algorithm = SHA256_WITH_ECDSA,
            parameters = ByteString.EMPTY,
          )
      }
    }

    private fun generateKeyPair(): KeyPair {
      return KeyPairGenerator.getInstance(keyAlgorithm).run {
        initialize(keySize, SecureRandom())
        generateKeyPair()
      }
    }

    companion object {
      private const val DEFAULT_DURATION_MILLIS = 1000L * 60 * 60 * 24 // 24 hours.
    }