.\"	$OpenBSD: ipsec.conf.5,v 1.16 2005/08/11 09:26:27 hshoexer Exp $
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.\" Copyright (c) 2004 Mathieu Sauve-Frankel  All rights reserved.
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.Dd April 9, 2005
.Dt IPSEC.CONF 5
.Os
.Sh NAME
.Nm ipsec.conf
.Nd IPsec configuration file
.Sh DESCRIPTION
The
.Xr ipsec 4
protocol suite provides security services for IP according to rules or
definitions specified in
.Nm .
.Sh FLOWS
IPsec uses
.Em flows
to determine whether to apply security services to an IP packet or not.
The following security services 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.
.It Ic flow ah
AH provides authentication, integrity, and replay protection, but no
confidentiality.
.El
.Pp
For details on ESP and AH see
.Xr ipsec 4 .
When no service is specified,
.Xr ipsecctl 8
will use ESP.
The settings for the security services have to be negotiated by
.Xr isakmpd 8 .
As soon as a packet matches a flow,
.Xr isakmpd 8
automatically starts the negotiation.
See
.Xr isakmpd 8
for details.
.Pp
Parameters specify the packets to which a flow applies.
Some parameters are optional.
.Bl -tag -width xxxx
.It Ar in No or Ar out
This rule applies to incoming or outgoing packets.
If neither
.Ar in
nor
.Ar out
are specified,
.Xr ipsecctl 8
will assume the direction
.Ar out
for this rule and will construct a proper
.Ar in
rule.
Thus packets in both directions will be matched.
.It Xo
.Ar from
.Aq Ar src
.Ar to
.Aq Ar dst
.Ar peer
.Aq Ar remote
.Xc
This rule applies for packets with source address
.Aq Ar src
and destination address
.Aq Ar dst .
All addresses are specified in CIDR notation.
The
.Ar peer
parameter specifies the address of the remote endpoint of this particular
flow.
For host-to-host connections where
.Aq Ar dst
is identical to
.Aq Ar remote ,
the
.Ar peer
specification can be left out.
.El
.Sh IPSEC SAs
The security parameters for a
.Ar flow
are stored in the Security Association Database
(SADB).
The following rules enter SAs in the SADB:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It Ic esp
Enter an ESP SA.
.It Ic ah
Enter an AH SA.
.El
.Pp
Parameters specify the peers, Security Parameter Index (SPI),
cryptographic transforms, and key material to be used.
.Bl -tag -width xxxx
.It Xo
.Ar from
.Aq Ar src
.Ar to
.Aq Ar dst
.Xc
This SA is for a
.Ar flow
between the peers
.Aq Ar src
and
.Aq Ar dst .
.It Xo
.Ar spi
.Aq Ar number
.Xc
The SPI identifies a specific SA.
.Ar number
is a 32-bit value and needs to be unique.
.It Xo
.Ar auth
.Aq Ar algorithm
.Xc
For both
.Ar esp
and
.Ar ah
an authentication algorithm can be specified.
Possible algorithms are
.Ar hmac-md5 ,
.Ar hmac-ripemd160 ,
.Ar hmac-sha1 ,
.Ar hmac-sha2-256 ,
.Ar hmac-sha2-384 ,
.Ar hmc-sha2-512 ,
.Ar md5 ,
and
.Ar sha1 .
.Pp
If no algorithm is specified,
.Xr ipsecctl 8
will choose
.Ar hmac-sha2-256
by default.
.It Xo
.Ar enc
.Aq Ar algorithm
.Xc
For
.Ar esp
an encryption algorithm needs to be specified.
Possible algorithms are
.Ar 3des-cbc ,
.Ar des-cbc ,
.Ar aes ,
.Ar aesctr ,
.Ar blowfish ,
.Ar cast128 ,
.Ar null ,
and
.Ar skipjack .
.Pp
If no alogrithm is specified,
.Xr ipsecctl 8
will choose
.Ar aesctr
by default.
.It Xo
.Ar authkey
.Aq Ar keyspec
.Xc
.Ar keyspec
defines the authentication key to be used.
It is either a hexadecimal string or a file specified as follows:
.Bd -literal -offset -indent
authkey file "filename"
.Ed
.It Xo
.Ar enckey
.Aq Ar keyspec
.Xc
The encryption key is defined similar to
.Ar authkey .
.El
.Pp
It is very important that keys are not guessable.
One practical way of generating 160-bit (20-byte) keys is a follows:
.Bd -literal -offset indent
$ openssl rand 20 | hexdump -e '20/1 "%02x"'
.Ed
.Pp
For
.Ar spi ,
.Ar authkey ,
and
.Ar enckey ,
it is possible to specify two colon separated values.
.Xr ipsecctl 8
will then generate the matching incoming SA using the second values for
.Ar spi ,
.Ar authkey ,
and
.Ar enckey .
.Sh TCP MD5 SIGNATURES
RFC 2385 describes a mechanism to protect
.Xr tcp 4
sessions using MD5.
A Security Association (SA) for TCP MD5 signatures is set up using the
following rule:
.Bl -tag -width xxxx
.It Xo
.Ar tcpmd5
.Ar from
.Aq Ar src
.Ar to
.Aq Ar dst
.Ar spi
.Aq Ar number
.Ar authkey
.Aq Ar keyspec
.Xc
This rule applies for packets with source address
.Aq Ar src
and destination address
.Aq Ar dst .
All addresses are specified in CIDR notation.
The parameter
.Ar spi
is a 32-bit value defining the Security Parameter Index (SPI) for this SA.
.Pp
The authentication key to be used is a hexadecimal string of arbitrary length.
It is also possible to read the key from a file using this format:
.Bd -literal -offset -indent
authkey file "filename"
.Ed
.Pp
It is very important that the key is not guessable.
One practical way of generating 160-bit (20-byte) keys is as follows:
.Bd -literal -offset indent
$ openssl rand 20 | hexdump -e '20/1 "%02x"'
.Ed
.Pp
For both
.Ar spi
and
.Ar authkey
it is possible to specify two values separated by a colon.
.Xr ipsecctl 8
will then generate the matching incoming SA using the second values for
.Ar spi
and
.Ar authkey .
.El
.Pp
For details on how to enable TCP MD5 signatures see
.Xr tcp 4 .
.Sh EXAMPLES
.Bd -literal
# Host-to-host
flow esp from 192.168.3.14 to 192.168.3.100

# Same as above, but explicitly specifying "in" and "out" rules
flow esp out from 192.168.3.14  to 192.168.3.100
flow esp in  from 192.168.3.100 to 192.168.3.14

# Net-to-net
flow esp from 192.168.7.0/24 to 192.168.8.0/24 peer 192.168.3.12

# Same as above, but explicitly specifying "in" and "out" rules
flow esp out from 192.168.7.0/24 to 192.168.8.0/24 peer 192.168.3.12
flow esp in  from 192.168.8.0/24 to 192.168.7.0/24 peer 192.168.3.12

# Set up IPsec SAs for a 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
	auth hmac-sha2-256 enc aesctr authkey file "auth14:auth12" \e
	enckey file "enc14:enc12"

# Set up keys for TCP MD5 signatures
tcpmd5 from 192.168.3.14 to 192.168.3.27 spi 0x1000:0x1001 \e
	authkey 0xdeadbeef:0xbeefdead

# Set up keys for TCP MD5 signatures, read keys from files
tcpmd5 from 192.168.3.14 to 192.168.3.27 spi 0x1000:0x1001 \e
	authkey file "/path/to/key1:/path/to/key2"
.Ed
.Sh SEE ALSO
.Xr ipsec 4 ,
.Xr tcp 4 ,
.Xr isakmpd.conf 5 ,
.Xr ipsecctl 8 ,
.Xr isakmpd 8
.Sh HISTORY
The
.Nm
file format first appeared in
.Ox 3.8 .