ibreswan is a free software implementation of the most widely supported and standarized VPN protocol based on ("IPsec") and the Internet Key Exchange ("IKE"). These standards are produced and maintained by the Internet Engineering Task Force ("IETF"). Libreswan has been under active development for over 15 years, going back to The FreeS/WAN Project founded in 1997 by John Gilmore and Hugh Daniel. For more information, see the project's History. Libreswan supports IKE versions 1 and 2. It runs on Linux 2.4 to 4.x, FreeBSD and Apple OSX. On Linux, it can use the built-in IPsec stack ("XFRM/NETKEY") or its own IPsec stack ("KLIPS"). It uses the NSS crypto library. See the Supported Features.