Marshal.SecureStringToGlobalAllocUnicode(SecureString) Method
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Important
This API is not CLS-compliant.
Copies the contents of a managed SecureString object into unmanaged memory.
public:
static IntPtr SecureStringToGlobalAllocUnicode(System::Security::SecureString ^ s);public static IntPtr SecureStringToGlobalAllocUnicode (System.Security.SecureString s);[System.CLSCompliant(false)]
public static IntPtr SecureStringToGlobalAllocUnicode (System.Security.SecureString s);[System.Security.SecurityCritical]
public static IntPtr SecureStringToGlobalAllocUnicode (System.Security.SecureString s);static member SecureStringToGlobalAllocUnicode : System.Security.SecureString -> nativeint[<System.CLSCompliant(false)>]
static member SecureStringToGlobalAllocUnicode : System.Security.SecureString -> nativeint[<System.Security.SecurityCritical>]
static member SecureStringToGlobalAllocUnicode : System.Security.SecureString -> nativeintPublic Shared Function SecureStringToGlobalAllocUnicode (s As SecureString) As IntPtrParameters
The managed object to copy.
Returns
IntPtr
nativeint
The address, in unmanaged memory, where s was copied, or 0 if s is a SecureString object whose length is 0.
- Attributes
Exceptions
The s parameter is null.
There is insufficient memory available.
Examples
The following example demonstrates how to use the SecureStringToGlobalAllocUnicode method with the unmanaged LogonUser function to perform impersonation with the SecureString class. The example then uses the ZeroFreeGlobalAllocUnicode method to zero out and free the unmanaged string reference.
using System;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Security;
using System.Security.Principal;
class Example
{
// Define the Windows LogonUser and CloseHandle functions.
[DllImport("advapi32.dll", SetLastError = true, CharSet = CharSet.Unicode)]
internal static extern bool LogonUser(String username, String domain, IntPtr password,
int logonType, int logonProvider, ref IntPtr token);
[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
public extern static bool CloseHandle(IntPtr handle);
// Define the required LogonUser enumerations.
const int LOGON32_PROVIDER_DEFAULT = 0;
const int LOGON32_LOGON_INTERACTIVE = 2;
static void Main()
{
// Display the current user before impersonation.
Console.WriteLine("Before impersonation: {0}",
WindowsIdentity.GetCurrent().Name);
// Ask the user for a network domain.
Console.Write("Please enter your domain: ");
string domain = Console.ReadLine();
// Ask the user for a user name.
Console.Write("Please enter your user name: ");
string username = Console.ReadLine();
// Ask the user for a password.
Console.Write("Please enter your password: ");
SecureString passWord = GetPassword();
// Impersonate the account provided by the user.
try {
WindowsImpersonationContext userContext =
ImpersonateUser(passWord, username, domain);
// Display the current user after impersonation.
Console.WriteLine("After impersonation: {0}",
WindowsIdentity.GetCurrent().Name);
}
catch (ArgumentException e) {
Console.WriteLine("{0}: {1}", e.GetType().Name, e.Message);
}
catch (Win32Exception e) {
Console.WriteLine("{0}: {1}", e.GetType().Name, e.Message);
}
finally {
passWord.Dispose();
}
}
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;
}
public static WindowsImpersonationContext ImpersonateUser(SecureString password, string userName, string domainName)
{
IntPtr tokenHandle = IntPtr.Zero;
IntPtr passwordPtr = IntPtr.Zero;
bool returnValue = false;
int error = 0;
// Marshal the SecureString to unmanaged memory.
passwordPtr = Marshal.SecureStringToGlobalAllocUnicode(password);
// Pass LogonUser the unmanaged (and decrypted) copy of the password.
returnValue = LogonUser(userName, domainName, passwordPtr,
LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,
ref tokenHandle);
if (!returnValue && tokenHandle == IntPtr.Zero)
error = Marshal.GetLastWin32Error();
// Perform cleanup whether or not the call succeeded.
// Zero-out and free the unmanaged string reference.
Marshal.ZeroFreeGlobalAllocUnicode(passwordPtr);
// Close the token handle.
CloseHandle(tokenHandle);
// Throw an exception if an error occurred.
if (error != 0) {
throw new System.ComponentModel.Win32Exception(error);
}
// The token that is passed to the following constructor must
// be a primary token in order to use it for impersonation.
WindowsIdentity newId = new WindowsIdentity(tokenHandle);
return newId.Impersonate();
}
}
Imports System.ComponentModel
Imports System.Runtime.InteropServices
Imports System.Security
Imports System.Security.Principal
Module Example
' PInvoke into the Win32 API to provide access to the
' LogonUser and CloseHandle functions.
<DllImport("advapi32.dll", SetLastError:=True, CharSet:=CharSet.Unicode)> _
Function LogonUser(ByVal username As String, ByVal domain As String, _
ByVal password As IntPtr, ByVal logonType As Integer, _
ByVal logonProvider As Integer, ByRef token As IntPtr) _
As Boolean
End Function
<DllImport("kernel32.dll", CharSet:=CharSet.Auto)> _
Function CloseHandle(ByVal handle As IntPtr) As Boolean
End Function
' Define the required LogonUser enumerations.
Const LOGON32_PROVIDER_DEFAULT As Integer = 0
Const LOGON32_LOGON_INTERACTIVE As Integer = 2
Sub Main(ByVal args() As String)
' Display the current user before impersonation.
Console.WriteLine("Before impersonation: {0}",
WindowsIdentity.GetCurrent().Name)
' Ask the user for a network domain.
Console.Write("Please enter your domain:")
Dim domain As String = Console.ReadLine()
' Ask the user for a user name.
Console.Write("Please enter your user name:")
Dim username As String = Console.ReadLine()
' Ask the user for a password.
Console.Write("Please enter your password:")
Dim passWord As SecureString = GetPassword()
' Impersonate the account provided by the user.
Try
Dim userContext As WindowsImpersonationContext =
ImpersonateUser(passWord, username, domain)
' Display the current user after impersonation.
Console.WriteLine("After impersonation: {0}",
WindowsIdentity.GetCurrent().Name)
Catch e As ArgumentException
Console.WriteLine(e.Message)
Console.WriteLine("{0}: {1}", e.GetType().Name, e.Message)
Catch e As Win32Exception
Console.WriteLine("{0}: {1}", e.GetType().Name, e.Message)
Finally
passWord.Dispose()
End Try
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
Function ImpersonateUser(ByVal password As SecureString,
ByVal userName As String,
ByVal domainName As String) As WindowsImpersonationContext
Dim tokenHandle As IntPtr = IntPtr.Zero
Dim passwordPtr As IntPtr = IntPtr.Zero
Dim returnValue As Boolean = False
Dim err As Integer = 0
' Marshal the SecureString to unmanaged memory.
passwordPtr = Marshal.SecureStringToGlobalAllocUnicode(password)
' Pass LogonUser the unmanaged (and decrypted) copy of the password.
returnValue = LogonUser(userName, domainName, passwordPtr,
LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,
tokenHandle)
If Not returnValue AndAlso tokenHandle = IntPtr.Zero Then
err = Marshal.GetLastWin32Error()
End If
' Perform cleanup whether or not the call succeeded.
' Zero-out and free the unmanaged string reference.
Marshal.ZeroFreeGlobalAllocUnicode(passwordPtr)
' Close the token handle.
CloseHandle(tokenHandle)
' Throw an exception if an error occurred.
If err <> 0 Then
Throw New System.ComponentModel.Win32Exception(err)
End If
' The token that is passed to the following constructor must
' be a primary token in order to use it for impersonation.
Dim newId As New WindowsIdentity(tokenHandle)
Return newId.Impersonate()
End Function
End Module
Remarks
The SecureStringToGlobalAllocUnicode method is useful for custom marshaling or for use when mixing managed and unmanaged code. Because this method allocates the unmanaged memory required for a string, always free the memory by calling the ZeroFreeGlobalAllocUnicode method.
Applies to
Collaborate with us on GitHub
The source for this content can be found on GitHub, where you can also create and review issues and pull requests. For more information, see our contributor guide.
Feedback
Coming soon: Throughout 2024 we will be phasing out GitHub Issues as the feedback mechanism for content and replacing it with a new feedback system. For more information see: https://aka.ms/ContentUserFeedback.
Submit and view feedback for