GNU Libidn is a fully documented implementation of the Stringprep, Punycode and IDNA specifications. Libidn's purpose is to encode and decode internationalized domain name strings. There are native C, C# and Java libraries.

GSS is an implementation of the Generic Security Service Application Program Interface (GSS-API). GSS-API is used by network servers to provide security services, e.g., to authenticate SMTP/IMAP clients against SMTP/IMAP servers. GSS consists of a library and a manual. GSS is developed for the GNU/Linux system, but runs on over 20 platforms including most major Unix platforms and Windows, and many kind of devices including iPAQ handhelds and S/390 mainframes.

GnuTLS is a secure communications library implementing the SSL, TLS and DTLS 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 #12, OpenPGP and other required structures. It is aimed to be portable and efficient with focus on security and interoperability.

SASL is a framework for application protocols, such as SMTP or IMAP, to add authentication support. For example, SASL is used to prove to the server who you are when you access an IMAP server to read your e-mail.

Shishi is an implementation of the Kerberos 5 network authentication system, as specified in RFC 4120. Shishi can be used to authenticate users in distributed systems. Shishi contains a library ('libshishi') that can be used by application developers to add support for Kerberos 5. Shishi contains a command line utility ('shishi') that is used by users to acquire and manage tickets (and more). The server side, a Key Distribution Center, is implemented by 'shishid'. Of course, a manual documenting usage aspects as well as the programming API is included. Shishi currently supports AS/TGS...