private_recommendations_data_packing/secure_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 "secure_comparison_server.h"
//avoid circular includes
#include "secure_comparison_client.h"

namespace SeComLib {
namespace PrivateRecommendationsDataPacking {
    SecureComparisonServer::SecureComparisonServer (const Paillier &paillierCryptoProvider, const Dgk &dgkCryptoProvider, const BigInteger &similarityTreshold, const size_t l, const size_t bucketSize, const size_t maxPackedBuckets, const std::deque<BigInteger> &emptyBuckets, const std::string &configurationPath) :
        paillierCryptoProvider(paillierCryptoProvider),
        dgkCryptoProvider(dgkCryptoProvider),
        blindingFactorCache(paillierCryptoProvider, ComparisonBlindingFactorCacheParameters(configurationPath + ".BlindingFactorCache", bucketSize * maxPackedBuckets, emptyBuckets)),
        l(l),
        emptyBuckets(emptyBuckets),
        maxPackedBuckets(maxPackedBuckets),
        //the dgkComparisonServer operates on l + 1 bit values (due to the empty bit at the beginning of each bucket)
        dgkComparisonServer(std::make_shared<DgkComparisonServer>(paillierCryptoProvider, dgkCryptoProvider, l + 1)) {
        BigInteger twoTimestwoPowLMinusDelta = (BigInteger(2).GetPow(static_cast<unsigned long>(this->l)) - similarityTreshold) * 2;

        BigInteger one(1);
        BigInteger partialD = twoTimestwoPowLMinusDelta;
        for (size_t i = 1; i < maxPackedBuckets; ++i) {
            partialD += (one << (static_cast<unsigned long>(bucketSize * i))) * twoTimestwoPowLMinusDelta;//bucketSize = l + 2
        }

        this->encryptedPartialD = this->paillierCryptoProvider.EncryptIntegerNonrandom(partialD);
    }

    SecureComparisonServer::EncryptedUserData SecureComparisonServer::Compare (const PackedData &packedSimilarityValues, const size_t similarityValueCountInLastEncryption) {
        EncryptedUserData gammaVector;

        for (size_t encryptionIndex = 0; encryptionIndex < packedSimilarityValues.size(); ++encryptionIndex) {
            Paillier::Ciphertext D = packedSimilarityValues[encryptionIndex] + this->encryptedPartialD;

            const BlindingFactorContainer &blindingFactorContainer = this->blindingFactorCache.Pop();

            Paillier::Ciphertext z = D + blindingFactorContainer.encryptedR;

            //the last element of the packedSimilarityValues vector may contain fewer packed buckets
            size_t encryptedBucketsCount = encryptionIndex < packedSimilarityValues.size() - 1 ? this->maxPackedBuckets : similarityValueCountInLastEncryption;

            this->secureComparisonClient.lock()->UnpackZ(z, this->emptyBuckets, encryptedBucketsCount);

            for (size_t i = 0; i < encryptedBucketsCount; ++i) {
                this->secureComparisonClient.lock()->SetZi(i);

                //std::cout << "r_i: " << blindingFactorContainer.ri[i].ToString() << std::endl;
                gammaVector.emplace_back(this->dgkComparisonServer->ComputeDi(blindingFactorContainer.ri[i]));

                //this->secureComparisonClient.lock()->DebugPaillierEncryption(gammaVector.back());
            }
        }

        return gammaVector;
    }

    const BigInteger &SecureComparisonServer::GetEmptyBucket (const size_t index) const {
        return this->emptyBuckets.at(index);
    }

    void SecureComparisonServer::SetClient (const std::shared_ptr<SecureComparisonClient> &secureComparisonClient) {
        this->secureComparisonClient = secureComparisonClient;
        this->dgkComparisonServer->SetClient(secureComparisonClient->GetDgkComparisonClient());
    }

    const std::shared_ptr<DgkComparisonServer> &SecureComparisonServer::GetDgkComparisonServer () const {
        return this->dgkComparisonServer;
    }

}//namespace PrivateRecommendationsDataPacking
}//namespace SeComLib