Range of valid character for a base64 encoding

Question

I am interested in the following:
Is there a list of characters that would never occur as part of a base 64 encoded string?
For example *

Answer 1

https://en.wikipedia.org/wiki/Base64#Design

MIME's Base64 implementation uses A–Z, a–z, and 0–9 for the first 62 values

So for the most part you should expect only alphanumeric characters. The example table in this article shows '+' and '-' also; it's unlikely you would see '*'.

You can use http://www.motobit.com/util/base64-decoder-encoder.asp to convert to Base64 for example, and for '*' this returns "Kg=="