Boulder vs XiPKI

Boulder is an open-source ACME certificate authority written in Go and used to run Let’s Encrypt. ACME lets a certificate authority verify control of an identifier and allows subscribers to issue or revoke certificates for identifiers they control. Boulder divides its work among web front ends, registration and validation authorities, a certificate authority, storage authority, publisher, and CRL updater. These boundaries separate CA functions by security context, with the certificate authority receiving instructions from the registration authority. Components communicate through gRPC, and the software stores ACME accounts, authorizations, challenges, orders, and certificates. Boulder is free under the Mozilla Public License 2.0 and is listed for API, Linux, and self-hosted use. Maintainers recommend Docker and Docker Compose for development and experimentation, and document connecting Certbot or another ACME client to a local instance. That Docker environment is not suitable for production: it uses publicly available private key material, exposes debug ports, and is described as brittle when components fail. Boulder is built for Let’s Encrypt and Web PKI baseline requirements; maintainers say it often does not fit other organizations’ production needs.

XiPKI is an open-source public key infrastructure system for certification authority, registration authority, and OCSP responder functions, aimed at critical infrastructure. It supports multiple CAs in one instance, database clusters, and active instances for the same CA, with management through embedded OSGi commands and an API. Its CA gateway supports EST, SCEP, CMP, ACME, and its RESTful API. The OCSP responder handles RFC 2560, RFC 6960, and RFC 5019, along with signed and unsigned requests, health checks, and multiple certificate status sources. HSM connections use PKCS#11; listed devices include AWS CloudHSM, Nitrokey, nCipher, Sansec, SoftHSM, TASS, Thales, and Utimaco. The project describes native support for ML-DSA, ML-KEM, and composite post-quantum algorithms. XiPKI is free under Apache License 2.0. It supports Linux and macOS and requires Java 11 or later and Tomcat 10 or 11. Listed databases include DB2, MariaDB, MySQL, Oracle, PostgreSQL, H2, and HSQLDB.