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scheme-switching.cpp
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scheme-switching.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.
//==================================================================================
/*
Examples for scheme switching between CKKS and FHEW and back, with intermediate computations
*/
#include "openfhe.h"
#include "binfhecontext.h"
using namespace lbcrypto;
void SwitchCKKSToFHEW();
void SwitchFHEWtoCKKS();
void FloorViaSchemeSwitching();
void ComparisonViaSchemeSwitching();
void FuncViaSchemeSwitching();
void PolyViaSchemeSwitching();
void ArgminViaSchemeSwitching();
void ArgminViaSchemeSwitchingAlt();
void ArgminViaSchemeSwitchingUnit();
void ArgminViaSchemeSwitchingAltUnit();
std::vector<int32_t> RotateInt(const std::vector<int32_t>&, int32_t);
int main() {
SwitchCKKSToFHEW();
SwitchFHEWtoCKKS();
// FloorViaSchemeSwitching();
// FuncViaSchemeSwitching();
// PolyViaSchemeSwitching();
ComparisonViaSchemeSwitching();
ArgminViaSchemeSwitching();
ArgminViaSchemeSwitchingAlt();
// ArgminViaSchemeSwitchingUnit();
// ArgminViaSchemeSwitchingAltUnit();
return 0;
}
void SwitchCKKSToFHEW() {
/*
Example of switching a packed ciphertext from CKKS to multiple FHEW ciphertexts.
*/
std::cout << "\n-----SwitchCKKSToFHEW-----\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS
// Specify main parameters
uint32_t multDepth = 3;
uint32_t firstModSize = 60;
uint32_t scaleModSize = 50;
uint32_t ringDim = 4096;
SecurityLevel sl = HEStd_NotSet;
BINFHE_PARAMSET slBin = TOY;
uint32_t logQ_ccLWE = 25;
// uint32_t slots = ringDim / 2; // Uncomment for fully-packed
uint32_t slots = 16; // sparsely-packed
uint32_t batchSize = slots;
CCParams<CryptoContextCKKSRNS> parameters;
parameters.SetMultiplicativeDepth(multDepth);
parameters.SetFirstModSize(firstModSize);
parameters.SetScalingModSize(scaleModSize);
parameters.SetScalingTechnique(FLEXIBLEAUTOEXT);
parameters.SetSecurityLevel(sl);
parameters.SetRingDim(ringDim);
parameters.SetBatchSize(batchSize);
CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
// Enable the features that you wish to use
cc->Enable(PKE);
cc->Enable(KEYSWITCH);
cc->Enable(LEVELEDSHE);
cc->Enable(SCHEMESWITCH);
std::cout << "CKKS scheme is using ring dimension " << cc->GetRingDimension();
std::cout << ", number of slots " << slots << ", and supports a multiplicative depth of " << multDepth << std::endl
<< std::endl;
// Generate encryption keys
auto keys = cc->KeyGen();
// Step 2: Prepare the FHEW cryptocontext and keys for FHEW and scheme switching
SchSwchParams params;
params.SetSecurityLevelCKKS(sl);
params.SetSecurityLevelFHEW(slBin);
params.SetCtxtModSizeFHEWLargePrec(logQ_ccLWE);
params.SetNumSlotsCKKS(slots);
auto privateKeyFHEW = cc->EvalCKKStoFHEWSetup(params);
auto ccLWE = cc->GetBinCCForSchemeSwitch();
cc->EvalCKKStoFHEWKeyGen(keys, privateKeyFHEW);
std::cout << "FHEW scheme is using lattice parameter " << ccLWE->GetParams()->GetLWEParams()->Getn();
std::cout << ", logQ " << logQ_ccLWE;
std::cout << ", and modulus q " << ccLWE->GetParams()->GetLWEParams()->Getq() << std::endl << std::endl;
// Compute the scaling factor to decrypt correctly in FHEW; under the hood, the LWE mod switch will performed on the ciphertext at the last level
auto pLWE1 = ccLWE->GetMaxPlaintextSpace().ConvertToInt(); // Small precision
auto modulus_LWE = 1 << logQ_ccLWE;
auto beta = ccLWE->GetBeta().ConvertToInt();
auto pLWE2 = modulus_LWE / (2 * beta); // Large precision
double scale1 = 1.0 / pLWE1;
double scale2 = 1.0 / pLWE2;
// Perform the precomputation for switching
cc->EvalCKKStoFHEWPrecompute(scale1);
// Step 3: Encoding and encryption of inputs
// Inputs
std::vector<double> x1 = {0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0};
std::vector<double> x2 = {0.0, 271.0, 30000.0, static_cast<double>(pLWE2) - 2};
uint32_t encodedLength1 = x1.size();
uint32_t encodedLength2 = x2.size();
// Encoding as plaintexts
Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(x1, 1, 0, nullptr);
Plaintext ptxt2 = cc->MakeCKKSPackedPlaintext(x2, 1, 0, nullptr);
// Encrypt the encoded vectors
auto c1 = cc->Encrypt(keys.publicKey, ptxt1);
auto c2 = cc->Encrypt(keys.publicKey, ptxt2);
// Step 4: Scheme switching from CKKS to FHEW
// A: First scheme switching case
// Transform the ciphertext from CKKS to FHEW
auto cTemp = cc->EvalCKKStoFHEW(c1, encodedLength1);
std::cout << "\n---Decrypting switched ciphertext with small precision (plaintext modulus " << NativeInteger(pLWE1)
<< ")---\n"
<< std::endl;
std::vector<int32_t> x1Int(encodedLength1);
std::transform(x1.begin(), x1.end(), x1Int.begin(), [&](const double& elem) {
return static_cast<int32_t>(static_cast<int32_t>(std::round(elem)) % pLWE1);
});
ptxt1->SetLength(encodedLength1);
std::cout << "Input x1: " << ptxt1->GetRealPackedValue() << "; which rounds to: " << x1Int << std::endl;
std::cout << "FHEW decryption: ";
LWEPlaintext result;
for (uint32_t i = 0; i < cTemp.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, cTemp[i], &result, pLWE1);
std::cout << result << " ";
}
std::cout << "\n" << std::endl;
// B: Second scheme switching case
// Perform the precomputation for switching
cc->EvalCKKStoFHEWPrecompute(scale2);
// Transform the ciphertext from CKKS to FHEW (only for the number of inputs given)
auto cTemp2 = cc->EvalCKKStoFHEW(c2, encodedLength2);
std::cout << "\n---Decrypting switched ciphertext with large precision (plaintext modulus " << NativeInteger(pLWE2)
<< ")---\n"
<< std::endl;
ptxt2->SetLength(encodedLength2);
std::cout << "Input x2: " << ptxt2->GetRealPackedValue() << std::endl;
std::cout << "FHEW decryption: ";
for (uint32_t i = 0; i < cTemp2.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, cTemp2[i], &result, pLWE2);
std::cout << result << " ";
}
std::cout << "\n" << std::endl;
// C: Decompose the FHEW ciphertexts in smaller digits
std::cout << "Decomposed values for digit size of " << NativeInteger(pLWE1) << ": " << std::endl;
// Generate the bootstrapping keys (refresh and switching keys)
ccLWE->BTKeyGen(privateKeyFHEW);
for (uint32_t j = 0; j < cTemp2.size(); j++) {
// Decompose the large ciphertext into small ciphertexts that fit in q
auto decomp = ccLWE->EvalDecomp(cTemp2[j]);
// Decryption
auto p = ccLWE->GetMaxPlaintextSpace().ConvertToInt();
LWECiphertext ct;
for (size_t i = 0; i < decomp.size(); i++) {
ct = decomp[i];
LWEPlaintext resultDecomp;
// The last digit should be up to P / p^floor(log_p(P))
if (i == decomp.size() - 1) {
p = pLWE2 / std::pow(static_cast<double>(pLWE1), std::floor(std::log(pLWE2) / std::log(pLWE1)));
}
ccLWE->Decrypt(privateKeyFHEW, ct, &resultDecomp, p);
std::cout << "(" << resultDecomp << " * " << NativeInteger(pLWE1) << "^" << i << ")";
if (i != decomp.size() - 1) {
std::cout << " + ";
}
}
std::cout << std::endl;
}
}
void SwitchFHEWtoCKKS() {
std::cout << "\n-----SwitchFHEWtoCKKS-----\n" << std::endl;
std::cout << "Output precision is only wrt the operations in CKKS after switching back.\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS to be switched into
// A. Specify main parameters
ScalingTechnique scTech = FIXEDAUTO;
// for r = 3 in FHEWtoCKKS, Chebyshev max depth allowed is 9, 1 more level for postscaling
uint32_t multDepth = 3 + 9 + 1;
if (scTech == FLEXIBLEAUTOEXT)
multDepth += 1;
uint32_t scaleModSize = 50;
uint32_t ringDim = 8192;
SecurityLevel sl = HEStd_NotSet; // If this is not HEStd_NotSet, ensure ringDim is compatible
uint32_t logQ_ccLWE = 28;
// uint32_t slots = ringDim/2; // Uncomment for fully-packed
uint32_t slots = 16; // sparsely-packed
uint32_t batchSize = slots;
CCParams<CryptoContextCKKSRNS> parameters;
parameters.SetMultiplicativeDepth(multDepth);
parameters.SetScalingModSize(scaleModSize);
parameters.SetScalingTechnique(scTech);
parameters.SetSecurityLevel(sl);
parameters.SetRingDim(ringDim);
parameters.SetBatchSize(batchSize);
CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
// Enable the features that you wish to use
cc->Enable(PKE);
cc->Enable(KEYSWITCH);
cc->Enable(LEVELEDSHE);
cc->Enable(ADVANCEDSHE);
cc->Enable(SCHEMESWITCH);
std::cout << "CKKS scheme is using ring dimension " << cc->GetRingDimension();
std::cout << ", number of slots " << slots << ", and supports a multiplicative depth of " << multDepth << std::endl
<< std::endl;
// Generate encryption keys.
auto keys = cc->KeyGen();
// Step 2: Prepare the FHEW cryptocontext and keys for FHEW and scheme switching
auto ccLWE = std::make_shared<BinFHEContext>();
ccLWE->BinFHEContext::GenerateBinFHEContext(TOY, false, logQ_ccLWE, 0, GINX, false);
// LWE private key
LWEPrivateKey lwesk;
lwesk = ccLWE->KeyGen();
std::cout << "FHEW scheme is using lattice parameter " << ccLWE->GetParams()->GetLWEParams()->Getn();
std::cout << ", logQ " << logQ_ccLWE;
std::cout << ", and modulus q " << ccLWE->GetParams()->GetLWEParams()->Getq() << std::endl << std::endl;
// Step 3. Precompute the necessary keys and information for switching from FHEW to CKKS
cc->EvalFHEWtoCKKSSetup(ccLWE, slots, logQ_ccLWE);
cc->SetBinCCForSchemeSwitch(ccLWE);
cc->EvalFHEWtoCKKSKeyGen(keys, lwesk);
// Step 4: Encoding and encryption of inputs
// For correct CKKS decryption, the messages have to be much smaller than the FHEW plaintext modulus!
auto pLWE1 = ccLWE->GetMaxPlaintextSpace().ConvertToInt(); // Small precision
uint32_t pLWE2 = 256; // Medium precision
auto modulus_LWE = 1 << logQ_ccLWE;
auto beta = ccLWE->GetBeta().ConvertToInt();
auto pLWE3 = modulus_LWE / (2 * beta); // Large precision
// Inputs
std::vector<int> x1 = {1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0};
std::vector<int> x2 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15};
if (x1.size() < slots) {
std::vector<int> zeros(slots - x1.size(), 0);
x1.insert(x1.end(), zeros.begin(), zeros.end());
x2.insert(x2.end(), zeros.begin(), zeros.end());
}
// Encrypt
std::vector<LWECiphertext> ctxtsLWE1(slots);
for (uint32_t i = 0; i < slots; i++) {
ctxtsLWE1[i] =
ccLWE->Encrypt(lwesk, x1[i]); // encrypted under small plantext modulus p = 4 and ciphertext modulus
}
std::vector<LWECiphertext> ctxtsLWE2(slots);
for (uint32_t i = 0; i < slots; i++) {
ctxtsLWE2[i] =
ccLWE->Encrypt(lwesk, x1[i], FRESH,
pLWE1); // encrypted under larger plaintext modulus p = 16 but small ciphertext modulus
}
std::vector<LWECiphertext> ctxtsLWE3(slots);
for (uint32_t i = 0; i < slots; i++) {
ctxtsLWE3[i] =
ccLWE->Encrypt(lwesk, x2[i], FRESH, pLWE2,
modulus_LWE); // encrypted under larger plaintext modulus and large ciphertext modulus
}
std::vector<LWECiphertext> ctxtsLWE4(slots);
for (uint32_t i = 0; i < slots; i++) {
ctxtsLWE4[i] =
ccLWE->Encrypt(lwesk, x2[i], FRESH, pLWE3,
modulus_LWE); // encrypted under large plaintext modulus and large ciphertext modulus
}
// Step 5. Perform the scheme switching
auto cTemp = cc->EvalFHEWtoCKKS(ctxtsLWE1, slots, slots);
std::cout << "\n---Input x1: " << x1 << " encrypted under p = " << 4 << " and Q = " << ctxtsLWE1[0]->GetModulus()
<< "---" << std::endl;
// Step 6. Decrypt
Plaintext plaintextDec;
cc->Decrypt(keys.secretKey, cTemp, &plaintextDec);
plaintextDec->SetLength(slots);
std::cout << "Switched CKKS decryption 1: " << plaintextDec << std::endl;
// Step 5'. Perform the scheme switching
cTemp = cc->EvalFHEWtoCKKS(ctxtsLWE2, slots, slots, pLWE1, 0, pLWE1);
std::cout << "\n---Input x1: " << x1 << " encrypted under p = " << NativeInteger(pLWE1)
<< " and Q = " << ctxtsLWE2[0]->GetModulus() << "---" << std::endl;
// Step 6'. Decrypt
cc->Decrypt(keys.secretKey, cTemp, &plaintextDec);
plaintextDec->SetLength(slots);
std::cout << "Switched CKKS decryption 2: " << plaintextDec << std::endl;
// Step 5''. Perform the scheme switching
cTemp = cc->EvalFHEWtoCKKS(ctxtsLWE3, slots, slots, pLWE2, 0, pLWE2);
std::cout << "\n---Input x2: " << x2 << " encrypted under p = " << pLWE2
<< " and Q = " << ctxtsLWE3[0]->GetModulus() << "---" << std::endl;
// Step 6''. Decrypt
cc->Decrypt(keys.secretKey, cTemp, &plaintextDec);
plaintextDec->SetLength(slots);
std::cout << "Switched CKKS decryption 3: " << plaintextDec << std::endl;
// Step 5'''. Perform the scheme switching
std::setprecision(logQ_ccLWE + 10);
auto cTemp2 = cc->EvalFHEWtoCKKS(ctxtsLWE4, slots, slots, pLWE3, 0, pLWE3);
std::cout << "\n---Input x2: " << x2 << " encrypted under p = " << NativeInteger(pLWE3)
<< " and Q = " << ctxtsLWE4[0]->GetModulus() << "---" << std::endl;
// Step 6'''. Decrypt
Plaintext plaintextDec2;
cc->Decrypt(keys.secretKey, cTemp2, &plaintextDec2);
plaintextDec2->SetLength(slots);
std::cout << "Switched CKKS decryption 4: " << plaintextDec2 << std::endl;
}
void FloorViaSchemeSwitching() {
std::cout << "\n-----FloorViaSchemeSwitching-----\n" << std::endl;
std::cout << "Output precision is only wrt the operations in CKKS after switching back.\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS
ScalingTechnique scTech = FLEXIBLEAUTO;
// for r = 3 in FHEWtoCKKS, Chebyshev max depth allowed is 9, 1 more level for postscaling
uint32_t multDepth = 3 + 9 + 1;
if (scTech == FLEXIBLEAUTOEXT)
multDepth += 1;
uint32_t scaleModSize = 50;
uint32_t ringDim = 8192;
SecurityLevel sl = HEStd_NotSet;
BINFHE_PARAMSET slBin = TOY;
uint32_t logQ_ccLWE = 23;
uint32_t slots = 16; // sparsely-packed
uint32_t batchSize = slots;
CCParams<CryptoContextCKKSRNS> parameters;
parameters.SetMultiplicativeDepth(multDepth);
parameters.SetScalingModSize(scaleModSize);
parameters.SetScalingTechnique(scTech);
parameters.SetSecurityLevel(sl);
parameters.SetRingDim(ringDim);
parameters.SetBatchSize(batchSize);
CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
// Enable the features that you wish to use
cc->Enable(PKE);
cc->Enable(KEYSWITCH);
cc->Enable(LEVELEDSHE);
cc->Enable(ADVANCEDSHE);
cc->Enable(SCHEMESWITCH);
std::cout << "CKKS scheme is using ring dimension " << cc->GetRingDimension();
std::cout << ", number of slots " << slots << ", and supports a multiplicative depth of " << multDepth << std::endl
<< std::endl;
// Generate encryption keys.
auto keys = cc->KeyGen();
// Step 2: Prepare the FHEW cryptocontext and keys for FHEW and scheme switching
SchSwchParams params;
params.SetSecurityLevelCKKS(sl);
params.SetSecurityLevelFHEW(slBin);
params.SetCtxtModSizeFHEWLargePrec(logQ_ccLWE);
params.SetNumSlotsCKKS(slots);
params.SetNumValues(slots);
auto privateKeyFHEW = cc->EvalSchemeSwitchingSetup(params);
auto ccLWE = cc->GetBinCCForSchemeSwitch();
cc->EvalSchemeSwitchingKeyGen(keys, privateKeyFHEW);
// Generate bootstrapping key for EvalFloor
ccLWE->BTKeyGen(privateKeyFHEW);
std::cout << "FHEW scheme is using lattice parameter " << ccLWE->GetParams()->GetLWEParams()->Getn();
std::cout << ", logQ " << logQ_ccLWE;
std::cout << ", and modulus q " << ccLWE->GetParams()->GetLWEParams()->Getq() << std::endl << std::endl;
// Set the scaling factor to be able to decrypt; under the hood, the LWE mod switch will be performed on the ciphertext at the last level
auto modulus_LWE = 1 << logQ_ccLWE;
auto beta = ccLWE->GetBeta().ConvertToInt();
auto pLWE = modulus_LWE / (2 * beta); // Large precision
double scaleCF = 1.0 / pLWE;
cc->EvalCKKStoFHEWPrecompute(scaleCF);
// Step 3: Encoding and encryption of inputs
// Inputs
std::vector<double> x1 = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0};
// Encoding as plaintexts
Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(x1, 1, 0, nullptr);
// Encrypt the encoded vectors
auto c1 = cc->Encrypt(keys.publicKey, ptxt1);
// Step 4: Scheme switching from CKKS to FHEW
auto cTemp = cc->EvalCKKStoFHEW(c1);
// Step 5: Evaluate the floor function
uint32_t bits = 2;
std::vector<LWECiphertext> cFloor(cTemp.size());
for (uint32_t i = 0; i < cTemp.size(); i++) {
cFloor[i] = ccLWE->EvalFloor(cTemp[i], bits);
}
std::cout << "Input x1: " << ptxt1->GetRealPackedValue() << std::endl;
std::cout << "Expected result for EvalFloor with " << bits << " bits: ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << (static_cast<int>(ptxt1->GetRealPackedValue()[i]) >> bits) << " ";
}
LWEPlaintext pFloor;
std::cout << "\nFHEW decryption p = " << NativeInteger(pLWE)
<< "/(1 << bits) = " << NativeInteger(pLWE) / (1 << bits) << ": ";
for (uint32_t i = 0; i < cFloor.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, cFloor[i], &pFloor, pLWE / (1 << bits));
std::cout << pFloor << " ";
}
std::cout << "\n" << std::endl;
// Step 6: Scheme switching from FHEW to CKKS
auto cTemp2 = cc->EvalFHEWtoCKKS(cFloor, slots, slots, pLWE / (1 << bits), 0, pLWE / (1 << bits));
Plaintext plaintextDec2;
cc->Decrypt(keys.secretKey, cTemp2, &plaintextDec2);
plaintextDec2->SetLength(slots);
std::cout << "Switched floor decryption modulus_LWE mod " << NativeInteger(pLWE) / (1 << bits) << ": "
<< plaintextDec2 << std::endl;
}
void FuncViaSchemeSwitching() {
std::cout << "\n-----FuncViaSchemeSwitching-----\n" << std::endl;
std::cout << "Output precision is only wrt the operations in CKKS after switching back.\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS
// 1 for CKKS to FHEW, 14 for FHEW to CKKS
uint32_t multDepth = 9 + 3 + 2;
uint32_t scaleModSize = 50;
uint32_t ringDim = 2048;
SecurityLevel sl = HEStd_NotSet;
BINFHE_PARAMSET slBin = TOY;
uint32_t logQ_ccLWE = 25;
uint32_t slots = 8; // sparsely-packed
uint32_t batchSize = slots;
CCParams<CryptoContextCKKSRNS> parameters;
parameters.SetMultiplicativeDepth(multDepth);
parameters.SetScalingModSize(scaleModSize);
parameters.SetScalingTechnique(FIXEDAUTO);
parameters.SetSecurityLevel(sl);
parameters.SetRingDim(ringDim);
parameters.SetBatchSize(batchSize);
CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
// Enable the features that you wish to use
cc->Enable(PKE);
cc->Enable(KEYSWITCH);
cc->Enable(LEVELEDSHE);
cc->Enable(ADVANCEDSHE);
cc->Enable(SCHEMESWITCH);
std::cout << "CKKS scheme is using ring dimension " << cc->GetRingDimension();
std::cout << ", and number of slots " << slots << std::endl << std::endl;
// Generate encryption keys.
auto keys = cc->KeyGen();
// Step 2: Prepare the FHEW cryptocontext and keys for FHEW and scheme switching
SchSwchParams params;
params.SetSecurityLevelCKKS(sl);
params.SetSecurityLevelFHEW(slBin);
params.SetArbitraryFunctionEvaluation(true);
params.SetCtxtModSizeFHEWLargePrec(logQ_ccLWE);
params.SetNumSlotsCKKS(slots);
params.SetNumValues(slots);
auto privateKeyFHEW = cc->EvalSchemeSwitchingSetup(params);
auto ccLWE = cc->GetBinCCForSchemeSwitch();
cc->EvalSchemeSwitchingKeyGen(keys, privateKeyFHEW);
// Generate the bootstrapping keys for EvalFunc in FHEW
ccLWE->BTKeyGen(privateKeyFHEW);
std::cout << "FHEW scheme is using lattice parameter " << ccLWE->GetParams()->GetLWEParams()->Getn();
std::cout << ", logQ " << logQ_ccLWE;
std::cout << ", and modulus q " << ccLWE->GetParams()->GetLWEParams()->Getq() << std::endl << std::endl;
// Set the scaling factor to be able to decrypt; under the hood, the LWE mod switch will be performed on the ciphertext at the last level
auto pLWE =
ccLWE->GetMaxPlaintextSpace().ConvertToInt(); // Small precision because GenerateLUTviaFunction needs p < q
double scaleCF = 1.0 / pLWE;
cc->EvalCKKStoFHEWPrecompute(scaleCF);
// Step 3: Initialize the function
// Initialize Function f(x) = x^3 + 2x + 1 % p
auto fp = [](NativeInteger m, NativeInteger p1) -> NativeInteger {
if (m < p1)
return (m * m * m + 2 * m * m + 1) % p1;
else
return ((m - p1 / 2) * (m - p1 / 2) * (m - p1 / 2) + 2 * (m - p1 / 2) * (m - p1 / 2) + 1) % p1;
};
// Generate LUT from function f(x)
auto lut = ccLWE->GenerateLUTviaFunction(fp, pLWE);
// Step 4: Encoding and encryption of inputs
// Inputs
std::vector<double> x1 = {0.0, 0.3, 2.0, 4.0, 5.0, 6.0, 7.0, 8.0};
// Encoding as plaintexts
Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(x1, 1, 0, nullptr);
// Encrypt the encoded vectors
auto c1 = cc->Encrypt(keys.publicKey, ptxt1);
// Step 5: Scheme switching from CKKS to FHEW
auto cTemp = cc->EvalCKKStoFHEW(c1);
std::cout << "Input x1: " << ptxt1->GetRealPackedValue() << std::endl;
std::cout << "FHEW decryption: ";
LWEPlaintext result;
for (uint32_t i = 0; i < cTemp.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, cTemp[i], &result, pLWE);
std::cout << result << " ";
}
// Step 6: Evaluate the function
std::vector<LWECiphertext> cFunc(cTemp.size());
for (uint32_t i = 0; i < cTemp.size(); i++) {
cFunc[i] = ccLWE->EvalFunc(cTemp[i], lut);
}
std::cout << "\nExpected result x^3 + 2*x + 1 mod p: ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << fp(static_cast<int>(x1[i]) % pLWE, pLWE) << " ";
}
LWEPlaintext pFunc;
std::cout << "\nFHEW decryption mod " << NativeInteger(pLWE) << ": ";
for (uint32_t i = 0; i < cFunc.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, cFunc[i], &pFunc, pLWE);
std::cout << pFunc << " ";
}
std::cout << "\n" << std::endl;
// Step 7: Scheme switching from FHEW to CKKS
auto cTemp2 = cc->EvalFHEWtoCKKS(cFunc, slots, slots, pLWE, 0, pLWE);
Plaintext plaintextDec2;
cc->Decrypt(keys.secretKey, cTemp2, &plaintextDec2);
plaintextDec2->SetLength(slots);
std::cout << "\nSwitched decryption modulus_LWE mod " << NativeInteger(pLWE)
<< " works only for messages << p: " << plaintextDec2 << std::endl;
// Transform through arcsine
cTemp2 = cc->EvalFHEWtoCKKS(cFunc, slots, slots, 4, 0, 2);
cc->Decrypt(keys.secretKey, cTemp2, &plaintextDec2);
plaintextDec2->SetLength(slots);
std::cout << "Arcsin(switched result) * p/2pi gives the correct result if messages are < p/4: ";
for (uint32_t i = 0; i < slots; i++) {
double x = std::max(std::min(plaintextDec2->GetRealPackedValue()[i], 1.0), -1.0);
std::cout << std::asin(x) * pLWE / (2 * Pi) << " ";
}
std::cout << "\n";
}
void ComparisonViaSchemeSwitching() {
std::cout << "\n-----ComparisonViaSchemeSwitching-----\n" << std::endl;
std::cout << "Output precision is only wrt the operations in CKKS after switching back.\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS
ScalingTechnique scTech = FLEXIBLEAUTO;
uint32_t multDepth = 17;
if (scTech == FLEXIBLEAUTOEXT)
multDepth += 1;
uint32_t scaleModSize = 50;
uint32_t firstModSize = 60;
uint32_t ringDim = 8192;
SecurityLevel sl = HEStd_NotSet;
BINFHE_PARAMSET slBin = TOY;
uint32_t logQ_ccLWE = 25;
uint32_t slots = 16; // sparsely-packed
uint32_t batchSize = slots;
CCParams<CryptoContextCKKSRNS> parameters;
parameters.SetMultiplicativeDepth(multDepth);
parameters.SetScalingModSize(scaleModSize);
parameters.SetFirstModSize(firstModSize);
parameters.SetScalingTechnique(scTech);
parameters.SetSecurityLevel(sl);
parameters.SetRingDim(ringDim);
parameters.SetBatchSize(batchSize);
parameters.SetSecretKeyDist(UNIFORM_TERNARY);
parameters.SetKeySwitchTechnique(HYBRID);
parameters.SetNumLargeDigits(3);
CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
// Enable the features that you wish to use
cc->Enable(PKE);
cc->Enable(KEYSWITCH);
cc->Enable(LEVELEDSHE);
cc->Enable(ADVANCEDSHE);
cc->Enable(SCHEMESWITCH);
std::cout << "CKKS scheme is using ring dimension " << cc->GetRingDimension();
std::cout << ", number of slots " << slots << ", and supports a multiplicative depth of " << multDepth << std::endl
<< std::endl;
// Generate encryption keys
auto keys = cc->KeyGen();
// Step 2: Prepare the FHEW cryptocontext and keys for FHEW and scheme switching
SchSwchParams params;
params.SetSecurityLevelCKKS(sl);
params.SetSecurityLevelFHEW(slBin);
params.SetCtxtModSizeFHEWLargePrec(logQ_ccLWE);
params.SetNumSlotsCKKS(slots);
params.SetNumValues(slots);
auto privateKeyFHEW = cc->EvalSchemeSwitchingSetup(params);
auto ccLWE = cc->GetBinCCForSchemeSwitch();
ccLWE->BTKeyGen(privateKeyFHEW);
cc->EvalSchemeSwitchingKeyGen(keys, privateKeyFHEW);
std::cout << "FHEW scheme is using lattice parameter " << ccLWE->GetParams()->GetLWEParams()->Getn();
std::cout << ", logQ " << logQ_ccLWE;
std::cout << ", and modulus q " << ccLWE->GetParams()->GetLWEParams()->Getq() << std::endl << std::endl;
// Set the scaling factor to be able to decrypt; the LWE mod switch is performed on the ciphertext at the last level
auto pLWE1 = ccLWE->GetMaxPlaintextSpace().ConvertToInt(); // Small precision
auto modulus_LWE = 1 << logQ_ccLWE;
auto beta = ccLWE->GetBeta().ConvertToInt();
auto pLWE2 = modulus_LWE / (2 * beta); // Large precision
double scaleSignFHEW = 1.0;
cc->EvalCompareSwitchPrecompute(pLWE2, scaleSignFHEW);
// Step 3: Encoding and encryption of inputs
// Inputs
std::vector<double> x1 = {0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0};
std::vector<double> x2(slots, 5.25);
// Encoding as plaintexts
Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(x1, 1, 0, nullptr, slots);
Plaintext ptxt2 = cc->MakeCKKSPackedPlaintext(x2, 1, 0, nullptr, slots);
// Encrypt the encoded vectors
auto c1 = cc->Encrypt(keys.publicKey, ptxt1);
auto c2 = cc->Encrypt(keys.publicKey, ptxt2);
// Compute the difference to compare to zero
auto cDiff = cc->EvalSub(c1, c2);
// Step 4: CKKS to FHEW switching and sign evaluation to test correctness
Plaintext pDiff;
cc->Decrypt(keys.secretKey, cDiff, &pDiff);
pDiff->SetLength(slots);
std::cout << "Difference of inputs: ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << pDiff->GetRealPackedValue()[i] << " ";
}
const double eps = 0.0001;
std::cout << "\nExpected sign result from CKKS: ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << int(std::round(pDiff->GetRealPackedValue()[i] / eps) * eps < 0) << " ";
}
std::cout << "\n";
auto LWECiphertexts = cc->EvalCKKStoFHEW(cDiff, slots);
LWEPlaintext plainLWE;
std::cout << "\nFHEW decryption with plaintext modulus " << NativeInteger(pLWE2) << ": ";
for (uint32_t i = 0; i < LWECiphertexts.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, LWECiphertexts[i], &plainLWE, pLWE2);
std::cout << plainLWE << " ";
}
std::cout << "\nExpected sign result in FHEW with plaintext modulus " << NativeInteger(pLWE2) << " and scale "
<< scaleSignFHEW << ": ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << (static_cast<int>(std::round(pDiff->GetRealPackedValue()[i] * scaleSignFHEW)) % pLWE2 -
pLWE2 / 2.0 >=
0)
<< " ";
}
std::cout << "\n";
std::cout << "Obtained sign result in FHEW with plaintext modulus " << NativeInteger(pLWE2) << " and scale "
<< scaleSignFHEW << ": ";
std::vector<LWECiphertext> LWESign(LWECiphertexts.size());
for (uint32_t i = 0; i < LWECiphertexts.size(); ++i) {
LWESign[i] = ccLWE->EvalSign(LWECiphertexts[i]);
ccLWE->Decrypt(privateKeyFHEW, LWESign[i], &plainLWE, 2);
std::cout << plainLWE << " ";
}
std::cout << "\n";
// Step 5: Direct comparison via CKKS->FHEW->CKKS
auto cResult = cc->EvalCompareSchemeSwitching(c1, c2, slots, slots);
Plaintext plaintextDec3;
cc->Decrypt(keys.secretKey, cResult, &plaintextDec3);
plaintextDec3->SetLength(slots);
std::cout << "Decrypted switched result: " << plaintextDec3 << std::endl;
// Step 2': Recompute the scaled matrix using a larger scaling
scaleSignFHEW = 8.0;
cc->EvalCompareSwitchPrecompute(pLWE2, scaleSignFHEW);
// Step 4': CKKS to FHEW switching and sign evaluation to test correctness
LWECiphertexts = cc->EvalCKKStoFHEW(cDiff, slots);
std::cout << "\nFHEW decryption with plaintext modulus " << NativeInteger(pLWE2) << " and scale " << scaleSignFHEW
<< ": ";
for (uint32_t i = 0; i < LWECiphertexts.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, LWECiphertexts[i], &plainLWE, pLWE2);
std::cout << plainLWE << " ";
}
std::cout << "\nExpected sign result in FHEW with plaintext modulus " << NativeInteger(pLWE2) << " and scale "
<< scaleSignFHEW << ": ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << (static_cast<int>(std::round(pDiff->GetRealPackedValue()[i] * scaleSignFHEW)) % pLWE2 -
pLWE2 / 2.0 >=
0)
<< " ";
}
std::cout << "\n";
std::cout << "Obtained sign result in FHEW with plaintext modulus " << NativeInteger(pLWE2) << " and scale "
<< scaleSignFHEW << ": ";
for (uint32_t i = 0; i < LWECiphertexts.size(); ++i) {
LWESign[i] = ccLWE->EvalSign(LWECiphertexts[i]);
ccLWE->Decrypt(privateKeyFHEW, LWESign[i], &plainLWE, 2);
std::cout << plainLWE << " ";
}
std::cout << "\n";
// Step 5': Direct comparison via CKKS->FHEW->CKKS
cResult = cc->EvalCompareSchemeSwitching(c1, c2, slots, slots);
cc->Decrypt(keys.secretKey, cResult, &plaintextDec3);
plaintextDec3->SetLength(slots);
std::cout << "Decrypted switched result: " << plaintextDec3 << std::endl;
// Step 2'': Recompute the scaled matrix using other parameters
std::cout
<< "\nFor very small LWE plaintext modulus and initial fractional inputs, the sign does not always behave properly close to the boundaries at 0 and p/2."
<< std::endl;
scaleSignFHEW = 1.0;
cc->EvalCompareSwitchPrecompute(pLWE1, scaleSignFHEW);
// Step 4'': CKKS to FHEW switching and sign evaluation to test correctness
LWECiphertexts = cc->EvalCKKStoFHEW(cDiff, slots);
std::cout << "\nFHEW decryption with plaintext modulus " << NativeInteger(pLWE1) << ": ";
for (uint32_t i = 0; i < LWECiphertexts.size(); ++i) {
ccLWE->Decrypt(privateKeyFHEW, LWECiphertexts[i], &plainLWE, pLWE1);
std::cout << plainLWE << " ";
}
std::cout << "\nExpected sign result in FHEW with plaintext modulus " << NativeInteger(pLWE1) << " and scale "
<< scaleSignFHEW << ": ";
for (uint32_t i = 0; i < slots; ++i) {
std::cout << (static_cast<int>(std::round(pDiff->GetRealPackedValue()[i] * scaleSignFHEW)) % pLWE1 -
pLWE1 / 2.0 >=
0)
<< " ";
}
std::cout << "\n";
std::cout << "Obtained sign result in FHEW with plaintext modulus " << NativeInteger(pLWE1) << " and scale "
<< scaleSignFHEW << ": ";
for (uint32_t i = 0; i < LWECiphertexts.size(); ++i) {
LWESign[i] = ccLWE->EvalSign(LWECiphertexts[i]);
ccLWE->Decrypt(privateKeyFHEW, LWESign[i], &plainLWE, 2);
std::cout << plainLWE << " ";
}
std::cout << "\n";
// Step 5'': Direct comparison via CKKS->FHEW->CKKS
cResult = cc->EvalCompareSchemeSwitching(c1, c2, slots, slots, 0, scaleSignFHEW);
cc->Decrypt(keys.secretKey, cResult, &plaintextDec3);
plaintextDec3->SetLength(slots);
std::cout << "Decrypted switched result: " << plaintextDec3 << std::endl;
}
void ArgminViaSchemeSwitching() {
std::cout << "\n-----ArgminViaSchemeSwitching-----\n" << std::endl;
std::cout << "Output precision is only wrt the operations in CKKS after switching back\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS
uint32_t scaleModSize = 50;
uint32_t firstModSize = 60;
uint32_t ringDim = 8192;
SecurityLevel sl = HEStd_NotSet;
BINFHE_PARAMSET slBin = TOY;
uint32_t logQ_ccLWE = 25;
bool oneHot = true; // Change to false if the output should not be one-hot encoded
uint32_t slots = 16; // sparsely-packed
uint32_t batchSize = slots;
uint32_t numValues = 16;
ScalingTechnique scTech = FLEXIBLEAUTOEXT;
// 13 for FHEW to CKKS, log2(numValues) for argmin
uint32_t multDepth = 9 + 3 + 1 + static_cast<int>(std::log2(numValues));
if (scTech == FLEXIBLEAUTOEXT)
multDepth += 1;
CCParams<CryptoContextCKKSRNS> parameters;
parameters.SetMultiplicativeDepth(multDepth);
parameters.SetScalingModSize(scaleModSize);
parameters.SetFirstModSize(firstModSize);
parameters.SetScalingTechnique(scTech);
parameters.SetSecurityLevel(sl);
parameters.SetRingDim(ringDim);
parameters.SetBatchSize(batchSize);
CryptoContext<DCRTPoly> cc = GenCryptoContext(parameters);
// Enable the features that you wish to use
cc->Enable(PKE);
cc->Enable(KEYSWITCH);
cc->Enable(LEVELEDSHE);
cc->Enable(ADVANCEDSHE);
cc->Enable(SCHEMESWITCH);
std::cout << "CKKS scheme is using ring dimension " << cc->GetRingDimension();
std::cout << ", and number of slots " << slots << ", and supports a depth of " << multDepth << std::endl
<< std::endl;
// Generate encryption keys
auto keys = cc->KeyGen();
// Step 2: Prepare the FHEW cryptocontext and keys for FHEW and scheme switching
SchSwchParams params;
params.SetSecurityLevelCKKS(sl);
params.SetSecurityLevelFHEW(slBin);
params.SetCtxtModSizeFHEWLargePrec(logQ_ccLWE);
params.SetNumSlotsCKKS(slots);
params.SetNumValues(numValues);
params.SetComputeArgmin(true);
auto privateKeyFHEW = cc->EvalSchemeSwitchingSetup(params);
auto ccLWE = cc->GetBinCCForSchemeSwitch();
cc->EvalSchemeSwitchingKeyGen(keys, privateKeyFHEW);
std::cout << "FHEW scheme is using lattice parameter " << ccLWE->GetParams()->GetLWEParams()->Getn();
std::cout << ", logQ " << logQ_ccLWE;
std::cout << ", and modulus q " << ccLWE->GetParams()->GetLWEParams()->Getq() << std::endl << std::endl;
// Scale the inputs to ensure their difference is correctly represented after switching to FHEW
double scaleSign = 512.0;
auto modulus_LWE = 1 << logQ_ccLWE;
auto beta = ccLWE->GetBeta().ConvertToInt();
auto pLWE = modulus_LWE / (2 * beta); // Large precision
// This formulation is for clarity
cc->EvalCompareSwitchPrecompute(pLWE, scaleSign);
// But we can also include the scaleSign in pLWE (here we use the fact both pLWE and scaleSign are powers of two)
// cc->EvalCompareSwitchPrecompute(pLWE / scaleSign, 1);
// Step 3: Encoding and encryption of inputs
// Inputs
std::vector<double> x1 = {-1.125, -1.12, 5.0, 6.0, -1.0, 2.0, 8.0, -1.0,
9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.25, 15.30};
if (x1.size() < numValues) {
std::vector<int> zeros(numValues - x1.size(), 0);
x1.insert(x1.end(), zeros.begin(), zeros.end());
}
std::cout << "Expected minimum value " << *(std::min_element(x1.begin(), x1.begin() + numValues)) << " at location "
<< std::min_element(x1.begin(), x1.begin() + numValues) - x1.begin() << std::endl;
std::cout << "Expected maximum value " << *(std::max_element(x1.begin(), x1.begin() + numValues)) << " at location "
<< std::max_element(x1.begin(), x1.begin() + numValues) - x1.begin() << std::endl
<< std::endl;
// Encoding as plaintexts
Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(x1); // Only if we we set batchsize
// Plaintext ptxt1 = cc->MakeCKKSPackedPlaintext(x1, 1, 0, nullptr, slots); // If batchsize is not set
// Encrypt the encoded vectors
auto c1 = cc->Encrypt(keys.publicKey, ptxt1);
// Step 4: Argmin evaluation
auto result = cc->EvalMinSchemeSwitching(c1, keys.publicKey, numValues, slots);
Plaintext ptxtMin;
cc->Decrypt(keys.secretKey, result[0], &ptxtMin);
ptxtMin->SetLength(1);
std::cout << "Minimum value: " << ptxtMin << std::endl;
cc->Decrypt(keys.secretKey, result[1], &ptxtMin);
if (oneHot) {
ptxtMin->SetLength(numValues);
std::cout << "Argmin indicator vector: " << ptxtMin << std::endl;
}
else {
ptxtMin->SetLength(1);
std::cout << "Argmin: " << ptxtMin << std::endl;
}
result = cc->EvalMaxSchemeSwitching(c1, keys.publicKey, numValues, slots);
Plaintext ptxtMax;
cc->Decrypt(keys.secretKey, result[0], &ptxtMax);
ptxtMax->SetLength(1);
std::cout << "Maximum value: " << ptxtMax << std::endl;
cc->Decrypt(keys.secretKey, result[1], &ptxtMax);
if (oneHot) {
ptxtMax->SetLength(numValues);
std::cout << "Argmax indicator vector: " << ptxtMax << std::endl;
}
else {
ptxtMax->SetLength(1);
std::cout << "Argmax: " << ptxtMax << std::endl;
}
}
void ArgminViaSchemeSwitchingAlt() {
std::cout << "\n-----ArgminViaSchemeSwitchingAlt-----\n" << std::endl;
std::cout << "Output precision is only wrt the operations in CKKS after switching back\n" << std::endl;
// Step 1: Setup CryptoContext for CKKS
uint32_t scaleModSize = 50;
uint32_t firstModSize = 60;
uint32_t ringDim = 8192;
SecurityLevel sl = HEStd_NotSet;
BINFHE_PARAMSET slBin = TOY;