gogo9th
commented
1 month ago Hi,
I figured out another more concrete issue: the noise budgets of PhantomFHE ciphertexts seem to be actually lower than those of SEAL ciphertexts, even under the same crypto parameter setup. I found this issue because my software using PhantomFHE does not generate correct results, while everything works correctly when using the original SEAL library.
Below I create the minimal reproducible example code for this issue:
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <stdlib.h>
using namespace std;
#ifdef SEAL
#include "seal/seal.h"
using namespace seal;
#elif defined(PHANTOM)
#include "phantom.h"
using namespace phantom;
using namespace phantom::arith;
using namespace phantom::util;
#endif
int main()
{
vector<int> coeff_mod_list = {60, 60, 60, 60, 60, 60};
EncryptionParameters parms(scheme_type::bfv);
vector<Modulus> mod_list;
//if (poly_modulus_degree == 16384)
mod_list = CoeffModulus::Create(16384, coeff_mod_list);
//else
// mod_list = CoeffModulus::BFVDefault(poly_modulus_degree);
parms.set_poly_modulus_degree(16384);
parms.set_coeff_modulus(mod_list);
parms.set_plain_modulus(PlainModulus::Batching(16384, 22));
#if defined(SEAL) || defined(SEAL_PHANTOM)
SEALContext context(parms);
SecretKey sk;
PublicKey pk;
RelinKeys relin_keys;
GaloisKeys gal_keys;
KeyGenerator keygen(context);
Evaluator evaluator(context);
BatchEncoder batch_encoder(context);
keygen.create_public_key(pk);
sk = keygen.secret_key();
stringstream relin_stream, gal_stream;
keygen.create_relin_keys().save(relin_stream);
keygen.create_galois_keys().save(gal_stream);
relin_keys.load(context, relin_stream);
gal_keys.load(context, gal_stream);
Encryptor encryptor(context, pk);
encryptor.set_secret_key(sk); // set it up in the SEAL context
Decryptor decryptor = Decryptor(context, sk);
#elif defined(PHANTOM)
PhantomContext context(parms);
PhantomSecretKey sk(context);
PhantomPublicKey pk = sk.gen_publickey(context);
PhantomRelinKey relin_keys(sk.gen_relinkey(context));
PhantomGaloisKey gal_keys = sk.create_galois_keys(context);
PhantomBatchEncoder batch_encoder = PhantomBatchEncoder(context);
#endif
vector<uint64_t> vec(16384, 0);
#if defined(PHANTOM)
PhantomPlaintext pt;
PhantomCiphertext ct;
batch_encoder.encode(context, vec, pt);
sk.encrypt_symmetric(context, pt, ct);
#elif defined(SEAL)
Plaintext pt;
Ciphertext ct;
batch_encoder.encode(vec, pt);
encryptor.encrypt_symmetric(pt, ct);
#endif
for (int i = 0; i < 4; i++)
{ cout << "Changing multiplicative chain index from " << i << " -> " << i + 1 << endl;
#if defined(PHANTOM)
multiply_inplace(context, ct, ct);
relinearize_inplace(context, ct, relin_keys);
mod_switch_to_next_inplace(context, ct);
#elif defined(SEAL)
evaluator.multiply_inplace(ct, ct);
evaluator.relinearize_inplace(ct, relin_keys);
evaluator.mod_switch_to_next_inplace(ct);
#endif
vector<uint64_t> ret_list;
//assert(this->is_debug);
#if defined(PHANTOM)
PhantomPlaintext pt;
sk.decrypt(context, ct, pt);
batch_encoder.decode(context, pt, ret_list);
#elif defined(SEAL)
Plaintext pt;
decryptor.decrypt(ct, pt);
batch_encoder.decode(pt, ret_list);
#endif
if (ret_list[0] != 0)
{ cout << "- A decryption error found at multiplicative chain index : " << i << endl;
exit(0);
}
}
cout << "4 multiplications done successfuly" << endl;
return 0;
}
I also attach the complete source code for this example: src.zip
This example assumes that you have installbed both SEAL and PhantomFHE libraries on your Ubuntu 22.04 (or higher) machine. You only need to run:
unzip src.zip
cd src/build
cmake .. --fresh -DSEAL=ON # To compile with the SEAL library
make -j
./main # The 5 consecutive cipher multiplications should work fine
cmake .. --fresh -DPHANTOM=ON # To compile with the PhantomFHE library
make -j
./main # Only 2 consecutive cipher multiplications will work and the results gets corrupted afterwards
D4rkCrypto
Hi,
At examples/serialization.cu:255, I inserted the following line:
cout << "Noise: " << secret_key.invariant_noise_budget(context, x_symmetric_cipher_load) << endl;And if I run the example code, I get this output:
cipher noise budget is: 0Actually, it seems that even for the unmodified serialization.cu file, the noise budgets are all 0:
Shouldn't we expect the noise budgets to be some positive numbers?