Automatically selected ring dimension does not meet 128 bit security requirements

Library Questions
1

I really wanted to have 23 levels available after bootstrapping, so I decided to set dcrtBits=56. When I then let openfhe automatically determine and set the ring dimension for 128 bit security, I get this exception:

ParamsGenCKKSRNS(): The ring dimension found using estimated logQ(P) [131072] does does not meet security requirements. Report this problem to OpenFHE developers and set the ring dimension manually to 262144.

Here is the modified simple-ckks-bootstrapping.cpp example, to reproduce the error:

void SimpleBootstrapExample() {

CCParams<CryptoContextCKKSRNS> parameters;

SecretKeyDist secretKeyDist = UNIFORM_TERNARY;
parameters.SetSecretKeyDist(secretKeyDist);

ScalingTechnique rescaleTech = FLEXIBLEAUTO;
usint dcrtBits               = 56;
usint firstMod               = 60;

parameters.SetScalingModSize(dcrtBits);
parameters.SetScalingTechnique(rescaleTech);
parameters.SetFirstModSize(firstMod);

std::vector<uint32_t> levelBudget = {4, 4};


uint32_t levelsAvailableAfterBootstrap = 23;
usint depth = levelsAvailableAfterBootstrap + FHECKKSRNS::GetBootstrapDepth(levelBudget, secretKeyDist);
parameters.SetMultiplicativeDepth(depth);

CryptoContext<DCRTPoly> cryptoContext = GenCryptoContext(parameters);
usint ringDim = cryptoContext->GetRingDimension();

std::cout << "CKKS scheme is using ring dimension " << ringDim << std::endl << std::endl;
}

I will use other values for now, but I thought you might be interested in the problem, since the error message tells me to report it.

2

Thanks a lot for reporting it!