An Ephemeral PKI system that can act as a trust anchor for OpenStack PKI operations
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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


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: a local development instance in a python virtual environment, a local production instance or a test instance in a docker container.

For a development instance with virtualenv, run:

virtualenv .venv && source .venv/bin/activate && pip install .

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

python 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 anchor/

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 5016 on local network interface. This can be adjusted in the 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 -sha256

chmod 0400 CA/root-ca-unwrapped.key

Next, a new certificate request may be generated:

openssl req -out -nodes
-keyout -newkey rsa:2048 -subj "/" -sha256

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

curl -F user='myusername'
-F secret='simplepassword' -F encoding=pem -F 'csr=<'

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

Docker test environment

We have published a docker image for anchor at These instructions expect the reader to have a working Docker install already. Docker should not be used to serve Anchor in any production environments.

The behaviour of the Anchor container is controlled through docker volumes. To run a plain version of Anchor, with a default configuration and a dynamically generated private key simply invoke the container without any volumes. Note that Anchor exposes port 5016:

docker run -p 5016:5016 openstacksecurity/anchor

The recommended way to use the anchor container is to use a pre-compiled private key and certificate. You can read more about generating these (if you do not already have them) in this readme.

Once a key and certificate have been created, they can be provided to Anchor using docker volumes. In this example we've stored the sensitive data in /var/keys (note, docker must be able to access the folder where you have stored your keys). When the container starts it looks for a mounted volume in '/key' and files called root-ca-unwrapped.key and root-ca.crt that it will use.

docker run -p 5016:5016 -v /var/keys:/key anchor

Anchor is highly configurable, you can read more about Anchor configuration in the documentation here: the method for exposing configuration to Anchor is very similar as for keys, simply provide docker with the folder the config.json is within and create a volume called /config In the below example, Anchor will start with a custom configuration but as no key was provided it will generate one on the fly.

docker run -p 5016:5016 -v /var/config:/config anchor

Obviously it's possible to run Anchor with a custom configuration and a custom key/certificate by running the following (note in this case we've used -d to detach the container from our terminal)

docker run -d -p 5016:5016 -v /var/config:/config -v /var/keys:/key anchor

If you prefer to use locally built containers or want to modify the container build you can do that, we provide a simple Dockerfile to make the process easier.

Assuming you are already in the anchor directory, build a container called 'anchor' that runs the anchor service, with any local changes that have been made in the repo:

docker build -t anchor .

To start the service in the container and serve Anchor on port 5016:

docker run -p 5016:5016 anchor

When Anchor is running in a container, certificate requests will not pass validation unless the docker network is added as a source_cidr in the Anchor configuration and then passed into the container. Find the network by starting the container, inspecting the docker network and finding the anchor container:

docker run -p 5016:5016 --name=anchor anchor docker network inspect bridge

Under the 'containers' section, find the 'anchor' container and find the IPv4Address. For example:

"Containers": {
"6998a....5f4a57": {
"Name": "anchor",
"MacAddress": "02:42:ac:11:00:03", "IPv4Address": "",

Add this network as a source_cidr to the config.json, and pass it to the docker container as described above.

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 :5016 --venv path/to/venv --pecan -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.


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.

Currently 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


  • key_usage ensures only allowed_usage is requested for the


  • ca_status ensures the request does/doesn't require the CA flag
  • source_cidrs ensures the request comes from one of the ranges in


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

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




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": ""



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": "", "base": "ou=Users,dc=example,dc=com", "domain": "" "port": 636, "ssl": true



Signing backends

Anchor allows the use of configurable signing backend. Currently it provides two implementation: one based on ("anchor"), the other using PKCS#11 libraries ("pkcs11"). The first one is used in the sample config. Other backends may have extra dependencies: pkcs11 requires the PyKCS11 module, not required by anchor by default.

The resulting certificate is stored locally if the output_path is set to any string. This does not depend on the configured backend.

Backends can specify their own options - please refer to the backend documentation for the specific list. The default backend takes the following options:

  • cert_path: path where local CA certificate can be found
  • key_path: path to the key for that certificate
  • signing_hash: which hash method to use when producing signatures
  • valid_hours: number of hours the signed certificates are valid for

Sample configuration for the default backend:

"ca": {
"backend": "anchor" "cert_path": "CA/root-ca.crt", "key_path": "CA/root-ca-unwrapped.key", "output_path": "certs", "signing_hash": "sha256", "valid_hours": 24


Other backends may be created too. For more information, please refer to the documentation.


Anchor can modify the submitted CSRs in order to enforce some rules, remove deprecated elements, or just add information. Submitted CSR may be modified or entirely redone. Fixup are loaded from "anchor.fixups" namespace and can take parameters just like validators.

Reporting bugs and contributing

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