The GnuTLS manual

GnuTLS is a secure communications library implementing the SSL and TLS protocols and technologies around them. It provides a simple C language application programming interface (API) to access the secure communications protocols as well as APIs to parse and write X.509, PKCS #8, PKCS #12, OpenPGP structures and a simple API to access hardware tokens such as smart-cards using PKCS #11. The library is aimed to be portable and efficient with focus on security and interoperability. This book contains all the information required to create applications using GnuTLS.