Key Attestation for Entity Attestation Tokens (EAT)

This document defines a CWT-based Entity Attestation Token (EAT) profile and a new EAT claim that cryptographically bind a private key used to sign a certificate signing request (CSR), or the private key corresponding to an end-entity certificate used for TLS authentication, to an attested execution environment. The subject public key is conveyed using the EAT cnf claim defined in [RFC8747], and freshness uses the EAT nonce claim defined in [RFC9711]. The proof of possession of the subject key is obtained from the surrounding protocol, such as TLS certificate-based authentication or CSR signature verification. Because the EAT is signed by a hardware-backed Attestation Key (AK), successful verification of the EAT signature together with protocol-level proof of possession establishes a cryptographic binding between the private key and the attested platform state. This mechanism addresses key substitution attacks that arise when attestation evidence and the certificate private keys are validated independently.