point_mul.h

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/*
* (C) 2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_POINT_MUL_H_
#define BOTAN_POINT_MUL_H_

#include <botan/point_gfp.h>

namespace Botan {

class Modular_Reducer;

static const size_t PointGFp_SCALAR_BLINDING_BITS = 80;

class PointGFp_Base_Point_Precompute final
   {
   public:
      PointGFp_Base_Point_Precompute(const PointGFp& base_point,
                                     const Modular_Reducer& mod_order);

      PointGFp mul(const BigInt& k,
                   RandomNumberGenerator& rng,
                   const BigInt& group_order,
                   std::vector<BigInt>& ws) const;
   private:
      const PointGFp& m_base_point;
      const Modular_Reducer& m_mod_order;

      enum { WINDOW_BITS = 3 };
      enum { WINDOW_SIZE = (1 << WINDOW_BITS) - 1 };

      const size_t m_p_words;
      const size_t m_T_size;

      /*
      * This is a table of T_size * 3*p_word words
      */
      std::vector<word> m_W;
   };

class PointGFp_Var_Point_Precompute final
   {
   public:
      PointGFp_Var_Point_Precompute(const PointGFp& point,
                                    RandomNumberGenerator& rng,
                                    std::vector<BigInt>& ws);

      PointGFp mul(const BigInt& k,
                   RandomNumberGenerator& rng,
                   const BigInt& group_order,
                   std::vector<BigInt>& ws) const;
   private:
      const CurveGFp m_curve;
      const size_t m_p_words;
      const size_t m_window_bits;

      /*
      * Table of 2^window_bits * 3*2*p_word words
      * Kept in locked vector since the base point might be sensitive
      * (normally isn't in most protocols but hard to say anything
      * categorically.)
      */
      secure_vector<word> m_T;
   };

class PointGFp_Multi_Point_Precompute final
   {
   public:
      PointGFp_Multi_Point_Precompute(const PointGFp& g1,
                                      const PointGFp& g2);

      /*
      * Return (g1*k1 + g2*k2)
      * Not constant time, intended to use with public inputs
      */
      PointGFp multi_exp(const BigInt& k1,
                         const BigInt& k2) const;
   private:
      std::vector<PointGFp> m_M;
   };

}

#endif