feat: port GIP protocol and auth stack

Port the GIP protocol and authentication layers from medusalix/xone
into the C++ stack:

- crypto: SHA-256/HMAC (CommonCrypto), RSA PKCS#1 (Security.framework),
  and a self-contained P-256 ECDH validated against OpenSSL vectors
- auth: v1 (RSA) and v2 (ECDH) handshake state machine
- gip: header/varint/chunk handling and packet dispatch, with the kernel
  device model replaced by transport + client_listener interfaces

Adds test_crypto, test_auth, and test_gip suites.

Co-Authored-By: deepseek (deepseek/deepseek-v4-pro-0813): ported crypto, auth, and GIP

include/auth/auth.hpp

@@ -0,0 +1,92 @@
+#pragma once
+
+// ==============================================================================
+// GIP authentication handshake
+// ==============================================================================
+// Port target: medusalix/xone auth/auth.c + auth/auth.h.
+//
+// The kernel driver runs the RSA/ECDH exchanges on workqueues and speaks to
+// the controller through gip_send_authenticate(). Here the exchanges run
+// synchronously and the GIP layer is reached through the auth_sink callback
+// interface, which the gip::client implements.
+// ==============================================================================
+
+#include <array>
+#include <cstdint>
+#include <span>
+
+#include "auth/crypto.hpp"
+
+namespace xone::auth {
+
+using u8 = std::uint8_t;
+using u16 = std::uint16_t;
+
+// Wire sizes from the upstream auth.h.
+inline constexpr auto k_trailer_len = 8;
+inline constexpr auto k_random_len = 32;
+inline constexpr auto k_certificate_max_len = 1024;
+inline constexpr auto k_pubkey_len = 270;       // v1 RSA public key
+inline constexpr auto k_secret_len = 48;
+inline constexpr auto k_encrypted_pms_len = 256;
+inline constexpr auto k_transcript_len = 32;
+inline constexpr auto k_session_key_len = 16;
+inline constexpr auto k_pubkey2_len = 64;       // v2 EC public key (X || Y)
+inline constexpr auto k_secret2_len = 32;
+
+// Callback interface implemented by the GIP layer.
+class auth_sink {
+public:
+    virtual ~auth_sink() = default;
+
+    // Send an AUTHENTICATE command packet to the controller.
+    virtual auto send(std::span<u8 const> pkt, bool acknowledge) -> int = 0;
+
+    // Install the derived AES-CCMP session key (16 bytes).
+    virtual auto set_encryption_key(std::span<u8 const> key) -> int = 0;
+};
+
+// Runs the handshake for one controller. Port of struct gip_auth.
+class auth {
+public:
+    explicit auth(auth_sink& sink);
+
+    // Begin the handshake by sending the (v1) host hello.
+    auto start() -> int;
+
+    // Process one incoming AUTHENTICATE packet from the controller.
+    auto process_pkt(std::span<u8 const> data) -> int;
+
+private:
+    auto send_pkt(u8 cmd, void const* pkt, std::size_t len) -> int;
+    auto request_pkt(u8 cmd, std::uint16_t len) -> int;
+    auto send_hello() -> int;
+    auto send_hello2() -> int;
+    auto send_finish(u8 cmd) -> int;
+    auto send_complete() -> int;
+    auto exchange_rsa() -> void;
+    auto exchange_ecdh() -> void;
+    auto complete_handshake() -> void;
+    auto handle_pkt_acknowledge() -> int;
+    auto handle_pkt_data(std::span<u8 const> data) -> int;
+    auto dispatch_pkt(u8 cmd, std::span<u8 const> data) -> int;
+    auto handle_hello(std::span<u8 const> data) -> int;
+    auto handle_certificate(std::span<u8 const> data) -> int;
+    auto handle_finish(std::span<u8 const> data) -> int;
+    auto handle_hello2(std::span<u8 const> data) -> int;
+    auto handle_certificate2(std::span<u8 const> data) -> int;
+    auto handle_pubkey(std::span<u8 const> data) -> int;
+    auto get_transcript() -> std::array<u8, k_transcript_len>;
+
+    auth_sink& sink_;
+    sha256 transcript_;
+    u8 last_sent_command_ = 0;
+
+    std::array<u8, k_random_len> random_host_{};
+    std::array<u8, k_random_len> random_client_{};
+    std::array<u8, k_pubkey_len> pubkey_client_{};
+    std::array<u8, k_pubkey2_len> pubkey_client2_{};
+    std::array<u8, k_secret_len> master_secret_{};
+};
+
+} // namespace xone::auth