HOWTO: Using NSS with libreswan
The libreswan IKE daemon uses the Mozilla Network Security Services ("NSS") crypto library for all cryptographic functions during the IKE negotiation.
NSS is a userspace library utilized by the libreswan IKE daemon 'pluto' for cryptographic operations. NSS does not handle the IPsec crypto operations inside of the kernel; these are handled seperately by NETKEY or the KLIPS kernel module.
The NSS library exports a PKCS#11 API for the application to communicate to a cryptographic device. The cryptographic device is usually the "soft token" but can also be a Hardware Security Module (HSM).
The advantage of using NSS is that pluto does not need to know in detail how the cryptographic device works. Pluto does not access any private keys or data itself. Instead, it uses the PK11 wrapper API of NSS irrespective of the cryptographic device used. Pluto hands over work using the PK11 interface to NSS and never has direct access to the private key material itself. Both IKEv1 and IKEv2 operations are performed using NSS. Private RSA keys (raw RSA as well as X.509 based private RSA keys) are stored inside NSS. RSA keys are still referenced in /etc/ipsec.secrets. X.509 keys and certificates are referenced using their "nickname" instead of their filename in /etc/ipsec.conf.
While PreShared Key (PSK) calculations are done using NSS, the actual preshared key ("secret") is still stored in /etc/ipsec.secrets.
NSS command line tools
- certutil: Look and modify the NSS db. "ipsec initnss" and "ipsec look" use certutil under the hood.
- pk12util: import and export certificates and keys from and to the NSS db. The "ipsec import" command is a simple wrapper around this utility.
- modutil: Put NSS into FIPS mode
Creating the NSS db for use with libreswan
If you are not using a packaged libreswan version, you might need to create a new NSS db before you can start libreswan. This can be done using:
By default the NSS db is created in /etc/ipsec.d/
When creating a database, you are prompted for a password. The default libreswan package install for RHEL/Fedora/CentOS uses an empty password. It is up to the administrator to decide on whether to use a password or not. However, a non-empty database password must be provided when running in FIPS mode.
To change the empty password, run:
certutil -W -d /etc/ipsec.d
Enter return for the "old password", then enter your new password twice.
If you create the database with a password, and want to run NSS in FIPS mode, you must create a password file with the name "nsspassword" in the /etc/ipsec.d direcotry before starting libreswan. The "nsspassword" file must contain the password you provided when creating NSS database.
If the NSS db is protected with a non-empty password, the "nsspassword" file must exist for pluto to start. The syntax of the "nsspassword" file is:
The name of NSS softtoken (the default software NSS db) when NOT running in FIPS mode is "NSS Certificate DB". If you wish to use software NSS db with password "secret", you would have the following entry in the nsspassword file:
NSS Certificate DB:secret
If running NSS in FIPS mode, the name of NSS softtoken is "NSS FIPS 140-2 Certificate DB". If there are smartcards in the system, the entries for passwords should be entered in this file as well.
|Do not enter any spaces before or after the token name or password|
Using raw RSA keys with NSS
The "ipsec newhostkey" and "ipsec rsasigkey" utilities are used for creating raw RSA keys. If a non-default NSS directory is used, this can be specified using the -d option.
ipsec newhostkey --configdir /etc/ipsec.d [--password password] \ --output /etc/ipsec.secrets
The password is only required if the NSS database is protected with a non-empty password. All "private" compontents of the raw RSA key in /etc/ipsec.secrets such as the exponents and primes are filled in with the CKA ID, which serves as an identifier for NSS to look up the proper information in the NSS db during the IKE negotiation.
Public key information is directly available in /etc/ipsec.secrets and the "ipsec showhostkey" command can be used to generate left/rightrsasigkey= entries for /etc/ipsec.conf.
Using certificates with NSS
Any X.509 certificate management system can be used to generate Certificate Agencies, certificates, pkcs12 files and CRLs. Common tools people use are the openssl command, the GTK utility tinyca2, or the NSS certutil command.
An example using openssl can be found as part of the libreswan test suite at
Below, we will be using the nss tools to generate certificates
certutil -S -k rsa -n "ExampleCA" -s "CN=Example CA Inc" -v 12 \ -t "C,C,C" -x -d /etc/ipsec.d
It creates a certificate with RSA keys (-k rsa) with the nick name "ExampleCA", and with common name "Example CA Inc". The option "-v" specifies the certificates validity period. "-t" specifies the attributes of the certificate. "C" is required for creating a CA certificate. "-x" means self signed. "-d" specifies the path of the database directory.
It is not a requirement to create the CA in NSS database. The CA certificate can be obtained from third parties
To create a user certificate signed by the above CA
certutil -S -k rsa -c "ExampleCA" -n "user1" -s "CN=User Common Name" \ -w 12 -t "u,u,u" -d /etc/ipsec.d
This creates a user cert with nick name "user1" with attributes "u,u,u" signed by the CA cert "ExampleCA".
|You must provide a nick name when creating a user certificate, because pluto reads the user certificate from the NSS database based on the user certificate's nickname|
Configuring certificates in ipsec.conf and ipsec.secrets
In ipsec.conf, the leftcert= option takes a certificate nickname as argument. For example if the nickname of the user cert is "hugh", then it can be "leftcert=hugh".
If you are migrating from openswan without NSS, you were used to specify the filename for the certificate in the leftcert= option. Filenames are not valid in libreswan - only the nickname can be used.
In ipsec.secrets, we need to list the certificate nickname to inform pluto there is a certificate within the NSS db. This is specified using:
: RSA nickname
In openswan and freeswan without NSS it was required to specify a file name or password. With libreswan, this is not required. Private keys were stored in /etc/ipsec.d/private/ This directory is also not used with libreswan.
The directories /etc/ipsec.d/cacerts/ and /etc/ipsec.d/crls/ can still be used.
NOTE: the freeswan and openswan directories /etc/ipsec.d/aacerts/ and /etc/ipsec.d/acerts/ are not used with libreswan.
If you use an external CA certificate, you can either import it into the NSS db or place it in the /etc/ipsec.d/cacerts/ directory. Note that the preferred method is to store it inside the NSS db.
Importing third-party certificates into NSS
If you do not have the third-party certificate in the PKCS#12 format, use openssl to create a PKCS#12 file:
openssl pkcs12 -export -in cert.pem -inkey key.pem \ -certfile cacert.pem -out YourName.p12 [-name YourName]
Now you can import the file into the NSS db:
ipsec import YourName.p12
NOTE: the ipsec import command uses "pk12util -i YourName.p12 -d /etc/ipsec.d"
If you did not pick a name using the -name option, you can use certutil -L -d /etc/ipsec.d to figure out the name NSS picked durnig the import.
Add following to /etc/ipsec.secrets file:
: RSA "YourName"
To specify the certificate in ipsec.conf, use a line like:
Exporting a CA(?) certificate to load on another libreswan machine
Paul: wouldn't this also include the private key which we don't want? Paul: add "ipsec export"?
To export the CA certificate:
pk12util -o cacert1.p12 -n cacert1 -d /etc/ipsec.d
Copy the file "cacert1.p12" to the new machine and import it using:
ipsec import cacert1.p12 certutil -M -n cacert1 -t "C,C,C" -d /etc/ipsec.d
An example connection for ipsec.conf would look like:
conn pluto-1-2 left=126.96.36.199 leftid="CN=usercert1" leftrsasigkey=%cert leftcert=usercert1 right=188.8.131.52 rightid="CN=usercert2" rightrsasigkey=%cert auto=add
Configuring a smartcard with NSS
Required library: libcoolkey
To make smartcard tokens visible through NSS
modutil -add <module_name> -libfile libcoolkeypk11.so \ -dbdir <nss_database_dir_name> \ -mechanisms <mechanisms_separted_by_colons>
An example of mechanisms can be: RC2:RC4:DES:DH:SHA1:MD5:MD2:SSL:TLS:AES:CAMELLIA.
To check whether the token is visible or not, run
modutil -list -dbdir <nss_database_dir_name>