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eval-sign.cpp
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eval-sign.cpp
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//==================================================================================
// BSD 2-Clause License
//
// Copyright (c) 2014-2022, NJIT, Duality Technologies Inc. and other contributors
//
// All rights reserved.
//
// Author TPOC: contact@openfhe.org
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//==================================================================================
/*
Example for the FHEW scheme large precision sign evaluation
*/
#define PROFILE
#include "binfhecontext.h"
using namespace lbcrypto;
int main() {
// Sample Program: Step 1: Set CryptoContext
auto cc = BinFHEContext();
// Set the ciphertext modulus to be 1 << 17
// Note that normally we do not use this way to obtain the input ciphertext.
// Instead, we assume that an LWE ciphertext with large ciphertext
// modulus is already provided (e.g., by extracting from a CKKS ciphertext).
// However, we do not provide such a step in this example.
// Therefore, we use a brute force way to create a large LWE ciphertext.
uint32_t logQ = 17;
cc.GenerateBinFHEContext(STD128, false, logQ, 0, GINX, false);
uint32_t Q = 1 << logQ;
int q = 4096; // q
int factor = 1 << int(logQ - log2(q)); // Q/q
int p = cc.GetMaxPlaintextSpace().ConvertToInt() * factor; // Obtain the maximum plaintext space
// 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: Extract the MSB and decrypt to check the result
// Note that we check for 8 different numbers
for (int i = 0; i < 8; i++) {
// We first encrypt with large Q
auto ct1 = cc.Encrypt(sk, p / 2 + i - 3, FRESH, p, Q);
// Get the MSB
ct1 = cc.EvalSign(ct1);
LWEPlaintext result;
cc.Decrypt(sk, ct1, &result, 2);
std::cout << "Input: " << i << ". Expected sign: " << (i >= 3)
<< ". "
"Evaluated Sign: "
<< result << std::endl;
}
return 0;
}