#X.509

A tiny publish-only service that keeps a root CA reachable without making it touchable: it serves the root certificate and its revocation list, while the root key and every signature stay on an offline host — reusable by any project with its own CA.

A Rust timestamp authority that stamps a document's hash with a signed, NTP-backed time per RFC 3161, so PDF signatures stay verifiable after their certificates expire — issuing and renewing its own signing certificate, with public OCSP and CRL.

An issuing certificate authority in Rust that gives each PDF signer a certificate of their own, then answers every reader's question — is it still valid? — through a public OCSP responder and revocation list, and hands the signing service each key and chain as PKCS#12.

The digital signature platform of the City Government of South Tangerang: signers prove who they are, sign PDFs to PAdES B-LTA with certificates from the platform's own authorities, and anyone can verify the result — version 2, which I designed, built and operate.