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Marshal.SecureStringToCoTaskMemUnicode Method

.NET Framework 3.5

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

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)

Syntax

C++

JScript

[SecurityPermissionAttribute(SecurityAction.LinkDemand, Flags = SecurityPermissionFlag.UnmanagedCode)]
public static IntPtr SecureStringToCoTaskMemUnicode(
	SecureString s
)

Parameters

s: Type: System.Security.SecureString
The managed SecureString object to copy.

Return Value

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

Exceptions

Exception	Condition
ArgumentNullException	The s parameter is null.
NotSupportedException	The current computer is not running Windows 2000 Service Pack 3 or later.
OutOfMemoryException	There is insufficient memory available.

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.

Note:
This method uses SecurityAction.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.

Note:

This method uses SecurityAction.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.

Notes to Callers:

This method is supported only on computers running Windows 2000 Service Pack 3 or later.

Examples

The following code 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.Diagnostics;
using System.Runtime.InteropServices;
using System.Security;
using System.Security.Principal;
using System.Text;

namespace SecureStringExample
{

    class MarshalExample
    {


        static void Main(string[] args)
        {
            IntPtr unmanagedRef = IntPtr.Zero;

            try
            {
                // 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);


            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
            finally
            {
                if (unmanagedRef != IntPtr.Zero)
                {
                    Console.WriteLine("Zeroing out unmanaged memory...");

                    Marshal.ZeroFreeCoTaskMemUnicode(unmanagedRef);
                }

            }

            Console.WriteLine("Done.");

            Console.ReadLine();


        }

        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;
        }
    }
}

.NET Framework Security

SecurityPermission
for permission to call unmanaged code.
Associated enumeration: UnmanagedCode Security action: LinkDemand

Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0

Reference

Marshal Class

Marshal Members

System.Runtime.InteropServices Namespace

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