Installation and Configuration Guide

X.509 FreeS/WAN-Version 1.4.8

Contents

  1. Summary
  2. Acknowledgements
  3. Installation
    1. The X.509 distribution
    2. Installing the X.509 patch
    3. Enabling dynamic LDAP URL fetching
    4. Installing FreeS/WAN with X.509 on a fresh kernel
    5. Adding X.509 on top of a working FreeS/WAN IPsec stack
  4. Configuring the connections - ipsec.conf
    1. Configuring my side
    2. Multiple certificates
    3. Configuring the peer side using CA certificates
    4. Handling Virtual IPs and wildcard subnets
    5. Protocol and port selectors
    6. IPsec policies based on wildcards
    7. IPsec policies based on CA certificates
    8. Sending certificate requests
  5. Configuring certificates and CRLs
    1. Installing CA certificates
    2. Installing optional certificate revocation lists (CRLs)
    3. Dynamic update of certificates and CRLs
    4. CRL policy
    5. Configuring the peer side using locally stored certificates
  6. Configuring the private key - ipsec.secrets
    1. Loading private key files in PKCS#1 format
    2. Entering passphrases interactively  (NEW)
    3. Multiple private keys
  7. Generating X.509 certificates and CRLs with OpenSSL
    1. Generating a CA certificate
    2. Generating a host or user certificate
    3. Generating a CRL
    4. Revoking a certificate
  8. Smartcard support
    1. Compiling FreeS/WAN with smartcard support
    2. Configuring a smartcard-based connection
    3. Entering the PIN code
    4. Configuring a smartcard using pkcs15-init
  9. Configuring the clients
    1. FreeS/WAN
    2. PGPnet
    3. Safenet/Soft-PK/Soft-Remote
    4. SSH Sentinel
    5. Windows 2000/XP
  10. Monitoring functions   (NEW)
  11. Firewall support functions
    1. Environment variables in the updown script
    2. Sample updown script for iptables
  12. Using the patch with FreeS/WAN and raw RSA keys
  13. Using the patch with OpenPGP certificates
    1. OpenPGP certificates
    2. OpenPGP private keys
    3. Monitoring functions
    4. Suppressing certificate request messages

1. Summary

The X.509 patch supports RSA-based authentication using X.509 or OpenPGP certificates between a Linux FreeS/WAN security gateway and an unlimited number of IPsec peers.

  • Version 0.9 of the patch introduced certification authorities (CAs), hierarchical trust chains and certificate revocation lists (CRLs), thereby eliminating the need to store peer certificates locally on the Linux security gateway.
  • Version 0.9.10 introduced support of multiple certificates and corresponding private keys as described in sections 4.2 and 6.2.
  • Version 1.0.0 improves the support of OpenPGP certificates which can now be used concurrently with X.509 certificates. For details consult section 13.
  • Version 1.1.0 introduced dynamic CRL fetching supporting http, ftp, file and ldap crlDistributionPoints. For details refer to section 3.3 and 5.3.
  • Version 1.1.1 introduced protocol and port selectors for outbound IPsec SAs.
  • Version 1.2.0 brought IPsec policies based on wildcards(*) in distinguished names (ID_DER_ASN1_DN). For details see section 4.6.
  • Version 1.3.0 introduced IPsec policies based on certification authorities (several root and/or intermediate CAs). This feature will facilitate the setup of extranets giving restricted VPN access to third parties (e.g. customers or suppliers). For details refer to section 4.7.
  • Version 1.4.0 brings smartcard support. The functionality is based on the PKCS#15 cryptotoken interface provided by the OpenSC project. For details see section 8.

Compatibility has successfully been  tested with peers running the following IPsec clients:

FreeS/WAN PGPnet, SafeNet/Soft-PK, SafeNet/SoftRemote,
SSH Sentinel
, Microsoft Windows 2000 and Windows XP.

Furthermore interoperability with the following VPN gateways has been demonstrated during the IPsec 2001 Conference in Paris:

Cisco IOS Routers, Cisco PIX Firewall, Cisco VPN 3000,
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 X.509-enabled FreeS/WAN. The latest addition has been the successful interoperability with the Check Point VPN-1 NG gateway.

2. Acknowledgements

Major contributions to the X.509 patch for Linux FreeS/WAN have come from Marco Bertossa, Andreas Hess, Patric Lichtsteiner, Andreas Schleiss, and Roger Wegmann, all present or former students of the Zurich University of Applied Sciences in Winterthur (Switzerland). The support of Virtual IPs and the DHCP-over-IPsec protocol has been developped and coded by Mario Strasser, research assistant at the ZHW. Smartcard support has been provided
by the ZHW students Christoph Gysin and Simon Zwahlen.

Stephane Laroche from Colubris has contributed dynamic CRL fetching.

Stephen J. Bevan has contributed the enforcement of port and protocol selectors on outbound traffic based on extended eroutes.

The X.509 patch also integrates the original contribution by Kai Martius supporting RSA based authentication using OpenPGP certificates and PGP's proprietary Key IDs.

The development of the patch is coordinated by Andreas Steffen, professor for Communications and Security at the ZHW. 

3. Installation

3.1 The X.509 distribution

The X.509 patch distribution contains the following files:

README

This installation and configuration guide in ASCII format

CHANGES

Change history for the X.509 patch

freeswan.diff

Patch for the freeswan directory

ipsec.secrets.template

Template for /etc/ipsec.secrets

3.2. Installing the X.509 patch

Copy the patch freeswan.diff to  the FreeS/WAN source directory and type:

patch -p1 < freeswan.diff

This applies all necessary changes to the pluto directory as well as to the scripts utils/auto and utils/_confread.

3.3 Enabling dynamic LDAP URL fetching

By default LDAP support will not be compiled into Pluto. In order to enable dynamic LDAP URL fetching, one of the two following lines must be uncommented in the programs/pluto/Makefile:

# Uncomment to enable dynamic CRL fetching using LDAP V3
LDAP_VERSION=3
# Uncomment to enable dynamic CRL fetching using LDAP V2
#LDAP_VERSION=2

Compilation will be successful only if the OpenLDAP 2.x header files and the ldap library are present. The latest OpenLDAP releases require the LDAP V3 protocol whereas older versions use LDAP V2.

http, ftp, and file URLs are fetched using the curl command line tool. LDAP source code support is not required for these types of URLs.

3.4 Compiling and installing FreeS/WAN with X.509>

After you have applied the X.509 patch, compilation and installation is done in exactly the same way as with standard FreeS/WAN. Please consult the FreeS/WAN documentation for the details.
In order to compile and install the userland programs, change into the FreeS/WAN top source directory and type

make programs

followed by

make install

Since the introduction of the protocol and port selectors in version 0.9.16 it is now also necessary to recompile the kernel part of FreeS/WAN. If you want to build KLIPS as a module then you can do this with the command

make module

 After successful module compilation, copy the module

 ./linux/net/ipsec/ipsec.o

into the directory

/lib/modules/<kernel version>/kernel/net

As a last step you must restart FreeS/WAN to enable the X.509 features

 ipsec setup restart

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 FreeS/WAN security gateway into the conn %default section of the configuration file /etc/ipsec.conf. If we assume throughout this document that the FreeS/WAN security gateway is left and the peer is right (of course you could define the directions also the other way round) then we can write

conn %default
     # use RSA based authentication with certificates
     authby=rsasig
     rightrsasigkey=%cert
     # my side is left - the FreeS/WAN SG
     left=160.85.22.2
     leftcert=pulpoCert.pem
     # load connection definitions automatically
     auto=add

The X.509 certificate by which the FreeS/WAN security gateway will authenticate itself by sending it in binary form to its peers as part of the Internet Key Exchange (IKE) is specified by the line

leftcert=pulpoCert.pem

The certificate can either be stored in base64 PEM-format or the binary DER-format. Irrespective of the file suffix, Pluto "automagically" determines the correct format. Therefore

leftcert=pulpoCert.der

or

leftcert=pulpoCert.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 FreeS/WAN's own certificates from locally stored trusted peer certificates (see section 5.5 for details), they could also be stored in a subdirectory within the default directory /etc/ipsec.d/certs, as e.g. in

leftcert=mycerts/pulpoCert.pem

Absolute pathnames are also possible, as in

leftcert=/usr/ssl/certs/pulpoCert.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=@pulpo.strongsec.com

 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=strongSec GmbH, CN=pulpo.strongsec.com"

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

Starting with version 0.9.10, the X.509 patch 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 FreeS/WAN 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 FreeS/WAN 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 FreeS/WAN 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=strongSec GmbH, CN=wroclaw.strongsec.com"

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 strongSec GmbH, 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=strongSec GmbH/CN=wroclaw.strongsec.com"

This is the representation extracted from the certificate by the OpenSSL command line option

openssl x509 -in wroclawCert.pem -noout -subject

The following X.501 RDNs are supported by the X.509 patch

 DC

 Domain Component

 C

 Country

 ST

 State or province

 L

 Locality or town

 O

 Organisation

 OU

 Organisational Unit

 CN

 Common Name

 ND

 Name Distinguisher, 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

 UID

 User ID

 ID

 X.500 Unique Identifier

 TCGID

 [Siemens] Trust Center Global ID

With the roadwarrior connection definition listed above, an IPsec SA for the FreeS/WAN security gateway pulpo.strongsec.com itself can be established. If any roadwarrior should be able to reach e.g. the two subnets 10.0.1.0/24 and 10.0.3.0/24 behind the security gateway then the following connection definitions will make this possible

conn rw1
     right=%any
     leftsubnet=10.0.1.0/24
    
conn rw3
     right=%any
     leftsubnet=10.0.3.0/24

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 soggy
     right=%any
     rightid=@soggy.strongsec.com
     
conn ewa
     right=%any
     rightid=ewa@strongsec.com
     
conn wroclaw
     right=%any
     rightid="C=CH, O=strongSec GmbH, CN=wroclaw.strongsec.com"

When the IP address of a peer is known to be stable, it can be specified as well. This entry is mandatory when the FreeS/WAN host wants to act as the initiator an IPSec connection.

conn soggy
     right=160.85.22.3
     rightid=@soggy.strongsec.com
     
conn ewa
     right=160.85.22.8
     rightid=ewa@strongsec.com
     
conn wroclaw
     right=160.85.22.8
     rightid="C=CH, O=strongSec GmbH, CN=wroclaw.strongsec.com"
     
conn frosch
     right=160.85.22.5

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 others a left and leftcert entry, as well as a  rightrsasigkey parameter set to the magic value %cert , signifying that the public key will be extracted from a X.509 certificates sent by the peer.

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 FreeS/WAN security gateway the following entries are required in /etc/ipsec.conf:

conn rw1
     right=%any
     righsubnet=10.0.1.5/32

conn rw2
     right=%any
     rightsubnet=10.0.1.5.47/32

conn rw3
     right=%any
     rightsubnet=10.0.1.128/28

With the new wildcard parameter rightsubnetwithin these three entries can be reduced to the single connection definition

conn rw
     right=%any
     rightsubnetwithin=10.0.1.0/24

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 10.0.1.0/24). For each roadwarrior a connection instance tailored to the subnet of the particular client will be created, based on the generic rightsubnetwithin template.

This new feature introduced with version 0.9.12 of the X.509 patch 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

Version 0.9.14 of the X.509 patch offers 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=@pluto.strongsec.com
     leftprotoport=icmp

conn http
     right=%any
     rightprotoport=6
     left=%defaultroute
     leftid=@pluto.strongsec.com
     leftprotoport=6/80

conn dhcp
     right=%any
     rightprotoport=udp/bootpc
     left=%defaultroute
     leftid=@pluto.strongsec.com
     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 auto --status

lists the following connection definitions:

"icmp": 160.85.106.10[@pulpo.strongsec.com]:1/0...%any:1/0
"http": 160.85.106.10[@pulpo.strongsec.com]:6/80...%any:6/00
"dhcp": 0.0.0.0/0===160.85.106.10[@pulpo.strongsec.com]: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. Version 0.9.24 of the X.509 patch 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 also be 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 explicitely because by default it is set to the issuer field of the certificate loaded vialeftcert. 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 FreeS/WAN is the initiator. As a responder FreeS/WAN sends the desired CA only for non-roadwarrior connections.

5. Configuring certificates and CRLs

5.1 Installing the CA certificates

X.509 certificates received by FreeS/WAN 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 the X.509 patch version 0.9 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

Multiple CAs are supported, but presently they just create a large pool of valid user or host certificates and cannot be assigned to specific connection definitions in /etc/ipsec.conf.

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 the directory 

/etc/ipsec.d/crls

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 in the crls directory 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 in either 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 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 dynamic replacement of the various files:

ipsec auto --rereadsecrets

reload file /etc/ipsec.secrets

ipsec auto --rereadcacerts

reload files in /etc/ipsec.d/cacerts directory

ipsec auto --rereadcrls

reload files in /etc/ipsec.d/crls directory

ipsec auto --rereadall

ipsec auto --rereadsecrets
           --rereadcacerts
           --rereadcrls

Starting with version 1.1.0 of the X.509 patch, CRLs can be automatically fetched from an HTTP or LDAP server using the CRL distribution points contained in X.509 certificates. The command

ipsec auto --listcrls

shows any pending fetch requests:

Oct 31 00:29:53 2002, trials: 2
    issuer: 'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
    distPts: 'http://www.strongsec.com/ca/cert.crl'
             'ldap://ldap.strongsec.com/o=strongSec GmbH, c=CH
                 ?certificateRevocationList?base
                 ?(objectClass=certificationAuthority)'

In the example above, a http and a 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=strongSec GmbH, CN=strongSec Root CA'
    distPts: 'http://www.strongsec.com/ca/cert.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=strongSec GmbH, CN=strongSec Root CA'
    distPts: 'http://www.strongsec.com/ca/cert.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 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 this can be done by setting  the strictcrlpolicy option 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 is present in /etc/ipsec.conf. 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 stand still will ensue.

As mentioned earlier the default setting is strictcrlpolicy=no

5.5 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 soggy
     right=%any
     rightid=@soggy.strongsec.com
     rightcert=soggyCert.cer

conn wroclaw
     right=160.85.22.8
     rightcert=wroclawCert.der

If a peer certificate contains a subjectAltName extension, then this can be used to specify an alternative rightid or leftid type, respectively, as the example "conn soggy" shows. If no rightid or leftid 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 FreeS/WAN's own certificates, the following two definitions are also valid for trusted peer certificates:

rightcert=peercerts/wroclawCert.der

or

rightcert=/usr/ssl/certs/wroclawCert.der

6. Installing the private key - ipsec.secrets

6.1 Loading private key files in PKCS#1 format

Starting with version 0.9.8 of the X.509 patch, Pluto 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 pulpoKey.pem

uses a relative pathname. In that case Pluto will look for the private key file in the directory

/etc/ipsec.d/private

As an alternative an absolute pathname can be given as in

: RSA /usr/ssl/private/pulpoKey.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 pulpoKey.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 pulpoKey.pem -out pulpoKey.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 pulpoKey.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 pulpoCert.p12 
               -out pulpoKey.pem

if the key file pulpoKey.pem is to be secured again by a passphrase, or

openssl pkcs12 -nocerts -nodes -in pulpoCert.p12
               -out pulpoKey.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 pulpoKey.pem %prompt

Since FreeS/WAN 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 auto --rereadsecrets

and which causes the prompt

need passphrase for '/etc/ipsec.d/private/pulpoKey.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 passphrase prompting.

6.3 Multiple private keys

 Starting with version 0.9.10 of the X.509 patch, multiple private keys are supported. 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. 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 FreeS/WAN.

7.1 Generating a CA certificate

The OpenSSL statement

openssl req -x509 -days 1460 -newkey rsa:2048 \
            -keyout caKey.pem -out caCert.pem

creates a 2048 bit RSA private key caKey.pem and a self-signed CA certificate caCert.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 certificates to be in binary DER format then the following command achieves this transformation:

openssl x509 -in caCert.pem -outform DER -out caCert.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.

7.2 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:soggy.strongsec.com

if you want to identify the host by its Fully Qualified Domain Name (FQDN ), or

subjectAltName=IP:160.85.22.3

if you want the ID to be of type IPV4_ADDR . Of course you could  include both ID types with

subjectAltName=DNS:soggy.strongsec.com,IP:160.85.22.3

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:ewa@strongsec.com

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.

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 hostKey.pem \
               -in hostCert.pem -name "soggy" \
               -certfile caCert.pem -caname "Root CA" \
               -out hostCert.p12

7.3 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.

7.4 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

8. Smartcard Support

8.1 Compiling FreeS/WAN with smartcard support

By default smartcard support will not be compiled into Pluto. In order to enable smartcard-based authentication, the following line must be uncommented in the programs/pluto/Makefile:

#Uncomment this line to enable smartcard support
SMARTCARD=1

Compilation will be successful only if the OpenSC header files and the opensc library available from

 http://www.opensc.org

are present. Currently the version opensc-0.8.0, using pcsc-lite, usbtoken or openct drivers is supported.

8.2 Configuring a smartcard-based connection

Defining a smartcard-based connection in ipsec.conf is easy:

conn tandoori
     right=160.85.22.10
     rightid=@tandoori.strongsec.com
     rightrsasigkey=%cert
     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 the default entry

leftcert=%smartcard

which stands for the full notation

leftcert=%smartcard0:45

is sufficient. The general notation

leftcert=%smartcard<reader nr>:<PKCS#15 key id>

supports the simultaneous use of several smartcard readers and cryptotokens and can access multiple RSA private keys and corresponding X.509 certificates stored on a crypto device.

8.3 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<reader nr>:<PKCS#15 key id> "<PIN code>"

On a personal notebook computer 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 auto --up tandoori

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
     rightrsasigkey=%cert
     left=%defaultroute
     leftcert=%smartcard1:50
     auto=add

But if there is a corresponding entry

: PIN %smartcard1:50 %prompt

in ipsec.secrets, then the standard command

ipsec auto --rereadsecrets

or the alias

ipsec secrets

can be used to enter the PIN code for this connection interactively. The command

ipsec auto --listcards

can be executed at any time to check the current status of the PIN code[s].
 

8.4 Configuring a smartcard with pkcsc15-init

FreeS/WAN'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 --create-pkcs15 --profile 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 then 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 FreeS/WAN.

9. Configuring the clients

9.1 FreeS/WAN

A FreeS/WAN to FreeS/WAN 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  (FreeS/WAN)

DER_ASN1_DN

-

FQDN

DNS:

USER_FQDN

email:

IPV4_ADDR

IP:

leftid  (FreeS/WAN)

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 FreeS/WAN 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 FreeS/WAN security gateway must be an ASN.1 distinguished name.

In the receiving direction PGPnet accepts all four ID types from FreeS/WAN.

Connection Definition ID type

subjectAltName

rightid  (PGPnet)

DER_ASN1_DN

-

leftid  (FreeS/WAN)

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 or SafeNet/Soft-Remote accept all four ID types coming from FreeS/WAN.

Connection Definition ID type

subjectAltName

rightid  (SafeNet/Soft-PK)

DER_ASN1_DN

-

FQDN

DNS:

USER_FQDN

email:

IPV4_ADDR

IP:

leftid  (FreeS/WAN)

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 FreeS/WAN.

Connection Definition ID type

subjectAltName

rightid  (SSH Sentinel)

DER_ASN1_DN

-

FQDN

DNS:

USER_FQDN

email:

IPV4_ADDR

IP:

leftid  (FreeS/WAN)

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 FreeS/WAN security gateway must be an ASN.1 distinguished name.

 In the receiving direction Windows 2000 or Windows XP accept all four ID types from FreeS/WAN.

Connection Definition ID type

subjectAltName

rightid  (Windows 2000/XP)

DER_ASN1_DN

-

leftid  (FreeS/WAN)

DER_ASN1_DN

-

FQDN

DNS:

USER_FQDN

email:

IPV4_ADDR

IP:

10. Monitoring functions

The X.509 patch offers the following monitoring functions:

ipsec auto [--utc] --listpubkeys

This command 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:

Apr 10 00:10:31 2002, 1024 RSA Key AwEAAb8F/,
   until Jun 09 18:29:32 2002 ok
   ID_DER_ASN1_DN 'C=CH, O=strongSec GmbH, CN=soggy.strongsec.com'
   Issuer 'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
Apr 09 20:57:49 2002, 1024 RSA Key AwEAAbl5j,
   until Feb 13 11:19:25 2003 ok
   ID_USER_FQDN 'Andreas.Steffen@zhwin.ch'
   Issuer 'C=CH, O=ZHW, CN=ZHW Root CA'
Apr 09 20:57:49 2002, 1024 RSA Key AwEAAbl5j,
   until Feb 13 11:19:25 2003 ok
   ID_USER_FQDN 'sna@zhwin.ch'
   Issuer 'C=CH, O=ZHW, CN=ZHW Root CA'

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

A public key can be associated with several IDs, e.g. using class=subjectAltNames in certificates and an ID can possess several public keys, e.g. retrieved from a secure DNS server.

The command

ipsec auto [--utc] --listcerts

lists all local certificates, both FreeS/WAN's own and those of trusted peer loaded via leftcert and rightcert, respectively. The output has the form

May 01 07:09:47 2002, count: 2
       subject: 'C=CH, O=ZHW, OU=IKT, CN=Andreas Steffen'
       issuer:  'C=CH, O=ZHW, OU=IKT, CN=ZHW Root CA'
       serial:   1f
       pubkey:   1024 RSA Key AwEAAbl5j
       validity: not before Feb 13 11:19:25 2002 ok
                 not after Feb 13 11:19:25 2003 ok
May 01 07:09:47 2002, count: 10
       subject: 'C=CH, O=strongSec GmbH, CN=pulpo.strongsec.com'
       issuer:  'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
       serial:   04
       pubkey:   1024 RSA Key AwEAAfic+, has private key
       validity: not before Jun 09 18:38:04 2001 ok
                 not after  Jun 09 18:38:04 2002 ok
       subjkey:  02:f7:77:c4:05:ee:12:74:ea:34:0d:7a:a3:...
       authkey:  af:80:d5:c6:02:1c:96:78:b3:85:a5:65:a2:...
       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 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 auto [--utc] --listcacerts

lists all CA certificates that have been loaded from /etc/ipsec.d/cacerts.

The output has the form

May 01 07:09:47 2002, count: 1
       subject: 'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
       issuer:  'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
       serial:   00
       pubkey:   2048 RSA Key AwEAAcLG1
       validity: not before May 02 23:02:35 2001 ok
                 not after  May 01 23:02:35 2005 ok
       subjkey:  af:80:d5:c6:02:1c:96:78:b3:85:a5:65:a2:...
       authkey:  af:80:d5:c6:02:1c:96:78:b3:85:a5:65:a2:...
       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 SHA-1 hash over the public key of the issuer who signed the CA certificate. With Root CA certificates  authorityKeyIdentifier and subjectKeyIdentifier must be equal.
  • the serial number of the issuer's certificate.

The command

ipsec auto [--utc] --listcrls

lists all CRLs that have been loaded from /etc/ipsec.d/crls.

The output has the form

Oct 30 22:57:51 2002, revoked certs: 37
       issuer: 'C=CH, O=strongSec GmbH, CN=strongSec Root CA'
       distPts: 'http://www.strongsec.com/ca/cert.crl'
       updates: this Oct 15 23:42:12 2002
                next Nov 14 22:42:12 2002 ok
       authkey: af:80:d5:c6:02:1c:96:78:b3:85:a5:65:a2:...
       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 or a warning message, since CRL updates are currently not enforced by the X.509 patch
  • 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 auto [--utc] --listcards

lists all smartcard records that are currently in use by Pluto. The output has the form


Jul 08 17:12:49 2003, count: 2
    reader: 0, id: 50, has no pin
Jul 08 17:12:50 2003, count: 6
    reader: 0, id: 45, has valid pin

and shows

  • the date the certificate was read from the smartcard record
  • the count shows how many connections and secret pin entries point to the smartcard record
  • the smartcard reader or cryptotoken number. With a single reader or cryptotoken this number is usually 0.
  • the ID of the certificate/private key record. With a single certificate this ID is usually 45
  • the status of the PIN: no | valid | invalid

The command

ipsec auto [--utc] -listall

is equivalent to

ipsec auto [--utc] -listpubkeys
ipsec auto [--utc] -listcerts
ipsec auto [--utc] -listcacerts
ipsec auto [--utc] -listcrls
ipsec auto [--utc] -listcards

11. Firewall support functions

11.1 Environment variables in the updown script

The X.509 patch makes the following environment variables available in the updown script indicated by the leftupdown parameter:

Variable Example Comment

$PLUTO_PEER_ID

ewa@strongsec.com

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

@pulpo.strongsec.com 

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 Sample updown script for iptables

The template _updown.x509 that can be found in the programs/_updown.x509 directory of the FreeS/WAN distribution after applying the X.509 patch, can be used as an updown script to dynamically insert and delete iptables firewall rules. The 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 firewall vpn:
+ @wroclaw.strongsec.com 160.85.106.2 -- 160.85.106.1 == 0.0.0.0/0
Jul 19 22:15:17 firewall vpn:
- @wroclaw.strongsec.com 160.85.106.2 -- 160.85.106.1 == 0.0.0.0/0

12. Using the patch with FreeS/WAN and raw RSA keys

Standard FreeS/WAN as it is available from www.freeswan.org does public key authentication base on raw RSA public keys that are directly defined in /etc/ipsec.conf

rightrsasigkey=0sAq4c....

When 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 X.509 enabled FreeS/WAN does not send a CR if the RSA key has been statically loaded using rightrsasigkey. A problem remains when roadwarriors initiate a connection. Since X.509 enabled FreeS/WAN 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 standard 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. Using the patch with OpenPGP certificates

The X.509 patch also supports RSA-based authentication using OpenPGP certificates and OpenPGP V3 fingerprints employed as KEY_ID identifiers.

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 legacy RSA private keys can be unlocked with the help of GnuPG and the IDEA extension (see http://www.gnupg.org/gph/en/pgp2x.html) using the following 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 auto --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 the config setup section of  /etc/ipsec.conf.

 


X.509 FreeS/WAN patch:

Copyright © 2000, Andreas Hess, Patric Lichtsteiner, Roger Wegmann
Copyright © 2001, Marco Bertossa, Andreas Schleiss 
Copyright © 2002, Mario Strasser <mast@gmx.net>
Copyright © 2003, Christoph Gysin, Simon Zwahlen

Copyright © 2000-2003, Andreas Steffen <andreas.steffen@zhwin.ch>
Zurich University of Applied Sciences in Winterthur, Switzerland

 Dynamic CRL fetching

Copyright © 2002, Stephane Laroche <stephane.laroche@colubris.com>

 Port and Protocol selectors for outbound traffic

Copyright © 2002, Stephen J. Bevan <stephen@dino.dnsalias.com>

PGPnet-RSA parts of patch:

Copyright © 2000, Kai Martius <kai@secunet.de >

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.

 


8.10.2003  info@strongsec.com FreeS/WAN