Let's Encrypt vs OpenCA PKI

Let’s Encrypt is a global Certificate Authority that provides SSL/TLS certificates for HTTPS connections. The ACME protocol verifies control of a domain, and compatible clients can automate issuance, management, and renewal. Its client directory includes Apache HTTP Server, Caddy, nginx, Kubernetes, Docker, and Windows/IIS environments. Certificates are Domain Validation only; Let’s Encrypt says it does not plan to issue Organization Validation or Extended Validation certificates. Wildcard certificates are available through the DNS-01 challenge. Standard certificates last 90 days, with an optional six-day lifetime; these periods cannot be adjusted. Subscribers generate and manage private keys on their own servers. Issued and revoked certificates are publicly recorded, and the service says its certificates are trusted by most browsers and operating systems. Certificates cost nothing. A registered domain can receive up to 50 certificates every seven days under published rate limits. Direct subscriber support is not offered.

OpenCA PKI is free, open-source software for establishing and managing a public key infrastructure, with an out-of-the-box Certification Authority. It is intended for on-premises deployment and is listed for Linux, macOS, self-hosted, and web environments. The project says it implements commonly used protocols with full-strength cryptography; listed capabilities include SCEP support, HSM integration, and certificate profiles. The download page lists OpenCA PKI (SpecialK) version 1.5.1. Installation requires other software, including OpenLDAP, OpenSSL, Apache, and Apache mod_ssl, and OpenCA Tools version 1.3.0 is listed as a prerequisite to install first. The project dates to 1998 and describes its work as volunteer-driven and managed through collaboration and consensus. Community support is available through mailing lists, forums, and online chat; independent third parties offer paid support. Security concerns can be reported privately by email or publicly through the project issue trackers. The documentation page says downloadable documentation is unavailable and notes that the OpenCA Guide for version 0.9.2 is outdated in some parts.