HOWTO: Using NSS with libreswan

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The libreswan IKE daemon uses the Mozilla Network Security Services ("NSS") crypto library for all cryptographic functions during the IKE negotiation.

Introduction

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 and those are not 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 as shipped by Red Hat is a FIPS certified library. Libreswan is currently in the process of obtaining a FIPS certification for http://www.redhat.com/products/enterprise-linux/ [RHEL7].



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.
  • crlutil: import CRLs into the NSS db.

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:

ipsec initnss

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 sql:/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:

token_1_name:the_password
token_2_name:the_password

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.

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 --nssdir /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.

# ipsec showhostkey --list
< 1> RSA keyid: AwEAAbScF ckaid: 2ad438fc7f3b65706f0381520f9f106a9eba7a96
# ipsec showhostkey --left --ckaid 2ad438fc7f3b65706f0381520f9f106a9eba7a96
	# rsakey AwEAAbScF
	leftrsasigkey=0sAwEAAbScFcIsVh6ee/nd7n4VEBRWnpuxefzzDFktmikoUcO76/gql0f67ySeugs8B/N7u/Jcn7NoOJmDZrcD4p5t2Qddzw5yl1sd2na6vN/eQvCFPrjHz6qX67qx+jExe8Jd6UxvwQC3bzGkJr8vt3sWpsUyfNsNdoxO7tE5uzumHv2Cm9Cwts80k4+I+qF1bKALY5jn/xAR1UGhZDxymfYfNJm0+dSmzMp8J9yw9fN5tt6eUKB/cuRHn7wfKEAd2E9PYcLeXaDnMJHyslIIxK5GXRK0nNGxMqPdJIzp4t1jBOJhd6HMEiaW9K08hVdwiz9pMTIM+DDhPvtMueR2WZ7KUSM=

The leftrsasigkey= can now be used in a connection configuration in 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

To create a certificate authority (CA certficate)

certutil -S -k rsa -n "ExampleCA" -s "CN=Example CA Inc" -v 12 \
        -t "CT,C,C" -x -d sql:/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" \
        -v 12 -t "u,u,u" -d sql:/etc/ipsec.d

This creates a user cert with nick name "user1" with attributes "u,u,u" signed by the CA cert "ExampleCA".

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.

leftcert=nickname

On Libreswan version 3.15 and older it is required to add entry 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 files into NSS

Importing user credentials (.crt, .key and .p12 files)

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 sql:/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.

To specify the certificate in ipsec.conf, use a line like:

leftcert=YourName

If you use libreswan 3.15 or older then add following to /etc/ipsec.secrets file to load private key. This is not necessary on later versions:

: RSA "YourName"

Importing CAcerts

The CAname is a friendly_name to refer to the CA certificate inside NSS. If your NSS db is procted by a password, specify it as the last item on the command line. For DER formatted certificates use:


certutil -A -i /path/YourCA.der -d sql:/etc/ipsec.d -n "CAname" -t 'CT,,'

For PEM formatted CA certificates use:

certutil -A -a -i /path/YourCA.pem -d sql:/etc/ipsec.d -n "CAname" -t 'CT,,'

Importing CRLs

For pem files use:

crlutil -I -i /path/yourcrl.der -d sql:/etc/ipsec.d -a  -B

For dir files use:

crlutil -I -i /path/yourcrl.der -d sql:/etc/ipsec.d -B

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, including the private key:

pk12util -o cacert1.p12 -n cacert1 -d sql:/etc/ipsec.d

Normally you would just want the CA cert. To extract just the CA cert without the private key:

certutil -L -n "CA nickname" -d sql:/etc/ipsec.d/ -a > theca.crt

You can also use -x instead of -a for binary DER encoding.

Copy the .p12 or .crt file to the new machine.

To import the .crt file:

certutil -A -i theca.crt -n "CA nickname" -t "CT,," -d /etc/ipsec.d/

To import the .p12 file:

ipsec import cacert1.p12
certutil -M -n cacert1 -t "CT,," -d sql:/etc/ipsec.d

An example connection for ipsec.conf would look like:

conn pluto-1-2
        left=1.2.3.4
        leftid="CN=usercert1"
        leftrsasigkey=%cert
        leftcert=usercert1
        right=5.6.7.8
        rightid="CN=usercert2"
        rightrsasigkey=%cert
        auto=add

Configuring a smartcard with NSS

Required library: libcoolkey or other PKCS#11 compatible library

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>

Using NSS in FIPS mode

If the system is running in FIPS mode, the NSS library and libreswan will automatically also run in FIPS mode. To check if libreswan is running in FIPS mode, run:

ipsec whack --fipsstatus

To see more detailed information about the FIPS status of the operating system and libreswan, the selfcheck command can be run:

# ipsec pluto --selftest
Pluto initialized
FIPS Product: NO
FIPS Kernel: NO
FIPS Mode: NO
[...]
FIPS HMAC integrity support [enabled]
FIPS mode disabled for pluto daemon
FIPS HMAC integrity verification self-test passed
[...]
Encryption algorithms:
  AES_CCM_16              IKEv1:     ESP     IKEv2:     ESP     FIPS  {256,192,*128}  aes_ccm, aes_ccm_c
  AES_CCM_12              IKEv1:     ESP     IKEv2:     ESP     FIPS  {256,192,*128}  aes_ccm_b
  AES_CCM_8               IKEv1:     ESP     IKEv2:     ESP     FIPS  {256,192,*128}  aes_ccm_a
  3DES_CBC                IKEv1: IKE ESP     IKEv2: IKE ESP     FIPS  [*192]  3des
  AES_GCM_16              IKEv1:     ESP     IKEv2: IKE ESP     FIPS  {256,192,*128}  aes_gcm, aes_gcm_c
  AES_GCM_12              IKEv1:     ESP     IKEv2: IKE ESP     FIPS  {256,192,*128}  aes_gcm_b
  AES_GCM_8               IKEv1:     ESP     IKEv2: IKE ESP     FIPS  {256,192,*128}  aes_gcm_a
  AES_CTR                 IKEv1: IKE ESP     IKEv2: IKE ESP     FIPS  {256,192,*128}  aesctr
  AES_CBC                 IKEv1: IKE ESP     IKEv2: IKE ESP     FIPS  {256,192,*128}  aes
  NULL_AUTH_AES_GMAC      IKEv1:     ESP     IKEv2:     ESP     FIPS  {256,192,*128}  aes_gmac
Hash algorithms:
  SHA1                    IKEv1: IKE         IKEv2:             FIPS  sha
  SHA2_256                IKEv1: IKE         IKEv2:             FIPS  sha2, sha256
  SHA2_384                IKEv1: IKE         IKEv2:             FIPS  sha384
  SHA2_512                IKEv1: IKE         IKEv2:             FIPS  sha512
PRF algorithms:
  HMAC_SHA1               IKEv1: IKE         IKEv2: IKE         FIPS  sha, sha1
  HMAC_SHA2_256           IKEv1: IKE         IKEv2: IKE         FIPS  sha2, sha256, sha2_256
  HMAC_SHA2_384           IKEv1: IKE         IKEv2: IKE         FIPS  sha384, sha2_384
  HMAC_SHA2_512           IKEv1: IKE         IKEv2: IKE         FIPS  sha512, sha2_512
Integrity algorithms:
  HMAC_SHA1_96            IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  sha, sha1, sha1_96, hmac_sha1
  HMAC_SHA2_512_256       IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  sha512, sha2_512, sha2_512_256, hmac_sha2_512
  HMAC_SHA2_384_192       IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  sha384, sha2_384, sha2_384_192, hmac_sha2_384
  HMAC_SHA2_256_128       IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  sha2, sha256, sha2_256, sha2_256_128, hmac_sha2_256
  AES_CMAC_96             IKEv1:     ESP AH  IKEv2:     ESP AH  FIPS  aes_cmac
  NONE                    IKEv1:     ESP     IKEv2: IKE ESP     FIPS  null
DH algorithms:
  NONE                    IKEv1:             IKEv2: IKE ESP AH  FIPS  null, dh0
  MODP2048                IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  dh14
  MODP3072                IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  dh15
  MODP4096                IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  dh16
  MODP6144                IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  dh17
  MODP8192                IKEv1: IKE ESP AH  IKEv2: IKE ESP AH  FIPS  dh18
  DH19                    IKEv1: IKE         IKEv2: IKE ESP AH  FIPS  ecp_256, ecp256
  DH20                    IKEv1: IKE         IKEv2: IKE ESP AH  FIPS  ecp_384, ecp384
  DH21                    IKEv1: IKE         IKEv2: IKE ESP AH  FIPS  ecp_521, ecp521
testing AES_GCM_16:
  empty string
  one block
  two blocks
  two blocks with associated data
testing AES_CTR:
  Encrypting 16 octets using AES-CTR with 128-bit key
  Encrypting 32 octets using AES-CTR with 128-bit key
  Encrypting 36 octets using AES-CTR with 128-bit key
  Encrypting 16 octets using AES-CTR with 192-bit key
  Encrypting 32 octets using AES-CTR with 192-bit key
  Encrypting 36 octets using AES-CTR with 192-bit key
  Encrypting 16 octets using AES-CTR with 256-bit key
  Encrypting 32 octets using AES-CTR with 256-bit key
  Encrypting 36 octets using AES-CTR with 256-bit key
testing AES_CBC:
  Encrypting 16 bytes (1 block) using AES-CBC with 128-bit key
  Encrypting 32 bytes (2 blocks) using AES-CBC with 128-bit key
  Encrypting 48 bytes (3 blocks) using AES-CBC with 128-bit key
  Encrypting 64 bytes (4 blocks) using AES-CBC with 128-bit key

Note various non-FIPS allowed algorithms are missing from the selftest, such as MD5, CHACHA20POLY1305, MODP1536, etc etc.

For example using RHEL8/CentOS8, placing the system in FIPS mode using the following commands is enough for libreswan to run in FIPS mode:

fips-mode-setup --enable
reboot

If the Linux distribution offers no easy way to place the system in FIPS mode, this can be done manually. For the Operating System to be considered in FIPS mode, the Linux kernel (compiled with FIPS support) must have been booted with the kernel command option fips=1 and the file /etc/system-fips needs to exist (but can be 0 bytes in size). The system-fips file is often created by dracut-fips. Additionally, the NSS database has to be (re)configured to be in FIPS mode. This can be done using:

modutil -dbdir sql:/etc/ipsec.d -fips true -force

To check if the NSS database is in FIPS mode, use:

modutil -dbdir sql:/etc/ipsec.d -chkfips true