Private keys must be without line breaks. Old keyboxes often used DER-in-hex, which is now rejected.
The standard introduces keybox chaining —a single device can have multiple keyboxes, with the attestation server selecting the most recent, unrevoked one. This allows OEMs to push over-the-air (OTA) updates that replace compromised keyboxes without a full system rewrite.
: Usually consists of three certificates (Device, Intermediate, and Root) in PEM format. Implementation Guide
: Ensure the file has proper root permissions (usually 0644 or 0600 ) so the system can read it.