Client to Authenticator Protocol (CTAP)

Standard interoperation between a user platform (e.g. a laptop) and a user-controlled cryptographic authenticator.

• ITU-T Recommendation X.1278.

Based in the Universal 2nd Factor (U2F) authentication standard.

Variants

CTAP1/U2F

FIDO U2F.

Raw message format

CTAP2

For FIDO2 authenticators (aka WebAuthn authenticators).

CBOR (Concise Binary Object Representation) data serialization format.

• Loosely based on JSON but in a binary format.