The cert-spec.txt [document references various Certificate types](https://gitweb.torproject.org/torspec.git/tree/cert-spec.txt#n93) in a section 4.2, but there exists no such complete documentation in any of the -spec.txt files. The section 4.2 that it appears to reference [is in prop 220](https://gitweb.torproject.org/torspec.git/tree/proposals/220-ecc-id-keys.txt#n438) which includes specs for each of the cert types mentioned: * Link key certificate certified by Ed25519 signing key * Ed25519 TLS authentication key certified by Ed25519 signing key * RSA cross-certificate for Ed25519 identity key