Bug or bad params? divison by zero NTL

[AlexDanDuna]

I'm really not sure why, but this code gives me an NTL division by zero error upon attempting to encrypt a 1 :(. It appears to be because for some reason in the public key, the 'ptxtSpace' is zero and it reaches a point where a division by this value is done.. NOTE: I generated m, gens, ords, mvec using parmams.cpp.

`#include

include

include <NTL/BasicThreadPool.h>

NTL_CLIENT

include "FHE.h"

include "EncryptedArray.h"

include "intraSlot.h"

include "binaryArith.h"

include "binaryCompare.h"

typedef unsigned long uLong;

using namespace std; using namespace NTL;

int main() { SetNumThreads(12);

uLong m, p, r;

m = 1001;
p = 2;
r = 1;

uLong L, c;
L = 30; // 30 levels without bootstrapping
c = 3;  // numCols of KeySwitch matrix

vector<long> gens {430, 274};
vector<long> ords {6, 2};
Vec<long> mvec;
mvec.append(7);
mvec.append(143);

FHEcontext context (m, p, r, gens, ords);
buildModChain(context, L, c, 7);
context.makeBootstrappable(mvec, 0, false, true); // BOOTSTRAPPING!

EncryptedArray ea(context);
std::vector<zzX> unpackSlotEncoding;
buildUnpackSlotEncoding(unpackSlotEncoding, ea);

FHESecKey secretKey (context);
FHEPubKey publicKey = secretKey;

uLong w = 64; // Hamming weight
secretKey.GenSecKey(w);
addSome1DMatrices(secretKey);
addFrbMatrices(secretKey);
secretKey.genRecryptData();

Ctxt encBit(publicKey);
publicKey.Encrypt(encBit, to_ZZX(1));

return 0;

}`

[fionser]

• call GenSecKey first
• then create the public key
• Or to use reference rather than copy construction, like FHEPubKey const& publicKey{secretKey};

[AlexDanDuna]

I.. I .. I would've never guessed that was the problem. Thank you SO much! using GenSecKey actually solved the problem. I'll also use the reference advice!

[fionser]

@PhantomR You can think in this way

1. you create an empty secret key
2. then you create a new public key based on the empty secret key
3. then you fill in the secrete key. But the public key is still empty.

[AlexDanDuna]

It makes a lot of sense now! Thak you! :)