OpenProcessToken (advapi32)
Last changed: -149.173.6.25
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Summary
The OpenProcessToken() function opens the access token associated with a process. Using this function we can get a handle to the access token associated to the process. If needed we can use this handle with GetTokenInformation() function to get SID and other information inside that token. For more information feel free to contact me at jacobabraham2001@yahoo.com.

C# Signature:

[DllImport("advapi32.dll", SetLastError=true)]
static extern bool OpenProcessToken(IntPtr ProcessHandle,
    UInt32 DesiredAccess, out IntPtr TokenHandle);

VB Signature:

Declare Function OpenProcessToken Lib "advapi32.dll" (ProcessHandle As IntPtr, _
   DesiredAccess As Integer, ByRef TokenHandle As IntPtr) As Boolean

Notes:

None.

Tips & Tricks:

Use these for DesiredAccess

    public const UInt32 STANDARD_RIGHTS_REQUIRED = 0x000F0000;
    public const UInt32 STANDARD_RIGHTS_READ = 0x00020000;
    public const UInt32 TOKEN_ASSIGN_PRIMARY = 0x0001;
    public const UInt32 TOKEN_DUPLICATE = 0x0002;
    public const UInt32 TOKEN_IMPERSONATE = 0x0004;
    public const UInt32 TOKEN_QUERY = 0x0008;
    public const UInt32 TOKEN_QUERY_SOURCE = 0x0010;
    public const UInt32 TOKEN_ADJUST_PRIVILEGES = 0x0020;
    public const UInt32 TOKEN_ADJUST_GROUPS = 0x0040;
    public const UInt32 TOKEN_ADJUST_DEFAULT = 0x0080;
    public const UInt32 TOKEN_ADJUST_SESSIONID = 0x0100;
    public const UInt32 TOKEN_READ = (STANDARD_RIGHTS_READ | TOKEN_QUERY);
    public const UInt32 TOKEN_ALL_ACCESS = (STANDARD_RIGHTS_REQUIRED | TOKEN_ASSIGN_PRIMARY |
        TOKEN_DUPLICATE | TOKEN_IMPERSONATE | TOKEN_QUERY | TOKEN_QUERY_SOURCE |
        TOKEN_ADJUST_PRIVILEGES | TOKEN_ADJUST_GROUPS | TOKEN_ADJUST_DEFAULT |
        TOKEN_ADJUST_SESSIONID);

Source
Link to http://groups.google.com/group/microsoft.public.dotnet.general/browse_thread/thread/5742d50ec2e9f798/c702b8d7771f9016?lnk=st&q=OpenProcessToken+0x00020000&rnum=1&hl=en#c702b8d7771f9016

Sample Code:

    [DllImport("advapi32.dll", SetLastError = true)]
    public static extern bool OpenProcessToken(IntPtr ProcessHandle, UInt32 DesiredAccess, out IntPtr TokenHandle);
    private static uint STANDARD_RIGHTS_REQUIRED = 0x000F0000;
    private static uint STANDARD_RIGHTS_READ = 0x00020000;
    private static uint TOKEN_ASSIGN_PRIMARY = 0x0001;
    private static uint TOKEN_DUPLICATE = 0x0002;
    private static uint TOKEN_IMPERSONATE = 0x0004;
    private static uint TOKEN_QUERY = 0x0008;
    private static uint TOKEN_QUERY_SOURCE = 0x0010;
    private static uint TOKEN_ADJUST_PRIVILEGES = 0x0020;
    private static uint TOKEN_ADJUST_GROUPS = 0x0040;
    private static uint TOKEN_ADJUST_DEFAULT = 0x0080;
    private static uint TOKEN_ADJUST_SESSIONID = 0x0100;
    private static uint TOKEN_READ = (STANDARD_RIGHTS_READ | TOKEN_QUERY);
    private static uint TOKEN_ALL_ACCESS = (STANDARD_RIGHTS_REQUIRED | TOKEN_ASSIGN_PRIMARY |
        TOKEN_DUPLICATE | TOKEN_IMPERSONATE | TOKEN_QUERY | TOKEN_QUERY_SOURCE |
        TOKEN_ADJUST_PRIVILEGES | TOKEN_ADJUST_GROUPS | TOKEN_ADJUST_DEFAULT |
        TOKEN_ADJUST_SESSIONID);

     [DllImport("advapi32.dll", SetLastError = true)]
    public static extern bool GetTokenInformation(IntPtr TokenHandle, TOKEN_INFORMATION_CLASS TokenInformationClass, IntPtr TokenInformation, uint TokenInformationLength, out uint ReturnLength);
    public enum TOKEN_INFORMATION_CLASS
    {
        TokenUser = 1,
        TokenGroups,
        TokenPrivileges,
        TokenOwner,
        TokenPrimaryGroup,
        TokenDefaultDacl,
        TokenSource,
        TokenType,
        TokenImpersonationLevel,
        TokenStatistics,
        TokenRestrictedSids,
        TokenSessionId,
        TokenGroupsAndPrivileges,
        TokenSessionReference,
        TokenSandBoxInert,
        TokenAuditPolicy,
        TokenOrigin
    }

    public static byte[] GetSIDByteArr(IntPtr processHandle)
    {
        int MAX_INTPTR_BYTE_ARR_SIZE = 512;
        IntPtr tokenHandle;
        byte[] sidBytes;

        // Get the Process Token
        if (!OpenProcessToken(processHandle, TOKEN_READ, out tokenHandle))
        throw new ApplicationException("Could not get process token.  Win32 Error Code: " + Marshal.GetLastWin32Error());

        uint tokenInfoLength = 0;
        bool result;
        result = GetTokenInformation(tokenHandle, TOKEN_INFORMATION_CLASS.TokenUser, IntPtr.Zero, tokenInfoLength, out tokenInfoLength);  // get the token info length
        IntPtr tokenInfo = Marshal.AllocHGlobal((int)tokenInfoLength);
        result = GetTokenInformation(tokenHandle, TOKEN_INFORMATION_CLASS.TokenUser, tokenInfo, tokenInfoLength, out tokenInfoLength);  // get the token info

        // Get the User SID
        if (result)
        {
        TOKEN_USER tokenUser = (TOKEN_USER)Marshal.PtrToStructure(tokenInfo, typeof(TOKEN_USER));
        sidBytes = new byte[MAX_INTPTR_BYTE_ARR_SIZE];  // Since I don't yet know how to be more precise w/ the size of the byte arr, it is being set to 512
        Marshal.Copy(tokenUser.User.Sid, sidBytes, 0, MAX_INTPTR_BYTE_ARR_SIZE);  // get a byte[] representation of the SID
        }
        else throw new ApplicationException("Could not get process token.  Win32 Error Code: " + Marshal.GetLastWin32Error());

        return sidBytes;
    }

    // ******** Example: Call GetSIDByteArr() *************//
    Process[] myProcesses = Process.GetProcesses();
    foreach (Process myProcess in myProcesses)
    {
        byte[] sidBytes = Utility.GetSIDByteArr(myProcess.Handle);
    }
    // ****************************************************//

Alternative Managed API:

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Documentation
OpenProcessToken on MSDN