private_recommendations_utils/dgk_comparison_server.cpp

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/*
SeComLib
Copyright 2012-2013 TU Delft, Information Security & Privacy Lab (http://isplab.tudelft.nl/)

Contributors:
Inald Lagendijk (R.L.Lagendijk@TUDelft.nl)
Mihai Todor (todormihai@gmail.com)
Thijs Veugen (P.J.M.Veugen@tudelft.nl)
Zekeriya Erkin (z.erkin@tudelft.nl)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
#include "dgk_comparison_server.h"
//avoid circular includes
#include "dgk_comparison_client.h"

namespace SeComLib {
namespace PrivateRecommendationsUtils {
    DgkComparisonServer::DgkComparisonServer (const Paillier &paillierCryptoProvider, const Dgk &dgkCryptoProvider, const size_t l) :
        paillierCryptoProvider(paillierCryptoProvider),
        dgkCryptoProvider(dgkCryptoProvider),
        l(l) {
    }

    Paillier::Ciphertext DgkComparisonServer::Compare (const BigInteger &rModTwoPowL) const {
        BigInteger c = RandomProvider::GetInstance().GetRandomInteger(1);

        Dgk::Ciphertext tau = this->computeTau(rModTwoPowL, c);

        Dgk::Ciphertext tl;
        if (c == 0) {
            tl = tau;
        }
        else {
            tl = this->dgkCryptoProvider.GetEncryptedOne(false) - tau;
        }

        tl = this->dgkCryptoProvider.RandomizeCiphertext(tl);
        return this->dgkComparisonClient.lock()->ConvertToPaillier(tl);
    }

    Paillier::Ciphertext DgkComparisonServer::ComputeDi (const BigInteger &ri) const {
        BigInteger CiSP = RandomProvider::GetInstance().GetRandomInteger(1);

        Dgk::Ciphertext CiPSP = this->computeTau(ri, CiSP);

        CiPSP = this->dgkCryptoProvider.RandomizeCiphertext(CiPSP);

        Paillier::Ciphertext diPSP = this->dgkComparisonClient.lock()->ComputeDiPSP(CiPSP);

        int diSP;
        if (CiSP != static_cast<long>(ri.GetBit(this->GetMSBPosition()))) {
            diSP = 1;
        }
        else {
            diSP = 0;
        }

        if (diSP == 0) {
            return diPSP;
        }
        else {
            return this->paillierCryptoProvider.GetEncryptedOne(false) - diPSP;
        }
    }

    Dgk::Ciphertext DgkComparisonServer::computeTau (const BigInteger &a, const BigInteger &tSP) const {
        Dgk::Ciphertext b0 = this->dgkComparisonClient.lock()->GetBi(0);

        Dgk::Ciphertext t;

        if (a.GetBit(0) == 0) {
            t = this->dgkCryptoProvider.GetEncryptedZero(false);
        }
        else {
            t = this->dgkCryptoProvider.GetEncryptedOne(false) - b0;
        }

        for (size_t i = 1; i < this->l; ++i) {
            BigInteger c = RandomProvider::GetInstance().GetRandomInteger(1);

            Dgk::Ciphertext tau;
            
            //perform blinding
            if (c == 0) {
                tau = t;
            }
            else {
                tau = this->dgkCryptoProvider.GetEncryptedOne(false) - t;
            }

            tau = this->dgkCryptoProvider.RandomizeCiphertext(tau);

            Dgk::Ciphertext tb = this->dgkComparisonClient.lock()->GetTb(tau, i);

            Dgk::Ciphertext bi = this->dgkComparisonClient.lock()->GetBi(i);

            if (c == 1) {
                tb = bi - tb;
            }

            if (a.GetBit(i) == 0) {
                t = t - tb;
            }
            else {
                t = tb + (this->dgkCryptoProvider.GetEncryptedOne(false) - bi);
            }
        }
        
        if (tSP == 0) {
            return t;
        }
        else {
            return this->dgkCryptoProvider.GetEncryptedOne(false) - t;
        }
    }

    size_t DgkComparisonServer::GetMSBPosition () const {
        return this->l;
    }

    void DgkComparisonServer::SetClient (const std::shared_ptr<DgkComparisonClient> &dgkComparisonClient) {
        this->dgkComparisonClient = dgkComparisonClient;
    }

}//namespace PrivateRecommendationsUtils
}//namespace SeComLib