How Can I Read and Modify NTFS Alternate Data Streams Using .NET?

Reading and Modifying NTFS Alternate Data Streams Using .NET

NTFS Alternate Data Streams (ADS) are hidden data streams associated with regular files in the New Technology File System (NTFS). These streams can be used to store additional information, such as user comments, version history, or multimedia content, without affecting the primary file data.

Reading ADS

To read an ADS, you can use the CreateFileW function with the dwDesiredAccess parameter set to GENERIC_WRITE. This will open the stream for both reading and writing. You can then use the ReadFile function to read the stream's contents.

Modifying ADS

To modify an ADS, you can use the CreateFileW function with the dwDesiredAccess parameter set to GENERIC_WRITE. This will open the stream for both reading and writing. You can then use the WriteFile function to write new contents to the stream.

Here is a C# example of how to read and modify an ADS:

using System.Runtime.InteropServices;

class Program
{
    static void Main(string[] args)
    {
        // Open the main file stream
        var mainStream = NativeMethods.CreateFileW(
            "testfile",
            NativeConstants.GENERIC_WRITE,
            NativeConstants.FILE_SHARE_WRITE,
            IntPtr.Zero,
            NativeConstants.OPEN_ALWAYS,
            0,
            IntPtr.Zero);

        // Open the ADS stream
        var stream = NativeMethods.CreateFileW(
            "testfile:stream",
            NativeConstants.GENERIC_WRITE,
            NativeConstants.FILE_SHARE_WRITE,
            IntPtr.Zero,
            NativeConstants.OPEN_ALWAYS,
            0,
            IntPtr.Zero);

        // Write data to the ADS stream
        var data = "Hello world!";
        NativeMethods.WriteFile(stream, data, data.Length, out var bytesWritten, IntPtr.Zero);

        // Close the ADS stream
        NativeMethods.CloseHandle(stream);

        // Close the main file stream
        NativeMethods.CloseHandle(mainStream);
    }
}

public partial class NativeMethods
{

    /// Return Type: HANDLE->void*
    ///lpFileName: LPCWSTR->WCHAR*
    ///dwDesiredAccess: DWORD->unsigned int
    ///dwShareMode: DWORD->unsigned int
    ///lpSecurityAttributes: LPSECURITY_ATTRIBUTES->_SECURITY_ATTRIBUTES*
    ///dwCreationDisposition: DWORD->unsigned int
    ///dwFlagsAndAttributes: DWORD->unsigned int
    ///hTemplateFile: HANDLE->void*
    [DllImportAttribute("kernel32.dll", EntryPoint = "CreateFileW")]
    public static extern System.IntPtr CreateFileW(
        [InAttribute()] [MarshalAsAttribute(UnmanagedType.LPWStr)] string lpFileName, 
        uint dwDesiredAccess, 
        uint dwShareMode, 
        [InAttribute()] System.IntPtr lpSecurityAttributes, 
        uint dwCreationDisposition, 
        uint dwFlagsAndAttributes, 
        [InAttribute()] System.IntPtr hTemplateFile
    );

    /// Return Type: BOOL->int
    ///hFile: HANDLE->void*
    ///lpBuffer: LPVOID->void*
    ///nNumberOfBytesToWrite: DWORD->unsigned int
    ///lpNumberOfBytesWritten: LPDWORD->DWORD*
    ///lpOverlapped: LPOVERLAPPED->_OVERLAPPED*
    [DllImportAttribute("kernel32.dll", EntryPoint = "WriteFile")]
    public static extern int WriteFile(
        System.IntPtr hFile, 
        [InAttribute()] System.IntPtr lpBuffer, 
        uint nNumberOfBytesToWrite, 
        out uint lpNumberOfBytesWritten, 
        [InAttribute()] System.IntPtr lpOverlapped
    );

    /// Return Type: BOOL->int
    ///hObject: HANDLE->void*
    [DllImportAttribute("kernel32.dll", EntryPoint = "CloseHandle")]
    public static extern int CloseHandle(
        [InAttribute()] System.IntPtr hObject
    );

}


public partial class NativeConstants
{

    /// GENERIC_WRITE -> (0x40000000L)
    public const int GENERIC_WRITE = 1073741824;

    /// FILE_SHARE_DELETE -> 0x00000004
    public const int FILE_SHARE_DELETE = 4;

    /// FILE_SHARE_WRITE -> 0x00000002
    public const int FILE_SHARE_WRITE = 2;

    /// FILE_SHARE_READ -> 0x00000001
    public const int FILE_SHARE_READ = 1;

    /// OPEN_ALWAYS -> 4
    public const int OPEN_ALWAYS = 4;
}

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