小结

1.EncryptionParameters类

• set_poly_modulus_degree()：设置多项式模数
• set_coeff_modulus()：设置密文模数
• set_plain_modulus()：设置明文模数

//BFV
EncryptionParameters parms(scheme_type::bfv);

size_t poly_modulus_degree = 4096;
parms.set_poly_modulus_degree(poly_modulus_degree);
parms.set_coeff_modulus(CoeffModulus::BFVDefault(poly_modulus_degree));
parms.set_plain_modulus(1024);
//parms.set_plain_modulus(PlainModulus::Batching(poly_modulus_degree, 20));

//CKKS
EncryptionParameters parms(scheme_type::ckks);

size_t poly_modulus_degree = 8192;
parms.set_poly_modulus_degree(poly_modulus_degree);
parms.set_coeff_modulus(CoeffModulus::Create(poly_modulus_degree,{60,40,40,60}));

double scale = pow(2.0,40);

创建context

SEALContext context(parms);

/*
    判断Encoder标志是否开启
*/
auto qualifiers = context.first_context_data()->qualifiers();

2.KeyGenerator类

• secret_key()：生成私钥
• create_public_key()：生成公钥
• create_relin_keys()：生成重新线性化密钥
• create_galois_keys()：生成galois密钥

KeyGenerator keygen(context);

auto secret_key = keygen.secret_key();
PublicKey public_key;
keygen.create_public_key(public_key);
RelinKeys relin_keys;
keygen.create_relin_keys(relin_keys);
GaloisKeys gal_keys;
keygen.create_galois_keys(gal_keys);

3.BatchEncoder/CKKSEncoder类

(1)BatchEncoder

• slot_count()
• encode()：编码
• decode()：解码

BatchEncoder batch_encoder(context);

size_t slot_count = batch_encoder.slot_count();
size_t row_size = slot_count / 2;

vector<uint64_t> pod_matrix(slot_count, 0ULL);
pod_matrix[0] = 0ULL;
pod_matrix[1] = 1ULL;
pod_matrix[2] = 2ULL;
pod_matrix[3] = 3ULL;
pod_matrix[row_size] = 4ULL;
pod_matrix[row_size + 1] = 5ULL;
pod_matrix[row_size + 2] = 6ULL;
pod_matrix[row_size + 3] = 7ULL;

Plaintext plain_matrix;
batch_encoder.encode(pod_matrix, plain_matrix);

vector<uint64_t> pod_result;
batch_encoder.decode(plain_matrix, pod_result);

(2)CKKSEncoder

CKKSEncoder encoder(context);

size_t slot_count = encoder.slot_count();
vector<double> input{ 0.0, 1.1, 2.2, 3.3 };

Plaintext plain;
double scale = pow(2.0, 30);
encoder.encode(input, scale, plain);

vector<double> output;
encoder.decode(plain, output);

4.Encryptor/Evaluator/Decryptor类

Encryptor encryptor(context,public_key);
Evaluator evaluator(context);
Decryptor decryptor(context,secret_key);

(1)Encryptor

• encrypt()

encryptor.encrypt(plain, encrypted);

(2)Evaluator

• square_inplace()：平方
• square()
• relinearize_inplace()：重新线性化
• rescale_to_next_inplace()：rescale
• mod_switch_to_next_inplace()：切换到下一个level

evaluator.square_inplace(encrypted);
evaluator.relinearize_inplace(encrypted, relin_keys);

evaluator.square(x1_encrypted, x3_encrypted);
evaluator.relinearize_inplace(x3_encrypted, relin_keys);

evaluator.mod_switch_to_next_inplace(encrypted);

(3)Decryptor

• decrypt()
• invariant_noise_budget()：可用噪声预算

decryptor.decrypt(encrypted, plain);

decryptor.invariant_noise_budget(encrypted)

5.save()/load()

使用save()函数将密文存入指定文件；
使用load()函数从指定文件载入密文。

(密钥同理)

void saveCiphertext(Ciphertext encrypted, string filename){
  ofstream ct;
  ct.open(filename, ios::binary);
  encrypted.save(ct);
};

/* 
  If you can't / don't want / don't need to verify the encryption parameters
*/
Ciphertext unsafe_loadCiphertext(string filename){

  ifstream ct;
  ct.open(filename, ios::binary);
  Ciphertext result;
  result.unsafe_load(context);

  return result;
};

/*
 Verifying encryption parameters
*/
Ciphertext loadCiphertext(string filename, EncryptionParameters parms){

  auto context = SEALContext::Create(parms);

  ifstream ct;
  ct.open(filename, ios::binary);
  Ciphertext result;
  result.load(context, ct);

  return result;
};