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Automatic IPsec Configuration for Ubuntu with Racoon

Using the certificate distribution mechanism built into keylime, you can automatically configure keylime to use IPsec to securely communicate with other machines in a network.

Overview

These scripts allow machines running the keylime agent to create a virtual private network between them, that is protected by cryptographic keys bootstrapped by keylime. Keylime will also automatically remove failed machines from the network. The scripts work by leveraging two features of keylime: automatic certificate generation/delivery, and the ability run scripts provided in the payload after successful bootstrapping. The following high level actions will happen:

  • The tenant will first run generate.py in this folder to generate the IPsec configuration files to pass to the tenant. The tenant must specify the subnets/ips that they wish for machines to always use IPsec to communicate.
  • The tenant will generate a new CA (if one hasn't been generated yet) and then generate a new cert/key combo for the agent to be bootstrapped
  • The tenant will include the IPsec config files generated above with the --include option
  • Tenant and verifier will bootstrap the agent and derive a key as normal
  • Once the bootstrap key has been derived, keylime will decrypt and extract the zipped payload that includes both the cert/key and the ipsec config.
  • Then keylime will run the provided autorun.sh script. This script will install/configure IPsec using the certificate provided.
  • At this point, IPsec will initialize and run between any specified IPs or subnets.

To support revocation:

  • The tenant must host the CA's CRL and listen for revocations. keylime_ca -c listen will do this job
  • If the verifier determines that an agent has failed its integrity check, it will create and sign a revocation notice that it will distribute to all the machines over 0mq
  • The tenant's CRL listener will receive and validate the revocation, update the CRL using the CA private key, and publish it to a locally running websever.
  • In parallel, all the other machines in the network will also receive the revocation notice and retrieve the new CRL from the tenant. It is important that the certificates include the appropriate address for the CRL or this won't work.
  • The other machines in the network will also search their active IPsec security associations for the revoked machine and force IKE re-negotiation with them. Because the CRL has also been updated, this will cause the machines to be unable to do key agreement with the machine running the revoked agent and block any traffic to it.

Pre-requisites

This set of scripts works with Ubuntu Linux 16.04. It may work with other versions of Ubuntu, but they have not been tested. Keylime will install both racoon and ipsec-tools packages and configure them. If you have racoon installed already on some other platform, these scripts may configure it.

In addition to basic keylime setup, the following configuration options must be set in the keylime.conf. Many of these are defaults, so it shouldn't be hard to achieve this configuration.

keylime.conf on each agent

To support automatic revocation, the revocation notifier must be enabled and reachable by all machines. Set the IP/port to the verifier that hosts the revocation notifier:

revocation_notifier_ip = xxx.xxx.xxx.xxx
revocation_notifier_port = xxxx
listen_notifications = True
revocation_cert = default

To enable cert mode and payload scripts the following options should be set:

extract_payload = True
payload_script=autorun.sh

keylime.conf on the verifier

The verifier must host the revocation notifier:

revocation_notifier = True

keylime.conf on the tenant

Finally: the tenant must setup the [ca] section of the config file with appropriate cert_* options. Importantly, the following option must be set with the ip/port of the crl listener:

cert_crl_dist = http://xxx.xxx.xxx.xxx:port/crl

Bootstrapping an agent with IPsec Configuration

First, generate the ipsec config files using generate.py in this directory. It takes in a file with 1 or more subnets to enable IPsec to/from. You can also specify single hosts using the notation 192.168.1.1/32 The order in which the lines in the file are specified is how they'll be encoded into ipsec-tools.conf.

python generate.py file.txt

Example: generate.py file.txt

# Any file starting with # will be ignored
# All Subnets after ipsec are enabled by default
ipsec
192.168.0.0/24
172.22.2.4/32
# All subnets after exclude will not use ipsec
exclude
192.168.0.1/32

This script will output the files you need to include into the directory ipsec-extra

Next provision an agent as you would normally. Be sure to use the --cert option to generate a certificate. Also include the files generated above using --include.

keylime_tenant -t 192.168.0.100 -u agent1 --cert myca --include ipsec-extra

Revocation Support

To support revocation, you must run a CRL host/listener. This will host a copy of the CRL on a web server and listen for notification of revocation from the verifier. To run this service:

keylime_ca -c listen -d myca

It will start up a web server and listen for notifications. Be sure that the cert_crl_dist option is set to point to this server.

If an agent is revoked, the listener will update the CRL. All the agents will run their configured revocation actions:

local_action_update_crl
local_action_deletesa

These actions update the CRL by curling it from the tenant service and then search for and delete any IPsec security associations that were created using the revoked certificate serial number. Within a second or two, all machines in the network should stop communicating with the revoked machine.

IPsec Configuration

Keylime uses racoon to setup IPsec. By default, it uses AES256 in CBC mode and SHA256 for HMAC. It uses modp2048 for DH and PFS support. It will re-key after 12 hours. See src/racoon.conf for more details. Keylime does not currently check the hostname of the certificate, only that it was valid and signed. This configuration is for demonstration purposes only. It is neither the most secure nor the most efficient IPsec setup. If you customize src/racoon.conf, these scripts will distribute and act upon them.