Caliptra Device Identity Authentication

Purpose and scope

This document provides an overview of device identity authentication for a Caliptra-integrated SoC and identifies the specifications that define its certificate model, certificate store, and provisioning lifecycle.

A Caliptra integration provides identity, measured boot, and attestation capabilities to the SoC. For device identity, Caliptra protects the identity private key on behalf of the SoC. Private key material remains within the Caliptra security boundary. The device uses the protected key to sign attestation evidence presented to a remote verifier.

A certificate chain binds the corresponding public key to a PKI trust anchor. To authenticate the evidence, the verifier validates the certificate chain against a configured trust anchor and verifies the evidence signature using the certified public key. Successful authentication establishes that the evidence was signed with the corresponding private key; it does not establish that the reported device state is acceptable. The verifier makes that determination by evaluating the authenticated claims against its security policy.

Device identity comprises two lifecycle activities:

  • Identity provisioning establishes a Vendor, Owner, or Tenant endorsement for a device key.
  • Runtime authentication has the device sign evidence with its identity key and present the corresponding certificate chain. The remote verifier validates that chain to a trusted root before evaluating the signed evidence.

The Caliptra device identity model and its integration are described by three documents:

MCI certificate command codes are reserved in External Mailbox Commands, but their formats and implementation are planned. SPDM certificate message formats are defined by the SPDM specifications.