public_key deals with public key related file formats, digital signatures and X-509 certificates. It is a library application that provides encode/decode, sign/verify, encrypt/decrypt and similar functionality, it does not read or write files it expects or returns file contents or partial file contents as binaries.
It is assumed that the reader has a basic understanding of the concepts of using public keys and digital certificates.
The public_key decode and encode functions will try to use the NIFs which are in the ASN1 compilers runtime modules if they can be found. So for the best performance you want to have the ASN1 application in the path of your system.