Attempting to use FIXEDMANUAL or FIXEDAUTO Scaling Technique

Library Questions
1

Hi, I’m new to using OpenFHE. I’m having trouble using the FIXEDMANUAL or FIXEDAUTO scaling techniques with CKKS. Maybe I’m doing something wrong with the setup or something but whenever I set the scaling technique to FIXEDMANUAL or FIXEDAUTO, creating a plaintext hangs indefinitely while it does not when the scaling technique to FLEXIBLEAUTOEXT.

Below is a code sample (running on OpenFHE v1.2.3) that shows what I mean:

#include <vector>
#include <iostream>
#include <cmath>

#include "openfhe.h"

using namespace lbcrypto;

int main() {
    int ring_dim = 1 << 14;
    int num_slots = ring_dim / 2;

    // Set up encryption parameters for CKKS
    CCParams<CryptoContextCKKSRNS> parameters;
    parameters.SetMultiplicativeDepth(1);
    parameters.SetScalingModSize(40);
    parameters.SetRingDim(ring_dim);
    parameters.SetBatchSize(num_slots);
    parameters.SetSecurityLevel(HEStd_128_classic);

    // The following lines do not work because it hangs when creating a plaintext
    parameters.SetScalingTechnique(FIXEDMANUAL); 
    // parameters.SetScalingTechnique(FIXEDAUTO);

    // The following commented out line does work, however
    // parameters.SetScalingTechnique(FLEXIBLEAUTOEXT);

    std::cout << "Generating crypto context..." << std::endl;
    // Create CryptoContext
    CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
    cc->Enable(PKE);
    cc->Enable(KEYSWITCH);
    cc->Enable(LEVELEDSHE);

    std::cout << "Generating keys..." << std::endl;
    // Generate public and secret keys
    auto keys = cc->KeyGen();
    cc->EvalMultKeyGen(keys.secretKey);

    // Scale
    double scale = pow(2.0, 40);

    // Create some plaintexts
    std::vector<double> vec1 = {1.0, 2.0, 3.0, 4.0};

    std::cout << "Creating plaintext..." << std::endl;
    // Gets stuck here when using FIXEDMANUAL scaling technique
    Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(vec1, scale);

    std::cout << "Encrypting plaintext..." << std::endl;
    // Encrypt the plaintexts
    auto ctxt1 = cc->Encrypt(keys.publicKey, ptxt1);

    std::cout << "Adding ciphertext with plaintext..." << std::endl;
    // Perform ptxt-ctxt addition
    auto ctxt_ptxt_add = cc->EvalAdd(ctxt1, ptxt1);

    std::cout << "Decrypting and printing plaintext..." << std::endl;
    // Decrypt and print results
    Plaintext result;
    cc->Decrypt(keys.secretKey, ctxt_ptxt_add, &result);
    std::cout << "ptxt-ctxt addition result: " << result->GetRealPackedValue() << std::endl;

    return 0;
}

I also noticed that the ManualRescaleDemo does not set the ScalingTechnique to FIXEDMANUAL. Am I missing something for how to use the different scaling techniques?

2

Why are you passing the scale here?

You should set the scale using the crypto-context parameters as follows:
parameters.SetScalingModSize(40);

Please follow the example “simple-real-numbers.cpp” to use and configure CKKS properly.

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