diff --git a/websocket-sharp/Net/AuthenticationBase.cs b/websocket-sharp/Net/AuthenticationBase.cs
index 1d08612e..10775049 100644
--- a/websocket-sharp/Net/AuthenticationBase.cs
+++ b/websocket-sharp/Net/AuthenticationBase.cs
@@ -129,6 +129,23 @@ namespace WebSocketSharp.Net
       return res;
     }
 
+    internal abstract string ToBasicString ();
+
+    internal abstract string ToDigestString ();
+
+    #endregion
+
+    #region Public Methods
+
+    public override string ToString ()
+    {
+      return _scheme == AuthenticationSchemes.Basic
+             ? ToBasicString ()
+             : _scheme == AuthenticationSchemes.Digest
+               ? ToDigestString ()
+               : String.Empty;
+    }
+
     #endregion
   }
 }
diff --git a/websocket-sharp/Net/AuthenticationChallenge.cs b/websocket-sharp/Net/AuthenticationChallenge.cs
index d7afe0df..3472204b 100644
--- a/websocket-sharp/Net/AuthenticationChallenge.cs
+++ b/websocket-sharp/Net/AuthenticationChallenge.cs
@@ -102,12 +102,12 @@ namespace WebSocketSharp.Net
                : null;
     }
 
-    internal string ToBasicString ()
+    internal override string ToBasicString ()
     {
       return String.Format ("Basic realm=\"{0}\"", Parameters["realm"]);
     }
 
-    internal string ToDigestString ()
+    internal override string ToDigestString ()
     {
       var output = new StringBuilder (128);
 
@@ -142,19 +142,5 @@ namespace WebSocketSharp.Net
     }
 
     #endregion
-
-    #region Public Methods
-
-    public override string ToString ()
-    {
-      var schm = Scheme;
-      return schm == AuthenticationSchemes.Basic
-             ? ToBasicString ()
-             : schm == AuthenticationSchemes.Digest
-               ? ToDigestString ()
-               : String.Empty;
-    }
-
-    #endregion
   }
 }
diff --git a/websocket-sharp/Net/AuthenticationResponse.cs b/websocket-sharp/Net/AuthenticationResponse.cs
index 5b7b2893..cc49b372 100644
--- a/websocket-sharp/Net/AuthenticationResponse.cs
+++ b/websocket-sharp/Net/AuthenticationResponse.cs
@@ -269,7 +269,7 @@ namespace WebSocketSharp.Net
       return res;
     }
 
-    internal string ToBasicString ()
+    internal override string ToBasicString ()
     {
       var userPass = String.Format ("{0}:{1}", Parameters["username"], Parameters["password"]);
       var cred = Convert.ToBase64String (Encoding.UTF8.GetBytes (userPass));
@@ -277,7 +277,7 @@ namespace WebSocketSharp.Net
       return "Basic " + cred;
     }
 
-    internal string ToDigestString ()
+    internal override string ToDigestString ()
     {
       var output = new StringBuilder (256);
       output.AppendFormat (
@@ -318,16 +318,6 @@ namespace WebSocketSharp.Net
                : null;
     }
 
-    public override string ToString ()
-    {
-      var schm = Scheme;
-      return schm == AuthenticationSchemes.Basic
-             ? ToBasicString ()
-             : schm == AuthenticationSchemes.Digest
-               ? ToDigestString ()
-               : String.Empty;
-    }
-
     #endregion
   }
 }