GnuTLS (GNU Transport Layer Security Library ) is a free implementation of SSL, TLS and DTLS protocols for setting up encrypted network connections.

GnuTLS provides similar functionality to OpenSSL, but is licensed under GPL or LGPL and can thus unlike OpenSSL on systems where OpenSSL does not belong to the normal distribution entirety without further u in GPL - licensed software like Gnome, Exim, Lynx. etc. are involved.

In addition to the most implemented in OpenSSL functions support GnuTLS TLSv1.1, TLSv1.2, zlib compression, authentication, Secure Remote Protocol (SRP ), X.509 and OpenPGP keys. With GnuTLS the command line program gnutls - cli, gnutls -serv, the utility and troubleshooting the TLS / SSL connections, the application program gnutls -cli -debug is set up.