How Can I Read, Write, and Delete NTFS Alternate Data Streams in .NET?

NTFS Alternate Data Streams Access in .NET

Manipulating NTFS Alternate Data Streams (ADS) is essential for various scenarios, including security and data hiding. .NET provides functionalities to both read and modify these streams.

Reading ADS

To read a data stream attached to a file, use the CreateFileW function:

using System.Runtime.InteropServices;

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
    );

}

Call CreateFileW with the file name followed by the stream name, separated by a colon (:). For example:

var stream = NativeMethods.CreateFileW("testfile:stream", ...);

Modifying ADS

To write to or modify a stream, simply use the returned file handle to perform I/O operations. For instance, to write to the stream:

using System.Runtime.InteropServices;

class Program
{
    static void Main(string[] args)
    {
        var stream = NativeMethods.CreateFileW("testfile:stream", ...);
        NativeMethods.WriteFile(stream, ...);
    }
}

public partial class NativeMethods
{

    /// Return Type: BOOL->int
    ///hFile: HANDLE->void*
    ///lpBuffer: LPCVOID->void*
    ///nNumberOfBytesToWrite: DWORD->unsigned int
    ///lpNumberOfBytesWritten: LPDWORD->DWORD*
    ///lpOverlapped: LPOVERLAPPED->OVERLAPPED*
    [DllImportAttribute("kernel32.dll", EntryPoint = "WriteFile")]
    [return: MarshalAsAttribute(UnmanagedType.Bool)]
    public static extern bool WriteFile(
        [InAttribute()] System.IntPtr hFile, 
        [InAttribute()] System.IntPtr lpBuffer, 
        uint nNumberOfBytesToWrite, 
        [OutAttribute()] [MarshalAsAttribute(UnmanagedType.U4)] out uint lpNumberOfBytesWritten, 
        [InAttribute()] System.IntPtr lpOverlapped
    );

}

Similarly, you can delete a stream using:

using System.Runtime.InteropServices;

class Program
{
    static void Main(string[] args)
    {
        var stream = NativeMethods.CreateFileW("testfile:stream", ...);
        NativeMethods.DeleteFile(stream);
    }
}

public partial class NativeMethods
{

    /// Return Type: BOOL->int
    ///lpFileName: LPCWSTR->WCHAR*
    [DllImportAttribute("kernel32.dll", EntryPoint = "DeleteFileW")]
    [return: MarshalAsAttribute(UnmanagedType.Bool)]
    public static extern bool DeleteFileW([InAttribute()] [MarshalAsAttribute(UnmanagedType.LPWStr)] string lpFileName);
}

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