Summary This code snippet presents VB6's class module to perform base64 encoding and decoding using MSXML.

Using code from this short article you can easily do the following:

 - Perform base64 encoding
 - Perform base64 decoding
 - Perform conversion of a byte array to the string
 - Perform conversion of a scalar variable to the byte array

Base64 encoding/decoding becomes as easy as ABC:

  Dim o As CBase64   ' base64 encoder/decoder class
  Dim strSrc As String  ' source test string
  Dim strDst As String  ' destination (base64 encoded) test string
  Dim strRes As String  ' restored (base64 decoded) strDst

  strSrc = Test string                 ' set value for test string
  Set o = New CBase64             ' create new instance on CBase64 class
  strDst = o.Encode(strSrc)         ' encode
  strRes = o.Decode2Str(strDst)  ' decode

In attachment you can find a test VB6 project.

Enjoy!

Additional information

Option Explicit '+ ' CBase64 ' ' Purpose: ' - Perform base64 encoding ' - Perform base64 decoding ' - Perform conversion of a byte array to the string ' - Perform conversion of a scalar variable to the byte array ' ' Written by: Shamil Slakhetdinov 11-Jan-2002 ' e-mail: shamil@daisy.spb.ru ' ' Public domain - can be used without any restrictions provided the info ' about the author is left unchanged '- Private mxmlDOC As Object ' XML DOM document Private Sub Class_Initialize() ' Create XML DOC document Set mxmlDOC = CreateObject("MSXML.DOMDocument") End Sub Public Function Encode(ByRef vvarBinValue As Variant) As String ' ' Purpose: ' Execute base64 encoding of input parameter ' Parameters: ' vvarBinValue - input parameter - usually byte array but ' in general can be any non object type ' Returns: ' A string - base64 encoded representation of the input parameter ' Dim xmlNode As Object ' MSXML.IXMLDOMNode Dim strTmp As String Dim lngS As Long, lngE As Long ' create XML node named "ENCODER" Set xmlNode = mxmlDOC.createElement("ENCODER") With xmlNode ' set XML node's data type = "bin.base64" .dataType = "bin.base64" If LCase(Left(TypeName(vvarBinValue), 4)) = "byte" Then ' if input parameter - byte array - just assign it to the ' nodeTypedValue property of XML node .nodeTypedValue = vvarBinValue Else ' if input parameter isn't a byte array then convert it ' to byte array and assign to the nodeTypedValue property ' of XML node .nodeTypedValue = Scalar2BytArray(vvarBinValue) End If ' extract base64 encoded value enclosed into ' <ENCODER ...> ' ...base64 coded value... ' </ENCODER> ' tags into strTmp temp string strTmp = xmlNode.xml End With ' get the position of the first char after the end of the beginning tag lngS = InStr(strTmp, ">") + 1 ' get the position of the ending tag lngE = InStr(lngS, strTmp, "<") ' extract base64 encoded value and assign it as the return value of the function Encode = Mid(strTmp, lngS, lngE - lngS) End Function Public Function Decode(ByVal vstr As String) As Byte() ' ' Purpose: ' Execute decoding of base64 encoded input parameter ' Parameters: ' vstr - base64 encoded string ' Returns: ' A byte array - decoded input parameter ' Dim strXML As String Dim xmlNode As Object ' MSXML.IXMLDOMNode ' make well formed XML string strXML = "<DECODER xmlns:dt=""urn:schemas-microsoft-com:datatypes"" " & _ "dt:dt=""bin.base64"">" & _ vstr & _ "</DECODER>" With mxmlDOC ' load XML document from string .loadXML strXML ' select XML node DECODER Set xmlNode = .selectSingleNode("DECODER") ' get decoded value and assign it as the function return value Decode = xmlNode.nodeTypedValue End With End Function Public Function Decode2Str(ByVal vstr As String) As String ' ' Purpose: ' Execute decoding of base64 encoded input parameter ' Parameters: ' vstr - base64 encoded string ' Returns: ' A string - decoded input parameter ' ' execute decoding, convert decoded byte array into string and ' set this string as the return value of the function Decode2Str = BytArray2Scalar(Me.Decode(vstr)) End Function Public Function Scalar2BytArray(ByRef vvarScalarValue As Variant) As Byte() ' ' Purpose: ' Execute conversion of scalar value to a byte array ' Parameters: ' vvarScalarValue - scalar value ' Returns: ' A byte array ' Dim strTmp As String Dim barr() As Byte Dim i As Long ' assign input scalar value to the string - ' during this assign default conversion will be perfomed strTmp = vvarScalarValue ' redim array to make it big enough to keep all ' the chars of the string strTmp ReDim barr(Len(strTmp) - 1) For i = 0 To UBound(barr) ' assign all the chars of strTmp to the corresponding ' elements of the byte array barr(i) = Asc(Mid(strTmp, i + 1, 1)) Next i ' assign byte array as a return value of the function Scalar2BytArray = barr End Function Public Function BytArray2Scalar(ByRef abyt() As Byte) As String ' ' Purpose: ' Execute conversion of byte array to the string ' Parameters: ' abyt() - byte array ' Returns: ' A string representation of the byte array ' Dim strTmp As String Dim barr() As Byte Dim i As Long strTmp = "" If UBound(abyt) > -1 Then ' extract all the elements of the byte array and concatenate ' them to form a temp string strTmp For i = 0 To UBound(abyt) strTmp = strTmp & Chr(abyt(i)) Next i End If ' assign temp string strTmp as the return value of the function BytArray2Scalar = strTmp End Function