How to do it...

1. Start by adding a new Windows forms project to your solution.
2. Call the project winformSecure and click on the OK button.
3. In the Toolbox, search for the TextBox control and add it to your form.
4. Lastly, add a button control to your form. You can resize this form, however you like to look more like a login form:

5. With the textbox control selected on the Windows forms, open up the Properties panel and click on the Events button (it looks like a lightning bolt). In the Key group, double-click on the KeyPress event to create the handler in the code behind:

The code that is created for you is the KeyPress event handler for the textbox control. This will fire whenever a user presses a key on the keyboard:

        private void textBox1_KeyPress(object sender,  KeyPressEventArgs e) 
        { 

        }

6. Back in the Properties panel, expand the Behavior group and change the value of UseSystemPasswordChar to True:

7. In the code behind, add the followingusing statement:

        using System.Runtime.InteropServices;

8. Add the SecureString variable as a global variable to your Windows forms:

        SecureString secure = new SecureString();

9. Then, in the KeyPress event, append the KeyChar value to the SecureString variable every time the user presses a key. You might want to add code to ignore certain key presses, but this is beyond the scope of this recipe:

        private void textBox1_KeyPress(object sender,  KeyPressEventArgs e) 
        { 
          secure.AppendChar(e.KeyChar); 
        }

10. Then, in the Login button's event handler, add the following code to read the value from the SecureString object. Here, we are working with unmanaged memory and unmanaged code:

        private void btnLogin_Click(object sender, EventArgs e) 
        { 
          IntPtr unmanagedPtr = IntPtr.Zero; 

          try 
          { 
            if (secure == null) 
            throw new ArgumentNullException("Password not defined");        
            unmanagedPtr = Marshal.SecureStringToGlobalAllocUnicode(
              secure);
            MessageBox.Show($"SecureString password to validate is 
                            {Marshal.PtrToStringUni(unmanagedPtr)}"); 
          } 
          catch(Exception ex) 
          { 
            MessageBox.Show(ex.Message); 
          } 
          finally 
          { 
            Marshal.ZeroFreeGlobalAllocUnicode(unmanagedPtr); 
            secure.Dispose(); 
          } 
        }

11. Run your Windows forms application and type in a password:

12. Then click on the Login button. You will then see the password you typed in displayed in the message box: