Marshal.SecureStringToCoTaskMemUnicode(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 SecureStringToCoTaskMemUnicode(System::Security::SecureString ^ s);

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

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

Public Shared Function SecureStringToCoTaskMemUnicode (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 SecureStringToCoTaskMemUnicode method to marshal and decrypt the contents of a SecureString object to a block of unmanaged memory. It then uses the ZeroFreeCoTaskMemUnicode method to zero out and dispose the unmanaged block.

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

class Example
{
    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.SecureStringToCoTaskMemUnicode(passWord);
        passWord.Dispose();

        if (unmanagedRef != IntPtr.Zero) {
            Console.WriteLine("Zeroing out unmanaged memory...");
            Marshal.ZeroFreeCoTaskMemUnicode(unmanagedRef);
        }
        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;
     }
 }
// The example displays output like the following:
//       Please enter your password: **********
//       Copying and decrypting the string to unmanaged memory...
//       Zeroing out unmanaged memory...
//       Done.

Imports System.Runtime.InteropServices
Imports System.Security

Module Example
    Public 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.SecureStringToCoTaskMemUnicode(passWord)
        passWord.Dispose()

        If unmanagedRef <> IntPtr.Size Then
            Console.WriteLine("Zeroing out unmanaged memory...")
            Marshal.ZeroFreeCoTaskMemUnicode(unmanagedRef)
        End If
        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
' The example displays output like the following:
'       Please enter your password: **********
'       Copying and decrypting the string to unmanaged memory...
'       Zeroing out unmanaged memory...
'       Done.

Remarks

The SecureStringToCoTaskMemUnicode 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 the ZeroFreeCoTaskMemUnicode method. The characters of the string are copied as Unicode characters.