Marshal.SecureStringToCoTaskMemAnsi(SecureString) Method

Definition

Namespace:

System.Runtime.InteropServices

Assembly:

System.Runtime.InteropServices.dll

Source:

Marshal.cs

Important

This API is not CLS-compliant.

Copies the contents of a managed SecureString object to a block of memory allocated from the unmanaged COM task allocator.

public:
 static IntPtr SecureStringToCoTaskMemAnsi(System::Security::SecureString ^ s);

public static IntPtr SecureStringToCoTaskMemAnsi (System.Security.SecureString s);

static member SecureStringToCoTaskMemAnsi : System.Security.SecureString -> nativeint

Public Shared Function SecureStringToCoTaskMemAnsi (s As SecureString) As IntPtr

Parameters

s

SecureString

The managed object to copy.

Returns

IntPtr

nativeint

The address, in unmanaged memory, where the s parameter was copied to, or 0 if a null object was supplied.

Exceptions

ArgumentNullException

The s parameter is null.

OutOfMemoryException

There is insufficient memory available.

Examples

The following example uses the SecureStringToCoTaskMemAnsi method to marshal and decrypt the contents of a SecureString object to a block of unmanaged memory. It then uses the ZeroFreeCoTaskMemAnsi method to zero out and dispose the unmanaged block.

using System;
using System.Runtime.InteropServices;
using System.Security;

class MarshalExample
{
     static void Main()
     {
         IntPtr unmanagedRef = IntPtr.Zero;

          // Ask the user for a password.
          Console.Write("Please enter your password: ");

          SecureString passWord = GetPassword();

          Console.WriteLine("Copying and decrypting the string to unmanaged memory...");

          // Copy the Secure string to unmanaged memory (and decrypt it).
          unmanagedRef = Marshal.SecureStringToCoTaskMemAnsi(passWord);

          if (unmanagedRef != IntPtr.Zero)
          {
              Console.WriteLine("Zeroing out unmanaged memory...");

              Marshal.ZeroFreeCoTaskMemAnsi(unmanagedRef);
          }
          passWord.Dispose();

         Console.WriteLine("Done.");
     }

     public static SecureString GetPassword()
     {
         SecureString password = new SecureString();

         // get the first character of the password
         ConsoleKeyInfo nextKey = Console.ReadKey(true);

         while (nextKey.Key != ConsoleKey.Enter)
         {
             if (nextKey.Key == ConsoleKey.Backspace)
             {
                 if (password.Length > 0)
                 {
                     password.RemoveAt(password.Length - 1);

                     // erase the last * as well
                     Console.Write(nextKey.KeyChar);
                     Console.Write(" ");
                     Console.Write(nextKey.KeyChar);
                 }
             }
             else
             {
                 password.AppendChar(nextKey.KeyChar);
                 Console.Write("*");
             }

             nextKey = Console.ReadKey(true);
         }

         Console.WriteLine();

         // lock the password down
         password.MakeReadOnly();
         return password;
     }
}

Imports System.Runtime.InteropServices
Imports System.Security

Module Example
    Sub Main()
        Dim unmanagedRef As IntPtr

         ' Ask the user for a password.
         Console.Write("Please enter your password: ")
         Dim passWord As SecureString = GetPassword()

         Console.WriteLine("Copying and decrypting the string to unmanaged memory...")

         ' Copy the Secure string to unmanaged memory (and decrypt it).
         unmanagedRef = Marshal.SecureStringToCoTaskMemAnsi(passWord)

         If unmanagedRef <> IntPtr.Size Then
             Console.WriteLine("Zeroing out unmanaged memory...")
             Marshal.ZeroFreeCoTaskMemAnsi(unmanagedRef)
         End If
         passWord.Dispose()

        Console.WriteLine("Done.")
    End Sub



    Function GetPassword() As SecureString
        Dim password As New SecureString()

        ' get the first character of the password
        Dim nextKey As ConsoleKeyInfo = Console.ReadKey(True)

        While nextKey.Key <> ConsoleKey.Enter
            If nextKey.Key = ConsoleKey.BackSpace Then
                If password.Length > 0 Then
                    password.RemoveAt(password.Length - 1)

                    ' erase the last * as well
                    Console.Write(nextKey.KeyChar)
                    Console.Write(" ")
                    Console.Write(nextKey.KeyChar)
                End If
            Else
                password.AppendChar(nextKey.KeyChar)
                Console.Write("*")
            End If

            nextKey = Console.ReadKey(True)
        End While

        Console.WriteLine()

        ' lock the password down
        password.MakeReadOnly()
        Return password

    End Function
End Module

Remarks

The SecureStringToCoTaskMemAnsi method is useful for custom marshaling or when mixing managed and unmanaged code. Because this method allocates the unmanaged memory required for a string, always free the memory by calling ZeroFreeCoTaskMemAnsi. The characters of the string are copied as ANSI characters.