Base64 encoding

Base64 is a group of similar encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation.
Base64 encoding schemes are commonly used when there is a need to encode binary data that needs be stored and transferred over media that are designed to deal with textual data.

to encode

openssl base64 -in INPUT_FILE -out OUTPUT_FILE

and to decode from Base64:

openssl base64 -d -in INPUT_FILE -out OUTPUT_FILE