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Step Certificates

An online certificate authority and related tools for secure automated certificate management, so you can use TLS everywhere.

For more information and docs see the Step website and the blog post announcing Step Certificate Authority.

Why?

Managing your own public key infrastructure (PKI) can be tedious and error prone. Good security hygiene is hard. Setting up simple PKI is out of reach for many small teams, and following best practices like proper certificate revocation and rolling is challenging even for experts.

This project is part of smallstep's broader security architecture, which makes it much easier to implement good security practices early, and incrementally improve them as your system matures.

Table of Contents

• Installing
• Documentation
• Terminology
• Getting Started
• Commonly Asked Questions
• Recommended Defaults
• How To Create A New Release
• Versioning
• LICENSE
• CHANGELOG

Installing

These instructions will install an OS specific version of the step binary on your local machine.

Mac OS

Install step via Homebrew:

brew install smallstep/smallstep/step

Linux

Download the latest Debian package from releases:

wget https://github.com/smallstep/certificates/releases/download/X.Y.Z/step_X.Y.Z_amd64.deb

Install the Debian package:

sudo dpkg -i step-ca_X.Y.Z_amd64.deb

Documentation

Documentation can be found in three places:

1. On the command line with step ca help xxx where xxx is the subcommand you are interested in. Ex: step help ca provisioners list

2. On the web at https://smallstep.com/docs/step-ca

3. In your browser with step ca help --http :8080 and visiting http://localhost:8080

Terminology

PKI - Public Key Infrastructure

A set of roles, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to facilitate the secure electronic transfer of information for a range of network activities.

Provisioners

Provisioners are people or code that are registered with the CA and authorized to issue "provisioning tokens". Provisioning tokens are single use tokens that can be used to authenticate with the CA and get a certificate.

Getting Started

Demonstrates setting up your own PKI and certificate authority using step ca and getting certificates using the step command line tool and SDK.

Prerequisites

1. Step CLI

2. Step CA

Initializing PKI and configuring the Certificate Authority

To initialize a PKI and configure the Step Certificate Authority run:

step ca init

You'll be asked for a name for your PKI. This name will appear in your CA certificates. It doesn't really matter what you choose. The name of your organization or your project will suffice.

If you run:

tree .

You should see:

.
├── certs
│   ├── intermediate_ca.crt
│   └── root_ca.crt
├── config
│   └── ca.json
└── secrets
    ├── intermediate_ca_key
    └── root_ca_key

The files created include:

• root_ca.crt and root_ca_key: the root certificate and private key for your PKI
• intermediate_ca.crt and intermediate_ca_key: the intermediate certificate and private key that will be used to sign leaf certificates
• ca.json: the configuration file necessary for running the Step CA.

All of the files endinging in _key are password protected using the password you chose during PKI initialization.

What's Inside ca.json?

ca.json is responsible for configuring communication, authorization, and default new certificate values for the Step CA. Below is a short list of definitions and descriptions of available configuration attributes.

• root: location of the root certificate on the filesystem. The root certificate is used to mutually authenticate all api clients of the CA.

• crt: location of the intermediate certificate on the filesystem. The intermediate certificate is returned alongside each new certificate, allowing the client to complete the certificate chain.

• key: location of the intermediate private key on the filesystem. The intermediate key signs all new certificates generated by the CA.

• password: optionally store the password for decrypting the intermediate private key (this should be the same password you chose during PKI initialization). If the value is not stored in configuration then you will be prompted for it when starting the CA.

• address: e.g. 127.0.0.1:8080 - address and port on which the CA will bind and respond to requests.

• dnsNames: comma separated list of DNS Name(s) for the CA.

• logger: the default logging format for the CA is text. The other options is json.

• tls: settings for negotiating communication with the CA; includes acceptable ciphersuites, min/max TLS version, etc.

• authority: controls the request authorization and signature processes.

  • template: default ASN1DN values for new certificates.

  • claims: default validation for requested attributes in the certificate request. Can be overriden by similar claims objects defined by individual provisioners.

    • minTLSCertDuration: do not allow certificates with a duration less than this value.

    • maxTLSCertDuration: do not allow certificates with a duration greater than this value.

    • defaultTLSCertDuration: if no certificate validity period is specified, use this value.

    • disableIssuedAtCheck: disable a check verifying that provisioning tokens must be issued after the CA has booted. This is one prevention against token reuse. The default value is false. Do not change this unless you know what you are doing.

  • provisioners: list of provisioners. Each provisioner has a name, associated public/private keys, and an optional claims attribute that will override any values set in the global claims directly underneath authority.

step ca init will generate one provisioner. New provisioners can be added by running step ca provisioner add.

Running the CA

To start the CA run:

step-ca $STEPPATH/config/ca.step

Configure Your Environment

Many of the cli utilities under step ca [sub-command] interface directly with a running instance of the Step CA. The CA exposes an HTTP API and clients are required to connect using TLS over HTTP (aka HTTPS). As part of bootstraping the Step CA, a certificate was generated using the root of trust that was created when you initilialized your PKI. In order to properly validate this certificate clients need access to the public root of trust, aka the public root certificate. If you are using the Step CLI on the same host where you initialized your PKI (the root_ca.crt is stored on disk locally), then you can continue to setting up a default.json, otherwise we will show you how to easily download your root certificate in the following step.

Download the Root Certificate

The next few steps are a guide for downloading the root certificate of your PKI from a running instance of the CA. First we'll define two servers:

• remote server: This is the server where the Step CA is running. This may also be the server where you initialized your PKI, but for security reasons you may have done that offline.

• local server: This is the server that wants access to the step ca [sub-command]

• ca-url: This is the url at which the CA is listening for requests. This should be a combination of the DNS name and port entered during PKI initialization. In the examples below we will use https://ca.smallstep.com:8080.

1. Get the Fingerprint.

   From the remote server:

   $ FP=$(step certificate fingerprint ./path/to/root_ca.crt)
   

2. Request the certificate from the running CA.

   From the local server:

   $ step ca root $STEPPATH/secrets/root_ca.crt --fingerprint $FP --ca-url "https:ca.smallstep.com:8080"
   

3. Test.

   Now let's test the root certificate by generating a new provisioner token:

   * step ca health --ca-url "https:ca.smallstep.com:8080" --root $STEPPATH/secrets/root_ca.crt
   

Setting up Environment Defaults

This is optional, but we recommend you populate a defaults.json file with a few variables that will make your command line experience much more pleasant.

$ cat > $STEPPATH/config/defaults.json
{
    "ca-url": "https://<dns-name>:<port>",
    "ca-config": "/home/user/.step/config/ca.json"
    "root": "/home/user/.step/certs/root_ca.crt"
}

• ca-curl: Use the DNS name and port that you used when initializing the CA.

• root: Path to the root certificate on the file system.

• ca-config: Path to the CA configuration file. Only used by CLI commands that read or modify the CA configuration (e.g. step ca provisioner [add|delete|list].

You can always override these values with command-line flags or environment variables.

Test your $STEPPATH/config/defaults.json file:

$ step ca health

Hot Reload

It is important that the CA be able to handle configuration changes with no downtime. Our CA has a built in reload function allowing it to:

1. Finish processing existing connections while blocking new ones.
2. Parse the configuration file and re-initialize the API.
3. Begin accepting blocked and new connections.

reload is triggered by sending a SIGHUP to the PID (see man kill for your OS) of the Step CA process. A few important details to note when using reload:

• The location of the modified configuration must be in the same location as it was in the original invocation of step-ca. So, if the original command was

$ step-ca ./.step/config/ca.json

then, upon reload, the Step CA will read it's new configuration from the same configuration file.

• Step CA requires the password to decrypt the intermediate certificate, again, upon reload. You can auotmate this in one of two ways:

  • Use the --password-file flag in the original invocation.
  • Use the top level password attribute in the ca.json configuration file.

Let's issue a certificate!

There are two steps to issuing a certificate at the command line:

1. Generate a provisioning token using your provisioning credentials.
2. Generate a CSR and exchange it, along with the provisioning token, for a certificate.

If you would like to generate a certificate from the command line, the Step CLI provides a single command that will prompt you to select and decrypt an authorized provisioner and then request a new certificate.

$ step ca certificate "foo.example.com" foo.crt foo.key

If you would like to generate certificates on demand from an automated configuration management solution (no user input) you would split the above flow into two commands.

$ TOKEN=$(step ca token foo.example.com \
    --kid 4vn46fbZT68Uxfs9LBwHkTvrjEvxQqx-W8nnE-qDjts \
    --ca-url https://ca.example.com \
    --root /path/to/root_ca.crt  --password-file /path/to/provisioner/password)

$ step ca certificate "foo.example.com" foo.crt foo.key --token "$TOKEN" \
    --ca-url https://ca.example.com --root /path/to/root_ca.crt

You can take a closer look at the contents of the certificate using step certificate inspect:

$ step certificate inspect foo.crt

List|Add|Remove Provisioners

The Step CA configuration is initialized with one provisioner; one entity that is authorized by the CA to generate provisioning tokens for new certificates. We encourage you to have many provisioners - ideally one for each entity in your infrastructure.

Why should I be using multiple provisioners?

• Each certificate generated by the Step CA contains the ID of the provisioner that issued the provisioning token authorizing the creation of the cert. This ID is stored in the X.509 ExtraExtensions of the certificate under OID: 1.3.6.1.4.1.37476.9000.64.1 and can be inspected by running step certificate inspect foo.crt. These IDs can and should be used to debug and gather information about the origin of a certificate. If every member of your ops team and the configuration management tools all use the same provisioner to authorize new certificates you lose valuable visibility into the workings of your PKI.
• Each provisioner should require a unique password to decrypt it's private key -- we can generate unique passwords for you but we can't force you to use them. If you only have one provisioner then every entity in the infrastructure will need access to that one password. Jim from your dev ops team should not be using the same provisioner/password combo to authorize certificates for debugging as Chef is for your CICD - no matter how trustworthy Jim says he is.

Let's begin by listing the existing provisioners:

$ bin/step ca provisioner list

Now let's add a provisioner for Jim.

$ bin/step ca provisioner add jim@smallstep.com --create

NOTE: This change will not affect the Step CA until a reload is forced by sending a SIGHUP signal to the process.

List the provisioners again and you will see that nothing has changed.

$ bin/step ca provisioner list

Now let's reload the CA. You will need to re-enter your intermediate password unless it's in your ca.json or your are using --password-file.

$ ps aux | grep step-ca   # to get the PID
$ kill -1 <pid>

Once the CA is running again, list the provisioners, again.

$ bin/step ca provisioner list

Boom! Magic. Now suppose Jim forgets his password ('come on Jim!'), and he'd like to remove his old provisioner. Get the kid (Key ID) of Jim's provisioner by listing the provisioners and finding the appropriate one. Then run:

$ bin/step ca provisioner remove jim@smallstep.com --kid <kid>

Then reload the CA and verify that Jim's provisioner is no longer returned in the provisioner list.

We can also remove all of Jim's provisioners, supposing Jim forgot all the passwords ('really Jim?'), by running the following:

$ bin/step ca provisioner remove jim@smallstep.com --all

The same entity may have multiple provisioners for authorizing different types of certs. Each of these provisioners must have unique keys.

Notes on Securing the Step CA and your PKI.

In this section we recommend a few best practices when it comes to running, deploying, and managing your own online CA and PKI. Security is a moving target and we expect out recommendations to change and evolve as well.

Initializing your PKI

When you initialize your PKI two private keys are generated; one intermediate private key and one root private key. It is very important that these private keys are kept secret. The root private key should be moved around as little as possible, preferably not all - meaning it never leaves the server on which it was created.

Passwords

When you intialize your PKI (step ca init) the root and intermediate private keys will be encrypted with the same password. We recommend that you change the password with which the intermediate was encrypted at your earliest convenience.

$ step crypto change-pass $STEPPATH/secrets/intermediate_ca_key

Once you've changed the intermediate private key password you should never have to use the root private key password again.

We encourage users to always use a password manager to generate random passwords or let Step CLI generate passwords for you.

The next important matter is how your passwords are stored. We recommend using a password manager. There are many to choose from and the choice will depend on the risk & security profile of your organization.

In addition to using a password manager to store all passwords (private key, provisioner, etc.) we recommend using a threshold cryptography algorithm like Shamir's Secret Sharing to divide the root private key across a handful of trusted parties.

Provisioners

When you intialize your PKI (step ca init) a default provisioner will be created and it's private key will be encrypted using the same password used to encrypt the root private key. Before deploying the Step CA you should remove this provisioner and add new ones that are encrypted with new, secure, random passwords. See the section on managing provisioners.

Deploying

• Refrain from entering passwords for private keys or provisioners on the command line. Use the --password-file flag whenever possible.
• Run the Step CA as a new user and make sure that the config files, private keys, and passwords used by the CA are stored in such a way that only this new user has permissions to read and write them.
• Use short lived certificates. Our default validity period for new certificates is 24 hours. You can configure this value in the ca.json file. Shorter is better - less time to form an attack.
• Short lived certificates are not a replacement for CRL and OCSP. CRL and OCSP are features that we plan to implement, but are not yet available. In the mean time short lived certificates are a decent alternative.
• Keep your hosts secure by enforcing AuthN and AuthZ for every connection. SSH access is a big one.

The Future

We plan to build more tools that facilitate the use and management of zero trust networks.

• Tell us what you like and don't like about managing your PKI - we're eager to help solve problems in this space.
• Tell us what features you'd like to see - open issues or hit us on Twitter.

Versioning

We use SemVer for versioning. For the versions available, see the tags on this repository.

License

This project is licensed under the MIT License - see the LICENSE file for details

Individual Contributor License