Boulder

This is an implementation of an ACME-based CA. The ACME protocol allows the CA to automatically verify that an applicant for a certificate actually controls an identifier, and allows domain holders to issue and revoke certificates for their domains. Boulder is the software that runs Let's Encrypt. This component model lets us separate the function of the CA by security context. The Web Front End, Validation Authority, OCSP Responder and Publisher need access to the Internet, which puts them at greater risk of compromise. The Registration Authority can live without Internet connectivity, but still needs to talk to the Web Front End and Validation Authority. The Certificate Authority need only receive instructions from the Registration Authority. All components talk to the SA for storage. Internally, the logic of the system is based around five types of objects: accounts, authorizations, challenges, orders (for ACME v2) and certificates.