A certificate authority is worth exactly as much as the protection around its private key. Everything else — the policy document, the audit, the naming — is bookkeeping if the key sits in a file that a backup job copies somewhere else.
A root CA wants to be offline, and this is the right shape for it
The standard advice for a private PKI is a root that is generated once, signs a handful of intermediates, and then goes into a safe for a decade. A network HSM is a poor fit for that: it is a powered appliance in a rack, which is the opposite of offline. A USB device you can seal in a bag with a signed inventory sheet is what the procedure actually describes.
The key is generated on the card and is non-extractable, so the ceremony has nothing to shred afterwards — there is no key file that briefly existed on a laptop. The device also signs an attestation of its own firmware and the card fitted in it, which belongs in the ceremony record.
Backup is the part people get wrong
A root key that exists in one device is one dropped device away from re-issuing your entire PKI. The card supports encrypted key backup: at initialisation you choose how many shares the device key encryption key is split into, and you hold all of them, so a wrapped copy of the root can be restored onto a replacement device without the key ever existing outside hardware.
Be clear-eyed about what that is. The shares are combined by XOR and all of them are needed — it is n-of-n, not a threshold scheme. Splitting them between custodians gives you dual control over a restore; it does not let you recover from a lost share. Plan the custody accordingly, and rehearse a restore before you need one.
The tooling is ordinary
Initialisation and backup use sc-hsm-tool. Keys, requests and certificates can be managed with OpenSSL over PKCS#11, with XCA if you would rather click, or with EJBCA if you are running a real CA with profiles and an enrolment API. None of that is KeyNub software, so your CA never depends on us being here.
One warning worth reading twice: fifteen wrong SO-PIN attempts destroy the card, and there is no factory reset, because the reset command authenticates against the SO-PIN too. Write it down, keep it where a second person can reach it, and do not guess.
Where to go next
A private CA is the use case this hardware suits best. See also code signing, EJBCA, TLS server keys, or the hardware security module overview and the datasheet.
The KeyNub HSM ships from Munich. Ask us if you want to talk through a deployment first, or order one.
