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

Encrypting the challenge with the server's public key

Answer

Hashing the user's PIN with SHA-256 and sending it to the server

Answer

Verifying the server's certificate chain before proceeding

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

To uniquely identify each individual authenticator device

Answer

To store the user's public key for later verification

Answer

To encode the cryptographic algorithm used for the credential

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

Curve25519 (X25519)

Answer

P-384 (secp384r1)

Answer

P-521 (secp521r1)

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

Each authentication generates a fresh ephemeral key pair that is discarded afterward

Answer

The credential key pair is rotated on every successful login

Answer

The server never stores any key material, ensuring future sessions are secret

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

The private key is encrypted with the user's PIN and stored on the server

Answer

The private key is split between the authenticator and the relying party using threshold cryptography

Answer

The private key is wrapped with the relying party's public key and stored in the browser

Question 6

What is the role of the 'rpIdHash' in the authenticatorData structure during FIDO2 authentication?

Accepted Answer

It binds the assertion to the specific relying party, preventing cross-origin replay

Answer

It proves the server's identity by including its TLS certificate hash

Answer

It identifies the user account associated with this credential

Answer

It contains the hash of the user's password for legacy compatibility

Question 7

Which COSE algorithm identifier represents EdDSA using the Ed25519 curve in FIDO2?

Accepted Answer

-8

Answer

-7

Answer

-35

Answer

-36