Conversion from byte array to base64 and back
The reason the encoded array is longer by about a quarter is that base-64 encoding uses only six bits out of every byte; that is its reason of existence - to encode arbitrary data, possibly with zeros and other non-printable characters, in a way suitable for exchange through ASCII-only channels, such as e-mail.
The way you get your original array back is by using Convert.FromBase64String:
byte[] temp_backToBytes = Convert.FromBase64String(temp_inBase64);