This repository was archived by the owner on Jun 30, 2025. It is now read-only.
This repository was archived by the owner on Jun 30, 2025. It is now read-only.
Fail to encrypt using OpenMP, and a possible solution #71
Description
When using encrypt inside a omp parallel for loop, the error ippMontExp: set Mont input error. is very likely to occur, especially when the plaintext is large, e.g., close to N.
Here is the simplest code to reproduce the problem.
int main()
{
ipcl::KeyPair keyPair = ipcl::generateKeypair(2048);
std::cout << "N=" << *keyPair.pub_key.getN() << std::endl;
std::cout << "N^2=" << *keyPair.pub_key.getNSQ() << std::endl;
std::vector<BigNumber> bignums;
for (size_t i = 0; i < 100; i++)
{
bignums.push_back(BigNumber(uint32_t(i + 1)));
}
for (size_t t = 0; t < 100; t++)
{
std::cout << "Start to encrypt 100 BigNumbers ==== time " << t << std::endl;
BigNumber N = *keyPair.pub_key.getN();
BigNumber moded = N - bignums[t];
#pragma omp parallel for
for (size_t i = 0; i < 100; i++)
{
keyPair.pub_key.encrypt(ipcl::PlainText(moded));
}
std::cout << "Encrypted 100 BigNumbers" << std::endl;
}
}The error seems to be caused by the ippsMod_BN function, which somehow modifies the data of modulus (the m_nquare field) during its computation. Hence it is not thread-safe.
However, I notice that copying m_square in raw_encrypt probably fixes the problem.
std::vector<BigNumber> PublicKey::raw_encrypt(const std::vector<BigNumber>& pt,
bool make_secure) const {
std::size_t pt_size = pt.size();
BigNumber nsq = *m_nsquare; // This code copies the data of m_nsquare
std::vector<BigNumber> ct(pt_size);
for (std::size_t i = 0; i < pt_size; i++)
// ct[i] = (*m_n * pt[i] + 1) % (*m_nsquare);
ct[i] = (*m_n * pt[i] + 1) % nsq;
if (make_secure) applyObfuscator(ct);
return ct;
}