eval-function.cpp

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// Copyright (c) 2014-2022, NJIT, Duality Technologies Inc. and other contributors
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/*
  Example for the FHEW scheme small precision arbitrary function evaluation
 */

#include <cmath>
#include "binfhecontext.h"
#include "math/hal/intnat/backendnat.h"

using namespace lbcrypto;

int main() {
    // Sample Program: Step 1: Set CryptoContext
    auto cc = BinFHEContext();
    cc.GenerateBinFHEContext(STD128, true, 12);

    // uint32_t n = 512;
    // uint32_t N = 1<<10;
    // NativeInteger q(1<<10); //q|2N
    // NativeInteger Q(((1 << 20) + 1));
    // double std = pow(2,-4);
    // uint32_t baseKS = 1<<5;
    // uint32_t baseG = 1<<5;
    // uint32_t baseR = 32;
    
    // cc.GenerateBinFHEContext(n, N, q, Q, std, baseKS, baseG, baseR, GINX);

    // Sample Program: Step 2: Key Generation

    // Generate the secret key
    auto sk = cc.KeyGen();

    std::cout << "Generating the bootstrapping keys..." << std::endl;

    // Generate the bootstrapping keys (refresh and switching keys)
    cc.BTKeyGen(sk);

    std::cout << "Completed the key generation." << std::endl;

    // Sample Program: Step 3: Create the to-be-evaluated funciton and obtain its corresponding LUT
    int p = 32;  // Obtain the maximum plaintext space

    // Initialize Function f(x) = x^3 % p
    auto fp = [](NativeInteger m, NativeInteger p1) -> NativeInteger {
        if (m < p1/2)
            return NativeInteger(1);
        else
            return p1 - 1 ;
    };

    // Generate LUT from function f(x)
    auto lut = cc.GenerateLUTviaFunction(fp, p);
    std::cout << "Evaluate x^3%" << p << "." << std::endl;

    // Sample Program: Step 4: evalute f(x) homomorphically and decrypt
    // Note that we check for all the possible plaintexts.
    for (int i = 0; i < p; i++) {
        auto ct1 = cc.Encrypt(sk, i % p, FRESH, p);

        auto ct_cube = cc.EvalFunc(ct1, lut);

        LWEPlaintext result;

        cc.Decrypt(sk, ct_cube, &result, p);

        std::cout << "Input: " << i << ". Expected: " << fp(i, p) << ". Evaluated = " << result << std::endl;
    }

    return 0;
}