.\"	$OpenBSD: ipsec.conf.5,v 1.124 2010/01/02 20:15:15 schwarze Exp $
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.\" Copyright (c) 2004 Mathieu Sauve-Frankel  All rights reserved.
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.Dd $Mdocdate: January 2 2010 $
.Dt IPSEC.CONF 5
.Os
.Sh NAME
.Nm ipsec.conf
.Nd IPsec configuration file
.Sh DESCRIPTION
The
.Nm
file specifies rules and definitions for IPsec,
which provides security services for IP datagrams.
IPsec itself is a pair of protocols:
Encapsulating Security Payload (ESP),
which provides integrity and confidentiality;
and Authentication Header (AH),
which provides integrity.
The IPsec protocol itself is described in
.Xr ipsec 4 .
.Pp
In its most basic form, a
.Em flow
is established between hosts and/or networks,
and then Security Associations
.Pq Em SA
are established,
which detail how the desired protection will be achieved.
IPsec uses flows
to determine whether to apply security services to an IP packet or not.
.Pp
Generally speaking
an automated keying daemon,
such as
.Xr isakmpd 8 ,
is used to set up flows and establish SAs,
by specifying an
.Sq ike
line in
.Nm
(see
.Sx AUTOMATIC KEYING ,
below).
An authentication method,
such as public key authentication,
will also have to be set up:
see the
.Sx PKI
section of
.Xr isakmpd 8
for information on the types of authentication available,
and the procedures for setting them up.
.Pp
The keying daemon,
.Xr isakmpd 8 ,
can be enabled to run at boot time via the
.Va isakmpd_flags
variable in
.Xr rc.conf.local 8 .
Note that it will probably need to be run with at least the
.Fl K
option, to avoid
.Xr keynote 4
policy checking.
The
.Nm
configuration itself is loaded at boot time
if the variable
.Va ipsec
is set to
.Dv YES
in
.Xr rc.conf.local 8 .
A utility called
.Xr ipsecctl 8
is also available to load
.Nm
configurations, and can additionally be used
to view and modify IPsec flows.
.Pp
An alternative method of setting up SAs is also possible using
manual keying.
Manual keying is not recommended,
but can be convenient for quick setups and testing.
Those procedures are documented within this page.
.Sh IPSEC.CONF FILE FORMAT
Lines beginning with
.Sq #
and empty lines are regarded as comments,
and ignored.
Lines may be split using the
.Sq \e
character.
.Pp
Addresses can be specified in CIDR notation (matching netblocks),
as symbolic host names, interface names, or interface group names.
.Pp
Certain parameters can be expressed as lists, in which case
.Xr ipsecctl 8
generates all the necessary combinations.
For example:
.Bd -literal -offset indent
ike esp from {192.168.1.1, 192.168.1.2} to \e
	{10.0.0.17, 10.0.0.18} peer 192.168.10.1
.Ed
.Pp
Will expand to:
.Bd -literal -offset indent
ike esp from 192.168.1.1 to 10.0.0.17 peer 192.168.10.1
ike esp from 192.168.1.1 to 10.0.0.18 peer 192.168.10.1
ike esp from 192.168.1.2 to 10.0.0.17 peer 192.168.10.1
ike esp from 192.168.1.2 to 10.0.0.18 peer 192.168.10.1
.Ed
.Pp
Macros can be defined that will later be expanded in context.
Macro names must start with a letter, and may contain letters, digits
and underscores.
Macro names may not be reserved words (for example
.Ic flow ,
.Ic from ,
.Ic esp ) .
Macros are not expanded inside quotes.
.Pp
For example:
.Bd -literal -offset indent
remote_gw = "192.168.3.12"
flow esp from 192.168.7.0/24 to 192.168.8.0/24 peer $remote_gw
.Ed
.Pp
Additional configuration files can be included with the
.Ic include
keyword, for example:
.Bd -literal -offset indent
include "/etc/macros.conf"
.Ed
.Sh AUTOMATIC KEYING
In this scenario,
.Nm
is used to set up flows and SAs automatically using
.Xr isakmpd 8 .
Some examples of setting up automatic keying:
.Bd -literal -offset 3n
# Set up a VPN:
# First between the gateway machines 192.168.3.1 and 192.168.3.2
# Second between the networks 10.1.1.0/24 and 10.1.2.0/24
ike esp from 192.168.3.1 to 192.168.3.2
ike esp from 10.1.1.0/24 to 10.1.2.0/24 peer 192.168.3.2
.Ed
.Pp
The commands are as follows:
.Bl -tag -width xxxx
.It Xo
.Ic ike
.Op Ar mode
.Op Ar encap
.Op Ar tmode
.Xc
.Ar mode
specifies the IKE mode to use:
one of
.Ar passive ,
.Ar active ,
or
.Ar dynamic .
When
.Ar passive
is specified,
.Xr isakmpd 8
will not immediately start negotiation of this tunnel, but wait for an incoming
request from the remote peer.
When
.Ar active
or
.Ar dynamic
is specified, negotiation will be started at once.
The
.Ar dynamic
mode will additionally enable Dead Peer Detection (DPD) and use the
local hostname as the identity of the local peer, if not specified by
the
.Ic srcid
parameter.
.Ar dynamic
mode should be used for hosts with dynamic IP addresses like road
warriors or dialup hosts.
If omitted,
.Ar active
mode will be used.
.Pp
.Ar encap
specifies the encapsulation protocol to be used.
Possible protocols are
.Ar esp
and
.Ar ah ;
the default is
.Ar esp .
.Pp
.Ar tmode
describes the encapsulation mode to be used.
Possible modes are
.Ar tunnel
and
.Ar transport ;
the default is
.Ar tunnel .
.It Ic proto Ar protocol
The optional
.Ic proto
parameter restricts the flow to a specific IP protocol.
Common protocols are
.Xr icmp 4 ,
.Xr tcp 4 ,
and
.Xr udp 4 .
For a list of all the protocol name to number mappings used by
.Xr ipsecctl 8 ,
see the file
.Pa /etc/protocols .
.It Xo
.Ic from Ar src
.Op Ic port Ar sport
.Oo ( Ar srcnat ) Oc
.Ic to Ar dst
.Op Ic port Ar dport
.Xc
This rule applies for packets with source address
.Ar src
and destination address
.Ar dst .
The keyword
.Ar any
will match any address (i.e. 0.0.0.0/0).
If the
.Ar src
argument specifies a fictional source ID,
the
.Ar srcnat
parameter can be used to specify the actual source address.
This can be used in outgoing NAT/BINAT scenarios as described below.
Host addresses are parsed as type
.Dq IPV4_ADDR ;
adding the suffix /32 will change the type to
.Dq IPV4_ADDR_SUBNET ,
which can improve interoperability with some IKE implementations.
.Pp
The optional
.Ic port
modifiers restrict the flows to the specified ports.
They are only valid in conjunction with the
.Xr tcp 4
and
.Xr udp 4
protocols.
Ports can be specified by number or by name.
For a list of all port name to number mappings used by
.Xr ipsecctl 8 ,
see the file
.Pa /etc/services .
.It Ic local Ar localip Ic peer Ar remote
The
.Ic local
parameter specifies the address or FQDN of the local endpoint.
Unless we are multi-homed or have aliases,
this option is generally not needed.
.Pp
The
.Ic peer
parameter specifies the address or FQDN of the remote endpoint.
For host-to-host connections where
.Ar dst
is identical to
.Ar remote ,
this option is generally not needed as it will be set to
.Ar dst
automatically.
If it is not specified or if the keyword
.Ar any
is given, the default peer is used.
.It Xo
.Ar mode
.Ic auth Ar algorithm
.Ic enc Ar algorithm
.Ic group Ar group
.Xc
These parameters define the mode and cryptographic transforms to be
used for the phase 1 negotiation.
During phase 1
the machines authenticate and set up an encrypted channel.
.Pp
The mode can be either
.Ar main ,
which specifies main mode, or
.Ar aggressive ,
which specifies aggressive mode.
Possible values for
.Ic auth ,
.Ic enc ,
and
.Ic group
are described below in
.Sx CRYPTO TRANSFORMS .
.Pp
If omitted,
.Xr ipsecctl 8
will use the default values
.Ar main ,
.Ar hmac-sha1 ,
.Ar aes ,
and
.Ar modp1024 .
.It Xo
.Ic quick auth Ar algorithm
.Ic enc Ar algorithm
.Ic group Ar group
.Xc
These parameters define the cryptographic transforms to be used for
the phase 2 negotiation.
During phase 2
the actual IPsec negotiations happen.
.Pp
Possible values for
.Ic auth ,
.Ic enc ,
and
.Ic group
are described below in
.Sx CRYPTO TRANSFORMS .
If
.Ic group
is specified,
Perfect Forward Security (PFS) is used.
If the value
.Ar none
is used, PFS is disabled.
.Pp
If omitted,
.Xr ipsecctl 8
will use the default values
.Ar hmac-sha2-256
and
.Ar aes ;
PFS will only be used if the remote side requests it.
.It Ic srcid Ar string Ic dstid Ar string
.Ic srcid
defines an ID of type
.Dq USER_FQDN
or
.Dq FQDN
that will be used by
.Xr isakmpd 8
as the identity of the local peer.
If the argument is an email address (bob@example.com),
.Xr ipsecctl 8
will use USER_FQDN as the ID type.
Anything else is considered to be an FQDN.
If
.Ic srcid
is omitted,
the default is to use the IP address of the connecting machine.
.Pp
.Ic dstid
is similar to
.Ic srcid ,
but instead specifies the ID to be used
by the remote peer.
.It Ic psk Ar string
Use a pre-shared key
.Ar string
for authentication.
If this option is not specified,
public key authentication is used (see
.Xr isakmpd 8 ) .
.It Ic tag Ar string
Add a
.Xr pf 4
tag to all packets of phase 2 SAs created for this connection.
This will allow matching packets for this connection by defining
rules in
.Xr pf.conf 5
using the
.Cm tagged
keyword.
.Pp
The following variables can be used in tags to include information
from the remote peer on runtime:
.Pp
.Bl -tag -width $domain -compact -offset indent
.It Ar $id
The remote phase 1 ID.
It will be expanded to
.Ar id-type/id-value ,
e.g.\&
.Ar fqdn/foo.bar.org .
.It Ar $domain
Extract the domain from IDs of type FQDN or UFQDN.
.El
.Pp
For example, if the ID is
.Ar fqdn/foo.bar.org
or
.Ar ufqdn/user@bar.org ,
.Dq ipsec-$domain
expands to
.Dq ipsec-bar.org .
The variable expansion for the
.Ar tag
directive occurs only at runtime, not during configuration file parse time.
.El
.Sh PACKET FILTERING
IPsec traffic appears unencrypted on the
.Xr enc 4
interface
and can be filtered accordingly using the
.Ox
packet filter,
.Xr pf 4 .
The grammar for the packet filter is described in
.Xr pf.conf 5 .
.Pp
The following components are relevant to filtering IPsec traffic:
.Bl -ohang -offset indent
.It external interface
Interface for ISAKMP traffic and encapsulated IPsec traffic.
.It proto udp port 500
ISAKMP traffic on the external interface.
.It proto udp port 4500
ISAKMP NAT-Traversal traffic on the external interface.
.It proto ah \*(Ba esp
Encapsulated IPsec traffic
on the external interface.
.It enc0
Interface for outgoing traffic before it's been encapsulated,
and incoming traffic after it's been decapsulated.
State on this interface should be interface bound;
see
.Xr enc 4
for further information.
.It proto ipencap
[tunnel mode only]
IP-in-IP traffic flowing between gateways
on the enc0 interface.
.It tagged ipsec-example.org
Match traffic of phase 2 SAs using the
.Ic tag
keyword.
.El
.Pp
If the filtering rules specify to block everything by default,
the following rule
would ensure that IPsec traffic never hits the packet filtering engine,
and is therefore passed:
.Bd -literal -offset indent
set skip on enc0
.Ed
.Pp
In the following example, all traffic is blocked by default.
IPsec-related traffic from gateways {192.168.3.1, 192.168.3.2} and
networks {10.0.1.0/24, 10.0.2.0/24} is permitted.
.Bd -literal -offset indent
block on sk0
block on enc0

pass  in on sk0 proto udp from 192.168.3.2 to 192.168.3.1 \e
	port {500, 4500}
pass out on sk0 proto udp from 192.168.3.1 to 192.168.3.2 \e
	port {500, 4500}

pass  in on sk0 proto esp from 192.168.3.2 to 192.168.3.1
pass out on sk0 proto esp from 192.168.3.1 to 192.168.3.2

pass  in on enc0 proto ipencap from 192.168.3.2 to 192.168.3.1 \e
	keep state (if-bound)
pass out on enc0 proto ipencap from 192.168.3.1 to 192.168.3.2 \e
	keep state (if-bound)
pass  in on enc0 from 10.0.2.0/24 to 10.0.1.0/24 \e
	keep state (if-bound)
pass out on enc0 from 10.0.1.0/24 to 10.0.2.0/24 \e
	keep state (if-bound)
.Ed
.Pp
.Xr pf 4
has the ability to filter IPsec-related packets
based on an arbitrary
.Em tag
specified within a ruleset.
The tag is used as an internal marker
which can be used to identify the packets later on.
This could be helpful,
for example,
in scenarios where users are connecting in from differing IP addresses,
or to support queue-based bandwidth control,
since the enc0 interface does not support it.
.Pp
The following
.Xr pf.conf 5
fragment uses queues for all IPsec traffic with special
handling for developers and employees:
.Bd -literal -offset indent
altq on sk0 cbq bandwidth 1000Mb \e
	queue { deflt, developers, employees, ipsec }
    queue deflt bandwidth 10% priority 0 cbq(default ecn)
    queue developers bandwidth 75% priority 7 cbq(borrow red)
    queue employees bandwidth 5% cbq(red)
    queue ipsec bandwidth 10% cbq(red)

pass out on sk0 proto esp queue ipsec

pass out on sk0 tagged ipsec-developers.bar.org queue developers
pass out on sk0 tagged ipsec-employees.bar.org queue employees
.Ed
.Pp
The tags will be assigned by the following
.Nm
example:
.Bd -literal -offset indent
ike esp from 10.1.1.0/24 to 10.1.2.0/24 peer 192.168.3.2 \e
	tag ipsec-$domain
.Ed
.Sh OUTGOING NETWORK ADDRESS TRANSLATION
In some network topologies it is desirable to perform NAT on traffic leaving
through the VPN tunnel.
In order to achieve that,
the
.Ar src
argument is used to negotiate the desired network ID with the peer
and the
.Ar srcnat
parameter defines the true local subnet,
so that a correct SA can be installed on the local side.
.Pp
For example,
if the local subnet is 192.168.1.0/24 and all the traffic
for a specific VPN peer should appear as coming from 10.10.10.1,
the following configuration is used:
.Bd -literal -offset indent
ike esp from 10.10.10.1 (192.168.1.0/24) to 192.168.2.0/24 \e
	peer 10.10.20.1
.Ed
.Pp
Naturally,
a relevant NAT rule is required in
.Xr pf.conf 5 .
For the example above,
this would be:
.Bd -literal -offset indent
match on enc0 from 192.168.1.0/24 to 192.168.2.0/24 nat-to 10.10.10.1
.Ed
.Pp
From the peer's point of view,
the local end of the VPN tunnel is declared to be 10.10.10.1
and all the traffic arrives with that source address.
.Sh CRYPTO TRANSFORMS
It is very important that keys are not guessable.
One practical way of generating keys is to use
.Xr openssl 1 .
The following generates a 160-bit (20-byte) key:
.Bd -literal -offset indent
$ openssl rand 20 | hexdump -e '20/1 "%02x"'
.Ed
.Pp
The following authentication types are permitted with the
.Ic auth
keyword:
.Pp
.Bl -column "authenticationXX" "Key Length" -offset indent -compact
.It Em Authentication	Key Length
.It Li hmac-md5 Ta "128 bits"
.It Li hmac-ripemd160 Ta "160 bits" Ta "[phase 2 only]"
.It Li hmac-sha1 Ta "160 bits"
.It Li hmac-sha2-256 Ta "256 bits"
.It Li hmac-sha2-384 Ta "384 bits"
.It Li hmac-sha2-512 Ta "512 bits"
.El
.Pp
The following cipher types are permitted with the
.Ic enc
keyword:
.Pp
.Bl -column "authenticationXX" "Key Length" -offset indent -compact
.It Em Cipher	Key Length
.It Li des Ta "56 bits"
.It Li 3des Ta "168 bits"
.It Li aes Ta "128 bits"
.It Li aes-128 Ta "128 bits"
.It Li aes-192 Ta "192 bits"
.It Li aes-256 Ta "256 bits"
.It Li aesctr Ta "160 bits" Ta "[phase 2 only]"
.It Li blowfish Ta "160 bits"
.It Li cast Ta "128 bits"
.It Li skipjack Ta "80 bits"
.It Li null Ta "(none)" Ta "[phase 2 only]"
.El
.Pp
Use of DES or Skipjack as an encryption algorithm is not recommended
(except for backwards compatibility) due to their short key length.
Furthermore, attacks on Skipjack have shown severe weaknesses
in its structure.
.Pp
DES requires 8 bytes to form a 56-bit key and 3DES requires 24 bytes
to form its 168-bit key.
This is because the most significant bit of each byte is used for parity.
.Pp
The keysize of AES-CTR is actually 128-bit.
However as well as the key, a 32-bit nonce has to be supplied.
Thus 160 bits of key material have to be supplied.
.Pp
Using NULL with ESP will only provide authentication.
This is useful in setups where AH can not be used, e.g. when NAT is involved.
.Pp
The following group types are permitted with the
.Ic group
keyword:
.Pp
.Bl -column "authenticationXX" "Key Length" -offset indent -compact
.It Em Group	Size
.It Li modp768  Ta 768 Ta [DH group 1]
.It Li modp1024 Ta 1024 Ta [DH group 2]
.It Li modp1536 Ta 1536 Ta [DH group 5]
.It Li modp2048 Ta 2048 Ta [DH group 14]
.It Li modp3072 Ta 3072 Ta [DH group 15]
.It Li modp4096 Ta 4096 Ta [DH group 16]
.It Li modp6144 Ta 6144 Ta [DH group 17]
.It Li modp8192 Ta 8192 Ta [DH group 18]
.It Li none Ta 0 Ta [phase 2 only]
.El
.Sh MANUAL FLOWS
In this scenario,
.Nm
is used to set up flows manually.
IPsec uses flows
to determine whether to apply security services to an IP packet or not.
Some examples of setting up flows:
.Bd -literal -offset 3n
# Set up two flows:
# First between the machines 192.168.3.14 and 192.168.3.100
# Second between the networks 192.168.7.0/24 and 192.168.8.0/24
flow esp from 192.168.3.14 to 192.168.3.100
flow esp from 192.168.7.0/24 to 192.168.8.0/24 peer 192.168.3.12
.Ed
.Pp
The following types of flow are available:
.Bl -tag -width xxxx
.It Ic flow esp
ESP can provide the following properties:
authentication, integrity, replay protection, and confidentiality of the data.
If no flow type is specified,
this is the default.
.It Ic flow ah
AH provides authentication, integrity, and replay protection, but not
confidentiality.
.It Ic flow ipip
IPIP does not provide authentication, integrity, replay protection, or
confidentiality.
However, it does allow tunnelling of IP traffic over IP, without setting up
.Xr gif 4
interfaces.
.El
.Pp
The commands are as follows:
.Bl -tag -width xxxx
.It Ic in No or Ic out
This rule applies to incoming or outgoing packets.
If neither
.Ic in
nor
.Ic out
are specified,
.Xr ipsecctl 8
will assume the direction
.Ic out
for this rule and will construct a proper
.Ic in
rule.
Thus packets in both directions will be matched.
.It Ic proto Ar protocol
The optional
.Ic proto
parameter restricts the flow to a specific IP protocol.
Common protocols are
.Xr icmp 4 ,
.Xr tcp 4 ,
and
.Xr udp 4 .
For a list of all the protocol name to number mappings used by
.Xr ipsecctl 8 ,
see the file
.Pa /etc/protocols .
.It Xo
.Ic from Ar src
.Op Ic port Ar sport
.Ic to Ar dst
.Op Ic port Ar dport
.Xc
This rule applies for packets with source address
.Ar src
and destination address
.Ar dst .
The keyword
.Ar any
will match any address (i.e. 0.0.0.0/0).
The optional
.Ic port
modifiers restrict the flows to the specified ports.
They are only valid in conjunction with the
.Xr tcp 4
and
.Xr udp 4
protocols.
Ports can be specified by number or by name.
For a list of all port name to number mappings used by
.Xr ipsecctl 8 ,
see the file
.Pa /etc/services .
.It Ic local Ar localip
The
.Ic local
parameter specifies the address or FQDN of the local endpoint of this
flow and can be usually left out.
.It Ic peer Ar remote
The
.Ic peer
parameter specifies the address or FQDN of the remote endpoint of this
flow.
For host-to-host connections where
.Ar dst
is identical to
.Ar remote ,
the
.Ic peer
specification can be left out as it will be set to
.Ar dst
automatically.
Only if the keyword
.Ar any
is given is a flow without peer created.
.It Ic type Ar modifier
This optional parameter sets up special flows using modifiers.
By default,
.Xr ipsecctl 8
will automatically set up normal flows with the corresponding type.
.Ar modifier
may be one of the following:
.Pp
.Bl -tag -width "acquireXX" -offset indent -compact
.It acquire
Use IPsec and establish SAs dynamically.
Unencrypted traffic is permitted until it is protected by IPsec.
.It bypass
Matching packets are not processed by IPsec.
.It deny
Matching packets are dropped.
.It dontacq
Use IPsec.
If no SAs are available,
does not trigger
.Xr isakmpd 8 .
.It require
Use IPsec and establish SAs dynamically.
Unencrypted traffic is not permitted until it is protected by IPsec.
.It use
Use IPsec.
Unencrypted traffic is permitted.
Does not trigger
.Xr isakmpd 8 .
.El
.El
.Sh MANUAL SECURITY ASSOCIATIONS (SAs)
In this scenario,
.Nm
is used to set up SAs manually.
The security parameters for a flow
are stored in the Security Association Database (SADB).
An example of setting up an SA:
.Bd -literal -offset 3n
# Set up an IPsec SA for flows between 192.168.3.14 and 192.168.3.12
esp from 192.168.3.14 to 192.168.3.12 spi 0xdeadbeef:0xbeefdead \e
	authkey file "auth14:auth12" enckey file "enc14:enc12"
.Ed
.Pp
Parameters specify the peers, Security Parameter Index (SPI),
cryptographic transforms, and key material to be used.
The following rules enter SAs in the SADB:
.Pp
.Bl -tag -width "tcpmd5XX" -offset indent -compact
.It Ic esp
Enter an ESP SA.
.It Ic ah
Enter an AH SA.
.\".It Ic ipcomp
.\"Enter an IPCOMP SA.
.It Ic ipip
Enter an IPIP pseudo SA.
.It Ic tcpmd5
Enter a TCP MD5 SA.
.El
.Pp
The commands are as follows:
.Bl -tag -width xxxx
.It Ar mode
For ESP and AH
.\".Ic ipcomp
the encapsulation mode can be specified.
Possible modes are
.Ar tunnel
and
.Ar transport .
When left out,
.Ar tunnel
is chosen.
For details on modes see
.Xr ipsec 4 .
.It Ic from Ar src Ic to Ar dst
This SA is for a
.Ar flow
between the peers
.Ar src
and
.Ar dst .
.It Ic spi Ar number
The SPI identifies a specific SA.
.Ar number
is a 32-bit value and needs to be unique.
.It Ic auth Ar algorithm
For ESP and AH
an authentication algorithm can be specified.
Possible values
are described above in
.Sx CRYPTO TRANSFORMS .
.Pp
If no algorithm is specified,
.Xr ipsecctl 8
will choose
.Ar hmac-sha2-256
by default.
.\".It Xo
.\".Ic comp
.\".Aq Ar algorithm
.\".Xc
.\"The compression algorithm to be used.
.\"Possible algorithms are
.\".Ar deflate
.\"and
.\".Ar lzs .
.\"Note that
.\".Ar lzs
.\"is only available with
.\".Xr hifn 4
.\"because of the patent held by Hifn, Inc.
.It Ic enc Ar algorithm
For ESP
an encryption algorithm can be specified.
Possible values
are described above in
.Sx CRYPTO TRANSFORMS .
.Pp
If no algorithm is specified,
.Xr ipsecctl 8
will choose
.Ar aes
by default.
.It Ic authkey Ar keyspec
.Ar keyspec
defines the authentication key to be used.
It is either a hexadecimal string or a path to a file containing the key.
The filename may be given as either an absolute path to the file
or a relative pathname,
and is specified as follows:
.Bd -literal -offset indent
authkey file "filename"
.Ed
.It Ic enckey Ar keyspec
The encryption key is defined similarly to
.Ic authkey .
.It Xo
.Ic tcpmd5
.Ic from Ar src
.Ic to Ar dst
.Ic spi Ar number
.Ic authkey Ar keyspec
.Xc
TCP MD5 signatures are generally used between BGP daemons, such as
.Xr bgpd 8 .
Since
.Xr bgpd 8
itself already provides this functionality,
this option is generally not needed.
More information on TCP MD5 signatures can be found in
.Xr tcp 4 ,
.Xr bgpd.conf 5 ,
and RFC 2385.
.Pp
This rule applies for packets with source address
.Ar src
and destination address
.Ar dst .
The parameter
.Ic spi
is a 32-bit value defining the Security Parameter Index (SPI) for this SA.
The encryption key is defined similarly to
.Ic authkey .
.El
.Pp
Since an SA is directional, a second SA is normally configured in the
reverse direction.
This is done by adding a second, colon-separated, value to
.Ic spi ,
.Ic authkey ,
and
.Ic enckey .
.Sh SEE ALSO
.Xr openssl 1 ,
.Xr enc 4 ,
.\".Xr ipcomp 4 ,
.Xr ipsec 4 ,
.Xr tcp 4 ,
.Xr pf.conf 5 ,
.Xr ipsecctl 8 ,
.Xr isakmpd 8
.Sh HISTORY
The
.Nm
file format first appeared in
.Ox 3.8 .