How to operate with base64

Encode file:
$ base64 message.file > message.file.base64

Decode file:
$ base64 --decode message.file.base64 > message.file

Encode string:
$ echo "open message" | base64 > message.base64

Decode string:
$ echo "b3BlbiBtZXNzYWdlCg==" | base64 --decode > message.file