Configuring Certificate Authority with OpenSSL Skill

Configuring Certificate Authority with OpenSSL

Overview

A Certificate Authority (CA) is the trust anchor in a PKI hierarchy, responsible for issuing, signing, and revoking digital certificates. This skill covers building a two-tier CA hierarchy (Root CA + Intermediate CA) using OpenSSL and the Python cryptography library, including CRL distribution, OCSP responder configuration, and certificate policy management.

When to Use

When deploying or configuring configuring certificate authority with openssl capabilities in your environment
When establishing security controls aligned to compliance requirements
When building or improving security architecture for this domain
When conducting security assessments that require this implementation

Prerequisites

Familiarity with cryptography concepts and tools
Access to a test or lab environment for safe execution
Python 3.8+ with required dependencies installed
Appropriate authorization for any testing activities

Objectives

Create a Root CA with self-signed certificate
Create an Intermediate CA signed by the Root CA
Issue server and client certificates from the Intermediate CA
Configure Certificate Revocation Lists (CRLs)
Implement certificate policies and constraints
Build a complete PKI hierarchy programmatically

Key Concepts

CA Hierarchy

Root CA (offline, air-gapped)
  |
  +-- Intermediate CA (online, operational)
        |
        +-- Server Certificates
        +-- Client Certificates
        +-- Code Signing Certificates

Certificate Extensions

| Extension | Purpose | Critical | |-----------|---------|----------| | basicConstraints | CA:TRUE/FALSE, pathLenConstraint | Yes | | keyUsage | keyCertSign, cRLSign, digitalSignature | Yes | | extendedKeyUsage | serverAuth, clientAuth, codeSigning | No | | subjectKeyIdentifier | Hash of public key | No | | authorityKeyIdentifier | Issuer's key identifier | No | | crlDistributionPoints | URL to CRL | No | | authorityInfoAccess | OCSP responder URL | No |

Security Considerations

Root CA private key must be stored offline (air-gapped HSM)
Use minimum 4096-bit RSA or P-384 ECDSA for CA keys
Set path length constraints on intermediate CAs
Implement certificate policies (OIDs)
Enable CRL and OCSP for revocation checking
Audit all certificate issuance operations

Validation Criteria

[ ] Root CA self-signed certificate is valid
[ ] Intermediate CA certificate chains to Root CA
[ ] Issued certificates chain to Intermediate -> Root
[ ] Path length constraints are enforced
[ ] CRL is generated and accessible
[ ] Revoked certificates appear in CRL
[ ] Certificate policies are correctly embedded

Agent Skills: Configuring Certificate Authority with OpenSSL

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