Anchor

Anchor is an ephemeral PKI service that, based on certain conditions, automates the verification of CSRs and signs certificates for clients. The validity period can be set in the config file with hour resolution.

Ideas behind Anchor

A critical capability within PKI is to revoke a certificate - to ensure that it is no longer trusted by any peer. Unfortunately research has demonstrated that the two typical methods of revocation (Certificate Revocation Lists and Online Certificate Status Protocol) both have failings that make them unreliable, especially when attempting to leverage PKI outside of web-browser software.

Through the use of short-lifetime certificates Anchor introduces the concept of "passive revocation". By issuing certificates with lifetimes measured in hours, revocation can be achieved by simply not re-issuing certificates to clients.

The benefits of using Anchor instead of manual long-term certificates are:

• quick certificate revoking / rotation
• always tested certificate update mechanism (used daily)
• easy integration with certmonger for service restarting
• certificates are signed only when validation is passed
• signing certificates follows consistent process

Installation

In order to install Anchor from source, the following system dependencies need to be present:

• python 2.7
• python (dev files)
• libffi (dev)
• libssl (dev)

When everything is in place, Anchor can be installed in one of three ways. For development, run:

virtualenv .venv
. .venv/bin/activate
python setup.py develop

For installing into virtualenv, run:

virtualenv path/to/environment
. path/to/environment/bin/activate
python setup.py install

For installing in production, either install a perpared system package, or install globally in the system:

python setup.py install

Running the service

In order to run the service, it needs to be started via the pecan application server. The only extra parameter is a config file:

pecan serve config.py

For development, an additional --reload parameter may be used. It will cause the service to reload every time a source file is changed, however it requires installing an additional watchdog python module.

In the default configuration, Anchor will wait for web requests on port 5000 on local network interface. This can be adjusted in the config.py file.

Preparing a test environment

In order to test Anchor with the default configuration, the following can be done to create a test CA. The test certificate can be then used to sign the new certificates.

openssl req -out CA/root-ca.crt -keyout CA/root-ca-unwrapped.key \
    -newkey rsa:4096 -subj "/CN=Anchor Test CA" -nodes -x509 -days 365
chmod 0400 CA/root-ca-unwrapped.key

Next, a new certificate request may be generated:

openssl req -out anchor-test.example.com.csr -nodes \
    -keyout anchor-test.example.com.key -newkey rsa:2048 \
    -subj "/CN=anchor-test.example.com"

That reqest can be submitted using curl (while pecan serve config.py is running):

curl http://0.0.0.0:5000/sign -F user='myusername' \
    -F secret='simplepassword' -F encoding=pem \
    -F 'csr=<anchor-test.example.com.csr'

This will result in the signed request being created in the certs directory.

Running Anchor in production

Anchor shouldn't be exposed directly to the network. It's running via an application server (Pecan) and doesn't have all the features you'd normally expect from a http proxy - for example dealing well with deliberately slow connections, or using multiple workers. Anchor can however be run in production using a better frontend.

To run Anchor using uwsgi you can use the following command:

uwsgi --http-socket :5000 --venv path/to/venv --pecan config.py -p 4

In case a more complex scripted configuration is needed, for example to handle custom headers, rate limiting, or source filtering a complete HTTP proxy like Nginx may be needed. This is however out of scope for Anchor project. You can read more about production deployment in Pecan documentation.

Additionally, using an AppArmor profile for Anchor is a good idea to prevent exploits relying on one of the native libraries used by Anchor (for example OpenSSL). This can be done with sample profiles which you can find in the tools/apparmor.anchor_* files. The used file needs to be reviewed and updated with the right paths depending on the deployment location.

Validators

One of the main features of Anchor are the validators which make sure that all requests match a given set of rules. They're configured in config.json and the sample configuration includes a few of them.

Each validator takes a dictionary of options which provide the specific matching conditions.

Currenly available validators are:

• common_name ensures CN matches one of names in allowed_domains or ranges in allowed_networks

• alternative_names ensures alternative names match one of the names in allowed_domains

• alternative_names_ip ensures alternative names match one of the names in allowed_domains or IP ranges in allowed_networks

• blacklist_names ensures CN and alternative names do not contain any of the configured domains

• server_group ensures the group the requester is contained within group_prefixes

• extensions ensures only allowed_extensions are present in the request

• key_usage ensures only allowed_usage is requested for the certificate

• ca_status ensures the request does/doesn't require the CA flag

• source_cidrs ensures the request comes from one of the ranges in cidrs

A configuration entry for a validator might look like one from the sample config:

"key_usage": {
  "allowed_usage": [
    "Digital Signature",
    "Key Encipherment",
    "Non Repudiation"
  ]
}

Authentication

Anchor can use one of the following authentication modules: static, keystone, ldap.

Static: Username and password are present in config.json. This mode should be used only for development and testing.

"auth": { "static": { "secret": "simplepassword", "user": "myusername" } }

Keystone: Username is ignored, but password is a token valid in the configured keystone location.

"auth": { "keystone": { "url": "https://keystone.example.com" } }

LDAP: Username and password are used to bind to an LDAP user in a configured domain. User's groups for the server_group filter are retrieved from attribute memberOf in search for (sAMAccountName=username@domain). The search is done in the configured base.

"auth": {
  "ldap": {
    "host": "ldap.example.com",
    "base": "ou=Users,dc=example,dc=com",
    "domain": "example.com"
    "port": 636,
    "ssl": true
  }
}

Reporting bugs and contributing

For bug reporting and contributing, please check the CONTRIBUTING.md file.