Attestation is the process of proving the authenticity and trustworthiness of an authenticator or device. In authentication systems, it provides evidence that the authenticator (such as a hardware token, security key, or mobile device) is genuine and has not been tampered with.

An Attestation Certificate in FIDO2 is a digital X.509 certificate issued to an authenticator by its manufacturer or trusted authority. It is used during the attestation process to prove that the authenticator is genuine and originates from a known, trusted source.

When a user registers a new authenticator (e.g., security key or biometric device):

1. The authenticator generates a new key pair (public and private keys).
2. It produces an attestation statement, which includes the public key and device-specific details such as device model, batch number, or security characteristics.
3. The statement is signed with the attestation private key, and the signature can be verified using the attestation certificate.
4. The server (relying party) can use this information to decide whether to trust the authenticator based on its attestation type and metadata.

Purpose of the Attestation Certificate:

• Provides cryptographic proof that the key pair was generated inside a legitimate authenticator.
• Binds the attestation key to a particular manufacturer and device model.
• Enables the relying party (server) to check against the FIDO Metadata Service or trusted certificate chain to verify device trustworthiness.