diff --git a/TestClient/ClientForm.cs b/TestClient/ClientForm.cs
index 600ce70..8870002 100644
--- a/TestClient/ClientForm.cs
+++ b/TestClient/ClientForm.cs
@@ -134,23 +134,17 @@ namespace TestClient
 
         private void signButton_Click( object sender, EventArgs e )
         {
-            // Signing not yet supported in the NSspi library;
-            MessageBox.Show( "Signing not yet supported" );
-            return;
-
-            /*
             byte[] plaintext;
             byte[] cipherText;
             Message message;
 
             plaintext = Encoding.UTF8.GetBytes( this.sendTextbox.Text );
 
-            cipherText = this.context.Sign( plaintext );
+            cipherText = this.context.MakeSignature( plaintext );
 
             message = new Message( ProtocolOp.SignedMessage, cipherText );
 
             this.connection.Send( message );
-            */
         }
 
         private void connection_Received( Message message )
@@ -175,7 +169,7 @@ namespace TestClient
                 }
                 else if( message.Operation == ProtocolOp.SignedMessage )
                 {
-                    // Not yet supported
+                    HandleSigned( message );
                 }
             } );
         }
@@ -234,6 +228,21 @@ namespace TestClient
             this.receiveTextbox.Text += "Received encrypted message from server:\r\n" + text + "\r\n";
         }
 
+        private void HandleSigned( Message message )
+        {
+            byte[] plaintext;
+            string text;
+
+            if( this.context.VerifySignature( message.Data, out plaintext ) )
+            {
+                text = Encoding.UTF8.GetString( plaintext );
+                this.receiveTextbox.Text += "Received valid signed message from server:\r\n" + text + "\r\n";
+            }
+            else
+            {
+                this.receiveTextbox.Text += "Received *** invalid *** signed message from server.\r\n";
+            }
+        }
 
         private void UpdateButtons()
         {
diff --git a/TestServer/ServerForm.cs b/TestServer/ServerForm.cs
index 8d53c4b..386a27d 100644
--- a/TestServer/ServerForm.cs
+++ b/TestServer/ServerForm.cs
@@ -108,7 +108,15 @@ namespace TestServer
 
         private void signButton_Click( object sender, EventArgs e )
         {
-            // Not implemented.
+            byte[] plainText = Encoding.UTF8.GetBytes( this.sendTextbox.Text );
+            byte[] signedData;
+            Message message;
+
+            signedData = this.serverContext.MakeSignature( plainText );
+
+            message = new Message( ProtocolOp.SignedMessage, signedData );
+
+            this.server.Send( message );
         }
         
         private void UpdateButtons()
@@ -211,16 +219,21 @@ namespace TestServer
 
         private void HandleSigned( Message message )
         {
-            // Not implemented yet.
-            /*
             this.Invoke( (Action)delegate()
             {
-                byte[] plainText = this.serverContext.Decrypt( message.Data );
-                string text = Encoding.UTF8.GetString( plainText );
+                byte[] plainText;
 
-                this.receivedTextbox.Text += "Received encrypted message from client:\r\n" + text + "\r\n";
+                if( this.serverContext.VerifySignature( message.Data, out plainText ) )
+                {
+                    string text = Encoding.UTF8.GetString( plainText );
+
+                    this.receivedTextbox.Text += "Received valid signed message from client:\r\n" + text + "\r\n";
+                }
+                else
+                {
+                    this.receivedTextbox.Text += "Received *** invalid *** signed message from client.\r\n";
+                }
             } );
-             */
         }
 
         private void HandleUnknown( Message message )