src/connectivity/bluetooth/core/bt-host/sm/ecdh_key.h

// Copyright 2020 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef SRC_CONNECTIVITY_BLUETOOTH_CORE_BT_HOST_SM_ECDH_KEY_H_
#define SRC_CONNECTIVITY_BLUETOOTH_CORE_BT_HOST_SM_ECDH_KEY_H_

#include <cstdint>
#include <optional>

#include "fbl/macros.h"
#include "src/connectivity/bluetooth/core/bt-host/common/uint256.h"
#include "src/connectivity/bluetooth/core/bt-host/sm/smp.h"
#include "third_party/boringssl/src/include/openssl/base.h"

namespace bt::sm {

// Class exposing operations on ECDH keys needed for Secure Connections pairing. The only valid
// operation on a moved-from EcdhKey is to reassign it to an existing key.
class EcdhKey {
 public:
  // Returns a new public key on the P-256 Elliptic Curve parsed from a peer public key, or
  // std::nullopt if the peer key is not a valid point on the curve.
  static std::optional<EcdhKey> ParseFromPublicKey(sm::PairingPublicKeyParams pub_key);

  EcdhKey(EcdhKey&& other) noexcept;
  EcdhKey& operator=(EcdhKey&& other) noexcept;
  virtual ~EcdhKey();

  // Returns a representation of the public key for SMP (Vol. 3 Part H Section 3.5.6).
  sm::PairingPublicKeyParams GetSerializedPublicKey() const;

  // Returns the X/Y value of the public key as std::array wrappers for e.g. comparisons, crypto.
  UInt256 GetPublicKeyX() const;
  UInt256 GetPublicKeyY() const;

  const EC_KEY* boringssl_key() const { return key_; }

 protected:
  EcdhKey();

  EC_KEY* mut_boringssl_key() { return key_; }
  void set_boringssl_key(EC_KEY* k) { key_ = k; }

 private:
  EC_KEY* key_;
  DISALLOW_COPY_AND_ASSIGN_ALLOW_MOVE(EcdhKey);
};

// Specialization of EcdhKey used to ensure that when calculating the shared DH Key between two
// EcdhKeys, at least one has a private key.
class LocalEcdhKey : public EcdhKey {
 public:
  // Returns a new random public-private key pair on the P-256 Elliptic Curve used for DH Key
  // exchange in Secure Connections, or std::nullopt if allocation fails.
  static std::optional<LocalEcdhKey> Create();

  LocalEcdhKey(LocalEcdhKey&& other) noexcept;
  LocalEcdhKey& operator=(LocalEcdhKey&& other) noexcept;

  // Returns a 256-bit DHKey calculated from our private key and the peer public key.
  UInt256 CalculateDhKey(const EcdhKey& peer_public_key) const;

  // Used to verify correct DHKey calculation with known, non-random private and public keys.
  void SetPrivateKeyForTesting(const UInt256& private_key);

 private:
  LocalEcdhKey();
  DISALLOW_COPY_AND_ASSIGN_ALLOW_MOVE(LocalEcdhKey);
};

}  // namespace bt::sm

#endif  // SRC_CONNECTIVITY_BLUETOOTH_CORE_BT_HOST_SM_ECDH_KEY_H_