Microsoft KB Archive/268884

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How To Set or Retrieve the Authentication Level of a DCOM Client

Article ID: 268884

Article Last Modified on 8/30/2004


APPLIES TO

  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition


This article was previously published under Q268884

SUMMARY

If you need to set a custom value for the Authentication Level for a DCOM client application, you can use one of the following options:

  • Call CoInitializeSecurity.
  • Create an AppId in the registry that has a double word (DWORD) value set for AuthenticationLevel and map this AppId to the executable file name of your DCOM client.

This article uses the second option.

MORE INFORMATION

DCOM security settings are process-specific. If you do not set the AuthenticationLevel of the client's process, then the default AuthenticationLevel is used. Because you do not use CoInitilizeSecurity from your client to set the AuthenticationLevel and your client executable is not included in the Dcomcnfg utility, you must create your own registry mapping in order to set the client's authentication level either programmatically or by using Regedit.

Do the mapping in the registry by starting under:

HKEY_CLASSES_ROOT\AppId\


and then adding a key with the name of your client's executable name (myclient.exe). In this key there should be a string value, AppId, with your generated GUID. You also need to have a key under:

HKEY_CLASSES_ROOT\AppId\


with your generated GUID. In this key there should be a DWORD value, AuthenticationLevel, which is set to the value of the authentication level you want the client to use. This completes the registry mapping for the client's executable.

Assuming that your client executable is named myclient.exe, the mapping should look like the following in the registry.

Key Value
HKCR\AppId\myclient.exe     (Default)                      REG_SZ              (value not set)
     AppId                           REG_SZ              {GUID}
HKCR\AppId\{GUID}    (Default)                       REG_SZ              (value not set)
     AuthenticationLevel        REG_DWORD       0x00000001


The following is sample code for an application that creates the preceding registry entries for a given executable:

  1. Start a Standard EXE Project in Visual Basic. Form1 is created by default.
  2. Add two TextBox, two Label, and two CommandButton controls to the form.

  3. Add the following code to the form:

    Private Sub Command1_Click()
    If Text1 = "" Or Val(Text2) < 1 Or Val(Text2) > 6 Then Exit Sub
    SetAuthentication Val(Text2), Text1
End Sub

Private Sub Command2_Click()
    Dim auth As Integer
    auth = GetAuthenticationLevel(Text1)
    MsgBox "The Authentication Level for: " & Text1 & " is " & auth
End Sub

Private Sub Form_Load()
    With Me
        .Width = 3225
        .Height = 1950
        .Caption = "Set DCOM Client Authentication Level"
    End With
    With Command1
        .Height = 615
        .Width = 1450
        .Left = 1650
        .Top = 120
        .Caption = "Set Authentication Level"
        .TabIndex = 2
    End With
    With Command2
        .Height = 615
        .Width = 1450
        .Left = 1650
        .Top = 840
        .Caption = "Get Authentication Level"
        .TabIndex = 2
    End With
    With Text1
        .Text = ""
        .Height = 285
        .Left = 0
        .Top = 360
        .Width = 1455
        .TabIndex = 0
    End With
    With Text2
        .Text = ""
        .Height = 285
        .Left = 0
        .Top = 1200
        .Width = 255
        .TabIndex = 1
    End With
    With Label1
        .Caption = "Client EXE name"
        .Left = 0
        .Top = 0
    End With
    With Label2
        .Caption = "Authentication Level (1-6)"
        .Left = 0
        .Top = 720
    End With
End Sub

  4. On the Project menu, add a standard module to the project, and then paste the following code in the code module:

    Private Type GUID
    Data1 As Long
    Data2 As Integer
    Data3 As Integer
    Data4(7) As Byte
End Type

Private Const GUID_LENGTH As Long = 39

Private Const REG_SZ As Long = 1
Private Const REG_DWORD As Long = 4

Private Const ERROR_SUCCESS = 0
Private Const ERROR_NONE = 0

Private Const HKEY_CLASSES_ROOT = &H80000000

Private Const KEY_ALL_ACCESS = &H3F
Private Const KEY_QUERY_VALUE = &H1

Private Const REG_OPTION_NON_VOLATILE = 0

Private Declare Function RegCloseKey Lib "advapi32.dll" _
(ByVal hKey As Long) As Long

Private Declare Function RegCreateKeyEx Lib "advapi32.dll" Alias _
"RegCreateKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
ByVal Reserved As Long, ByVal lpClass As String, ByVal dwOptions _
As Long, ByVal samDesired As Long, ByVal lpSecurityAttributes _
As Long, phkResult As Long, lpdwDisposition As Long) As Long

Private Declare Function RegSetValueExString Lib "advapi32.dll" Alias _
"RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
ByVal Reserved As Long, ByVal dwType As Long, ByVal lpValue As _
String, ByVal cbData As Long) As Long

Private Declare Function RegSetValueExLong Lib "advapi32.dll" Alias _
"RegSetValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
ByVal Reserved As Long, ByVal dwType As Long, lpValue As Long, _
ByVal cbData As Long) As Long

Private Declare Function RegOpenKeyEx Lib "advapi32.dll" Alias _
"RegOpenKeyExA" (ByVal hKey As Long, ByVal lpSubKey As String, _
ByVal ulOptions As Long, ByVal samDesired As Long, phkResult As Long) _
As Long

Private Declare Function RegQueryValue Lib "advapi32.dll" Alias _
"RegQueryValueA" (ByVal hKey As Long, ByVal lpSubKey As String, _
ByVal lpValue As String, lpcbValue As Long) As Long

Private Declare Function RegQueryValueExString Lib "advapi32.dll" _
Alias "RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As String, _
ByVal lpReserved As Long, lpType As Long, ByVal lpData As String, _
lpcbData As Long) As Long

Private Declare Function RegQueryValueExLong Lib "advapi32.dll" Alias _
"RegQueryValueExA" (ByVal hKey As Long, ByVal lpValueName As _
String, ByVal lpReserved As Long, lpType As Long, lpData As _
Long, lpcbData As Long) As Long
      
Private Declare Function CoCreateGuid Lib "ole32.dll" (pGUID As GUID) _
As Long

Private Declare Function StringFromGUID2 Lib "ole32.dll" (pGUID As GUID, _
ByVal PointerToString As Long, ByVal MaxLength As Long) As Long

Public Function CreateGUID() As String
    Dim udtGUID As GUID
    Dim sGUID As String
    Dim lResult As Long
    If (CoCreateGuid(udtGUID) = 0) Then
        sGUID = String$(GUID_LENGTH, 0)
        lResult = StringFromGUID2(udtGUID, StrPtr(sGUID), GUID_LENGTH)
        CreateGUID = sGUID
    End If
End Function

Public Sub SetAuthentication(AuthLevel As Integer, ExeName As String)
    Dim hNewKey As Long
    Dim lRetVal As Long
    Dim sMyGUID As String
    Dim sNewKey As String
    Dim lpData As Long
    Dim lpcbData As Long
    
    lpData = CLng(AuthLevel)
    lpcbData = Len(lpData)
    sMyGUID = CreateGUID()
    sNewKey = "AppId\" & sMyGUID
    
    lRetVal = RegCreateKeyEx(HKEY_CLASSES_ROOT, sNewKey, 0&, _
       vbNullString, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, 0&, _
       hNewKey, lRetVal)
    lRetVal = RegSetValueExLong(hNewKey, "AuthenticationLevel", 0&, _
       REG_DWORD, lpData, lpcbData)
    RegCloseKey (hNewKey)
    
    sNewKey = "AppId\" & ExeName & ".exe"
    lRetVal = RegCreateKeyEx(HKEY_CLASSES_ROOT, sNewKey, 0&, _
       vbNullString, REG_OPTION_NON_VOLATILE, KEY_ALL_ACCESS, 0&, _
       hNewKey, lRetVal)
    lRetVal = RegSetValueExString(hNewKey, "AppId", 0&, REG_SZ, _
       sMyGUID, Len(sMyGUID))
    RegCloseKey (hNewKey)
    MsgBox sMyGUID
End Sub

Public Function GetAuthenticationLevel(ExeName As String) As Integer
    Dim hKey As Long
    Dim lRetVal As Long
    Dim sKeyName As String
    Dim lpData As String
    Dim lpdata2 As Long
    Dim lpcbData As Long
    Dim myappid As String
    Dim auth As Integer
    
    If ExeName = "" Then
        GetAuthenticationLevel = -1
        MsgBox "Invalid File Name"
        Exit Function
    End If
    
    lRetVal = RegOpenKeyEx(HKEY_CLASSES_ROOT, "AppId\" & ExeName, 0, _
       KEY_QUERY_VALUE, hKey)
    If lRetVal = ERROR_SUCCESS Then
        lpcbData = 40
        lpData = Space$(lpcbData)
        lRetVal = RegQueryValueExString(hKey, "AppId", 0&, REG_SZ, _
           lpData, lpcbData)
        If lRetVal = ERROR_NONE Then
            myappid = Left$(lpData, lpcbData - 1)
            RegCloseKey (hKey)
            sKeyName = "AppID\" & myappid & "\"
            lRetVal = RegOpenKeyEx(HKEY_CLASSES_ROOT, sKeyName, 0&, _
            KEY_ALL_ACCESS, hKey)
            If lRetVal = ERROR_SUCCESS Then
                lpdata2 = CLng(0)
                lpcbData = Len(lpdata2)
                lRetVal = RegQueryValueExLong(hKey, _
                   "AuthenticationLevel", 0&, REG_DWORD, lpdata2, lpcbData)
                If lRetVal = ERROR_NONE Then
                    auth = CInt(lpdata2)
                    GetAuthenticationLevel = auth
                Else
                    MsgBox lRetVal & " - Unable to read authentication level."
                    GetAuthenticationLevel = -2
                End If
            Else
                MsgBox lRetVal & " - Cannot find AppID for " & sKeyName
                GetAuthenticationLevel = -3
            End If
            RegCloseKey (hKey)
        Else
             MsgBox lRetVal & " - Cannot read AppID value for " & sKeyName
             GetAuthenticationLevel = -4
        End If
    Else
        MsgBox lRetVal & " - Cannot find exe name - " & sKeyName
        GetAuthenticationLevel = -5
    End If

Exit Function
QueryValueExExit:
    MsgBox lRetVal & " - Unexpected error"
    GetAuthenticationLevel = -7
    Exit Function
QueryValueExError:
    Resume QueryValueExExit
End Function
  5. Run the project. Type the executable file name of the client application into Text1, and then type the authentication level you want to set into Text2.
  6. Click the Set Authentication Level CommandButton. The mapping is now created in the registry and the authentication level is set for the client executable. Click the Get Authentication Level CommandButton and note that a message box appears containing the authentication level you just set.


REFERENCES

For more information on AppId, see the following directory in MSDN:

\Platform SDK\Component Services\COM\COM Fundamentals\Reference\Registry Entries\AppId


For additional information on securing objects in code, click the article numbers below to view the articles in the Microsoft Knowledge Base:

239561 How To Use CoInitializeSecurity in Visual Basic


249636 How To Use the CoSetProxyBlanket Function in Visual Basic



Additional query words: myclient

Keywords: kbhowto kbregistry kbsecurity kbdcom kbclientserver KB268884



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