.\" $OpenBSD: ipsec.conf.5,v 1.129 2010/09/23 11:43:51 mikeb Exp $ .\" .\" Copyright (c) 2004 Mathieu Sauve-Frankel All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: September 23 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 with the ISAKMP/Oakley a.k.a. IKEv1 protocol. To configure automatic keying using the IKEv2 protocol, see .Xr iked.conf 5 instead. 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 IKEv1 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 .Op Pq Ar srcnat .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 IKEv1 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 aes-128-gcm Ta "160 bits" Ta "[phase 2 only]" .It Li aes-192-gcm Ta "224 bits" Ta "[phase 2 only]" .It Li aes-256-gcm Ta "288 bits" Ta "[phase 2 only]" .It Li aes-128-gmac Ta "160 bits" Ta "[phase 2 only]" .It Li aes-192-gmac Ta "224 bits" Ta "[phase 2 only]" .It Li aes-256-gmac Ta "288 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. The same applies to AES-GCM and AES-GMAC. .Pp Using AES-GMAC or 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 .