FCP Public-Key Cryptography in FIDO 2

Question 1

In FIDO2, which cryptographic operation is performed by the authenticator during the authentication ceremony?

Accepted Answer

Signing the authenticatorData and clientDataHash with the credential private key

Answer

The authenticator signs the concatenation of authenticatorData and clientDataHash using the credential's private key to produce an assertion.

Question 2

What is the purpose of the 'aaguid' field in FIDO2 attestation statements?

Accepted Answer

To identify the model and manufacturer class of the authenticator

Answer

The AAGUID (Authenticator Attestation GUID) identifies the authenticator model/type, not a specific device instance.

Question 3

Which elliptic curve is most commonly used in FIDO2 credentials and identified by COSE key type -7?

Accepted Answer

P-256 (prime256v1 / secp256r1)

Answer

COSE algorithm ES256 (-7) uses ECDSA with the P-256 curve, the most widely supported curve in FIDO2 authenticators.

Question 4

What does 'forward secrecy' mean in the context of FIDO authentication key pairs?

Accepted Answer

Compromise of one credential's private key does not expose other credentials' keys

Answer

FIDO's per-credential, per-relying-party key pairs ensure that compromise of one credential does not affect any other credential.

Question 5

In CTAP2, how is the credential private key protected against extraction when using a hardware authenticator?

Accepted Answer

The private key is generated and stored entirely within the authenticator's secure element and never exported

Answer

Hardware authenticators store the private key inside a tamper-resistant secure element, making extraction computationally infeasible.

(FCP) FIDO Certified Professional Practice Test