source: trunk/src-cryptopp/mqv.h

// mqv.h - written and placed in the public domain by Wei Dai

//! \file mqv.h
//! \brief Classes for Menezes–Qu–Vanstone (MQV) key agreement

#ifndef CRYPTOPP_MQV_H
#define CRYPTOPP_MQV_H

#include "cryptlib.h"
#include "gfpcrypt.h"
#include "modarith.h"
#include "integer.h"
#include "algebra.h"
#include "misc.h"

NAMESPACE_BEGIN(CryptoPP)

//! \class MQV_Domain
//! \brief MQV domain for performing authenticated key agreement
//! \tparam GROUP_PARAMETERS doamin parameters
//! \tparam COFACTOR_OPTION cofactor option
//! \details GROUP_PARAMETERS paramters include the curve coefcients and the base point.
//!   Binary curves use a polynomial to represent its characteristic, while prime curves
//!   use a prime number.
//! \sa MQV, HMQV, FHMQV, and AuthenticatedKeyAgreementDomain
template <class GROUP_PARAMETERS, class COFACTOR_OPTION = CPP_TYPENAME GROUP_PARAMETERS::DefaultCofactorOption>
class MQV_Domain : public AuthenticatedKeyAgreementDomain
{
public:
        typedef GROUP_PARAMETERS GroupParameters;
        typedef typename GroupParameters::Element Element;
        typedef MQV_Domain<GROUP_PARAMETERS, COFACTOR_OPTION> Domain;

        //! \brief Construct a MQV domain
        MQV_Domain() {}

        //! \brief Construct a MQV domain
        //! \param params group parameters and options
        MQV_Domain(const GroupParameters &params)
                : m_groupParameters(params) {}

        //! \brief Construct a MQV domain
        //! \param bt BufferedTransformation with group parameters and options
        MQV_Domain(BufferedTransformation &bt)
                {m_groupParameters.BERDecode(bt);}

        //! \brief Construct a MQV domain
        //! \tparam T1 template parameter used as a constructor parameter
        //! \tparam T2 template parameter used as a constructor parameter
        //! \param v1 first parameter
        //! \param v2 second parameter
        //! \details v1 and v2 are passed directly to the GROUP_PARAMETERS object.
        template <class T1, class T2>
        MQV_Domain(T1 v1, T2 v2)
                {m_groupParameters.Initialize(v1, v2);}

        //! \brief Construct a MQV domain
        //! \tparam T1 template parameter used as a constructor parameter
        //! \tparam T2 template parameter used as a constructor parameter
        //! \tparam T3 template parameter used as a constructor parameter
        //! \param v1 first parameter
        //! \param v2 second parameter
        //! \param v3 third parameter
        //! \details v1, v2 and v3 are passed directly to the GROUP_PARAMETERS object.
        template <class T1, class T2, class T3>
        MQV_Domain(T1 v1, T2 v2, T3 v3)
                {m_groupParameters.Initialize(v1, v2, v3);}

        //! \brief Construct a MQV domain
        //! \tparam T1 template parameter used as a constructor parameter
        //! \tparam T2 template parameter used as a constructor parameter
        //! \tparam T3 template parameter used as a constructor parameter
        //! \tparam T4 template parameter used as a constructor parameter
        //! \param v1 first parameter
        //! \param v2 second parameter
        //! \param v3 third parameter
        //! \param v4 third parameter
        //! \details v1, v2, v3 and v4 are passed directly to the GROUP_PARAMETERS object.
        template <class T1, class T2, class T3, class T4>
        MQV_Domain(T1 v1, T2 v2, T3 v3, T4 v4)
                {m_groupParameters.Initialize(v1, v2, v3, v4);}

        //! \brief Retrieves the group parameters for this domain
        //! \return the group parameters for this domain as a const reference
        const GroupParameters & GetGroupParameters() const {return m_groupParameters;}

        //! \brief Retrieves the group parameters for this domain
        //! \return the group parameters for this domain as a non-const reference
        GroupParameters & AccessGroupParameters() {return m_groupParameters;}

        //! \brief Retrieves the crypto parameters for this domain
        //! \return the crypto parameters for this domain as a non-const reference
        CryptoParameters & AccessCryptoParameters() {return AccessAbstractGroupParameters();}

        //! \brief Provides the size of the agreed value
        //! \return size of agreed value produced  in this domain
        //! \details The length is calculated using <tt>GetEncodedElementSize(false)</tt>, which means the
        //!   element is encoded in a non-reversible format. A non-reversible format means its a raw byte array,
        //!   and it lacks presentation format like an ASN.1 BIT_STRING or OCTET_STRING.
        unsigned int AgreedValueLength() const {return GetAbstractGroupParameters().GetEncodedElementSize(false);}

        //! \brief Provides the size of the static private key
        //! \return size of static private keys in this domain
        //! \details The length is calculated using the byte count of the subgroup order.
        unsigned int StaticPrivateKeyLength() const {return GetAbstractGroupParameters().GetSubgroupOrder().ByteCount();}

        //! \brief Provides the size of the static public key
        //! \return size of static public keys in this domain
        //! \details The length is calculated using <tt>GetEncodedElementSize(true)</tt>, which means the
        //!   element is encoded in a reversible format. A reversible format means it has a presentation format,
        //!   and its an ANS.1 encoded element or point.
        unsigned int StaticPublicKeyLength() const {return GetAbstractGroupParameters().GetEncodedElementSize(true);}

        //! \brief Generate static private key in this domain
        //! \param rng a RandomNumberGenerator derived class
        //! \param privateKey a byte buffer for the generated private key in this domain
        //! \details The private key is a random scalar used as an exponent in the range <tt>[1,MaxExponent()]</tt>.
        //! \pre <tt>COUNTOF(privateKey) == PrivateStaticKeyLength()</tt>
        void GenerateStaticPrivateKey(RandomNumberGenerator &rng, byte *privateKey) const
        {
                Integer x(rng, Integer::One(), GetAbstractGroupParameters().GetMaxExponent());
                x.Encode(privateKey, StaticPrivateKeyLength());
        }

        //! \brief Generate a static public key from a private key in this domain
        //! \param rng a RandomNumberGenerator derived class
        //! \param privateKey a byte buffer with the previously generated private key
        //! \param publicKey a byte buffer for the generated public key in this domain
        //! \details The public key is an element or point on the curve, and its stored in a revrsible format.
        //!    A reversible format means it has a presentation format, and its an ANS.1 encoded element or point.
        //! \pre <tt>COUNTOF(publicKey) == PublicStaticKeyLength()</tt>
        void GenerateStaticPublicKey(RandomNumberGenerator &rng, const byte *privateKey, byte *publicKey) const
        {
                CRYPTOPP_UNUSED(rng);
                const DL_GroupParameters<Element> &params = GetAbstractGroupParameters();
                Integer x(privateKey, StaticPrivateKeyLength());
                Element y = params.ExponentiateBase(x);
                params.EncodeElement(true, y, publicKey);
        }

        unsigned int EphemeralPrivateKeyLength() const {return StaticPrivateKeyLength() + StaticPublicKeyLength();}
        unsigned int EphemeralPublicKeyLength() const {return StaticPublicKeyLength();}

        void GenerateEphemeralPrivateKey(RandomNumberGenerator &rng, byte *privateKey) const
        {
                const DL_GroupParameters<Element> &params = GetAbstractGroupParameters();
                Integer x(rng, Integer::One(), params.GetMaxExponent());
                x.Encode(privateKey, StaticPrivateKeyLength());
                Element y = params.ExponentiateBase(x);
                params.EncodeElement(true, y, privateKey+StaticPrivateKeyLength());
        }

        void GenerateEphemeralPublicKey(RandomNumberGenerator &rng, const byte *privateKey, byte *publicKey) const
        {
                CRYPTOPP_UNUSED(rng);
                memcpy(publicKey, privateKey+StaticPrivateKeyLength(), EphemeralPublicKeyLength());
        }

        bool Agree(byte *agreedValue,
                const byte *staticPrivateKey, const byte *ephemeralPrivateKey,
                const byte *staticOtherPublicKey, const byte *ephemeralOtherPublicKey,
                bool validateStaticOtherPublicKey=true) const
        {
                try
                {
                        const DL_GroupParameters<Element> &params = GetAbstractGroupParameters();
                        Element WW = params.DecodeElement(staticOtherPublicKey, validateStaticOtherPublicKey);
                        Element VV = params.DecodeElement(ephemeralOtherPublicKey, true);

                        Integer s(staticPrivateKey, StaticPrivateKeyLength());
                        Integer u(ephemeralPrivateKey, StaticPrivateKeyLength());
                        Element V = params.DecodeElement(ephemeralPrivateKey+StaticPrivateKeyLength(), false);

                        const Integer &r = params.GetSubgroupOrder();
                        Integer h2 = Integer::Power2((r.BitCount()+1)/2);
                        Integer e = ((h2+params.ConvertElementToInteger(V)%h2)*s+u) % r;
                        Integer tt = h2 + params.ConvertElementToInteger(VV) % h2;

                        if (COFACTOR_OPTION::ToEnum() == NO_COFACTOR_MULTIPLICTION)
                        {
                                Element P = params.ExponentiateElement(WW, tt);
                                P = m_groupParameters.MultiplyElements(P, VV);
                                Element R[2];
                                const Integer e2[2] = {r, e};
                                params.SimultaneousExponentiate(R, P, e2, 2);
                                if (!params.IsIdentity(R[0]) || params.IsIdentity(R[1]))
                                        return false;
                                params.EncodeElement(false, R[1], agreedValue);
                        }
                        else
                        {
                                const Integer &k = params.GetCofactor();
                                if (COFACTOR_OPTION::ToEnum() == COMPATIBLE_COFACTOR_MULTIPLICTION)
                                        e = ModularArithmetic(r).Divide(e, k);
                                Element P = m_groupParameters.CascadeExponentiate(VV, k*e, WW, k*(e*tt%r));
                                if (params.IsIdentity(P))
                                        return false;
                                params.EncodeElement(false, P, agreedValue);
                        }
                }
                catch (DL_BadElement &)
                {
                        return false;
                }
                return true;
        }

private:
        DL_GroupParameters<Element> & AccessAbstractGroupParameters() {return m_groupParameters;}
        const DL_GroupParameters<Element> & GetAbstractGroupParameters() const {return m_groupParameters;}

        GroupParameters m_groupParameters;
};

//! Menezes-Qu-Vanstone in GF(p) with key validation, AKA <a href="http://www.weidai.com/scan-mirror/ka.html#MQV">MQV</a>
//! \sa MQV, HMQV_Domain, FHMQV_Domain, AuthenticatedKeyAgreementDomain
typedef MQV_Domain<DL_GroupParameters_GFP_DefaultSafePrime> MQV;

NAMESPACE_END

#endif