// 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