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资源说明：Astaro build for StrongSwan
----------------------------
strongSwan - Configuration
----------------------------
Contents
--------
1. Overview
2. Quickstart
2.1 Site-to-Site case
2.2 Host-to-Host case
2.3 Four Tunnel case
2.4 Four Tunnel case the elegant way with source routing
2.5 Roadwarrior case
2.6 Roadwarrior case with virtual IP
3. Generating X.509 certificates and CRLs with OpenSSL
3.1 Generating a CA certificate
3.2 Generating a host or user certificate
3.3 Generating a CRL
3.4 Revoking a certificate
4. Configuring the connections - ipsec.conf
4.1 Configuring my side
4.2 Multiple certificates
4.3 Configuring the peer side using CA certificates
4.4 Handling Virtual IPs and wildcard subnets
4.5 Protocol and port selectors
4.6 IPsec policies based on wildcards
4.7 IPsec policies based on CA certificates
4.8 Sending certificate requests
4.9 IPsec policies based on group attributes
5. Configuring certificates and CRLs
5.1 Installing CA certificates
5.2 Installing optional Certificate Revocation Lists (CRLs)
5.3 Dynamic update of certificates and CRLs
5.4 Local caching of CRLs
5.5 Online Certificate Status Protocol (OCSP)
5.6 CRL policy
5.7 Configuring the peer side using locally stored certificates
6. Configuring the private keys - ipsec.secrets
6.1 Loading private key files in PKCS#1 format
6.2 Entering passphrases interactively
6.3 Multiple private keys
7. Configuring CA properties - ipsec.conf
8. Smartcard support
8.1 Configuring a smartcard-based connection
8.2 Entering the PIN code
8.3 PIN-pad equipped smartcard readers
8.4 Configuring a smartcard using pkcs15-init
8.5 PKCS#1 proxy functions
9. Configuring the clients
9.1 strongSwan
9.2 PGPnet
9.3 Safenet/Soft-Remote
9.4 SSH Sentinel
9.5 Windows 2000/XP
10. Monitoring functions
11. Firewall support functions
11.1 Environment variables in the updown script
11.2 Automatic insertion and deletion of iptables firewall rules
11.3 Sample Linux 2.6 _updown_espmark script for iptables < 1.3.5
12. Authentication with raw RSA public keys
13. Authentication with OpenPGP certificates
13.1 OpenPGP certificates
13.2 OpenPGP private keys
13.3 Monitoring functions
13.4 Suppression of certificate request messages
14. Additional features
14.1 Authentication and encryption algorithms
14.2 NAT traversal
14.3 Dead peer detection
14.4 IKE Mode Config Pull Mode
14.5 IKE Mode Config Push Mode
14.6 XAUTH - Extended Authentication (NEW)
15. Copyright statement and acknowledgements
1. Overview
--------
strongSwan is an OpenSource IPsec solution for the Linux operating system
and currently supports the following features:
* runs both on Linux 2.4 (KLIPS) and Linux 2.6 (native IPsec) kernels.
* strong 3DES, AES, Serpent, Twofish, or Blowfish encryption.
* Authentication based on X.509 certificates or preshared secrets.
* IPsec policies based on wildcards or intermediate CAs.
* Powerful and flexible IPsec policies based on group attributes.
* Retrieval of Certificate Revocation Lists (CRLs) via HTTP or LDAP.
* Local caching of fetched CRLs
* Full support of the Online Certificate Status Protocol (OCSP, RFC 2560).
* CA management functions including OCSP and CRL URIs and default LDAP server.
* Optional storage of RSA private keys on smartcards or USB crypto tokens
* Standardized PKCS#11 interface with optional proxy functions serving
external applications (disc encryption, etc.).
* NAT-Traversal (RFC 3947)
* Support of Virtual IPs via static configuration and IKE Mode Config
* XAUTH client and server functionality in conjunction with either PSK
or RSA IKE Main Mode authentication.
* Support of Delete SA and informational Notification messages.
* Dead Peer Detection (DPD, RFC 3706)
Compatibility has successfully been tested with peers running the following
IPsec clients:
FreeS/WAN, Openswan, SafeNet/SoftRemote, NCP Secure Entry Client,
SonicWALL Global VPN Client, The GreenBow, Microsoft Windows 2000/XP, etc.
Furthermore, interoperability with the following VPN gateways
has been demonstrated during the IPsec 2001 Conference in Paris:
Cisco IOS Routers, Cisco PIX firewall, Cisco VPN3000,
Nortel Contivity VPN Switch, NetScreen (FreeS/WAN as responder only),
OpenBSD with isakmpd, Netasq, Netcelo, and 6WIND.
Potentially any IPsec implementation with X.509 certificate support can
be made to cooperate with strongSwan. The latest addition has been the successful
interoperability with the Check Point VPN-1 NG gateway.
2. Quickstart
----------
In the following examples we assume for reasons of clarity that left designates
the local host and that right is the remote host. Certificates for users, hosts
and gateways are issued by a ficticious strongSwan CA. How to generate private keys
and certificates using OpenSSL will be explained in section 3. The CA certificate
"strongswanCert.pem" must be present on all VPN end points in order to be able to
authenticate the peers.
2.1 Site-to-site case
-----------------
In this scenario two security gateways moon and sun will connect the
two subnets moon-net and sun-net with each other through a VPN tunnel
set up between the two gateways:
10.1.0.0/16 -- | 192.168.0.1 | === | 192.168.0.2 | -- 10.2.0.0/16
moon-net moon sun sun-net
Configuration on gateway moon:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/moonCert.pem
/etc/ipsec.secrets:
: RSA moonKey.pem ""
/etc/ipsec.conf:
conn net-net
left=%defaultroute
leftsubnet=10.1.0.0/16
leftcert=moonCert.pem
right=192.168.0.2
rightsubnet=10.2.0.0/16
rightid="C=CH, O=Linux strongSwan, CN=sun.strongswan.org"
auto=start
Configuration on gateway sun:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/sunCert.pem
/etc/ipsec.secrets:
: RSA sunKey.pem ""
/etc/ipsec.conf:
conn net-net
left=%defaultroute
leftsubnet=10.2.0.0/16
leftcert=sunCert.pem
right=192.168.0.1
rightsubnet=10.1.0.0/16
rightid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
auto=start
2.2 Host-to-host case
-----------------
This is a setup between two single hosts which don't have a subnet behind
them. Although IPsec transport mode would be sufficient for host-to-host
connections we will use the default IPsec tunnel mode.
| 192.168.0.1 | === | 192.168.0.2 |
moon sun
Configuration on host moon:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/moonCert.pem
/etc/ipsec.secrets:
: RSA moonKey.pem ""
/etc/ipsec.conf:
conn host-host
left=%defaultroute
leftcert=moonCert.pem
right=192.168.0.2
rightid="C=CH, O=Linux strongSwan, CN=sun.strongswan.org"
auto=start
Configuration on host sun:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/sunCert.pem
/etc/ipsec.secrets:
: RSA sunKey.pem ""
/etc/ipsec.conf:
conn host-host
left=%defaultroute
leftcert=sunCert.pem
right=192.168.0.1
rightid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
auto=start
2.3 Four Tunnel case
----------------
In a site-to-site setup a system administrator logged into the local gateway
often would like to access the peer gateway or a server in the subnet behind
the peer gateway over a secure IPsec tunnel.Since IP packets leaving a gateway
via the outer network interface carry the IP address of this NIC, four IPsec
Security Associations (SAs) must be set up to achieve full connectivity. The
example below shows how this can be done without much additional typing work ,
using the "also" macro which includes connection definitions defined farther
down in the ipsec.conf file.
10.1.0.0/16 -- | 192.168.0.1 | === | 192.168.0.2 | -- 10.2.0.0/16
moon-net moon sun sun-net
Configuration on gateway moon:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/moonCert.pem
/etc/ipsec.secrets:
: RSA moonKey.pem ""
/etc/ipsec.conf:
conn net-net
leftsubnet=10.1.0.0/16
rightsubnet=10.2.0.0/16
also host-host
conn net-host
leftsubnet=10.1.0.0/16
also host-host
conn host-net
rightsubnet=10.2.0.0/16
also host-host
conn host-host
left=%defaultroute
leftcert=moonCert.pem
right=192.168.0.2
rightid="C=CH, O=Linux strongSwan, CN=sun.strongswan.org"
auto=start
Configuration on gateway sun:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/sunCert.pem
/etc/ipsec.secrets:
: RSA sunKey.pem ""
/etc/ipsec.conf:
conn net-net
leftsubnet=10.2.0.0/16
rightsubnet=10.1.0.0/16
also=host-host
conn net-host
leftsubnet=10.2.0.0/16
also=host-host
conn host-net
rightsubnet=10.1.0.0/16
also=host-host
conn host-host
left=%defaultroute
leftcert=sunCert.pem
right=192.168.0.1
rightid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
auto=start
2.4 The four tunnel case the elegant way with source routing
--------------------------------------------------------
As you certainly agree, the full four tunnel case described in the previous
section becomes quite complex. If we could force the source address of the
IP packets leaving the gateway through the outer interface to take on the
IP address of the inner interface then we could use the single subnet-to-subnet
tunnel from section 2.1. Such a setup becomes possible if we use the
source routing capabilites of the ip route command that is already used
by strongSwan's updown scripts.
10.1.0.0/16 -- | 192.168.0.1 | === | 192.168.0.2 | -- 10.2.0.0/16
moon-net moon sun sun-net
If we assume that the inner IP address of gateway moon is 10.1.0.1
and the inner IP address of gateway sun is 10.2.0.1 then the
insertion of the parameter
leftsourceip=10.1.0.1
in the connection definition of moon and
leftsourceip=10.2.0.1
on sun, respectively, will install source routing on both gateways.
As a result the command
ping 10.2.0.1
executed on moon will leave the gateway with a source address of
10.1.0.1 and will therefore take the net-net IPsec tunnel.
Configuration on gateway moon:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/moonCert.pem
/etc/ipsec.secrets:
: RSA moonKey.pem ""
/etc/ipsec.conf:
conn net-net
left=%defaultroute
leftsourceip=10.1.0.1
leftsubnet=10.1.0.0/16
leftcert=moonCert.pem
right=192.168.0.2
rightsubnet=10.2.0.0/16
rightid="C=CH, O=Linux strongSwan, CN=sun.strongswan.org"
auto=start
Configuration on gateway sun:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/sunCert.pem
/etc/ipsec.secrets:
: RSA sunKey.pem ""
/etc/ipsec.conf:
conn net-net
left=%defaultroute
leftsubnet=10.2.0.0/16
leftsourceip=10.2.0.1
leftcert=sunCert.pem
right=192.168.0.1
rightsubnet=10.1.0.0/16
rightid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
auto=start
2.5 Roadwarrior case
----------------
This is a very common case where a strongSwan gateway serves an arbitrary number
of remote VPN clients usually having dynamic IP addresses.
10.1.0.0/16 -- | 192.168.0.1 | === | x.x.x.x |
moon-net moon carol
Configuration on gateway moon:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/moonCert.pem
/etc/ipsec.secrets:
: RSA moonKey.pem ""
/etc/ipsec.conf:
conn rw
left=%defaultroute
leftsubnet=10.1.0.0/16
leftcert=moonCert.pem
right=%any
auto=add
Configuration on roadwarrior carol:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/carolCert.pem
/etc/ipsec.secrets:
: RSA carolKey.pem ""
/etc/ipsec.conf:
conn home
left=%defaultroute
leftcert=carolCert.pem
right=192.168.0.1
rightsubnet=10.1.0.0/16
rightid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
auto=start
2.6 Roadwarrior case with virtual IP
--------------------------------
Roadwarriors usually have dynamic IP addresses assigned by the ISP they are
currently attached to. In order to simplify the routing from moon-net back
to the remote access client carol it would be desirable if the roadwarrior had
an inner IP address chosen from a pre-assigned pool.
10.1.0.0/16 -- | 192.168.0.1 | === | x.x.x.x | -- 10.3.0.1
moon-net moon carol virtual IP
This virtual IP address can be assigned to a strongSwan roadwarrior by adding
the parameter
leftsourceip=10.3.0.1
to the roadwarrior's ipsec.conf. Of course the virtual IP of each roadwarrior
must be distinct. In our example it is chosen from the address pool
rightsubnetwithin=10.3.0.0/16
which can be added to the gateway's ipsec.conf so that a single connection
definition can handle multiple roadwarriors.
Configuration on gateway moon:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/moonCert.pem
/etc/ipsec.secrets:
: RSA moonKey.pem ""
/etc/ipsec.conf:
conn rw
left=%defaultroute
leftsubnet=10.1.0.0/16
leftcert=moonCert.pem
right=%any
rightsubnetwithin=10.3.0.0/16
auto=add
Configuration on roadwarrior carol:
/etc/ipsec.d/cacerts/strongswanCert.pem
/etc/ipsec.d/certs/carolCert.pem
/etc/ipsec.secrets:
: RSA carolKey.pem ""
/etc/ipsec.conf:
conn home
left=%defaultroute
leftsourceip=10.3.0.1
leftcert=carolCert.pem
right=192.168.0.1
rightsubnet=10.1.0.0/16
rightid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
auto=start
3. Generating certificates and CRLs with OpenSSL
---------------------------------------------
This section is not a full-blown tutorial on how to use OpenSSL. It just lists
a few points that are relevant if you want to generate your own certificates
and CRLs for use with strongSwan.
3.1 Generating a CA certificate
---------------------------
The OpenSSL statement
openssl req -x509 -days 1460 -newkey rsa:2048 \
-keyout strongswanKey.pem -out strongswanCert.pem
creates a 2048 bit RSA private key strongswanKey.pem and a self-signed CA
certificate strongswanCert.pem with a validity of 4 years (1460 days).
openssl x509 -in cert.pem -noout -text
lists the properties of a X.509 certificate cert.pem. It allows you to verify
whether the configuration defaults in openssl.cnf have been inserted correctly.
If you prefer the CA certificate to be in binary DER format then the following
command achieves this transformation:
openssl x509 -in strongswanCert.pem -outform DER -out strongswanCert.der
The directory /etc/ipsec.d/cacerts contains all required CA certificates either
in binary DER or in base64 PEM format. Irrespective of the file suffix, Pluto
"automagically" determines the correct format.
3.2 Generating a host or user certificate
-------------------------------------
The OpenSSL statement
openssl req -newkey rsa:1024 -keyout hostKey.pem \
-out hostReq.pem
generates a 1024 bit RSA private key hostKey.pem and a certificate request
hostReq.pem which has to be signed by the CA.
If you want to add a subjectAltName field to the host certificate you must edit
the OpenSSL configuration file openssl.cnf and add the following line in the
[ usr_cert ] section:
subjectAltName=DNS:moon.strongswan.org
if you want to identify the host by its Fully Qualified Domain Name (FQDN ), or
subjectAltName=IP:192.168.0.1
if you want the ID to be of type IPV4_ADDR. Of course you could include both
ID types with
subjectAltName=DNS:moon.strongswan.org,IP:192.168.0.1
but the use of an IP address for the identification of a host should be
discouraged anyway.
For user certificates the appropriate ID type is USER_FQDN which can be
specified as
subjectAltName=email:carol@strongswan.org
or if the user's e-mail address is part of the subject's distinguished name
subjectAltName=email:copy
Now the certificate request can be signed by the CA with the command
openssl ca -in hostReq.pem -days 730 -out hostCert.pem -notext
If you omit the -days option then the default_days value (365 days) specified
in openssl.cnf is used. The -notext option avoids that a human readable
listing of the certificate is prepended to the base64 encoded certificate
body.
If you want to use the dynamic CRL fetching feature described in section 4.7
then you may include one or several crlDistributionPoints in your end
certificates. This can be done in the [ usr_cert ] section of the openssl.cnf
configuration file:
crlDistributionPoints= @crl_dp
[ crl_dp ]
URI.1="http://crl.strongswan.org/strongswan.crl"
URI.2="ldap://ldap.strongswan.org/cn=strongSwan Root CA, o=Linux strongSwan
, c=CH?certificateRevocationList"
If you have only a single http distribution point then the short form
crlDistributionPoints="URI:http://crl.strongswan.org/strongswan.crl"
also works. Due to a known bug in OpenSSL this notation fails with ldap URIs.
Usually a Windows-based VPN client needs its private key, its host or
user certificate, and the CA certificate. The most convenient way to load
this information is to put everything into a PKCS#12 file:
openssl pkcs12 -export -inkey carolKey.pem \
-in carolCert.pem -name "carol" \
-certfile strongswanCert.pem -caname "strongSwan Root CA" \
-out carolCert.p12
3.3 Generating a CRL
----------------
An empty CRL that is signed by the CA can be generated with the command
openssl ca -gencrl -crldays 15 -out crl.pem
If you omit the -crldays option then the default_crl_days value (30 days)
specified in openssl.cnf is used.
If you prefer the CRL to be in binary DER format then this conversion
can be achieved with
openssl crl -in crl.pem -outform DER -out cert.crl
The directory /etc/ipsec.d/crls contains all CRLs either in binary DER
or in base64 PEM format. Irrespective of the file suffix, Pluto
"automagically" determines the correct format.
3.4 Revoking a certificate
----------------------
A specific host certificate stored in the file host.pem is revoked with the
command
openssl ca -revoke host.pem
Next the CRL file must be updated
openssl ca -gencrl -crldays 60 -out crl.pem
The content of the CRL file can be listed with the command
openssl crl -in crl.pem -noout -text
in the case of a base64 CRL, or alternatively for a CRL in DER format
openssl crl -inform DER -in cert.crl -noout -text
4. Configuring the connections - ipsec.conf
----------------------------------------
4.1 Configuring my side
-------------------
Usually the local side is the same for all connections. Therefore it makes
sense to put the definitions characterizing the strongSwan security gateway into
the conn %default section of the configuration file /etc/ipsec.conf. If we
assume throughout this document that the strongSwan security gateway is left and
the peer is right then we can write
conn %default
# my side is left - the freeswan security gateway
left=%defaultroute
leftcert=moonCert.pem
# load connection definitions automatically
auto=add
The X.509 certificate by which the strongSwan security gateway will authenticate
itself by sending it in binary form to its peers as part of the Internet Key
Exchange (IKE) is specified in the line
leftcert=moonCert.pem
The certificate can either be stored in base64 PEM-format or in the binary
DER-format. Irrespective of the file suffix, Pluto "automagically" determines
the correct format. Therefore
leftcert=moonCert.der
or
leftcert=moonCert.cer
would also be valid alternatives.
When using relative pathnames as in the examples above, the certificate files
must be stored in in the directory /etc/ipsec.d/certs. In order to distinguish
strongSwan's own certificates from locally stored trusted peer certificates
(see section 5.5 for details), they could also be stored in a subdirectory
below /etc/ipsec.d/certs as e.g. in
leftcert=mycerts/moonCert.pem
Absolute pathnames are also possible as in
leftcert=/usr/ssl/certs/moonCert.pem
As an ID for the VPN gateway we recommend the use of a Fully Qualified Domain
Name (FQDN) of the form
conn rw
right=%any
leftid=@moon.strongswan.org
Important: When an FQDN identifier is used it must be explicitly included as a
so called subjectAltName of type dnsName (DNS:) in the certificate indicated
by leftcert. For details on how to generate certificates with subjectAltNames,
please refer to section 7.2.
If you don't want to mess with subjectAltNames, you can use the certificate's
Distinguished Name (DN) instead, which is an identifier of type DER_ASN1_DN
and which can be written e.g. in the LDAP-type format
conn rw
right=%any
leftid="C=CH, O=Linux strongSwan, CN=moon.strongswan.org"
Since the subject's DN is part of the certificate, the leftid does not have to
be declared explicitly. Thus the entry
conn rw
right=%any
automatically assumes the subject DN of leftcert to be the host ID.
4.2 Multiple certificates
---------------------
strongSwan supports multiple local host certificates and corresponding
RSA private keys:
conn rw1
right=%any
rightid=@peer1.domain1
leftcert=myCert1.pem
# leftid is DN of myCert1
conn rw2
right=%any
rightid=@peer2.domain2
leftcert=myCert2.pem
# leftid is DN of myCert2
When peer1 initiates a connection then strongSwan will send myCert1 and will
sign with myKey1 defined in /etc/ipsec.secrets (see section 6.2) whereas
myCert2 and myKey2 will be used in a connection setup started from peer2.
4.3 Configuring the peer side using CA certificates
-----------------------------------------------
Now we can proceed to define our connections. In many applications we might
have dozens of mostly Windows-based road warriors connecting to a central
strongSwan security gateway. The following most simple statement:
conn rw
right=%any
defines the general roadwarrior case. The line right=%any literally means that
any IPSec peer is accepted, regardless of its current IP source address and its
ID, as long as the peer presents a valid X.509 certificate signed by a CA the
strongSwan security gateway puts explicit trust in. Additionally the signature
during IKE main mode gives proof that the peer is in possession of the private
RSA key matching the public key contained in the transmitted certificate.
The ID by which a peer is identifying itself during IKE main mode can by any of
the ID types IPV4_ADDR, FQDN, USER_FQDN or DER_ASN1_DN. If one of the first
three ID types is used, then the accompanying X.509 certificate of the peer
must contain a matching subjectAltName field of the type ipAddress (IP:),
dnsName (DNS:) or rfc822Name (email:), respectively. With the fourth type
DER_ASN1_DN the identifier must completely match the subject field of the
peer's certificate. One of the two possible representations of a
Distinguished Name (DN) is the LDAP-type format
rightid="C=CH, O=Linux strongSwan, CN=sun.strongswan.org"
Additional whitespace can be added everywhere as desired since it will be
automatically eliminated by the X.509 parser. An exception is the single
whitespace between individual words , like e.g. in Linux strongSwan, which is
preserved by the parser.
The Relative Distinguished Names (RDNs) can alternatively be separated by a
slash '/' instead of a comma ','
rightid="/C=CH/O=Linux strongSwan/CN=sun.strongswan.org"
This is the representation extracted from the certificate by the OpenSSL
command line option
openssl x509 -in sunCert.pem -noout -subject
The following RDNs are supported by strongSwan
+---------------------------------------------------+
| DC Domain Component |
|---------------------------------------------------|
| C Country |
|---------------------------------------------------|
| ST State or province |
|---------------------------------------------------|
| L Locality or town |
|---------------------------------------------------|
| O Organisation |
|---------------------------------------------------|
| OU Organisational Unit |
|---------------------------------------------------|
| CN Common Name |
|---------------------------------------------------|
| ND NameDistinguisher, used with CN |
|---------------------------------------------------|
| N Name |
|---------------------------------------------------|
| G Given name |
|---------------------------------------------------|
| S Surname |
|---------------------------------------------------|
| I Initials |
|---------------------------------------------------|
| T Personal title |
|---------------------------------------------------|
| E E-mail |
|---------------------------------------------------|
| Email E-mail |
|---------------------------------------------------|
| emailAddress E-mail |
|---------------------------------------------------|
| SN Serial number |
|---------------------------------------------------|
| serialNumber Serial number |
|---------------------------------------------------|
| D Description |
|---------------------------------------------------|
| ID X.500 Unique Identifier |
|---------------------------------------------------|
| UID User ID |
|---------------------------------------------------|
| TCGID [Siemens] Trust Center Global ID |
|---------------------------------------------------|
| unstructuredName Unstructured Name |
|---------------------------------------------------|
| UN Unstructured Name |
|---------------------------------------------------|
| employeeNumber Employee Number |
|---------------------------------------------------|
| EN Employee Number |
+---------------------------------------------------+
With the roadwarrior connection definition listed above, an IPsec SA for
the strongSwan security gateway moon.strongswan.org itself can be established.
If any roadwarrior should be able to reach e.g. the two subnets 10.1.0.0/24
and 10.1.3.0/24 behind the security gateway then the following connection
definitions will make this possible
conn rw1
right=%any
leftsubnet=10.1.0.0/24
conn rw3
right=%any
leftsubnet=10.1.3.0/24
If not all peers in possession of a X.509 certificate signed by a specific
certificate authority shall be given access to the Linux security gateway,
then either a subset of them can be barred by listing the serial numbers of
their certificates in a certificate revocation list (CRL) as specified in
section 5.2 or as an alternative, access can be controlled by explicitly
putting a roadwarrior entry for each eligible peer into ipsec.conf:
conn sun
right=%any
rightid=@sun.strongswan.org
conn carol
right=%any
rightid=carol@strongswan.org
conn dave
right=%any
rightid="C=CH, O=Linux strongSwan, CN=dave@strongswan.org"
When the IP address of a peer is known to be stable, it can be specified as
well. This entry is mandatory when the strongSwan host wants to act as the
initiator of an IPSec connection.
conn sun
right=192.168.0.2
rightid=@sun.strongswan.org
conn carol
right=192.168.0.100
rightid=carol@strongswan.org
conn dave
right=192.168.0.200
rightid="C=CH, O=Linux strongSwan, CN=dave@strongswan.org"
conn venus
right=192.168.0.50
In the last example the ID types FQDN, USER_FQDN, DER_ASN1_DN and IPV4_ADDR,
respectively, were used. Of course all connection definitions presented so far
have included the lines in the conn %defaults section, comprising among other
a left and leftcert entry.
4.4 Handling Virtual IPs and wildcard subnets
-----------------------------------------
Often roadwarriors are behind NAT-boxes with IPsec passthrough, which causes
the inner IP source address of an IPsec tunnel to be different from the
outer IP source address usually assigned dynamically by the ISP.
Whereas the varying outer IP address can be handled by the right=%any
construct, the inner IP address or subnet must always be declared in a
connection definition. Therefore for the three roadwarriors rw1 to rw3
connecting to a strongSwan security gateway the following entries are
required in /etc/ipsec.conf:
conn rw1
right=%any
righsubnet=10.4.0.5/32
conn rw2
right=%any
rightsubnet=10.4.0.47/32
conn rw3
right=%any
rightsubnet=10.4.0.128/28
With the wildcard parameter rightsubnetwithin these three entries can be
reduced to the single connection definition
conn rw
right=%any
rightsubnetwithin=10.4.0.0/24
Any host will be accepted (of course after successful authentication based on
the peer's X.509 certificate only) if it declares a client subnet lying totally
within the brackets defined by the wildcard subnet definition (in our example
10.4.0.0/24). For each roadwarrior a connection instance tailored to the
subnet of the particular client will be created,based on the generic
rightsubnetwithin template.
This strongSwan feature can also be helpful with VPN clients getting a
dynamically assigned inner IP from a DHCP server located on the NAT router box.
4.5 Protocol and Port Selectors
---------------------------
strongSwan offer the possibility to restrict the protocol and optionally the
ports in an IPsec SA using the rightprotoport and leftprotoport parameters.
Some examples:
conn icmp
right=%any
rightprotoport=icmp
left=%defaultroute
leftid=@moon.strongswan.org
leftprotoport=icmp
conn http
right=%any
rightprotoport=6
left=%defaultroute
leftid=@moon.strongswan.org
leftprotoport=6/80
conn l2tp # with port wildcard for Mac OS X Panther interoperability
right=%any
rightprotoport=17/%any
left=%defaultroute
leftid=@moon.strongswan.org
leftprotoport=17/1701
conn dhcp
right=%any
rightprotoport=udp/bootpc
left=%defaultroute
leftid=@moon.strongswan.org
leftsubnet=0.0.0.0/0 #allows DHCP discovery broadcast
leftprotoport=udp/bootps
rekey=no
keylife=20s
rekeymargin=10s
auto=add
Protocols and ports can be designated either by their numerical values
or by their acronyms defined in /etc/services.
ipsec status
shows the following connection definitions:
"icmp": 192.168.0.1[@moon.strongswan.org]:1/0...%any:1/0
"http": 192.168.0.1[@moon.strongswan.org]:6/80...%any:6/0
"l2tp": 192.168.0.1[@moon.strongswan.org]:17/1701...%any:17/%any
"dhcp": 0.0.0.0/0===192.168.0.1[@moon.strongswan.org]:17/67...%any:17/68
Based on the protocol and port selectors appropriate eroutes will be set
up, so that only the specified payload types will pass through the IPsec
tunnel.
4.6 IPsec policies based on wildcards
---------------------------------
In large VPN-based remote access networks there is often a requirement that
access to the various parts of an internal network must be granted selectively,
e.g. depending on the group membership of the remote access user. strongSwan
makes this possible by applying wildcard filtering on the VPN user's
distinguished name (ID_DER_ASN1_DN).
Let's make a practical example:
An organization has a sales department (OU=Sales) and a research group
(OU=Research). In the company intranet there are separate subnets for Sales
(10.0.0.0/24) and Research (10.0.1.0/24) but both groups share a common web
server (10.0.2.100). The VPN clients use Virtual IP addresses that are either
assigned statically or via DHCP-over-IPsec. The sales and research departments
use IP addresses from separate DHCP address pools (10.1.0.0/24) and (10.1.1.0/24),
respectively. An X.509 certificate is issued to each employee, containing in its
subject distinguished name the country (C=CH), the company (O=ACME),
the group membership(OU=Sales or OU=Research) and the common name (e.g.
CN=Bart Simpson).
The IPsec policy defined above can now be enforced with the following three
IPsec security associations:
conn sales
right=%any
rightid="C=CH, O=ACME, OU=Sales, CN=*"
rightsubnetwithin=10.1.0.0/24 # Sales DHCP range
leftsubnet=10.0.0.0/24 # Sales subnet
conn research
right=%any
rightid="C=CH, O=ACME, OU=Research, CN=*"
rightsubnetwithin=10.1.1.0/24 # Research DHCP range
leftsubnet=10.0.1.0/24 # Research subnet
conn web
right=%any
rightid="C=CH, O=ACME, OU=*, CN=*"
rightsubnetwithin=10.1.0.0/23 # Remote access DHCP range
leftsubnet=10.0.2.100/32 # Web server
rightprotoport=tcp # TCP protocol only
leftprotoport=tcp/http # TCP port 80 only
Of course group specific tunneling could be implemented on the
basis of the Virtual IP range specified by the rightsubnetwithin
parameter alone, but the wildcard matching mechanism guarantees that
only authorized user can access the corresponding subnets.
The '*' character is used as a wildcard in relative distinguished names (RDNs).
In order to match a wildcard template, the ID_DER_ASN1_DN of a peer must contain
the same number of RDNs (selected from the list in section 4.3) appearing in the
exact order defined by the template.
"C=CH, O=ACME, OU=Research, OU=Special Effects, CN=Bart Simpson"
matches the templates
"C=CH, O=ACME, OU=Research, OU=*, CN=*"
"C=CH, O=ACME, OU=*, OU=Special Effects, CN=*"
"C=CH, O=ACME, OU=*, OU=*, CN=*"
but not the template
"C=CH, O=ACME, OU=*, CN=*"
which doesn't have the same number of RDNs.
4.7 IPsec policies based on CA certificates
---------------------------------------
As an alternative to the wildcard based IPsec policies described in section 4.6,
access to specific client host and subnets can abe controlled on the basis of
the CA that issued the peer certificate
conn sales
right=%any
rightca="C=CH, O=ACME, OU=Sales, CN=Sales CA"
rightsubnetwithin=10.1.0.0/24 # Sales DHCP range
leftsubnet=10.0.0.0/24 # Sales subnet
conn research
right=%any
rightca="C=CH, O=ACME, OU=Research, CN=Research CA"
rightsubnetwithin=10.1.1.0/24 # Research DHCP range
leftsubnet=10.0.1.0/24 # Research subnet
conn web
right=%any
rightca="C=CH, O=ACME, CN=ACME Root CA"
rightsubnetwithin=10.1.0.0/23 # Remote access DHCP range
leftsubnet=10.0.2.100/32 # Web server
rightprotoport=tcp # TCP protocol only
leftprotoport=tcp/http # TCP port 80 only
In the example above, the connection "sales" can be used by peers
presenting certificates issued by the Sales CA, only. In the same way,
the use of the connection "research" is restricted to owners of certificates
issued by the Research CA. The connection "web" is open to both "Sales" and
"Research" peers because the required "ACME Root CA" is the issuer of the
Research and Sales intermediate CAs. If no rightca parameter is present
then any valid certificate issued by one of the trusted CAs in
/etc/ipsec.d/cacerts can be used by the peer.
The leftca parameter usually doesn't have to be set explicitly because
by default it is set to the issuer field of the certificate loaded via
leftcert. The statement
rightca=%same
sets the CA requested from the peer to the CA used by the left side itself
as e.g. in
conn sales
right=%any
rightca=%same
leftcert=mySalesCert.pem
4.8 Sending certificate requests
----------------------------
The presence of a rightca parameter also causes the CA to be sent as
part of the certificate request message when strongSwan is the initiator.
A special case occurs when strongSwan responds to a roadwarrior. If several
roadwarrior connections based on different CAs are defined then all eligible
CAs will be listed in Pluto�s certificate request message.
4.9 IPsec policies based on group attributes
----------------------------------------
X.509 attribute certificates are the most powerful mechanism for implementing
IPsec security policies. The rightgroups parameter in a connection definition
restricts the access to members of the listed groups only. An IPsec peer must
have a valid attribute certificate issued by a trusted Authorization Authority
and listing one of the requirede group attributes in order to get admitted.
conn sales
right=%any
rightgroups="Sales"
rightsubnetwithin=10.1.0.0/24 # Sales DHCP range
leftsubnet=10.0.0.0/24 # Sales subnet
conn research
right=%any
rightgroups="Research"
rightsubnetwithin=10.1.1.0/24 # Research DHCP range
leftsubnet=10.0.1.0/24 # Research subnet
conn web
right=%any
rightgroups="Sales, Research"
rightsubnetwithin=10.1.0.0/23 # Remote access DHCP range
leftsubnet=10.0.2.100/32 # Web server
rightprotoport=tcp # TCP protocol only
leftprotoport=tcp/http # TCP port 80 only
In the examples above membership of the group "Sales" is required for
connection sales and membership of "Research" for connection research
whereas connection web is accessible for both groups.
Currently the attribute certificates of the peers must be loaded statically
via the /etc/ipsec.d/acerts/ directory. In future releases of strongSwan it
will be possible to fetch them from an LDAP directory server.
5. Configuring certificates and CRLs
---------------------------------
5.1 Installing the CA certificates
------------------------------
X.509 certificates received by strongSwan during the IKE protocol are
automatically authenticated by going up the trust chain until a self-signed
root CA certificate is reached. Usually host certificates are directly signed
by a root CA, but strongSwan also supports multi-level hierarchies with
intermediate CAs in between. All CA certificates belonging to a trust chain
must be copied in either binary DER or base64 PEM format into the directory
/etc/ipsec.d/cacerts/
5.2 Installing optional certificate revocation lists (CRLs)
-------------------------------------------------------
By copying a CA certificate into /etc/ipsec.d/cacerts/, automatically all user
or host certificates issued by this CA are declared valid. Unfortunately
private keys might get compromised inadvertently or intentionally, personal
certificates of users leaving a company have to be blocked immediately, etc.
To this purpose certificate revocation lists (CRLs) have been created. CRLs
contain the serial numbers of all user or host certificates that have been
revoked due to various reasons.
After successful verification of the X.509 trust chain, Pluto searches its
list of CRLs either obtained by loading them from the /etc/ipsec.d/crls/
directory or fetching them dynamically from a HTTP or LDAP server for the
presence of a CRL issued by the CA that has signed the certificate.
If the serial number of the certificate is found in the CRL then the public key
contained in the certificate is declared invalid and the IPSec SA will not be
established. If no CRL is found or if the deadline defined in the nextUpdate
field of the CRL has been reached, a warning is issued but the public key will
nevertheless be accepted. CRLs must be stored either in binary DER or base64 PEM
format in the crls directory. Section 7.3 will explain in detail how CRLs can
be created using OpenSSL.
5.3 Dynamic update of certificates and CRLs
---------------------------------------
Pluto reads certificates and CRLs from their respective files during system
startup and keeps them in memory in the form of chained lists. X.509
certificates have a finite life span defined by their validity field. Therefore
it must be possible to replace CA or OCSP certificates kept in system memory
without disturbing established ISAKMP SAs. Certificate revocation lists should
also be updated in the regular intervals indicated by the nextUpdate field in
the CRL body. The following interactive commands allow the manual replacement
of the various files:
+---------------------------------------------------------------------------+
| ipsec rereadsecrets reload file /etc/ipsec.secrets |
|---------------------------------------------------------------------------|
| ipsec rereadcacerts reload all files in /etc/ipsec.d/cacerts/ |
|---------------------------------------------------------------------------|
| ipsec rereadaacerts reload all files in /etc/ipsec.d/aacerts/ |
|---------------------------------------------------------------------------|
| ipsec rereadocspcerts reload all files in /etc/ipsec.d/ocspcerts/ |
|---------------------------------------------------------------------------|
| ipsec rereadacerts reload all files in /etc/ipsec.d/acerts/ |
|---------------------------------------------------------------------------|
| ipsec rereadcrls reload all files in /etc/ipsec.d/crls/ |
|---------------------------------------------------------------------------|
| ipsec rereadall ipsec rereadsecrets |
| rereadcacerts |
| rereadaacerts |
| rereadocspcerts |
| rereadacerts |
| rereadcrls |
|---------------------------------------------------------------------------|
| ipsec purgeocsp purge the OCSP cache and fetching requests |
+---------------------------------------------------------------------------+
CRLs can also be automatically fetched from an HTTP or LDAP server by using
the CRL distribution points contained in X.509 certificates. The command
ipsec listcrls
shows any pending fetch requests:
Oct 31 00:29:53 2002, trials: 2
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
distPts: 'http://crl.strongswan.org/strongswan.crl'
'ldap://ldap.strongswan.org/o=Linux strongSwan, c=CH
?certificateRevocationList?base
?(objectClass=certificationAuthority)'
In the example above, an http and an ldap URL were extracted from a received
end certificate. An independent thread then tries to fetch a CRL from the
designated distribution points. The same thread also periodically checks
if any loaded CRLs are about to expire. The check interval can be defined in
the "config setup" section of the ipsec.conf file:
config setup
crlcheckinterval=600
In our example the thread wakes up every 600 seconds or 10 minutes in order
to check the validity of the CRLs or to retry any pending fetch requests:
List of X.509 CRLs:
Dec 19 09:35:31 2002, revoked certs: 40
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
distPts: 'http://crl.strongswan.org/strongswan.crl'
updates: this Dec 19 09:35:00 2002
next Dec 19 10:35:00 2002 warning (expires in 19 minutes)
List of fetch requests:
Dec 19 10:15:31 2002, trials: 1
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
distPts: 'http://crl.strongwan.org/strongswan.crl'
The first trial to update a CRL is started 2*crlcheckinterval before the
nextUpdate time, i.e. when less than 20 minutes are left in our practical
example. When crlcheckinterval is set to 0 (this is also the default value
when the parameter is not set in ipsec.conf) then the CRL checking and updating
thread is not started and dynamic CRL fetching is disabled.
5.4 Local caching of CRLs
---------------------
The the ipsec.conf option
config setup
cachecrls=yes
activates the local caching of CRLs that were dynamically fetched from an
HTTP or LDAP server. Cached copies are stored in /etc/ipsec.d/crls under a
unique filename formed from the issuer's SubjectKeyIdentifier and the suffix .crl.
With the cached copy the CRL is immediately available after pluto's startup.
When the local copy is about to expire it is automatically replaced with an
updated CRL fetched from one of the defined CRL distribution points.
5.5 Online Certificate Status Protocol (OCSP)
-----------------------------------------
The Online Certificate Status Protocol is defined by RFC 2560. It can be
used to query an OCSP server about the current status of an X.509 certificate
and is often used as a more dynamic alternative to a static Certificate
Revocation List (CRL). Both the OCSP request sent by the client and the OCSP
response messages returned by the server are transported via a standard
TCP/HTTP connection. Therefore cURL support must be enabled in pluto/Makefile:
# Uncomment this line to enable OCSP fetching using HTTP
LIBCURL=1
In the simplest OCSP setup, a default URI under which the OCSP server for a
given CA can be accessed is defined in ipsec.conf:
config setup
crlcheckinterval=600
ca strongswan
cacert=strongswanCert.pem
ocspuri=http://ocsp.strongswan.org:8880
auto=add
The HTTP port can be freely chosen. In our example we have assumed TCP port 8880.
The crlcheckinterval must be set to a value different from zero. Otherwise the
OCSP fetching thread will not be started.
The well-known openssl-0.9.7 package from http://www.openssl.org implements
an OCSP server that can be used in conjunction with an openssl-based Public
Key Infrastructure. The OCSP client integrated into Pluto does not contain
any OpenSSL code though, but is based on the existing ASN.1 functionality of
strongSwan.
The OpenSSL-based OCSP server is started with the following command:
openssl ocsp -index index.txt -CA strongswanCert.pem -port 8880 \
-rkey ocspKey.pem -rsigner ocspCert.pem \
-resp_no_certs -nmin 60 -text
The command consists of the parameters
-index index.txt is a copy of the OpenSSL index file containing the list of
all issued certificates. The certificate status in indext.txt
is designated either by V for valid or R for revoked. If
a new certificate is added or if a certificate is revoked
using the openssl ca command, the OCSP server must be restarted
in order for the changes in index.txt to take effect.
-CA the CA certificate
-port the HTTP port the OCSP server is listening on.
-rkey the private key used to sign the OCSP response. The use of the
sensitive CA private key is not recommended since this could
jeopardize the security of your production PKI if the OCSP
server is hacked. It is much better to generate a special
RSA private key just for OCSP signing use instead.
-rsigner the certificate of the OCSP server containing a public key which
matches the private key defined by -rkey and which can be used by
the client to check the trustworthiness of the signed OCSP response.
-resp_no_certs With this option the OCSP signer certificate defined by
-rsigner is not included in the OCSP response.
-nmin the validity interval of an OCSP response given in minutes.
2*crlcheckinterval before the expiration of the OCSP responses,
a new query will by pro-actively started by the Pluto fetching thread.
If nmin is missing or set to zero then the default validity interval
compiled into Pluto will be 2 minutes, leading to a quasi one-time
use of the OCSP status response which will not be periodically
refreshed by the fetching thread. In conjunction with the parameter
setting "strictcrlpolicy=yes" a real-time certificate status query
can be implemented in this way.
-text This option activates a verbose logging output, showing the contents
of both the received OCSP request and sent OCSP response.
How does Pluto get hold of the OCSP signer certificate? There are two
possibilities:
Either you put the OCSP certificate into the default directory
/etc/ipsec.d/ocspcerts
or alternatively Pluto can receive it as part of the OCSP response from the
remote OCSP server. In the latter case, how can Pluto make sure that
the server has indeed been authorized by the CA to deal out certificate status
information? In order to ascertain the OCSP signer capability, an extended
key usage attribute can be included in the OCSP server certificate. Just
insert the parameter
extendedKeyUsage=OCSPSigner
in the [ usr_cert ] section of your openssl.cnf configuration file before
the CA signs the OCSP server certificate.
For a given CA the corresponding ca section in ipsec.conf (see section 7) allows
to define the URI of a single OCSP server. As an alternative an OCSP URI can be
embedded into each host and user certificate by putting the line
authorityInfoAccess = OCSP;URI:http://ocsp.strongswan.org:8880
into the [ usr_cert ] section of your openssl.cnf configuration file.
If an OCSP authorityInfoAccess extension is present in a certificate then this
record overrides the default URI defined by the ca section.
5.6 CRL Policy
----------
By default Pluto is quite tolerant concerning the handling of CRLs. It is not
mandatory for a CRL to be present in /etc/ipsec.d/crls and if the expiration
date defined by the nextUpdate field of a CRL has been reached just a warning
is issued but a peer certificate will always be accepted if it has not been
revoked.
If you want to enforce a stricter CRL policy then you can do this by setting
the "strictcrlpolicy" option. This is done in the "config setup" section
of the ipsec.conf file:
config setup
strictcrlpolicy=yes
...
A certificate received from a peer will not be accepted if no corresponding
CRL or OCSP response is available. And if an ISAKMP SA re-negotiation takes
place after the nextUpdate deadline has been reached, the peer certificate
will be declared invalid and the cached RSA public key will be deleted, causing
the connection in question to fail. Therefore if you are going to use the
"strictcrlpolicy=yes" option, make sure that the CRLs will always be updated
in time. Otherwise a total standstill would ensue.
As mentioned earlier the default setting is "strictcrlpolicy=no"
5.7 Configuring the peer side using locally stored certificates
-----------------------------------------------------------
If you don't want to use trust chains based on CA certificates as proposed in
section 4.3 you can alternatively import trusted peer certificates directly
into Pluto. Thus you do not have to rely on the certificate to be transmitted
by the peer as part of the IKE protocol.
With the conn %default section defined in section 4.1 and the use of the
rightcert keyword for the peer side, the connection definitions in section 4.3
can alternatively be written as
conn sun
right=%any
rightid=@sun.strongswan.org
rightcert=sunCert.cer
conn carol
right=192.168.0.100
rightcert=carolCert.der
If the peer certificates are loaded locally then there is no sense in sending
any certificates to the other end via the IKE Main Mode protocol. Especially
if self-signed certificates are used which wouldn't be accepted any way by
the other side. In these cases it is recommended to add
leftsendcert=never
to the connection definition[s] in order to avoid the sending of the host's
own certificate. The default value is
leftsendcert=ifasked
If a peer does not send a certificate request then use the setting
leftsendcert=always
If a peer certificate contains a subjectAltName extension, then an alternative
rightid type can be used, as the example "conn sun" shows. If no rightid
entry is present then the subject distinguished name contained in the
certificate is taken as the ID.
Using the same rules concerning pathnames that apply to strongSwan's own
certificates, the following two definitions are also valid for trusted peer
certificates:
rightcert=peercerts/carolCert.der
or
rightcert=/usr/ssl/certs/carolCert.der
6. Installing the private key - ipsec.secrets
------------------------------------------
6.1 Loading private key files in PKCS#1 format
------------------------------------------
Besides strongSwan's raw private key format strongSwan has been enabled to
load RSA private keys in the PKCS#1 file format. The key files can be
optionally secured with a passphrase.
RSA private key files are declared in /etc/ipsec.secrets using the syntax
: RSA ""
The key file can be either in base64 PEM-format or binary DER-format. The
actual coding is detected "automagically" by Pluto. The example
: RSA moonKey.pem
uses a relative pathname. In this case Pluto will look for the key file
in the directory
/etc/ipsec.d/private
As an alternative an absolute pathname can be given as in
: RSA /usr/ssl/private/moonKey.pem
In both cases make sure that the key files are root readable only.
Often a private key must be transported from the Certification Authority
where it was generated to the target security gateway where it is going
to be used. In order to protect the key it can be encrypted with 3DES
using a symmetric transport key derived from a cryptographically strong
passphrase.
openssl genrsa -des3 -out moonKey.pem 1024
Because of the weak security, key files protected by single DES will not
be accepted by Pluto!!!
Once on the security gateway the private key can either be permanently
unlocked so that it can be used by Pluto without having to know a
passphrase
openssl rsa -in moonKey.pem -out moonKey.pem
or as an option the key file can remain secured. In this case the passphrase
unlocking the private key must be added after the pathname in
/etc/ipsec.secrets
: RSA moonKey.pem "This is my passphrase"
Some CAs distribute private keys embedded in a PKCS#12 file. Since Pluto
is not able yet to read this format directly, the private key part must
first be extracted using the command
openssl pkcs12 -nocerts -in moonCert.p12 -out moonKey.pem
if the key file moonKey.pem is to be secured again by a passphrase, or
openssl pkcs12 -nocerts -nodes -in moonCert.p12 -out moonKey.pem
if the private key is to be stored unlocked.
6.2 Entering passphrases interactively
----------------------------------
On a VPN gateway you would want to put the passphrase protecting the private
key file right into /etc/ipsec.secrets as described in the previous paragraph,
so that the gateway can be booted in unattended mode. The risk of keeping
unencrypted secrets on a server can be minimized by putting the box into a
locked room. As long as no one can get root access on the machine the private
keys are safe.
On a mobile laptop computer the situation is quite different. The computer can
be stolen or the user is leaving it unattended so that unauthorized persons
can get access to it. In theses cases it would be preferable not to keep any
passphrases openly in /etc/ipsec.secrets but to prompt for them interactively
instead. This is easily done by defining
: RSA moonKey.pem %prompt
Since strongSwan is usually started during the boot process, usually no
interactive console windows is available which can be used by Pluto to
prompt for the passphrase. This must be initiated by the user by typing
ipsec secrets
which actually is an alias for the existing command
ipsec rereadsecrets
and which causes the prompt
need passphrase for '/etc/ipsec.d/private/moonKey.pem'
Enter:
to appear. If the passphrase was correct and the private key file could be
successfully decrypted then
valid passphrase
results. Otherwise the prompt
invalid passphrase, please try again
Enter:
will give you another try. Entering a carriage return will abort the
the passphrase prompting.
6.3 Multiple private keys
---------------------
strongSwan supports multiple private keys. Since the connections defined
in ipsec.conf can find the correct private key based on the public key
contained in the certificate assigned by leftcert, default private key
definitions without specific IDs can be used
: RSA myKey1.pem ""
: RSA myKey2.pem ""
7. Configuring CA properties - ipsec.conf
--------------------------------------
Besides the definition of IPsec connections the ipsec.conf file can also
be used to configure a few properties of the certification authorities
needed to establish the X.509 trust chains. The following example shows
the parameters that are currently available:
ca strongswan
cacert=strongswanCert.pem
ocspuri=http://ocsp.strongswan.org:8880
crluri=http://crl.strongswan.org/strongswan.crl'
crluri2="ldap:///O=Linux strongSwan, C=CH?certificateRevocationList"
ldaphost=ldap.strongswan.org
auto=add
In a similar way as conn sections are used for connection definitions, an
arbitrary number of optional ca sections define the basic properties of CAs.
Each ca section is named with a unique label
ca strongswan
The only mandatory parameter is
cacert=strongswanCert.pem
which points to the CA certificate which usually resides in the default
directory /etc/ipsec.d/cacerts/ but could also be retrieved via an absolute
path name. If the CA certificate is stored on a smartcard then the
notation
cacert=%smartcard#
or alternatively
cacert=%smartcard:
can be used. The selection of smartcard slots is described in more detail
in section 8.1.
From the certificate the CA's distinguished name and the serial number
is extracted. If an optional subjectKeyAuthentifier is present then it can
be used to uniquely identify consecutive generations of CA certificates
carrying the same distinguished name.
The OCSP URI
ocspuri=http://ocsp.strongswan.org:8880
allows to define an individual OCSP server per CA. Also up to two additional
CRL distribution points (CDPs) can be defined
crluri=http://crl.strongswan.org/strongswan.crl'
crluri2="ldap:///O=Linux strongSwan, C=CH?certificateRevocationList"
which are added to any CDPs already present in the received certificates
themselves. The last parameter
ldaphost=ldap.strongswan.org
can be used to fill in the actual server name in LDAP CDPs where the host is missing
as e.g. in the crluri2 above. In future releases this ldaphost parameter might be used
to retrieve user, host and attribute certificates.
With the auto=add statement the ca definition is automatically loaded into Pluto during
system startup. Setting auto=ignore will ignore the ca section. Additional ca definitions
can be loaded from ipsec.conf during runtime with the command
ipsec auto --type ca --add strongswan-sales
and
ipsec auto --type ca --delete strongswan-sales
deletes the labeled ca entry. And finally the command
ipsec auto --type ca --replace strongswan
first deletes the old definition in Pluto's memory and then loads the updated version
from ipsec.conf. Any parameters which appear in several ca definitions can be put in
a common ca %default section
ca %default
ldaphost=ldap.strongswan.org
8. Smartcard support
-----------------
8.1 Configuring a smartcard-based connection
----------------------------------------
Defining a smartcard-based connection in ipsec.conf is easy:
conn sun
right=192.168.0.2
rightid=@sun.strongswan.org
left=%defaultroute
leftcert=%smartcard
auto=add
In most cases there is a single smartcard reader or cryptotoken and only one
RSA private key safely stored on the crypto device. Thus usually the entry
leftcert=%smartcard
which stands for the full notation
leftcert=%smartcard#1
is sufficient where the first certificate/private key object enumerated by
the PKCS#11 module is used. If several certificate/private key objects are
present then the nth object can be selected using
leftcert=%smartcard#
The command
ipsec listcards
gives an overview over all certificate objects made available by the PKCS#11
module.CA certificates are automatically available as trust anchors.
As an alternative the certificate ID and/or the slot number defined by
the PKCS#11 standard can be specified using the notation
leftcert=%smartcard:
Thus
leftcert=%smartcard:50
will look in all available slots for ID 0x50 starting with the first slot
(usually slot 0) whereas
leftcert=%smartcard4:50
will directly check slot 4 (which is usually the first slot on the second
reader/token when using the OpenSC library) for a key with ID 0x50.
8.2 Entering the PIN code
---------------------
Since the smartcard signing operation needed to sign the hash with the
RSA private key during IKE Main Mode is protected by a PIN code,
the secret PIN must be made available to Pluto.
For gateways that must be able to start IPsec tunnels automatically in
unattended mode after a reboot, the secret PIN can be stored statically
in ipsec.secrets
: PIN %smartcard "12345678"
or with the general notation
: PIN %smartcard# ""
or alternatively
: PIN %smartcard: ""
On personal notebooks that could get stolen, you wouldn't want to store
your PIN in ipsec.secrets. Thus the alternative form
: PIN %smartcard %prompt
will prompt you for the PIN when you start up the first IPsec connection
using the command
ipsec up sun
The auto command calls the whack function which in turn communicates with
Pluto over a socket. Since the whack function call is executed from a command
window, Pluto can prompt you for the PIN over this socket connection.
Unfortunately roadwarrior connections which just wait passively for peers
cannot be initiated via the command window:
conn rw
right=%any
left=%defaultroute
leftcert=%smartcard4:50
auto=add
But if there is a corresponding entry
: PIN %smartcard4:50 %prompt
in ipsec.secrets, then the standard command
ipsec rereadsecrets
or the alias
ipsec secrets
can be used to enter the PIN code for this connection interactively.
The command
ipsec listcards
can be executed at any time to check the current status of the PIN code[s].
8.3 PIN-pad equipped smartcard readers
----------------------------------
Smartcard readers with an integrated PIN-pad offer an increased security
level because the PIN entry cannot be sniffed on the host computer e.g.
by a surrepticiously installed key logger. In order to tell pluto not to
prompt for the PIN on the host itself, the entry
: PIN %smartcard:50 %pinpad
can be used in ipsec.secrets. Because the key pad does not cache the PIN in
the smartcard reader, it must be entered for every PKCS #11 session login.
By default pluto does a session logout after every RSA signature. In order
to avoid the repeated entry of the PIN code during the periodic IKE main
mode rekeyings, the following parameter can be set in the config setup
section of ipsec.conf:
config setup
pkcs11keepstate=yes
The default setting is pkcs11keepstate=no.
8.4 Configuring a smartcard with pkcsc15-init
-----------------------------------------
strongSwan's smartcard solution is based on the PKCS#15 "Cryptographic Token
Information Format Standard" fully supported by OpenSC library functions.
Using the command
pkcs15-init --erase-card --create-pkcs15
a fresh PKCS#15 file structure is created on a smartcard or cryptotoken.
With the next command
pkcs15-init --auth-id 1 --store-pin --pin "12345678" --puk "87654321"
--label "my PIN"
a secret PIN code with auth-id 1 is stored in an unretrievable location on
the smart card. The PIN will protect the RSA signing operation. If the PIN
is entered incorrectly more tha
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