el_gamal.h

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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 EL_GAMAL_HEADER_GUARD
#define EL_GAMAL_HEADER_GUARD

#include "big_integer.h"
#include "random_provider.h"
#include "crypto_provider.h"
#include "utils/config.h"
#include "el_gamal_ciphertext.h"

//include C++ headers
#include <map>
#include <stdexcept>

namespace SeComLib {
namespace Core {
    struct ElGamalPublicKey {
    public:
        BigInteger p;
        BigInteger q;
        BigInteger gq;
        BigInteger h;
    };

    struct ElGamalPrivateKey {
    public:
        BigInteger s;
    };

    struct ElGamalRandomizer {
        BigInteger x;

        BigInteger y;

        ElGamalRandomizer ();

        ElGamalRandomizer (const BigInteger &x, const BigInteger &y);
    };

    class ElGamal : public CryptoProvider<ElGamalPublicKey, ElGamalPrivateKey, ElGamalCiphertext, ElGamalRandomizer> {
    public:
        ElGamal (const bool precomputeDecryptionMap = false);

        ElGamal (const ElGamalPublicKey &publicKey);

        ElGamal (const ElGamalPublicKey &publicKey, const ElGamalPrivateKey &privateKey, const bool precomputeDecryptionMap = false);

        ~ElGamal () {}

        /* Base class methods */

        virtual bool GenerateKeys ();

        virtual BigInteger DecryptInteger (const Ciphertext &ciphertext) const;

        virtual Ciphertext EncryptIntegerNonrandom (const BigInteger &plaintext) const;

        virtual Randomizer GetRandomizer () const;

        virtual Ciphertext RandomizeCiphertext (const Ciphertext &ciphertext) const;

    #ifdef ENABLE_CRYPTO_PROVIDER_HOMOMORPHIC_OPERATIONS
        Ciphertext HomomorphicAdd (const Ciphertext &lhs, const Ciphertext &rhs) const;

        Ciphertext GetHomomorphicInverse (const Ciphertext &input) const;

        Ciphertext HomomorphicSubtract (const Ciphertext &lhs, const Ciphertext &rhs) const;

        Ciphertext HomomorphicMultiply (const Ciphertext &lhs, const BigInteger &rhs) const;
    #endif

        virtual const BigInteger &GetMessageSpaceUpperBound () const;

        virtual size_t GetMessageSpaceSize () const;

        /* /Base class methods */

        bool IsEncryptedZero (const Ciphertext &ciphertext) const;

    private:
        typedef std::map<const BigInteger, BigInteger> DecryptionMap;

        BigInteger messageSpaceThreshold;

        BigInteger g;

        bool precomputeDecryptionMap;

        DecryptionMap decryptionMap;

        /* Base class methods */

        virtual void validateParameters () {}

        virtual void doPrecomputations ();

        /* /Base class methods */

        ElGamal (const ElGamal &);

        ElGamal operator= (const ElGamal &);
    };
}//namespace Core
}//namespace SeComLib

#endif//EL_GAMAL_HEADER_GUARD