Question on PrecomputeCRTTables

Library Questions
1

Hello,

I have a question regarding PrecomputeCRTTables in CKKS.

I’ve found that sometimes when I run the code in CKKS with FLEXIBLEAUTO as the scaling technique, it returns the following exception:

'lbcrypto::OpenFHEException'
  what():  (...) CryptoParametersCKKSRNS::PrecomputeCRTTables - FLEXIBLEAUTO cannot support this number of levels in this parameter setting. Please use FIXEDMANUAL.

I checked that this exception is thrown from src/pke/lib/scheme/ckksrns/ckksrns-cryptoparameters.cpp.
However, for me, it was hard to clearly figure out when is the exact case for this exception only with the code.
I tried to find some related explanation about this on either comments or documentation, but I couldn’t.

Could you please help me for this or inform me some materials that I can refer to?

Thank you.

2

Please provide a minimum working examples for us to be able to reconstruct the error. All the parameters you feed to the cryptocontext are important to identify the cause.

3

Sorry for the poor identification.

Here’s the minimal code example that I’ve checked the exception mentioned above:

int main(void)
{
  CCParams<CryptoContextCKKSRNS> parameters;
  parameters.SetRingDim(32768);
  parameters.SetMultiplicativeDepth(10);
  parameters.SetFirstModSize(46);
  parameters.SetScalingModSize(18);
  parameters.SetSecurityLevel(HEStd_256_classic);
  parameters.SetScalingTechnique(FLEXIBLEAUTO);

  CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
  cc->Enable(PKE);
  cc->Enable(KEYSWITCH);
  cc->Enable(LEVELEDSHE);

  return 0;
}