HE-API提供一个统一的接口，屏蔽了底层使用的SHE library的细节，使对加密不是很了解的人也可以轻松掌握（代码在这里）。HE-API目前只支持HElib，通过使用不同的编译选项（FXPT，BINARY）来生成支持不同数据类型的库：helib.a.fxpt，helib.a.binary和helib.a.ulong。下面以testInteger函数为例，来分析如何使用：

template <unsigned long nb_tests>
int testInteger() {
  // Determine if the test should run
  #ifdef BINARY
  unsigned long run = HE::supports_bit_encryption;
  #else
  unsigned long run = HE::supports_unsigned_encryption;
  #endif

  if (!run) {
    return 0;
  }

  timing t;

  gmp_randclass prng(gmp_randinit_default);
//  prng.seed(0);
  prng.seed(time(NULL)); // To set different seeds

  void* parameters = nullptr;
  void* sk = nullptr;
  void* pk = nullptr;
  void* evk = nullptr;

  // Init
  t.start();
  HE::init(&parameters);
  t.stop("Init");

  // Keygen
  t.start();
  HE::keygen(parameters, &sk, &pk, &evk);
  t.stop("Keygen");
  // HE::serialize_sk("sk.bin", sk);
  // std::cout << "serialized?" << std::endl;

  // Random messages
  unsigned long* messages1 = new unsigned long[nb_tests];
  unsigned long* messages2 = new unsigned long[nb_tests];
  for (unsigned long i = 0; i < nb_tests; i++) {
    messages1[i] =
        mpz_class(prng.get_z_range(HE::plaintext_modulus)).get_ui();
    messages2[i] =
        mpz_class(prng.get_z_range(HE::plaintext_modulus)).get_ui();
  }

  // Encrypt
  void** ciphertexts1 = new void* [nb_tests];
  void** ciphertexts2 = new void* [nb_tests];
  t.start();
  for (unsigned long i = 0; i < nb_tests; i++) {
    HE::encryptInteger(pk, &(ciphertexts1[i]), messages1[i]);
    HE::encryptInteger(pk, &(ciphertexts2[i]), messages2[i]);
  }
  t.stop("Encrypt Integer", nb_tests * 2);

  // Decrypt
  unsigned long* messages1_decrypted = new unsigned long[nb_tests];
  unsigned long* messages2_decrypted = new unsigned long[nb_tests];
  t.start();
  for (unsigned long i = 0; i < nb_tests; i++) {
    HE::decryptInteger(sk, pk, ciphertexts1[i], &(messages1_decrypted[i]));
    HE::decryptInteger(sk, pk, ciphertexts2[i], &(messages2_decrypted[i]));
  }
  t.stop("Decrypt Integer", nb_tests * 2);

  // Correctness of decryption
  for (unsigned long i = 0; i < nb_tests; i++) {
    assert(messages1[i] == messages1_decrypted[i]);
    assert(messages2[i] == messages2_decrypted[i]);
  }

  // Homomorphic additions
  unsigned long* messages_added = new unsigned long[nb_tests];
  for (unsigned long i = 0; i < nb_tests; i++) {
    messages_added[i] = (messages1[i] + messages2[i]) % HE::plaintext_modulus;
  }
  void** ciphertexts_added = new void* [nb_tests];
  t.start();
  for (unsigned long i = 0; i < nb_tests; i++) {
    HE::add(pk, evk, &(ciphertexts_added[i]), ciphertexts1[i], ciphertexts2[i]);
  }
  t.stop("Homomorphic Addition", nb_tests);

  // Correctness of addition
  unsigned long* messages_added_decrypted = new unsigned long[nb_tests];
  for (unsigned long i = 0; i < nb_tests; i++) {
    HE::decryptInteger(sk, pk, ciphertexts_added[i],
                     &(messages_added_decrypted[i]));
    assert(messages_added_decrypted[i] == messages_added[i]);
  }

  // Homomorphic multiplications
  unsigned long* messages_multiplied = new unsigned long[nb_tests];
  for (unsigned long i = 0; i < nb_tests; i++) {
    messages_multiplied[i] = (messages1[i] * messages2[i]) % HE::plaintext_modulus;
  }
  void** ciphertexts_multiplied = new void* [nb_tests];
  t.start();
  for (unsigned long i = 0; i < nb_tests; i++) {
    HE::mul(pk, evk, &(ciphertexts_multiplied[i]), ciphertexts1[i],
          ciphertexts2[i]);
  }
  t.stop("Homomorphic Multiplication", nb_tests);

  // Correctness of multiplication
  unsigned long* messages_multiplied_decrypted = new unsigned long[nb_tests];
  for (unsigned long i = 0; i < nb_tests; i++) {
    HE::decryptInteger(sk, pk, ciphertexts_multiplied[i],
                     &(messages_multiplied_decrypted[i]));
    assert(messages_multiplied_decrypted[i] == messages_multiplied[i]);
  }

  delete[] messages1;
  delete[] messages2;
  delete[] messages_added;
  delete[] messages_added_decrypted;
  delete[] messages_multiplied;
  delete[] messages_multiplied_decrypted;

  for(long i=0; i< nb_tests; i++)
  {
      HE::freeup_ciphertext(pk,ciphertexts1[i]);
      HE::freeup_ciphertext(pk,ciphertexts2[i]);
      HE::freeup_ciphertext(pk,ciphertexts_added[i]);
      HE::freeup_ciphertext(pk,ciphertexts_multiplied[i]);
  }

  delete[] ciphertexts1;
  delete[] ciphertexts2;
  delete[] ciphertexts_added;
  delete[] ciphertexts_multiplied;

  HE::freeup_keys(parameters,sk,pk,evk);

  return 0;
}

（1）HE-API使用了gmp项目：
a）gmp_randclass类用来生成随机数：

......
gmp_randclass prng(gmp_randinit_default);
//  prng.seed(0);
prng.seed(time(NULL)); // To set different seeds
......
messages1[i] =
        mpz_class(prng.get_z_range(HE::plaintext_modulus)).get_ui();
messages2[i] =
        mpz_class(prng.get_z_range(HE::plaintext_modulus)).get_ui();

b）mpz_class用来表示整数。get_ui()返回mpz_class的最低位的unsigned long。以Binary为例，mpz_class(prng.get_z_range(HE::plaintext_modulus)).get_ui();随机返回0和1。

（2）另外就是需要注意加法和乘法时的取模运算：

......
messages_added[i] = (messages1[i] + messages2[i]) % HE::plaintext_modulus;
......
messages_multiplied[i] = (messages1[i] * messages2[i]) % HE::plaintext_modulus;

仍以Binary为例，此时PLAINTEXT_MODULUS的值为2，即要对2取模。操作数是1个bit，取值为0或1，加密结果对应的也是0或1。