ExtractDigits issue

[Pistonomaxime]

Maxime Pistono, maxime.pistono@imt-atlantique.fr Ubuntu 18.04.4 LTS (GNU/Linux 4.15.0-91-generic x86_64) I have three questions: -In the following code can I manually increase the parameter r? -If the answer is yes, why I cannot increase it more than 59? (maybe a code limitation) -The most important question. Why if I increase it (to 40 for example) digits extraction fail ? I also have a docker image of an "old" HElib version 1.0.0 beta1 on which if I increase the parameter r everything goes well.

  // Plaintext prime modulus
  unsigned long p = 2;
  // Cyclotomic polynomial - defines phi(m)
  unsigned long m = 3;
  // Hensel lifting (default = 1)
  unsigned long r = 1;
  // Number of bits of the modulus chain
  unsigned long bits = 300;
  // Number of columns of Key-Switching matix (default = 2 or 3)
  unsigned long c = 4;

  double lBound = 30.0;
  long bound = floor(lBound/log2((double)p));
  if (r<2 || r>bound) r = bound;
  //r = 40;
  std::cout << "Value of r = " << r << std::endl;

  long ll = NTL::NextPowerOfTwo(p);
  bits = 30*(r*ll*3 + 2);
  std::cout << "Value of bits = " << bits << std::endl;

  std::cout << "Initialising context object..." << std::endl;
  // Intialise context
  helib::Context context(m, p, r);
  // Modify the context, adding primes to the modulus chain
  std::cout  << "Building modulus chain..." << std::endl;
  buildModChain(context, bits, c);

  // Print the context
  context.zMStar.printout();
  std::cout << std::endl;

  // Print the security level
  std::cout << "Security: " << context.securityLevel() << std::endl;
  // Secret key management
  std::cout << "Creating secret key..." << std::endl;
  // Create a secret key associated with the context
  helib::SecKey secret_key(context);
  // Generate the secret key
  secret_key.GenSecKey();
  std::cout << "Generating key-switching matrices..." << std::endl;
  // Compute key-switching matrices that we need
  helib::addSome1DMatrices(secret_key);

  // Public key management
  // Set the secret key (upcast: SecKey is a subclass of PubKey)
  const helib::PubKey& public_key = secret_key;

  // Get the EncryptedArray of the context
  const helib::EncryptedArray& ea = *(context.ea);

  long nslots = ea.size();
  std::cout << "Number of slots: " << nslots << std::endl;

  std::vector<long> Stream(nslots);
  Stream[0] = 268435455;
  std::vector<long> Verification;

  helib::Ctxt E_Stream(public_key);
  ea.encrypt(E_Stream, public_key, Stream);
  ea.decrypt(E_Stream, secret_key, Verification);
  std::cout << "plaintext=" << helib::vecToStr(Verification) << std::endl;

  std::cout << "extracting " << r << " digits..." << std::flush;
  std::vector<helib::Ctxt> E_Bits;
  helib::extractDigits(E_Bits, E_Stream);
  std::cout << " done\n" << std::flush;

  for (long i=0; i<(long)E_Bits.size(); i++) {
      ea.decrypt(E_Bits[i], secret_key, Verification);
      std::cout << i << "th digit=" << helib::vecToStr(Verification) << std::endl;
  }

  return(0);

Thanks for your help.