Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format by translating it into a radix-64 representation. It is specified in RFC 4648.
See also documentation.
Simple encoding and decoding.
utop # #require "base64";;
utop # let enc = B64.encode "OCaml rocks!";;
val enc : string = "T0NhbWwgcm9ja3Mh"
utop # let plain = B64.decode enc;;
val plain : string = "OCaml rocks!"