Pad plaintext bytes so the encoded ciphertext has no base64 padding

Pad plaintext bytes so the encoded ciphertext has no base64 padding

Since base64 padding is ignored on decode, the padding can be deleted or replaced with junk data. As a result, it is possible to decode different strings into the same bytes. By padding the bytes so the bytes are a multiple of 3, there is never base64 padding and exactly one input yields the desired output.