.\" $OpenBSD: ipsec.4,v 1.5 1998/03/05 09:30:59 provos Exp $
.\" Copyright 1997 Niels Provos <provos@physnet.uni-hamburg.de>
.\" All rights reserved.
.\"
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.\"      This product includes software developed by Niels Provos.
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.\" Manual page, using -mandoc macros
.\"
.Dd September 5, 1997
.Dt IPSEC 4
.Os
.Sh NAME
.Nm ipsec
.Nd IP Security Protocol
.Sh SYNOPSIS
.Fd #include <net/encap.h>
.Fd #include <netinet/ip_ipsp.h>
.Fd #include <netinet/ip_esp.h>
.Fd #include <netinet/ip_ah.h>
.Ft int
.Fn socket AF_ENCAP SOCK_RAW AF_UNSPEC
.Sh DESCRIPTION
.Tn IPSec is a pair of protocols, 
.Nm ESP 
(for Encapsulting Security
Payload) and 
.Nm AH 
(for Authentication Header), which provide
security services for IP datagrams. Specifically, 
.Nm ESP 
provides
confidentiality, connectionless
integrity, anti-replay service and limited traffic flow
confidentiality. It optionally provides data origin authentication.
.Nm AH 
provides connectionless integrity, data
origin authentication and anti-replay service.
.Pp
This is done by inserting the appropriate header 
.Nm ( ESP 
or 
.Nm AH )
between the IP header and the payload. The inserted header,
along with the IP header destination address, provide enough
information to find the relevant state in the kernel (security
association) and handle the packet appropriately (decrypt, 
authenticate etc.)
.Pp
An SA (Security Association) is uniquely defined by the
.Nm SPI
(Security Parameter Index), which is a 32-bit integer, 
the remote IP address and the security protocol.
.Pp
The payload can be any of the usual IP protocols (TCP, UDP, ICMP
etc.) or IP itself, for those situations where IP tunneling is
required.
.Pp
This implementation makes use of a virtual interface 
.Nm enc0 ,
which can be used in packet filters to specify those
packets that have been successfully processed by IPSec.
.Pp
Security Associations can be set up manually with
the
.Xr ipsecadm 1
utility or the
.Xr photurisd 8
key management daemon.
.Sh BUGS
There's a lot more to be said on this subject. This is just a beginning.
.Sh SEE ALSO
.Xr ip 4 ,
.Xr intro 4 ,
.Xr inet 4 ,
.Xr tcp 4 ,
.Xr udp 4 ,
.Xr icmp 4 ,
.Xr ipsecadm 1 ,
.Xr rt 1 ,
.Xr rtdelete 1 ,
.Xr photurisd 8 .
.Sh ACKNOWLEDGMENTS
The authors of this code are John Ioannidis, Angelos D.
Keromytis and Niels Provos.
.Pp
Eric Young's libdeslite was used in this implementation for the
DES algorithm.
.Pp
Steve Reid's SHA-1 code was also used.
.Sh HISTORY
The IPsec protocol started in 1992, by John Ioannidis, Phil Karn 
and William Allen Simpson. In 1995, the former wrote an
implementation for BSD/OS. Angelos D. Keromytis ported it to
OpenBSD and NetBSD. The latest transforms and new features were
implemented by Angelos D. Keromytis and Niels Provos.