static constexpr size_t kHashKeyLength = 32;
  static constexpr uint64_t kScryptCost = 1 << 12;  // It must be a power of 2.
  static constexpr uint64_t kScryptBlockSize = 8;
  static constexpr uint64_t kScryptParallelization = 1;
  static constexpr size_t kScryptMaxMemory = 1024 * 1024 * 32;