SecureString::MakeReadOnly Method ()

 

Makes the text value of this secure string read-only.

Namespace:   System.Security
Assembly:  mscorlib (in mscorlib.dll)

public:
void MakeReadOnly()

Exception Condition
ObjectDisposedException

This secure string has already been disposed.

Initialize the text value of an instance of the SecureString class with the SecureString constructors, and modify the value with the Clear, RemoveAt, SetAt, InsertAt, and AppendChar methods.

After you have made your final modifications, use the MakeReadOnly method to make the value of the instance immutable (read-only). After the value is marked as read-only, any further attempt to modify it throws an InvalidOperationException.

The effect of invoking MakeReadOnly is permanent because the SecureString class provides no means to make the secure string modifiable again. Use the IsReadOnly method to test whether an instance of SecureString is read-only.

The following example demonstrates how the AppendChar and RemoveAt methods can be used to collect the characters in a password. After the password is collected, it is made read-only.

using namespace System;
using namespace System::Security;

void main()
{
   bool go = true;
   ConsoleKeyInfo cki;
   String^ m = L"\nEnter your password (up to 15 letters, numbers, and underscores)\n"
               L"Press BACKSPACE to delete the last character entered. " +
               L"\nPress Enter when done, or ESCAPE to quit:";
   SecureString ^ password = gcnew SecureString;
   int top;
   int left;

   // The Console.TreatControlCAsInput property prevents CTRL+C from
   // ending this example.
   Console::TreatControlCAsInput = true;

   Console::Clear();
   Console::WriteLine(m);

   top = Console::CursorTop;
   left = Console::CursorLeft;

   do {
      cki = Console::ReadKey(true);
      if (cki.Key == ConsoleKey::Escape)
         break;

      if (cki.Key == ConsoleKey::Backspace){
         if (password->Length > 0) {
            Console::SetCursorPosition(left + password->Length - 1, top);
            Console::Write(' ');
            Console::SetCursorPosition(left + password->Length - 1, top);
            password->RemoveAt(password->Length - 1);
         }
      }
      else {
         if ((password->Length < 15) &&
             (Char::IsLetterOrDigit( cki.KeyChar ) ||
              cki.KeyChar == '_') ) {
            password->AppendChar( cki.KeyChar );
            Console::SetCursorPosition( left + password->Length - 1, top );
            Console::Write("*");
         }
      }
   } while (cki.Key != ConsoleKey::Enter & password->Length < 15);

   // Make the password read-only to prevent modification.
   password->MakeReadOnly();
   // Dispose of the SecureString instance.
   delete password;

}
// The example displays output like the following:
//    Enter your password (up to 15 letters, numbers, and underscores)
//    Press BACKSPACE to delete the last character entered.
//    Press Enter when done, or ESCAPE to quit:
//    ************

.NET Framework
Available since 2.0
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