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Martin Willi f2c2d395ff - introduced autotools 
- first working version
  - make dist should work
  - things to do:
    - UML testing!
    - more cleanups
2006-05-16 14:24:03 +00:00

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----------------------------
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 (NEW)
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
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 configuratin and IKE Mode Config
* 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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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 "<optional passphrase>"
/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<74>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=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 <my keyfile> "<optional passphrase>"
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 "<optional passphrase1>"
: RSA myKey2.pem "<optional passphrase2>"
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#<n>
or alternatively
cacert=%smartcard<optional slot nr>:<key id>
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#<n>
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<optional slot nr>:<key id in hex format>
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#<n> "<PIN code>"
or alternatively
: PIN %smartcard<optional slot nr>:<key id> "<PIN code>"
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 than three times the smartcard will be locked
and the PUK code can be used to unlock the card again.
Next the RSA private key is transferred to the smartcard
pkcs15-init --auth-id 1 --store-private-key myKey.pem [--id 45]
By default the PKCS#15 smartcard record will be assigned the id 45.
Using the --id option multiple key records can be stored on a smartcard.
At last we load the matching X.509 certificate onto the smartcard
pkcs15-init --auth-id 1 --store-certificate myCert.pem [--id 45]
The pkcs15-tool can now be used to verify the contents of the smartcard.
pkcs15-tool --list-pins --list-keys --list-certificates
If everything is ok then you are ready to use the generated PKCS#15
structure with strongSwan.
8.5 PKCS#11 proxy functions
-----------------------
With the setting pkcs11keepstate=yes some PKCS#11 implementations
(e.g. OpenSC) will lock the access to the smartcard as soon as pluto has
opened a session and will thus prevent other application from sharing the
smartcard resource. In order to solve this locking problem, strongSwan
offers a PKCS#11 proxy service making use of the whack socket communication
channel. The setting
config setup
pkcs11proxy=yes
will enable the proxy mode that is disabled by default.
Currently two smartcard operations are supported: RSA encryption and
RSA decryption. The notation is as follows:
ipsec scdecrypt <encrypted data>
[--inbase 16|hex|64|base64|256|text|ascii]
[--outbase 16|hex|64|base64|256|text|ascii]
[--keyid <id>]
The default settings for inbase and outbase is hexadecimal.
Thus the simplest call has the form
ipsec scdecrypt bb952b71920094ce0696ef9b8b26...12e6
and the returned result might be a decrypted 128 bit AES key
000 8836362e030e6707c32ffaa0bdad5540
The leading three characters represent the return code of the whack channel
with 000 signifying that no error has occured. Here is another example showing
the use of the inbase and outbase attributes
ipsec scdecrypt m/ewDnTs0k...woE= --inbase base64 --outbase text
where the result has the form
000 This is a secret
By default the first RSA private key found by the PKCS#11 enumeration is
used. If a different key should be selected then the notation introduced
in sections 8.1 and 8.2 can be used:
--keyid %smartcard:50
--keyid %smartcard4:50
--keyid %smartcard#3
with --keyid %smartcard#1 being the default. If supported by the smartcard
and PKCS#11 library RSA encryption can be used with the notation
ipsec scencrypt <plaintext data>
[--inbase 16|hex|64|base64|256|text|ascii]
[--outbase 16|hex|64|base64|256|text|ascii]
[--keyid <id>]
with the example
ipsec scencrypt "This is a secret" --inbase ascii --outbase 64
returning the expected output
000 m/ewDnTs0k...woE=
9. Configuring the clients
-----------------------
9.1 strongSwan
----------
A strongSwan to strongSwan connection is symmetrical. Any of the four defined
ID types can be used, even different types on either end of the connection,
although this wouldn't make much sense.
+--------------------------------------------------------------+
| Connection Definition ID type subjectAltName |
|--------------------------------------------------------------|
| rightid (strongSwan) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
|--------------------------------------------------------------|
| leftid (strongSwan) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
+--------------------------------------------------------------+
9.2 PGPnet
------
Use the file peerCert.p12 to import PGPnet's X.509 certificate, the CA
certificate, plus the encrypted private key in binary PKCS#12 format into the
PGPkey tool. You will be prompted for the passphrase securing the private key.
Use the file myCert.pem to import the X.509 certificate of the strongSwan
security gateway into the PGPkey tool. The PGPkeyTool does not accept X.509
certificates in binary DER format, so it must be imported in base64 format:
-----BEGIN CERTIFICATE-----
M...
...
-----END CERTIFICATE-----
Make sure that there is no human-readable listing of the X.509 certificate in
front of the line
-----BEGIN CERTIFICATE-----
otherwise PGPnet will refuse to load the *.PEM file. Any surplus lines can
either be deleted by loading the certificate into a text editor or you can
apply the command
openssl x509 -in myCert.pem -out myCert.pem
to achieve the same effect.
With authentication based on X.509 certificates, PGPnet always sends the ID
type DER_ASN1_DN, therefore rightid in the connection definition of the
strongSwan security gateway must be an ASN.1 distinguished name.
In the receiving direction PGPnet accepts all four ID types from strongSwan.
+--------------------------------------------------------------+
| Connection Definition ID type subjectAltName |
|--------------------------------------------------------------|
| rightid (PGPnet) DER_ASN1_DN - |
|--------------------------------------------------------------|
| leftid (strongSwan) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
+--------------------------------------------------------------+
9.3 SafeNet/Soft-PK/Soft-Remote
---------------------------
SafeNet/Soft-PK and SafeNet/Soft-Remote can be configured to send their
identity either as DER_ASN1_DN, IPV4_ADDR, FQDN, or USER_FQDN.
In the receiving direction SafeNet/Soft-PK and SafeNet/Soft-Remote
accept all four ID types coming from strongSwan.
+--------------------------------------------------------------+
| Connection Definition ID type subjectAltName |
|--------------------------------------------------------------|
| rightid (SafeNet/Soft-PK) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
|--------------------------------------------------------------|
| leftid (strongSwan) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
+--------------------------------------------------------------+
9.4 SSH Sentinel
------------
SSH Sentinel sends its identity as DER_ASN1_DN if the subjectAltName field of
its certificate is empty. If a subjectAltName field is present, then the
corresponding type IPV4_ADDR, FQDN, or USER_FQDN is automatically chosen.
With several subjectAltName entries, the precedence of the different ID types
is not quite clear. In the receiving direction SSH Sentinel accepts all four
ID types from strongSwan.
+--------------------------------------------------------------+
| Connection Definition ID type subjectAltName |
|--------------------------------------------------------------|
| rightid (SSH Sentinel) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
|--------------------------------------------------------------|
| leftid (strongSwan) DER_ASN1_DN - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
+--------------------------------------------------------------+
9.5 Windows 2000/XP
---------------
Windows 2000 and Windows XP always send the ID type DER_ASN1_DN,
therefore rightid in the connection definition of the strongSwan
security gateway must be an ASN.1 distinguished name.In the
receiving direction Windows 2000/XP accepts all four ID types
from strongSwan.
+--------------------------------------------------------------+
| Connection Definition ID type subjectAltName |
|--------------------------------------------------------------|
| rightid (Windows 2000/XP) DER_ASN1_DN - |
|--------------------------------------------------------------|
| leftid (strongSwan) DER_ASN1_D - |
| FQDN DNS: |
| USER_FQDN email: |
| IPV4_ADDR IP: |
+--------------------------------------------------------------+
10. Monitoring functions
--------------------
strongSwan offers the following monitoring functions:
ipsec listalgs
lists all IKE and ESP cryptographic algorithms that are currently
registered with strongSwan.
The a listing has the following form:
List of registered IKE Encryption Algorithms:
#3 OAKLEY_BLOWFISH_CBC, blocksize: 64, keylen: 128-128-256
#5 OAKLEY_3DES_CBC, blocksize: 64, keylen: 192-192-192
#7 OAKLEY_AES_CBC, blocksize: 128, keylen: 128-128-256
#65004 OAKLEY_SERPENT_CBC, blocksize: 128, keylen: 128-128-256
#65005 OAKLEY_TWOFISH_CBC, blocksize: 128, keylen: 128-128-256
#65289 OAKLEY_TWOFISH_CBC_SSH, blocksize: 128, keylen: 128-128-256
List of registered IKE Hash Algorithms:
#1 OAKLEY_MD5, hashsize: 128
#2 OAKLEY_SHA, hashsize: 160
#4 OAKLEY_SHA2_256, hashsize: 256
#6 OAKLEY_SHA2_512, hashsize: 512
List of registered IKE DH Groups:
#2 OAKLEY_GROUP_MODP1024, groupsize: 1024
#5 OAKLEY_GROUP_MODP1536, groupsize: 1536
#14 OAKLEY_GROUP_MODP2048, groupsize: 2048
#15 OAKLEY_GROUP_MODP3072, groupsize: 3072
#16 OAKLEY_GROUP_MODP4096, groupsize: 4096
#17 OAKLEY_GROUP_MODP6144, groupsize: 6144
#18 OAKLEY_GROUP_MODP8192, groupsize: 8192
List of registered ESP Encryption Algorithms:
#3 ESP_3DES, blocksize: 64, keylen: 168-168
#7 ESP_BLOWFISH, blocksize: 64, keylen: 96-128
#12 ESP_AES, blocksize: 128, keylen: 128-256
#252 ESP_SERPENT, blocksize: 128, keylen: 128-256
#253 ESP_TWOFISH, blocksize: 128, keylen: 128-256
List of registered ESP Authentication Algorithms:
#1 AUTH_ALGORITHM_HMAC_MD5, keylen: 128-128
#2 AUTH_ALGORITHM_HMAC_SHA1, keylen: 160-160
#5 AUTH_ALGORITHM_HMAC_SHA2_256, keylen: 256-256
#7 AUTH_ALGORITHM_HMAC_SHA2_512, keylen: 512-512
The command
ipsec listpubkeys [--utc]
lists all public keys currently installed in the chained list of public
keys. These keys were statically loaded from ipsec.conf or aquired either
from received certificates or retrieved from secure DNS servers using
opportunistic mode.
The public key listing has the following form:
Feb 11 14:40:18 2005, 2048 RSA Key AwEAAa+uL,
until Sep 09 13:17:25 2009 ok
ID_FQDN '@moon.strongswan.org'
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
serial: '03'
Feb 11 14:40:18 2005, 2048 RSA Key AwEAAa+uL,
until Sep 09 13:17:25 2009 ok
ID_DER_ASN1_DN 'C=CH, O=Linux strongSwan, CN=moon.strongswan.org'
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
serial: '03'
Feb 11 13:36:53 2005, 2048 RSA Key AwEAAbgbh,
until Dec 31 22:43:18 2009 ok
ID_USER_FQDN 'carol@strongswan.org'
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
serial: '0a'
It consists of
- the date the public key was installed either in local time or UTC (--utc)
- the modulus size of the RSA key in bits
- a keyID consisting of 9 base64 symbols representing the public exponent
and the most significant bits of the modulus
- the expiration date of the public key (extracted from the certificate)
- the type and value of the ID associated with the public key.
- the issuer of the certificate the public key was extracted from.
- the serial number of the certificate the public key was extracted from.
A public key can be associated with several IDs, e.g. using subjectAltNames
in certificates and an ID can possess several public keys, e.g. retrieved
from a secure DNS server.
The command
ipsec listcerts [--utc]
lists all local certificates, both strongSwan's own and those of
trusted peer loaded via leftcert and rightcert, respectively.
The output has the form
Feb 11 13:36:47 2005, count: 4
subject: 'C=CH, O=Linux strongSwan, CN=moon.strongswan.org'
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
serial: 03
pubkey: 2048 RSA Key AwEAAa+uL, has private key
validity: not before Sep 10 13:17:25 2004 ok
not after Sep 09 13:17:25 2009 ok
subjkey: e5:e4:10:87:6c:2a:c4:be:ad:85:49:42:a6:de:76:58:30:3a:9f:c1
authkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
aserial: 00
and shows
- the date the certificate was installed either in local time or UTC (--utc)
- the count shows how many connections refer to this certificate
- the subject of the certificate
- the issuer of the certificate
- the serial number of the certificate
- the size and keyid of the RSA public key contained in the certificate.
the label "has private key" indicates that a matching RSA private key
has been found, defined or loaded in ipsec.secrets.
- the label "on smartcard" indicates that the certificate was loaded from
a smartcard or cryptotoken and that most probably a matching RSA private
key also resides on-card.
- the validity of the CA certificate expressed either in local time or
UTC (--utc). The validity is checked automatically resulting either
in an "ok" message or a "fatal" error message.
- the optional subjectKeyIdentifier extension which is a 20 byte SHA-1 hash
over the certificate's public key.
- the optional authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the issuer who signed the certificate.
- the serial number of the issuer's certificate.
The command
ipsec listcacerts [--utc]
lists all CA certificates that have been either been loaded from the directory
/etc/ipsec.d/cacerts/ or received via the IKE protocol. The output has the form
Feb 11 13:36:52 2005, count: 1
subject: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
serial: 00
pubkey: 2048 RSA Key AwEAAb/yX
validity: not before Sep 10 13:01:45 2004 ok
not after Sep 08 13:01:45 2014 ok
subjkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
authkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
aserial: 00
and shows
- the date the CA certificate was installed either in local time or UTC (--utc)
- the count is always set to 1
- the subject of the CA certificate
- the issuer of the CA certificate
- the serial number of the CA certificate
- the size and keyid of the RSA public key contained in the certificate.
- the validity of the CA certificate expressed either in local time or
UTC (--utc). The validity is checked automatically resulting either
in an "ok" message or a "fatal" error message.
- the optional subjectKeyIdentifier extension which is a 20 byte SHA-1 hash
over the CA certificate's public key.
- the optional authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the issuer who signed the CA certificate.
For Root CA certificates the authorityKeyIdentifier and subjectKeyIdentifier
fields must be equal.
- the serial number of the issuer's certificate.
The command
ipsec listaacerts [--utc]
lists all Authorization Authority certificates that have been loaded from
the directory /etc/ipsec.d/aacerts/.
The output has the form
Dec 20 13:29:55 2004, count: 1
subject: 'C=CH, O=strongSec GmbH, CN=strongSec Authorization Authority'
issuer: 'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
serial: 0f
pubkey: 2048 RSA Key AwEAAfazH
validity: not before Aug 24 13:41:56 2003 ok
not after Aug 23 13:41:56 2005 ok
subjkey: 56:89:b9:28:c9:1b:a0:00:7f:50:9d:ec:28:75:23:c1:1e:d1:dd:90
authkey: af:80:d5:c6:02:1c:96:78:b3:85:a5:65:a2:23:fd:ad:cf:e2:55:b2
aserial: 00
and shows
- the date the AA certificate was installed either in local time or UTC (--utc)
- the count is always set to 1
- the subject of the AA certificate
- the issuer of the AA certificate
- the serial number of the AA certificate
- the size and keyid of the RSA public key contained in the certificate.
- the validity of the AA certificate expressed either in local time or
UTC (--utc). The validity is checked automatically resulting either
in an "ok" message or a "fatal" error message.
- the optional subjectKeyIdentifier extension which is a 20 byte SHA-1 hash
over the AA certificate's public key.
- the optional authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the issuer who signed the AA certificate.
- the serial number of the issuer's certificate.
The command
ipsec listocspcerts [--utc]
lists all OCSO signer certificates that have been either loaded from
/etc/ipsec.d/ocspcerts/ or have been received included in the OCSP server
response. The output has the form
Feb 09 22:56:17 2005, count: 1
subject: 'C=CH, O=Linux strongSwan, OU=OCSP, CN=ocsp.strongswan.org'
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
serial: 09
pubkey: 2048 RSA Key AwEAAaonT
validity: not before Nov 19 17:29:28 2004 ok
not after Nov 18 17:29:28 2009 ok
subjkey: 88:07:0a:b8:ae:c7:c1:07:5c:be:68:6a:c4:a5:7f:81:1f:37:b5:56
authkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
aserial: 00
and shows
- the date the OCSP signer certificate was installed either in local time
or UTC (--utc)
- the count is always set to 1
- the subject of the OCSP signer certificate
- the issuer of the OCSP signer certificate
- the serial number of the OCSP signer certificate
- the size and keyid of the RSA public key contained in the certificate.
- the validity of the OCSP signer certificate expressed either in local time
or UTC (--utc). The validity is checked automatically resulting either
in an "ok" message or a "fatal" error message.
- the optional subjectKeyIdentifier extension which is a 20 byte SHA-1 hash
over the OCSP signer certificate's public key.
- the optional authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the issuer who signed the OCSP certificate.
- the serial number of the issuer's certificate.
The command
ipsec listacerts [--utc]
lists all X.509 attribute certificates that have been loaded from the directory
/etc/ipsec.d/acerts/.
The output has the form
Dec 20 13:29:56 2004
holder: 'C=CH, O=strongSec GmbH, CN=Andreas Steffen'
hissuer: 'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
hserial: 1e
groups: Research, Sales
issuer: 'C=CH, O=strongSec GmbH, CN=strongSec Authorization Authority'
serial: 2c
validity: not before Dec 19 14:51:38 2004 ok
not after Dec 20 14:51:38 2004 fatal (expired)
authkey: 56:89:b9:28:c9:1b:a0:00:7f:50:9d:ec:28:75:23:c1:1e:d1:dd:90
aserial: 0f
and shows
- the date the attribute certificate was installed either in local time
or UTC (--utc)
- the holder of the attribute certificate
- the issuer of holder's certificate
- the serial number of the holder's certificate
- the group attributes
- the issuing Authorization Authority of the attribute certificate
- the serial number of the attribute certificate
- the validity of the attribute certificate expressed either in local time or
UTC (--utc). The validity is checked automatically resulting either
in an "ok" message or a "fatal" error message.
- an authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the issuing Authorization Authority
- the serial number of the AA certificate.
The command
ipsec listgroups [--utc]
lists all group attributes either defined in right|leftgroups statements
in ipsec.conf or contained in loaded X.509 attribute certificates.
The output has the form
Dec 20 13:29:55 2004, count: 4
Research
Dec 20 13:30:04 2004, count: 1
Research New York
Dec 20 13:29:55 2004, count: 3
Sales
and shows
- the date the group attribute was first installed either in local time
or UTC (--utc)
- the count shows how many times the attribute is used
- the group name
The command
ipsec listcainfos [--utc]
lists the properties defined by the ca definition sections in ipsec.conf.
The output has the form
Jun 08 22:31:37 2004, "strongswan"
authname: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
ldaphost: 'ldap.strongswan.org'
ocspuri: 'http://ocsp.strongswan.org:8880'
distPts: 'http://crl.strongswan.org/strongswan.crl'
'ldap:///O=Linux strongSwan, C=CH?certificateRevocationList'
authkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
aserial: 00
and shows
- the date the CA definition was loaded either in local time or UTC (--utc)
- the name of the ca section
- the distinguished name of the CA
- an optional default ldap host for the CA
- an optional OCSP URI
- a maximum of two optional CRL distribution points
- the optional authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the CA.
- the serial number of the CA.
The command
ipsec listcrls [--utc]
lists all CRLs that have been loaded from /etc/ipsec.d/crls/.
The output has the form
Feb 11 13:37:00 2005, revoked certs: 1
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
distPts: 'http://crl.strongswan.org/strongswan.crl'
updates: this Feb 08 07:46:29 2005
next Mar 10 07:46:29 2005 ok
authkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
aserial: 00
and shows
- the date the CRL was installed either in local time or UTC (--utc)
- the number revoked certificates
- the issuer of the CRL
- the URLs of the distribution points where the CRL can be fetched from.
- the dates when the CRL was issued and when the next update
is expected, respectively, expressed either in local time or
UTC (--utc). It is automatically checked if the next update
deadline has passed, resulting either in an "ok" message, a
a "warning" message when strictcrlpolicy=no or a "fatal" message when
strictcrlpolicy=yes.
- the optional authorityKeyIdentifier extension which is a 20 byte SHA-1 hash
over the public key of the issuer who signed the CRL. This extension is
present in version 2 CRLs, only.
- the serial number of the issuer's certificate.
The command
ipsec listocsp [--utc]
lists the contents of the OCSP response cache. The output has the form
issuer: 'C=CH, O=Linux strongSwan, CN=strongSwan Root CA'
uri: 'http://ocsp.strongswan.org:8880'
authname: 13:9d:a0:9e:f4:32:ab:8f:e2:89:56:67:fa:d0:d4:e3:35:86:71:b9
authkey: 5d:a7:dd:70:06:51:32:7e:e7:b6:6d:b3:b5:e5:e0:60:ea:2e:4d:ef
aserial: 00
Feb 09 22:56:17 2005, until Feb 09 23:01:17 2005 warning (expires in 4 minutes)
serial: 0a, good
and shows
- the distinguished name of the CA handled by the OCSP server
- the http URI of the OCSP server.
- the 20 byte SHA-1 hash of the CA's distinguished name
- the 20 byte SHA-1 hash of the CA's public key
- the serial number of the CA's certificate
- a certificate status list showing
- the time the OCSP status was received
- an optional nextUpdate deadline (if missing the OCSP status will be
onetime with a lifetime of 2 minutes only).
- the serial number of the certificate
- the status of the certificate (good, revoked, unknown)
The command
ipsec listcards [--utc]
lists all smartcard records that are currently in use by Pluto.
The output has the form
Aug 17 16:47:59 2005, #1, count: 6
slot: 0, session closed, logged out, has valid pin
id: 45
label: 'strongSwan'
subject: 'C=CH, O=Linux strongSwan, CN=carol@strongswan.org'
with pkcs11keepstate=no and
Aug 17 16:47:59 2005, #1, count: 6
slot: 0, session opened, logged in, has pin pad
id: 45
label: 'strongSwan'
subject: 'C=CH, O=Linux strongSwan, CN=carol@strongswan.org'
with pkcs11keepstate=yes and shows
- the date the certificate was read from the smartcard record
- the certificate objects are numbered starting from #1
- the count shows how many connections and secret pin entries point
to the smartcard record
- the PKCS #11 slot number
- the PKCS #11 session state: closed | opened
- the PKCS #11 session login state: logged out | logged in
- the status of the PIN: no pin | valid pin | invalid pin | pin pad
- the ID of the certificate object
- the label of the certificate object
- the subject distinguished name of the certificate
The command
ipsec auto --listall [--utc]
is equivalent to
ipsec listalgs
ipsec listpubkeys [--utc]
ipsec listcerts [--utc]
ipsec listcacerts [--utc]
ipsec listaacerts [--utc]
ipsec listocspcerts [--utc]
ipsec listacerts [--utc]
ipsec listgroups [--utc]
ipsec listcainfos [--utc]
ipsec listcrls [--utc]
ipsec listocsp [--utc]
ipsec listcards [--utc]
11. Firewall support functions
--------------------------
11.1 Environment variables in the updown script
------------------------------------------
strongSwan makes the following environment variables available
in the updown script indicated by the leftupdown option:
+------------------------------------------------------------------+
| Variable Example Comment |
|------------------------------------------------------------------|
| $PLUTO_PEER_ID carol@strongswan.org USER_FQDN (1) |
|------------------------------------------------------------------|
| $PLUTO_PEER_PROTOCOL 17 udp (2) |
|------------------------------------------------------------------|
| $PLUTO_PEER_PORT 68 bootpc (3) |
|------------------------------------------------------------------|
| $PLUTO_PEER_CA C=CH, O=ACME, CN=Sales CA (4) |
|------------------------------------------------------------------|
| $PLUTO_MY_ID @moon.strongswan.org FQDN (1) |
|------------------------------------------------------------------|
| $PLUTO_MY_PROTOCOL 17 udp (2) |
|------------------------------------------------------------------|
| $PLUTO_MY_PORT 67 bootps (3) |
+------------------------------------------------------------------+
(1) $PLUTO_PEER_ID/$PLUTO_MY_ID contain the IDs of the two ends
of an established connection. In our examples these
correspond to the strings defined by rightid and leftid,
respectively.
(2) $PLUTO_PEER_PROTOCOL/$PLUTO_MY_PROTOCOL contain the protocol
defined by the rightprotoport and leftprotoport options,
respectively. Both variables contain the same protocol value.
The variables take on the value '0' if no protocol has been defined.
(3) $PLUTO_PEER_PORT/$PLUTO_MY_PORT contain the ports defined by
the rightprotoport and leftprotoport options, respectively.
The variables take on the value '0' if no port has been defined.
(4) $PLUTO_PEER_CA contains the distinguished name of the CA that
issued the peer's certificate.
11.2 Automatic insertion and deletion of iptables firewall rules
-----------------------------------------------------------
Starting with strongswan-2.7.0, the default _updown script automatically inserts
and deletes dynamic iptables firewall rules upon the establishment or teardown,
respectively, of an IPsec security association. This new feature is activated
with the line
leftfirewall=yes
and can be used when the following prerequisites are fulfilled:
- Linux 2.4.x kernel, KLIPS IPsec stack, and arbitrary iptables version.
Filtering of tunneled traffic is based on ipsecN interfaces.
- Linux 2.6.16 kernel or newer, native NETKEY IPsec stack, and
iptables-1.3.5 or newer. Filtering of tunneled traffic is based on
IPsec policy matching rules.
If you define a local client subnet with a netmask larger than /32 behind
the gateway then the automatically inserted FORWARD iptables rules will
not allow to access the internal IP address of the host although it is
part of the client subnet definition. If you want additional INPUT and
OUTPUT iptables rules to be inserted, so that the host itself can be accessed
then add the following line:
lefthostaccess=yes
The _updown script also features a logging facility which will register the
creation (+) and the expiration (-) of each successfully established VPN
connection in a special syslog file in the following concise and easily
readable format:
Jul 19 18:58:38 moon vpn:
+ @carol.strongswan.org 192.168.0.100 -- 192.168.0.1 == 10.1.0.0/16
Jul 19 22:15:17 moon vpn:
- @carol.strongswan.org 192.168.0.100 -- 192.168.0.1 == 10.1.0.0/16
11.3 Sample Linux 2.6 updown script for iptables < 1.3.5
---------------------------------------------------
If you are using a Linux 2.6 kernel older than 2.6.16 or an iptables version
older than 1.3.5 then the IPsec policy matching rules will not be available.
In order to make sure that only tunneled packets are accepted, a mark can be
set on incoming ESP packets. This "ESP" mark will be retained on the
decapsulated packet so that iptables rules inserted by the updown script can
check on the presence of this mark. For this purpose the template located in
programs/_updown_espmark
can be used. Store a copy of _updown_espmark e.g. in /etc/ipsec.updown and load
the script with the line
leftupdown=/etc/updown.ipsec.
In addition for the dynamic updown script to work the following static iptables rules
must be applied:
iptables -t mangle -A INPUT -p 50 -j MARK --set-mark 50
12. Authentication with raw RSA public keys
---------------------------------------
FreeS/WAN, as it is available from www.freeswan.org does public key
authentication with raw RSA public keys that are directly defined in
/etc/ipsec.conf
rightrsasigkey=0sAq4c....
When version 1.x of standard FreeS/WAN receives a certificate request (CR),
it immediately drops the negotiation because it does not know how to answer
the request. As a workaround strongSwan does not send a CR if the RSA
key has been statically loaded using [right/left]rsasigkey. A problem
remains with roadwarriors initiating a connection. Since strongSwan
does not know the identity of the initiating peer in advance, it will always
send a CR, causing the rupture of the IKE negotiation if the peer is a
version 1.x FreeS/WAN host. To circumvent this problem the configuration
parameter 'nocrsend' can be set in the config setup section of /etc/ipsec.conf:
config setup:
nocrsend=yes
With this entry no certificate request is sent in any connection.
The default setting is nocrsend=no.
13. Authentication with OpenPGP certificates
----------------------------------------
strongSwan also supports RSA based authentication using OpenPGP
certificates and OpenPGP V3 fingerprints used as an KEY_ID identifier.
13.1 OpenPGP certificates
--------------------
OpenPGP certificates containing RSA public keys can now directly be loaded
in ASCII armored PGP format using the leftcert and rightcert parameters
in /etc/ipsec.conf:
conn pgp
right=%any
righcert=peerCert.asc
left=%defaultroute
leftcert=gatewayCert.asc
The peer certificate must be stored locally (the default directory is
/etc/ipsec.d/certs) since currently no trust can be established for
PGP certificates received from a peer via the IKE protocol.
13.2 OpenPGP private keys
--------------------
PGP private keys in unencrypted form can now directly be loaded in ASCII
armored PGP format via an entry in /etc/ipsec.secrets:
: RSA gatewayKey.asc
Existing IDEA-encrypted RSA private keys can be unlocked with GnuPG and
the IDEA extension (see http://www.gnupg.org/gph/en/pgp2x.html) using
the commands
gpg --import gatewayCert.asc
gpg --allow-secret-key-import --import gatewayKey.asc
gpg --edit-key <gateway ID>
> passwd #change to empty password
> save
gpg -a --export-secret-key <gateway ID> gatewayKey.asc
13.3 Monitoring functions
--------------------
The command ipsec listcerts shows all loaded PGP certificates
in the following format:
Aug 28 09:51:55 2002, count: 1
fingerprint: 0x1ccfca12d93467ffa9d5093d87a465dc
pubkey: 1024 RSA Key ARHso6uKQ
created: Aug 27 08:51:39 2002
until: --- -- --:--:-- ---- ok (expires never)
The entries are
- the date the certificate was loaded either in local time or UTC (--utc)
- the V3 fingerprint consisting of the 16 byte MD5 hash of the public key
which is used as an ID of type KEY_ID
- the modulus size of the RSA key in bits
- a keyID consisting of 9 base64 symbols representing the public exponent
and the most significant bits of the modulus
- the creation date of the public key (extracted from the certificate)
- the optional expiration date of the public key (extracted from the
certificate)
13.4 Suppression of certificate request messages
-------------------------------------------
PGPnet configured to work with OpenPGP certificates aborts the IKE
negotiation when it receives a X.509 certificate. Therefore it is recommended
(mandatory for roadwarrior connections) to set
config setup:
nocrsend=yes
in /etc/ipsec.conf.
14. Additional Features
-------------------
14.1 Authentication and encryption algorithms
----------------------------------------
strongSwan supports the following suite of encryption and authentication
algorithms for both IKE and ESP payloads.
+------------------------------------------------------------------+
| IKE algorithms (negotiated in Phase 1 Main Mode) |
+------------------------------------------------------------------+
| Encryption algorithms: 3des, aes, serpent, twofish, blowfish |
|------------------------------------------------------------------|
| Hash algorithms: md5, sha, sha2 |
|------------------------------------------------------------------|
| DH groups: 1024, 1536, 2048, 3072, 4096, 6144, 8192 |
+------------------------------------------------------------------+
NOTE: For IKE the SHA-1 algorithm is denoted by "sha"
The cryptographic IKE algorithms listed above are a fixed part of the
strongSwan distribution. Particular algorithms can be added or removed
in the "programs/pluto/alg" directory.
+------------------------------------------------------------------+
| ESP algorithms (negotiated in Phase 2 Quick Mode) |
+------------------------------------------------------------------+
| Encryption algorithms: 3des, aes, serpent, twofish, blowfish |
|------------------------------------------------------------------|
| Hash algorithms: md5, sha1, sha2 |
|------------------------------------------------------------------|
| PFS groups: 1024, 1536, 2048, 3072, 4096, 6144, 8192 |
+------------------------------------------------------------------+
The cryptographic ESP algorithms listed above are a fixed part of the
strongSwan distribution. If your Linux 2.4 or 2.6 kernel includes the
CryptoAPI then additional ESP algorithms can be added or deleted as
kernel modules.
The IKE and ESP cryptographic algorithms to be proposed to the peer
as an initiator can be specified on a per connection basis in the form
conn normal
...
ike=aes128-sha-modp1536,3des-sha-modp1536
esp=aes128-sha1,3des-sha1
...
or if you are more paranoid
conn paranoid
...
ike=aes256-sha2_512-modp2048
esp=aes256-sha2_512
...
If the the "ike" and "esp" configuration parameters are missing in
ipsec.conf, then the default settings
ike=3des-md5-modp1536,3des-sha-modp1536,\
3des-md5-modp1024,3des-sha-modp1024
esp=3des-md5,3des-sha1
arre implicitly assumed. The 3DES encryption algorithm and the MD5 and
SHA-1 hash algorithms are hardcoded into strongSwan and cannot be removed.
If Perfect Forward Secrecy (PFS is desired), then a PFS group can be
optionally specified:
conn make_sure
...
pfs=yes
pfsgroup=modp2048,modp1536
...
If the "pfs" parameter is missing then "pfs=yes" is assumed by default.
This means that PFS must be disabled explicitly by setting "pfs=no".
If the "pfsgroup" parameter is missing then the default is
pfsgroup=<Phase1 DH group>
The "ike" and "esp" parameters are used to formulate one or several
transform proposals to the peer if the strongSwan VPN host is the initiator.
Attention! As a responder the first proposal from the peer is accepted that
is supported the by one of the registered algorithms listed by the command
ipsec listalgs
If the responder wants to restrict the allowed cipher suites the '!' flag
can be used to do so. The configuration
conn normal_but_strict
...
ike=aes128-sha-modp1536,3des-sha-modp1536!
esp=aes128-sha1,3des-sha1!
...
will only permit the listed algorithms defined above but no other methods
even if they might be supported by the responder.
14.2 NAT traversal
-------------
Currently please refer to README.NAT-Traversal document in the strongSwan
distribution.
14.3 Dead peer detection
--------------------
strongSwan implements the RFC 3706 Dead Peer Detection (DPD) keep-alive
scheme. If an established IPsec SA has been idle (i.e. without any traffic)
for N seconds (dpddelay=N) then strongSwan side sends a "hello" message
(R_U_THERE) and the peer replies with an acknowledge message (R_U_THERE_ACK).
If no response is received, the R_U_THERE messages are repeated until a DPD
timeout of M seconds (dpdtimeout=M) has elapsed. If still no traffic or
R_U_THERE_ACK packets were received, the peer is declared to be dead and all
SAs belonging to a common Phase 1 SA are deleted.
DPD support is tuneable on a per connection basis by using the dpdaction,
dpddelay and dpdtimeout directives:
conn roadwarrior
right=%any
left=%defaultroute
leftsubnet=10.1.0.0/16
dpdaction=clear
conn net-to-net
right=192.168.0.2
rightsubnet=10.2.0.0/16
left=%defaultroute
leftsubnet=10.1.0.0/16
dpdaction=hold
dpddelay=60
dpdtimeout=500
In the first example dpdaction=clear activates the DPD mechanism under the
condition that the peer supports RFC 3706. The values dpddelay=30s and
dpdtimeout=120s are assumed by default in the absence of these parameters, so
that during idle periods an R_U_THERE packet is sent every 30 seconds. If no
traffic or a no R_U_THERE_ACK packet is received from the peer within a
120 second time span, the peer will be declared dead and all SAs and associated
eroutes will be cleared.
In the second example R_U_THERE packets are sent every 60 seconds and the
parameter setting dpdaction=hold will put the eroute of the ruptured connection
into a %trap state, so that when new outgoing traffic will occur, the
correspondig connection will be automatically renegotiated as soon as the
peer is up again.
It is recommended to use dpdaction=hold for statically defined connections and
dpdaction=clear for dynamic roadwarrior connections. The default value is
dpdaction=none, which disables DPD.
14.4 IKE Mode Config
---------------
The IKE Mode Config protocol <draft-ietf-ipsec-isakmp-mode-cfg-04.txt> allows
the dynamic assignment of virtual IP addresses and optional DNS and WINS server
information to IPsec clients. Currently only "Mode Config Pull Mode" is
implemented where the client actively sends a Mode Config request to the server
in order to obtain a virtual IP.
Client side configuration (carol):
conn home
right=192.168.0.1
rightsubnet=10.1.0.0/16
rightid=@moon.strongswan.org
left=%defaultroute
leftsourceip=%modeconfig
leftcert=carolCert.pem
leftid=carol@strongswan.org
auto=start
Server side configuration (moon):
conn roadwarrior
right=%any
rightid=carol@strongswan.org
rightsourceip=10.3.0.1
left=%defaultroute
leftsubnet=10.1.0.0/16
leftcert=moonCert.pem
leftid=@moon.strongswan.org
auto=add
The wildcard %modeconfig or %modecfg used in the leftsourceip parameter of the
client will trigger a Mode Config request. Currently the server will return
the virtual IP address defined by the rightsourceip parameter. In the future
an LDAP-based lookup mechanism will be supported.
15. Copyright statement and acknowledgements
----------------------------------------
FreeS/WAN version base system:
Copyright (c) 1999-2004
Henry Spencer, Richard Guy Briggs,
D. Hugh Redelmeier, Sandy Harris, Claudia Schmeing,
Michael Richardson, Angelos D. Keromytis, John Ioannidis,
NAT-Traversal, ipsec starter, Delete SA and Notification messages:
Copyright (c) 2002-2003, Mathieu Lafon
Additional cryptoalgorithms (AES, etc):
Copyright (c) 2002-2003, JuanJo Ciarlante
Dead Peer Detection:
Copyright (c) 2002-2004
Ken Bantoft, JuanJo Ciarlante, Philip Craig,
Pawel Krawczyk, Srinvasan Venkataraman
Porting to Linux 2.6 kernel:
Copyright (c) 2003, Herbert Xu
Dynamic CRL fetching:
Copyright (c) 2002, Stephane Laroche
IKE Mode Config protocol:
Copyright (c) 2001-2002, Colubris Networks
Virtual IP and source routing:
Copyright (c) 2003, Tuomo Soini
Port and protocol selectors for outbound traffic:
Copyright (c) 2002, Stephen J. Bevan
PGPnet-RSA parts of patch:
Copyright (c) 2000, Kai Martius
X.509, OCSP and smartcard functionality:
Copyright (c) 2000, Andreas Hess, Patric Lichtsteiner, Roger Wegmann
Copyright (c) 2001, Marco Bertossa, Andreas Schleiss
Copyright (c) 2002, Uli Galizzi, Ariane Seiler, Mario Strasser
Copyright (c) 2002, Martin Berner, Lukas Suter
Copyright (c) 2003, Christoph Gysin, Simon Zwahlen
Copyright (c) 2004, David Buechi, Michael Meier
Copyright (c) 2000-2005, Andreas Steffen
Zurich University of Applied Sciences in Winterthur, Switzerland
scepclient:
Copyright (c) 2005, Jan Hutter, Martin Willi
Copyright (c) 2005-2006, Andreas Steffen
University of Applied Sciences in Rapperswil, Switzerland
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version. See http://www.fsf.org/copyleft/gpl.txt.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
-----------------------------------------------------------------------------
This file is RCSID $Id: README,v 1.33 2006/04/24 21:27:49 as Exp $
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