C++ Ctxt::smartAutomorph方法代码示例

void EncryptedArrayDerived<type>::shift1D(Ctxt& ctxt, long i, long k) const
{
  FHE_TIMER_START;
  const PAlgebra& al = context.zMStar;

  const vector< vector< RX > >& maskTable = tab.getMaskTable();

  RBak bak; bak.save(); tab.restoreContext();

  assert(&context == &ctxt.getContext());
  assert(i >= 0 && i < (long)al.numOfGens());

  long ord = al.OrderOf(i);

  if (k <= -ord || k >= ord) {
    ctxt.multByConstant(to_ZZX(0));
    return;
  }

  // Make sure amt is in the range [1,ord-1]
  long amt = k % ord;
  if (amt == 0) return;
  if (amt < 0) amt += ord;

  RX mask = maskTable[i][ord-amt];

  long val;
  if (k < 0)
    val = PowerMod(al.ZmStarGen(i), amt-ord, al.getM());
  else {
    mask = 1 - mask;
    val = PowerMod(al.ZmStarGen(i), amt, al.getM());
  }
  DoubleCRT m1(conv<ZZX>(mask), context, ctxt.getPrimeSet());
  ctxt.multByConstant(m1);   // zero out slots where mask=0
  ctxt.smartAutomorph(val);  // shift left by val
  FHE_TIMER_STOP;
}

// computes ctxt^{2^d-1} using a method that takes
// O(log d) automorphisms and multiplications
void fastPower(Ctxt& ctxt, long d) 
{
  assert(ctxt.getPtxtSpace()==2);
  if (d <= 1) return;

  Ctxt orig = ctxt;

  long k = NumBits(d);
  long e = 1;

  for (long i = k-2; i >= 0; i--) {
    Ctxt tmp1 = ctxt;
    tmp1.smartAutomorph(1L << e);
    ctxt.multiplyBy(tmp1);
    e = 2*e;

    if (bit(d, i)) {
      ctxt.smartAutomorph(2);
      ctxt.multiplyBy(orig);
      e += 1;
    }
  }
}

void EncryptedArrayDerived<type>::rotate(Ctxt& ctxt, long amt) const
{
  FHE_TIMER_START;

  const PAlgebra& al = context.zMStar;

  const vector< vector< RX > >& maskTable = tab.getMaskTable();

  RBak bak; bak.save(); tab.restoreContext();

  assert(&context == &ctxt.getContext());

  // Simple case: just one generator
  if (al.numOfGens()==1) { // VJS: bug fix: <= must be ==
    rotate1D(ctxt, 0, amt);
    return;
  }

  // Make sure that amt is in [1,nslots-1]
  amt %= (long) al.getNSlots();
  if (amt == 0) { return; }
  if (amt < 0) amt += al.getNSlots();

  // rotate the ciphertext, one dimension at a time
  long i = al.numOfGens()-1;
  long v = al.coordinate(i, amt);
  RX mask = maskTable[i][v];
  Ctxt tmp(ctxt.getPubKey());
  const RXModulus& PhimXmod = tab.getPhimXMod();

  // optimize for the common case where the last generator has order in
  // Zm*/(p) different than its order in Zm*. In this case we can combine
  // the rotate1D relative to this generator with the masking after the
  // rotation. This saves one mult-by-constant, since we use the same mask
  // inside rotate1D as in the loop below.

  if (al.SameOrd(i) || v==0) rotate1D(ctxt, i, v); // no need to optimize
  else {
    long ord = al.OrderOf(i);
    long val = PowerMod(al.ZmStarGen(i), v, al.getM());
    long ival = PowerMod(al.ZmStarGen(i), v-ord, al.getM());

    DoubleCRT m1(conv<ZZX>(maskTable[i][ord-v]), context, ctxt.getPrimeSet());
    tmp = ctxt;  // a copy of the ciphertext

    tmp.multByConstant(m1);    // only the slots in which m1=1
    ctxt -= tmp;               // only the slots in which m1=0
    ctxt.smartAutomorph(val);  // shift left by val
    tmp.smartAutomorph(ival);  // shift right by ord-val

    // apply rotation relative to next generator before combining the parts
    --i;
    v = al.coordinate(i, amt);
    rotate1D(ctxt, i, v); 
    rotate1D(tmp, i, v+1);
    ctxt += tmp;         // combine the two parts

    if (i <= 0) { return; }  // no more generators

    mask = ((mask * (maskTable[i][v] - maskTable[i][v+1])) % PhimXmod)
             + maskTable[i][v+1];  // update the mask for next iteration
  }

  // Handle rotation relative to all the other generators (if any)
  for (i--; i >= 0; i--) {
    v = al.coordinate(i, amt);

    DoubleCRT m1(conv<ZZX>(mask), context, ctxt.getPrimeSet());
    tmp = ctxt;
    tmp.multByConstant(m1); // only the slots in which mask=1
    ctxt -= tmp;            // only the slots in which mask=0

    rotate1D(tmp, i, v); 
    rotate1D(ctxt, i, v+1);
    ctxt += tmp;
    if (i>0) {
      mask = ((mask * (maskTable[i][v] - maskTable[i][v+1])) % PhimXmod)
             + maskTable[i][v+1];  // update the mask for next iteration
    }
  }
  FHE_TIMER_STOP;
}