secure_extremum_selection_server.hpp

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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.
*/
#ifndef SECURE_EXTREMUM_SELECTION_SERVER_IMPLEMENTATION_GUARD
#define SECURE_EXTREMUM_SELECTION_SERVER_IMPLEMENTATION_GUARD

namespace SeComLib {
namespace Core {
    template <typename T_SecureComparisonServer, typename T_SecureComparisonClient>
    SecureExtremumSelectionServer<T_SecureComparisonServer, T_SecureComparisonClient>::SecureExtremumSelectionServer (const Paillier &paillierCryptoProvider, const Dgk &dgkCryptoProvider, const std::string &configurationPath) :
        paillierCryptoProvider(paillierCryptoProvider),
        dgkCryptoProvider(dgkCryptoProvider),
        secureComparisonServer(std::make_shared<T_SecureComparisonServer>(paillierCryptoProvider, dgkCryptoProvider, configurationPath)),
        secureMultiplicationServer(std::make_shared<SecureMultiplicationServer<Paillier>>(paillierCryptoProvider, Utils::Config::GetInstance().GetParameter<size_t>(configurationPath + ".l"), configurationPath)) {
    }

    template <typename T_SecureComparisonServer, typename T_SecureComparisonClient>
    Paillier::Ciphertext SecureExtremumSelectionServer<T_SecureComparisonServer, T_SecureComparisonClient>::GetMinimum (const ItemContainer &items) const {
        if (items.size() < 2) {
            return *items.begin();
        }

        /* Create a vector of the minimums obtained by comparing each adjacent pair of items:
        @f$ [min] = \left\{\begin{array}{ll} [0 * (y - x) + x] = ([0] * [y - x])[x] = [x] & \text{if $ x < y $} \\ [1 * (y - x) + x] = ([1] * [y - x])[x] = [y] & \text{if $ x \geq y} \end{array} \right. @f$
        */
        ItemContainer temp;
        temp.reserve(items.size() / 2 + items.size() % 2);//inefficient ceil
        for (size_t i = 0; i < items.size() - 1; i += 2) {
            temp.push_back(this->secureMultiplicationServer->Multiply(this->secureComparisonServer->Compare(items[i], items[i + 1]), items[i + 1] - items[i]) + items[i]);
        }

        //for odd lenghts, we also want to keep the last element
        if (items.size() % 2 == 1) {
            temp.push_back(*items.rbegin());
        }

        return this->GetMinimum(temp);
    }

    template <typename T_SecureComparisonServer, typename T_SecureComparisonClient>
    Paillier::Ciphertext SecureExtremumSelectionServer<T_SecureComparisonServer, T_SecureComparisonClient>::GetMaximum (const ItemContainer &items) const {
        if (items.size() < 2) {
            return *items.begin();
        }

        /* Create a vector of the maximums obtained by comparing each adjacent pair of items:
        @f$ [max] = \left\{\begin{array}{ll} [0 * (x - y) + y] = ([0] * [x - y])[y] = [y] & \text{if $ x < y $} \\ [1 * (x - y) + y] = ([1] * [x - y])[y] = [x] & \text{if $ x \geq y} \end{array} \right. @f$
        */
        ItemContainer temp;
        temp.reserve(items.size() / 2 + items.size() % 2);//inefficient ceil
        for (size_t i = 0; i < items.size() - 1; i += 2) {
            temp.push_back(this->secureMultiplicationServer->Multiply(this->secureComparisonServer->Compare(items[i], items[i + 1]), items[i] - items[i + 1]) + items[i + 1]);
        }

        //for odd lenghts, we also want to keep the last element
        if (items.size() % 2 == 1) {
            temp.push_back(*items.rbegin());
        }

        return this->GetMaximum(temp);
    }

    template <typename T_SecureComparisonServer, typename T_SecureComparisonClient>
    void SecureExtremumSelectionServer<T_SecureComparisonServer, T_SecureComparisonClient>::SetClient (const std::shared_ptr<SecureExtremumSelectionClient<T_SecureComparisonServer, T_SecureComparisonClient>> &secureExtremumSelectionClient) {
        this->secureExtremumSelectionClient = secureExtremumSelectionClient;
        this->secureComparisonServer->SetClient(secureExtremumSelectionClient->GetSecureComparisonClient());
        this->secureMultiplicationServer->SetClient(secureExtremumSelectionClient->GetSecureMultiplicationClient());
    }

    template <typename T_SecureComparisonServer, typename T_SecureComparisonClient>
    const std::shared_ptr<T_SecureComparisonServer> &SecureExtremumSelectionServer<T_SecureComparisonServer, T_SecureComparisonClient>::GetSecureComparisonServer () const {
        return this->secureComparisonServer;
    }

    template <typename T_SecureComparisonServer, typename T_SecureComparisonClient>
    const std::shared_ptr<SecureMultiplicationServer<Paillier>> &SecureExtremumSelectionServer<T_SecureComparisonServer, T_SecureComparisonClient>::GetSecureMultiplicationServer () const {
        return this->secureMultiplicationServer;
    }

}//namespace Core
}//namespace SeComLib

#endif//SECURE_EXTREMUM_SELECTION_SERVER_IMPLEMENTATION_GUARD