Base64 Encoding & Decoding in vb6

Following two functions can be used for encoding string in base64. This is useful when you want to pass encrypted string etc on URL.

 Public Function Base64Encoding(StrToEncode As String) As String
    Static EncodeTable(0 To 63) As Byte
    
    Dim K As Long, OutStr() As Byte, StrIn() As Byte, Lng As Long
    
    If EncodeTable(0) = 0 Then
        For K = 0 To 25
            EncodeTable(K) = Asc("A") + K
        Next K
        
        For K = 0 To 25
            EncodeTable(K + 26) = Asc("a") + K
        Next K
        
        For K = 0 To 9
            EncodeTable(K + 52) = Asc("0") + K
        Next K
        
        EncodeTable(62) = Asc("+")
        EncodeTable(63) = Asc("/")
    End If
    
    If StrToEncode = "" Then Exit Function
    
    StrIn = StrConv(StrToEncode, vbFromUnicode)
    If (Len(StrToEncode) Mod 3) = 0 Then
        ReDim OutStr((Len(StrToEncode) \ 3) * 4 - 1)
    Else
        ReDim OutStr(((Len(StrToEncode) \ 3) + 1) * 4 - 1)
    End If
    
    For K = 0 To Len(StrToEncode) \ 3 - 1
        Lng = StrIn(K * 3 + 2) Or (StrIn(K * 3 + 1) * &H100&) Or (StrIn(K * 3) * &H10000)
        
        OutStr(K * 4 + 0) = EncodeTable((Lng And &HFC0000) \ &H40000)
        OutStr(K * 4 + 1) = EncodeTable((Lng And &H3F000) \ &H1000&)
        OutStr(K * 4 + 2) = EncodeTable((Lng And &HFC0&) \ &H40&)
        OutStr(K * 4 + 3) = EncodeTable(Lng And &H3F&)
    Next K
    
    If (Len(StrToEncode) Mod 3) = 1 Then
        Lng = StrIn(UBound(StrIn)) * &H10000
        
        OutStr(UBound(OutStr) - 3) = EncodeTable((Lng And &HFC0000) \ &H40000)
        OutStr(UBound(OutStr) - 2) = EncodeTable((Lng And &H3F000) \ &H1000&)
        OutStr(UBound(OutStr) - 1) = Asc("=")
        OutStr(UBound(OutStr) - 0) = Asc("=")
    ElseIf (Len(StrToEncode) Mod 3) = 2 Then
        Lng = (StrIn(UBound(StrIn)) * &H100&) Or (StrIn(UBound(StrIn) - 1) * &H10000)
        
        OutStr(UBound(OutStr) - 3) = EncodeTable((Lng And &HFC0000) \ &H40000)
        OutStr(UBound(OutStr) - 2) = EncodeTable((Lng And &H3F000) \ &H1000&)
        OutStr(UBound(OutStr) - 1) = EncodeTable((Lng And &HFC0&) \ &H40&)
        OutStr(UBound(OutStr) - 0) = Asc("=")
    End If
    
    Base64Encoding = StrConv(OutStr, vbUnicode)
End Function

Public Function Base64Decoding(StrToDecode As String, Optional CheckInvalidChars As Boolean = True) As String
    Static DecodeTable(0 To 255) As Byte
    
    Dim OutStr() As Byte, StrIn() As Byte
    Dim K As Long, Lng As Long
    
    If DecodeTable(0) = 0 Then
        For K = 0 To 255
            DecodeTable(K) = 255
        Next K
        
        For K = 0 To 25
            DecodeTable(K + 65) = K
        Next K
        
        For K = 26 To 51
            DecodeTable(K + 71) = K
        Next K
        
        For K = 52 To 61
            DecodeTable(K - 4) = K
        Next K
        
        DecodeTable(43) = 62
        DecodeTable(47) = 63
    End If
    
    If StrToDecode = "" Then Exit Function
    
    StrToDecode = Trim(StrToDecode)
    
    If CheckInvalidChars Then
        For K = 0 To 255
            If Not (Chr(K) Like "[A-Za-z0-9+/=]") Then
                StrToDecode = Replace(StrToDecode, Chr(K), "")
            End If
        Next K
    End If
    
    StrIn() = StrConv(StrToDecode, vbFromUnicode)
    ReDim OutStr(0 To ((Len(StrToDecode) \ 4) * 3 - 1))
    
    For K = 0 To Len(StrToDecode) \ 4 - 2
        Lng = DecodeTable(StrIn(K * 4 + 3))
        Lng = Lng Or (DecodeTable(StrIn(K * 4 + 2)) * &H40&)
        Lng = Lng Or (DecodeTable(StrIn(K * 4 + 1)) * &H1000&)
        Lng = Lng Or (DecodeTable(StrIn(K * 4 + 0)) * &H40000)
        
        OutStr(K * 3 + 0) = (Lng And &HFF0000) \ &H10000
        OutStr(K * 3 + 1) = (Lng And &HFF00&) \ &H100&
        OutStr(K * 3 + 2) = Lng And &HFF&
    Next K
    
    Lng = 0
    If DecodeTable(StrIn(K * 4 + 3)) <> 255 Then Lng = DecodeTable(StrIn(K * 4 + 3))
    If DecodeTable(StrIn(K * 4 + 2)) <> 255 Then Lng = Lng Or (DecodeTable(StrIn(K * 4 + 2)) * &H40&)
    If DecodeTable(StrIn(K * 4 + 1)) <> 255 Then Lng = Lng Or (DecodeTable(StrIn(K * 4 + 1)) * &H1000&)
    If DecodeTable(StrIn(K * 4 + 0)) <> 255 Then Lng = Lng Or (DecodeTable(StrIn(K * 4 + 0)) * &H40000)
    
    OutStr(K * 3 + 0) = (Lng And &HFF0000) \ &H10000
    OutStr(K * 3 + 1) = (Lng And &HFF00&) \ &H100&
    OutStr(K * 3 + 2) = Lng And &HFF&
    
    If StrIn(UBound(StrIn) - 1) = 61 Then
        Base64Decoding = Left(StrConv(OutStr, vbUnicode), UBound(OutStr) - 1)
    ElseIf StrIn(UBound(StrIn)) = 61 Then
        Base64Decoding = Left(StrConv(OutStr, vbUnicode), UBound(OutStr) - 0)
    Else
        Base64Decoding = StrConv(OutStr, vbUnicode)
    End If
End Function