seikaikyo/configuring-certificate-authority-with-openssl

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