FIDO Attestation and Metadata Flashcards

Which cryptographic algorithm is most commonly used in packed attestation for signing the attestation statement?

Answer: ECDSA with the P-256 curve and SHA-256 (ES256)

Packed attestation commonly uses ECDSA P-256 / SHA-256 (COSE algorithm ES256) because it provides strong security with small key sizes and efficient computation on authenticator hardware.

How does a relying party use an authenticator's AAGUID in relation to the FIDO Metadata Service?

Answer: The relying party uses the AAGUID as a lookup key to retrieve the authenticator's metadata statement from the MDS

The AAGUID extracted from authenticator data during registration is used as a primary key to query the FIDO MDS and retrieve the metadata statement for that specific authenticator model.

After receiving an attestation statement during registration, what steps does a relying party typically perform?

Answer: Verifies the attestation signature and certificate chain, then queries the MDS for current authenticator status

The relying party verifies the attestation signature and certificate chain locally, then looks up the authenticator's AAGUID in the MDS to check for current certification status or security advisories.

What does an authenticator status of 'REVOKED' in the FIDO MDS indicate?

Answer: The authenticator model has a known security vulnerability and credentials from it should no longer be trusted

A 'REVOKED' MDS status means the authenticator model has been compromised or found to have a critical security flaw, and relying parties implementing MDS checks should reject credentials from such devices.

What privacy concern arises specifically from using Basic attestation with batch attestation certificates?

Answer: The shared batch certificate across an authenticator model can be used to correlate registrations across different relying parties

Because all devices of the same batch share a single attestation certificate, a colluding set of relying parties could use that certificate to link registrations from the same device across different sites.

Which WebAuthn attestation conveyance preference allows the client platform to decide how to provide attestation, potentially using an Anonymization CA?

Answer: indirect

The 'indirect' conveyance preference gives the client discretion over how attestation is delivered, which may include routing it through an Anonymization CA to protect user privacy while maintaining trust.

What is the function of an Anonymization CA (AnonCA) in FIDO attestation?

Answer: It re-signs authenticator attestation statements with a different certificate, preventing cross-site tracking while preserving trust

An Anonymization CA receives the authenticator's raw attestation and re-signs it with a fresh certificate, breaking the linkability between authenticator model certificates across relying parties while still providing verifiable attestation trust.