Dim Shared As String B64
B64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" & _
"abcdefghijklmnopqrstuvwxyz" & _
"0123456789+/"

Function MIMEDecode(s As String ) As Integer
    If Len(s) Then
        MIMEdecode = Instr(B64,s) - 1
    Else
        MIMEdecode = -1
    End If
End Function

Function Decode64(s As String) As String
    Dim As Integer w1, w2, w3, w4
    Dim As String  mD
    For n As Integer = 1 To Len(s) Step 4
        w1 = MIMEdecode(Mid(s,n+0,1))
        w2 = MIMEdecode(Mid(s,n+1,1))
        w3 = MIMEdecode(Mid(s,n+2,1))
        w4 = MIMEdecode(Mid(s,n+3,1))
        If w2 >-1 Then mD+= Chr(((w1* 4 + Int(w2/16)) And 255))
        If w3 >-1 Then mD+= Chr(((w2*16 + Int(w3/ 4)) And 255))
        If w4 >-1 Then mD+= Chr(((w3*64 + w4        ) And 255))
    Next n
    Return mD
End Function

Dim As String msg64 = "VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVw" & _
"IHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g="
Print msg64
Print: Print(Decode64(msg64))
Sleep