rw.h

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

/// \file rw.h
/// \brief Classes for Rabin-Williams signature scheme
/// \details The implementation provides Rabin-Williams signature schemes as defined in
///   IEEE P1363. It uses Bernstein's tweaked square roots in place of square roots to
///   speedup calculations.
/// \sa <A HREF="http://cr.yp.to/sigs/rwsota-20080131.pdf">RSA signatures and Rabin–Williams
///   signatures: the state of the art (20080131)</A>, Section 6, <em>The tweaks e and f</em>.
/// \since Crypto++ 3.0

#ifndef CRYPTOPP_RW_H
#define CRYPTOPP_RW_H

#include "cryptlib.h"
#include "pubkey.h"
#include "integer.h"

NAMESPACE_BEGIN(CryptoPP)

/// \brief Rabin-Williams trapdoor function using the public key
/// \since Crypto++ 3.0, Tweaked roots using <em>e</em> and <em>f</em> since Crypto++ 5.6.4
class CRYPTOPP_DLL RWFunction : public TrapdoorFunction, public PublicKey
{
    typedef RWFunction ThisClass;

public:

    /// \brief Initialize a Rabin-Williams public key
    /// \param n the modulus
    void Initialize(const Integer &n)
        {m_n = n;}

    void BERDecode(BufferedTransformation &bt);
    void DEREncode(BufferedTransformation &bt) const;

    void Save(BufferedTransformation &bt) const
        {DEREncode(bt);}
    void Load(BufferedTransformation &bt)
        {BERDecode(bt);}

    Integer ApplyFunction(const Integer &x) const;
    Integer PreimageBound() const {return ++(m_n>>1);}
    Integer ImageBound() const {return m_n;}

    bool Validate(RandomNumberGenerator &rng, unsigned int level) const;
    bool GetVoidValue(const char *name, const std::type_info &valueType, void *pValue) const;
    void AssignFrom(const NameValuePairs &source);

    const Integer& GetModulus() const {return m_n;}
    void SetModulus(const Integer &n) {m_n = n;}

protected:
    Integer m_n;
};

/// \brief Rabin-Williams trapdoor function using the private key
/// \since Crypto++ 3.0, Tweaked roots using <em>e</em> and <em>f</em> since Crypto++ 5.6.4
class CRYPTOPP_DLL InvertibleRWFunction : public RWFunction, public TrapdoorFunctionInverse, public PrivateKey
{
    typedef InvertibleRWFunction ThisClass;

public:
    /// \brief Construct an InvertibleRWFunction
    InvertibleRWFunction() : m_precompute(false) {}

    /// \brief Initialize a Rabin-Williams private key
    /// \param n modulus
    /// \param p first prime factor
    /// \param q second prime factor
    /// \param u q<sup>-1</sup> mod p
    /// \details This Initialize() function overload initializes a private key from existing parameters.
    void Initialize(const Integer &n, const Integer &p, const Integer &q, const Integer &u);

    /// \brief Create a Rabin-Williams private key
    /// \param rng a RandomNumberGenerator derived class
    /// \param modulusBits the size of the modulus, in bits
    /// \details This function overload of Initialize() creates a new private key because it
    ///   takes a RandomNumberGenerator() as a parameter. If you have an existing keypair,
    ///   then use one of the other Initialize() overloads.
    void Initialize(RandomNumberGenerator &rng, unsigned int modulusBits)
        {GenerateRandomWithKeySize(rng, modulusBits);}

    void BERDecode(BufferedTransformation &bt);
    void DEREncode(BufferedTransformation &bt) const;

    void Save(BufferedTransformation &bt) const
        {DEREncode(bt);}
    void Load(BufferedTransformation &bt)
        {BERDecode(bt);}

    Integer CalculateInverse(RandomNumberGenerator &rng, const Integer &x) const;

    // GeneratibleCryptoMaterial
    bool Validate(RandomNumberGenerator &rng, unsigned int level) const;
    bool GetVoidValue(const char *name, const std::type_info &valueType, void *pValue) const;
    void AssignFrom(const NameValuePairs &source);
    /*! parameters: (ModulusSize) */
    void GenerateRandom(RandomNumberGenerator &rng, const NameValuePairs &alg);

    const Integer& GetPrime1() const {return m_p;}
    const Integer& GetPrime2() const {return m_q;}
    const Integer& GetMultiplicativeInverseOfPrime2ModPrime1() const {return m_u;}

    void SetPrime1(const Integer &p) {m_p = p;}
    void SetPrime2(const Integer &q) {m_q = q;}
    void SetMultiplicativeInverseOfPrime2ModPrime1(const Integer &u) {m_u = u;}

    virtual bool SupportsPrecomputation() const {return true;}
    virtual void Precompute(unsigned int unused = 0) {CRYPTOPP_UNUSED(unused); PrecomputeTweakedRoots();}
    virtual void Precompute(unsigned int unused = 0) const {CRYPTOPP_UNUSED(unused); PrecomputeTweakedRoots();}

    virtual void LoadPrecomputation(BufferedTransformation &storedPrecomputation);
    virtual void SavePrecomputation(BufferedTransformation &storedPrecomputation) const;

protected:
    void PrecomputeTweakedRoots() const;

protected:
    Integer m_p, m_q, m_u;

    mutable Integer m_pre_2_9p, m_pre_2_3q, m_pre_q_p;
    mutable bool m_precompute;
};

/// \brief Rabin-Williams keys
/// \since Crypto++ 3.0
struct RW
{
    CRYPTOPP_STATIC_CONSTEXPR const char* StaticAlgorithmName() {return "RW";}
    typedef RWFunction PublicKey;
    typedef InvertibleRWFunction PrivateKey;
};

/// \brief Rabin-Williams signature scheme
/// \tparam STANDARD signature standard
/// \tparam H hash transformation
/// \since Crypto++ 3.0
template <class STANDARD, class H>
struct RWSS : public TF_SS<RW, STANDARD, H>
{
};

NAMESPACE_END

#endif