PKICTL

Pkictl is a biased Public Key Infrastructure (PKI) management helper tool for implementing an internal network PKI. It's designed to make certificate, key creation, and management tasks formal, easy to initiate, and easy to automate. The complexities of the openssl settings are to be absorbed by the various configuration files, saving only execution of the tasks for the script itself.

My goal was to use the same configuration files, folder layout, and implementation behavior in every machine of my internal PKI infrastructure and use the same script for every task that entailed. The script also is designed to absorb the complexity of the Openssl CLI and configuration options and minimize accidental user error.

DISCLOSURE: I am not an openssl or security expert, but this script is the result of much research in order to get my openssl knowledge to a functional level. Don't blindly use this script. I stick pretty close to the configuration and layout demonstrated in this PKI tutorial, but it is still worth it to read up on some of the literature yourself if you truly need a functional understanding of it and not rely on random scripts you find scattered around the internet (including this one!).

STATUS: pkictl is v.0.10.0-beta

PKI Overview

Components

• Public Key Infrastructure (PKI): Security architecture where trust is conveyed through the signature of a trusted CA.
• Certificate Authority (CA): Entity issuing certificates and CRLs.
• Certificate: Public key and ID bound by a CA signature.
• Certificate Signing Request (CSR): Request for certification. Contains public key and ID to be certified.
• Certificate Revocation List (CRL): List of revoked certificates. Issued by a CA at regular intervals.

CA Types

• Root CA: CA at the root of a PKI hierarchy. Issues only CA certificates.
• Intermediate/Policy/Subordinate CA: CA below the root CA but not a signing CA. Issues only CA certificates.
• Signing/Issuing CA: CA at the bottom of a PKI hierarchy. Issues only end entity certificates.

Certificate Types

• Root Certificate: Self-signed CA certificate at the root of a PKI hierarchy. Serves as the PKI's trust anchor.
• CA Certificate: Certificate of a CA. Used to sign certificates and CRLs.
• End Entity/User Certificate: End-user certificate issued for one or more purposes: email-protection, server-auth, client-auth, code-signing, etc. A user certificate cannot sign other certificates.

Infrastructure Assumptions

This script makes assumptions about how you intend to build out your PKI. It assumes:

1. 3-tier hierarchy
   • One root CA
   • At least one intermediate CA. Can be n... parent/child CA's or n... sibling intermediate CA's.
   • A final generation of n... siblings of signing CA's.
2. 1-to-1 certificate/configuration pairing
   • One configuration file per CA
   • One configuration file per end entity CSR type.

Each generation inherits a copy of the chain from it's predecessors, so we have an opportunity to use/extend the line of certificates, using all the same CLI behavior and folder layout, indefinitely as needed keeping only the signing certificates we need on any particular machine and safely storing parent CA's we don't need elsewhere.

Setup

Remember that pkictl does not do any configuring itself, it merely initiates that which is already setup via configuration files. To use:

1. Plan out your PKI first.

   1. The three most important OpenSSL configuration settings are keyUsage, basicConstraints, and extendedKeyUsage. These are not general purpose and need to be specific to your PKI design in order for security policies to be enforced properly. This is why design must be pre-planned.

2. Modify the configuration files to match your design.

   1. Parity between the naming of the configuration files and all the openssl output must be preserved. This is how the script can sign certificates across generations and amongst sibling certificates. A strong naming convention is desirable anyway to help keep track of all the keys, CSR's, certificates etc. The name scheme for pkictl does the following:

      <domain/org name>-[<CA subdomain labels>...].root.<certificate type>[.<artifact suffix>][.<artifact file format>]

      where:

      • <domain/org name>: name of internal network. "Myorg.local"
      • <CA subdomain labels>: subordinate levels below "root". This is "sub", "tls.sub", "node.tls.sub", etc.
      • <certificate type>: "ca" for a configuration that issues certificate authorities, "ee" for a configuration that issues end entity certificates.
      • <artifact suffix>: determined by file type. ".csr", ".key", ".crt", ".crl", ".conf", etc.
      • <artifact file format>: if <artifact suffix> is supplied only, assume "PEM" ASCII format. When "DER" format is used, this suffix will be appended to the filename.

      An example hierarchy of this naming convention could look like this:

       myorg.local-root.ca
       └── myorg.local-sub.root.ca
           ├── myorg.local-tls.sub.root.ca
           │   └── server.myorg.local-node.tls.sub.root.ee
           └── myorg.local-email.sub.root.ca
               └── myorg.local-user.email.sub.root.ee
      

      Some Description:

      • myorg.local-root.ca: The root CA
        • myorg.local-sub.root.ca: An intermediate CA, child of root
          • myorg.local-tls.sub.root.ca: A signing CA, child of sub, grandchild of root
            • server.myorg.local-node.tls.sub.root.ee: An end entity certificate, child of tls.sub.root.ca, great-grandchild of root
          • myorg.local-email.sub.root.ca: A signing CA, child of sub, grandchild of root
            • server.myorg.local-user.email.sub.root.ee: An end entity certificate, child of email.sub.root.ca, great-grandchild of root

      The list of configuration files would be:

       .
       ├── myorg.local-root.ca.conf
       ├── myorg.local-sub.root.ca.conf
       ├── myorg.local-tls.sub.root.ca.conf
       ├── myorg.local-node.tls.sub.root.ee.conf
       ├── myorg.local-email.sub.root.ca.conf
       └── myorg.local-user.email.sub.root.ee.conf
      

3. Setup environment

   Configuration via the CLI is kept to an absolute minimum so that configuration files can store the configuration complexity, not your brain. However, some configuration is welcomed for certain items to allow for efficient use of configuration files.

   • CA Settings
     • $PKICTL_ORG: This sets "myorg.local" in the above examples. Must be the same as the "organizationName" value in the openssl configuration file.
     • $PKICTL_CONFIG_DIR: defaults to $PWD, sets location of configuration files.
     • $PKICTL_CA_DIR: defaults to $PWD, sets root location of your CA directory. This is where all newly generated certs and keys go.
     • $PKICTL_CA_EXTENSIONS: set this prior to signing commands to select alternate certificate extensions to include from your configuration file. When unset, defaults from your configuration file are used.
     • $PKICTL_CA_POLICY: set this prior to signing commands to select alternate distinguished name matching policies for signing your certificate. When unset, defaults from your configuration file are used.
   • PKCS#12 Import Settings
     • $PKICTL_SSL_DIR: defaults to /etc/ssl, make sure this coincides with where your operating system's OpenSSL installation stores its certs/keys. It is where pkictl eecert import will install the directory containing end-entity certs and private keys. The organization name is automatically extracted from the certificates themselves and used as a subfolder under /etc/ssl.
     • $PKICTL_CLIENTCERTS_DIR: defaults to /etc/ssl/certs, sets directory for symlinking root/intermediate CA certs if your installation has an alternative spot for imported certs (i.e. /usr/local/share/ca-certificates). In other words, a location where your installation's update-ca-certificates command can find your custom certs and do it's hashing.
     • $PKICTL_IMPORT_DIR: defaults to $PWD, sets location of where to look for PKCS#12 files for pkictl eecert import command.
     • $PKICTL_PKCS12_PASS: password used to open the PKCS#12 file.
     • $PKICTL_IMPORT_GROUP: group which will have RO access to newly imported private key. Defaults to 'ssl-cert'.
     • $PKICTL_IMPORT_USER: user which will be added to group 'ssl-cert' so that they can access the private key folder in general. However, only members of the group $PKICTL_IMPORT_GROUP can actually access the private key itself as it will be in it's own subdirectory. See the "Import" section below for details.
   • Misc. Settings
     • $PKICTL_SAFE_TEST: When set to 'true', all tasks that involve sudo, chown, or chmod with root or other system users/groups are skipped or run as current user instead with a notification message to alert user to what was not performed. This is for testing both manually and with the pkictl_test script.

Usage

The subcommands are grouped into 3 categories: rootca, subca, and eecert. Below are real examples using the provided configuration files.

Rootca

Setup a typical self-signed root certificate:

Usage: pkictl rootca <action>

• pkictl rootca init
• pkictl rootca request
• pkictl rootca sign
• pkictl rootca gencrl

Subca

Setup and manage the intermediate certificates from the first sub-root certificate, all the way to the issuing/signing certificates at the very bottom of the PKI hierarchy:

Usage: pkictl subca <action> <subca label> [<signing CA label>]

• pkictl subca init sub
• pkictl subca request sub
• pkictl subca sign tls.sub sub
• pkictl subca gencrl email.sub
• pkictl subca genpem sub root
• pkictl subca revoke sub root

Eecert

Issue and import end-entity certificates from the issuing/signing certificates at the bottom of the PKI hierarchy.

Usage: pkictl eecert <action> (<request label>|<end entity label>|<export name>) <signing CA label> [<output label>|<export name>]

• pkictl eecert request node.tls.sub tls.sub somehostname.localnet
• pkictl eecert sign somehostname.localnet tls.sub
• pkictl eecert genpkcs12 somehostname.localnet tls.sub exportname.somehost.localnet
• pkictl eecert revoke somehostname.localnet tls.sub
• pkictl eecert import exportname.somehost.localnet

Import

The pkictl eecert import sub-command takes the PKCS#12 bundle, extracts the certs and keys contained within, and imports them into logical and typical folder/file structures for various uses. The specific folder choices are highly configurable via environment variables and is designed with automation in mind.

The command will:

• create a re-usable folder structure based on the value of "organizationName" from the end entity certificate being imported.
• create a full chain bundle file from root to end-entity for nginx style packaging
• create a file of intermediate certificates for Apache style packaging
• split out all certs into individual files and place into your OS's ssl/certs directory
• extract private key
• run update-ca-certificates for you to hash and import them.

File permissions and ownership of private keys are a tricky, but critically important thing. A hybrid solution of best practices have been used here to allow for a pretty durable workflow when importing keys. A single server could potentially have multiple certificates and private keys for various programs. They should all be segregated by program and use-case.

1. First, we make sure a system group named 'ssl-cert' exists.
2. Only members of that group can even access the private key folder (at /etc/ssl/Myorg/private for example), which is 710 root:ssl-cert by default.
3. We then make a sub-folder in the private folder named $PKICTL_IMPORT_GROUP. So a default folder of private/ssl-cert will be 710 root:ssl-cert and the keys within it will be 640 root:ssl-cert.
4. During subsequent import processes, if pkictl eecert import is run with env var PKICTL_IMPORT_GROUP=my-prog, then new subfolder is created such as private/my-prog with 710 root:my-prog and the keys within are 640 root:my-prog.
5. Users/groups won't be created, but will be checked before trying to chown things. User creation should be handle by the process that needs to act as that user. The script will fail if they don't exist.
6. All imported keys will default to ssl-cert, and thus be stored in that folder under that group. This is a great default, but also allows other programs to create their own folders with their own groups. The key segregation visually reflects the user/group segregation. Groups/programs/users only have access to the keys meant for them and them only.
7. A purely private/root folder with root:root keys can also be made to work as well in this usage pattern for mail and web servers that start as root first, then drop privileges later.

Sources

• Official Sources
  • OpenSSL Docs
  • PKI-Tutorial
  • Digital Ocean OpenSSL Essentials
  • Github self-signed SSL certificate document
  • PKI Implementation for the Linux Admin
• Blogs
  • Multiple Blog Posts by Jamie Nguyen
  • Be Your Own CA by George Notaras
  • Becoming a x509 Certificate Authority by David Pashley
  • Be Your Own Certificate Authority with OpenSSL by Bas van de Wiel
  • Hierarchies in PKI

License

MIT