Hello,

I need ideas, concepts to realize the following things:

I have a service (vb.net) running on a workstation communicating with a
client application.
The data flow does not need to be encrypted, but it must be validated that
it comes from a specific client.

I want to make sure that the client application authenticates to the service
before sending data.
The client of this service should be a local administrator of the
workstation.

How can this be done in a secure way (communicating with the service and
(windows) authentication without possibility of man in the middle attacks.)

GM,

We have the same type of scenerio.  We have the following code in our
service and our remote client application calls the authenticate method
(via interface) to logon to the domain.

Hope this helps.

Cheers,
Rob Panosh
Advanced Software Designs.


---- Sample Code ---

Imports System.Security.Principal
Imports System.Security.Permissions
Imports System.Runtime.InteropServices
Imports System.Environment


Public Class Logon

    '''
-----------------------------------------------------------------------------
    ''' <summary>
    ''' Authenticate a user against the network's users.
    ''' </summary>
    ''' <param name="userName">User name of the user to
authenticate.</param>
    ''' <param name="password">Password of the user to
authenticate.</param>
    ''' <param name="domain">The domain that is used to authenticate
users on the network (primary domain controller).</param>
    ''' <returns>Success if the correct credentials are passed to this
function.</returns>
    ''' <remarks>
    ''' </remarks>
    ''' <history>
    '''     [dave]    12/9/2004    Created
    ''' </history>
    '''
-----------------------------------------------------------------------------
    Public Shared Function Authenticate(ByVal userName As String, ByVal
password As String, ByVal domain As String) As Boolean

        Dim tokenHandle As New IntPtr(0)
        Try

            Const LOGON32_PROVIDER_DEFAULT As Integer = 0
            Const LOGON32_LOGON_INTERACTIVE As Integer = 2
            tokenHandle = IntPtr.Zero

            'Call the LogonUser function to obtain a handle to an
access token.
            Dim returnValue As Boolean = LogonUser(userName, domain,
password, LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT,
tokenHandle)

            If returnValue = False Then

                'This function returns the error code that the last
unmanaged function returned.
                Dim ret As Integer = Marshal.GetLastWin32Error()
                Dim errmsg As String = GetErrorMessage(ret)

                Throw New System.Exception(errmsg)

            Else

                'Create the WindowsIdentity object for the Windows user
account that is
                'represented by the tokenHandle token.
                Dim newId As New WindowsIdentity(tokenHandle)
                Dim userperm As New WindowsPrincipal(newId)

                'Verify whether the Windows user has administrative
credentials.
                If userperm.IsInRole(WindowsBuiltInRole.Administrator)
Then

                Else

                End If

            End If

            'Free the access token.
            If Not System.IntPtr.op_Equality(tokenHandle, IntPtr.Zero)
Then
                CloseHandle(tokenHandle)
            End If

        Catch ex As Exception
            Throw ex ' MessageBox.Show("Exception occurred. " +
ex.Message)
        End Try

    End Function


    'The LogonUser function tries to log on to the local computer
    'by using the specified user name. The function authenticates
    'the Windows user with the password provided.
    Private Declare Auto Function LogonUser Lib "advapi32.dll" (ByVal
lpszUsername As [String], _
       ByVal lpszDomain As [String], ByVal lpszPassword As [String], _
       ByVal dwLogonType As Integer, ByVal dwLogonProvider As Integer,
_
       ByRef phToken As IntPtr) As Boolean

    'The FormatMessage function formats a message string that is passed
as input.
    <DllImport("kernel32.dll")> _
    Public Shared Function FormatMessage(ByVal dwFlags As Integer,
ByRef lpSource As IntPtr, _
       ByVal dwMessageId As Integer, ByVal dwLanguageId As Integer,
ByRef lpBuffer As [String], _
       ByVal nSize As Integer, ByRef Arguments As IntPtr) As Integer
    End Function

    'The CloseHandle function closes the handle to an open object such
as an Access token.
    Public Declare Auto Function CloseHandle Lib "kernel32.dll" (ByVal
handle As IntPtr) As Boolean

    'The GetErrorMessage function formats and then returns an error
message
    'that corresponds to the input error code.
    Public Shared Function GetErrorMessage(ByVal errorCode As Integer)
As String
        Dim FORMAT_MESSAGE_ALLOCATE_BUFFER As Integer = &H100
        Dim FORMAT_MESSAGE_IGNORE_INSERTS As Integer = &H200
        Dim FORMAT_MESSAGE_FROM_SYSTEM As Integer = &H1000

        Dim msgSize As Integer = 255
        Dim lpMsgBuf As String
        Dim dwFlags As Integer = FORMAT_MESSAGE_ALLOCATE_BUFFER Or
FORMAT_MESSAGE_FROM_SYSTEM Or FORMAT_MESSAGE_IGNORE_INSERTS

        Dim lpSource As IntPtr = IntPtr.Zero
        Dim lpArguments As IntPtr = IntPtr.Zero
        'Call the FormatMessage function to format the message.
        Dim returnVal As Integer = FormatMessage(dwFlags, lpSource,
errorCode, 0, lpMsgBuf, _
                msgSize, lpArguments)
        If returnVal = 0 Then
            Throw New Exception("Failed to format message for error
code " + errorCode.ToString() + ". ")
        End If
        Return lpMsgBuf
    End Function


GM wrote:
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