ctap2-proto: Add authenticator::client_pin::auth_protocol::{Authenticator, Platform} trait defitions

Adds traits to define the Platform and Authenticator abstract
definitions for the PIN/UV Auth Protocol.

crates/ctap2-proto/src/authenticator/client_pin/auth_protocol.rs

@@ -1,6 +1,63 @@
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
+pub trait Authenticator {
+    type Error; // TODO: Can the error cases be enumerated here?
+
+    /// This process is run by the authenticator at power-on.
+    fn initialize(&mut self) -> Result<(), Self::Error>;
+
+    /// Generates a fresh public key.
+    fn regenerate(&mut self) -> Result<(), Self::Error>;
+
+    /// Generates a fresh pinUvAuthToken.
+    fn reset_pin_uv_auth_token(&mut self) -> Result<(), Self::Error>;
+
+    /// Returns the authenticator’s public key as a COSE_Key structure.
+    fn get_public_key(&self) -> Result<cosey::PublicKey, Self::Error>;
+
+    /// Processes the output of encapsulate from the peer and produces a shared
+    /// secret, known to both platform and authenticator.
+    fn decapsulate(&self, peer_cose_key: cosey::PublicKey) -> Result<Vec<u8>, Self::Error>;
+
+    /// Decrypts a ciphertext, using sharedSecret as a key, and returns the
+    /// plaintext.
+    fn decrypt(&self, ciphertext: &[u8]) -> Result<Vec<u8>, Self::Error>;
+
+    /// Verifies that the signature is a valid MAC for the given message. If the
+    /// key parameter value is the current pinUvAuthToken, it also checks
+    /// whether the pinUvAuthToken is in use or not.
+    fn verify(&self, key: &[u8], message: &[u8], signature: &[u8]) -> Result<(), Self::Error>;
+}
+
+pub trait Platform {
+    type Error; // TODO: Can the error cases be enumerated here?
+    /// This is run by the platform when starting a series of transactions
+    /// with a specific authenticator.
+    fn initialize(&self) -> Result<(), Self::Error>;
+
+    /// Generates an encapsulation for the authenticator’s public key and
+    /// returns the message to transmit and the shared secret.
+    fn encapsulate(
+        &self,
+        peer_cose_key: cosey::PublicKey,
+    ) -> Result<(cosey::PublicKey, Vec<u8>), Self::Error>; // TODO: Return a struct for OK variant?
+
+    /// Encrypts a plaintext to produce a ciphertext, which may be longer
+    /// than the plaintext. The plaintext is restricted to being a
+    /// multiple of the AES block size (16 bytes) in length.
+    // TODO: Return a specific type instead of raw bytes?
+    fn encrypt(&self, key: &[u8], plaintext: &[u8]) -> Result<Vec<u8>, Self::Error>;
+
+    /// Decrypts a ciphertext and returns the plaintext.
+    // TODO: Return a specific type instead of raw bytes?
+    fn decrypt(&self, key: &[u8], ciphertext: &[u8]) -> Result<Vec<u8>, Self::Error>;
+
+    /// Computes a MAC of the given message.
+    // TODO: Return a specific type instead of raw bytes?
+    fn authenticate(&self, key: &[u8], message: &[u8]) -> Result<Vec<u8>, Self::Error>;
+}
+
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
 #[cfg_attr(
     feature = "serde",