Base64 decode VBS function (vb decoder algorithm), source code

This article contains a full VBS source code of a Base64 decode function (base64 decoder). You can use the function, for example, to decode basic http authentication info - username and password, or to decode incomming emails.

Base64Decode VBS function can only work with small amount of data - VBS does not enable to work with buffers to improve performance. Consumed processor time rapidly grows with source data length (by square). Please use Base64 property of ByteArray object (ScriptUtilities library, C++ COM object, comercial) if you want to work with large data. ByteArray lets you also work with codepage (charset) conversions and provides binary file access and binary-to-string conversion. ScriptUtilities is also available with source code.
See also:

Base64 encode VBS function - reverse encoding function.

Online Base64 decoder and encoder - realtime http sample to encode/decode Base64 texts and binary files.

Online Base16 (hex string) decoder and encoder - similar sample for hexstring (samples for SQL command with binary and image fields)
Next table contains consumed processor time of this VBS code (Base64Encode) and C++ (Base64) on Duron 700 processor. You can see that VBS function is usable for maximum of 50-100 kB.

Source size [B]	VBS	C++ Base64	VBS	C++ Base64
Source size [B]	Procesor time [ms], Encode		Procesor time [ms], Decode
100 B	2.2	0.04	2.3	0.03
1 kB	22	0.06	23	0.10
5 kB	116	0.20	120	0.42
10 kB	248	0.37	255	0.82
20 kB	855	1.00	744	1.90
50 kB	6.6 s	0.003 s	6.4 s	0.004 s
100 kB	36 s	0.006 s	24 s	0.010 s
500 kB	~1000 s	0.032 s	~700 s	0.050 s
1 MB	~5000 s	0.068 s	~3500 s	0.110 s

' Decodes a base-64 encoded string (BSTR type).
' 1999 - 2004 Antonin Foller, http://www.motobit.com
' 1.01 - solves problem with Access And 'Compare Database' (InStr)
Function Base64Decode(ByVal base64String)
  'rfc1521
  '1999 Antonin Foller, Motobit Software, http://Motobit.cz
  Const Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
  Dim dataLength, sOut, groupBegin
  
  'remove white spaces, If any
  base64String = Replace(base64String, vbCrLf, "")
  base64String = Replace(base64String, vbTab, "")
  base64String = Replace(base64String, " ", "")
  
  'The source must consists from groups with Len of 4 chars
  dataLength = Len(base64String)
  If dataLength Mod 4 <> 0 Then
    Err.Raise 1, "Base64Decode", "Bad Base64 string."
    Exit Function
  End If

  
  ' Now decode each group:
  For groupBegin = 1 To dataLength Step 4
    Dim numDataBytes, CharCounter, thisChar, thisData, nGroup, pOut
    ' Each data group encodes up To 3 actual bytes.
    numDataBytes = 3
    nGroup = 0

    For CharCounter = 0 To 3
      ' Convert each character into 6 bits of data, And add it To
      ' an integer For temporary storage.  If a character is a '=', there
      ' is one fewer data byte.  (There can only be a maximum of 2 '=' In
      ' the whole string.)

      thisChar = Mid(base64String, groupBegin + CharCounter, 1)

      If thisChar = "=" Then
        numDataBytes = numDataBytes - 1
        thisData = 0
      Else
        thisData = InStr(1, Base64, thisChar, vbBinaryCompare) - 1
      End If
      If thisData = -1 Then
        Err.Raise 2, "Base64Decode", "Bad character In Base64 string."
        Exit Function
      End If

      nGroup = 64 * nGroup + thisData
    Next
    
    'Hex splits the long To 6 groups with 4 bits
    nGroup = Hex(nGroup)
    
    'Add leading zeros
    nGroup = String(6 - Len(nGroup), "0") & nGroup
    
    'Convert the 3 byte hex integer (6 chars) To 3 characters
    pOut = Chr(CByte("&H" & Mid(nGroup, 1, 2))) + _
      Chr(CByte("&H" & Mid(nGroup, 3, 2))) + _
      Chr(CByte("&H" & Mid(nGroup, 5, 2)))
    
    'add numDataBytes characters To out string
    sOut = sOut & Left(pOut, numDataBytes)
  Next

  Base64Decode = sOut
End Function

Next sample is a simple ASP page, which does not enable anonymous users (without username and password), but users with any username and any password are alowed.

<%
Dim UID, PWD
GetUser UID, PWD
If UID = "" Then
'or If Not HasAccess(UID, PWD) Then
  Response.Status = "401 Access Denied"
  Response.Write "Some page with info about user names And registration"
End If

Sub GetUser(LOGON_USER, LOGON_PASSWORD)
  Dim UP, Pos, Auth
  Auth = Request.ServerVariables("HTTP_AUTHORIZATION")
  LOGON_USER = ""
  LOGON_PASSWORD = ""
  If LCase(Left(Auth, 5)) = "basic" Then
    UP = Base64Decode(Mid(Auth, 7))
    Pos = InStr(UP, ":")
    If Pos > 1 Then
      LOGON_USER = Left(UP, Pos - 1)
      LOGON_PASSWORD = Mid(UP, Pos + 1)
    End If
  End If
End Sub
%>

There is no good idea to allow access with any username/password. But you can write your own function which lets you authenticate usernames/passwords against database.

Base64 decode VBS function (vb decoder algorithm), source codeMOTOBIT.COM

See also

Copyright and use this code