X.509 is a public key infrastructure used mostly on the Internet. It consists of certificates which include public keys and identifiers, signed by an authority. Authorities must be exchanged over a second channel to establish the trust relationship. This library implements most parts of RFC5280 and RFC6125. The Public Key Cryptography Standards (PKCS) defines encoding and decoding (in ASN.1 DER and PEM format), which is also implemented by this library - namely PKCS 1, PKCS 5, PKCS 7, PKCS 8, PKCS 9, PKCS 10, and PKCS 12.