Botan::EC_Point_Multi_Point_Precompute Class Reference

#include <point_mul.h>

Public Member Functions
	EC_Point_Multi_Point_Precompute (const EC_Point &g1, const EC_Point &g2)
EC_Point	multi_exp (const BigInt &k1, const BigInt &k2) const

Detailed Description

Definition at line 64 of file point_mul.h.

Constructor & Destructor Documentation

EC_Point_Multi_Point_Precompute()

Botan::EC_Point_Multi_Point_Precompute::EC_Point_Multi_Point_Precompute	(	const EC_Point &	g1,
		const EC_Point &	g2 )

Definition at line 274 of file point_mul.cpp.

                                                                                                     {
   if(x.on_the_curve() == false || y.on_the_curve() == false) {
      m_M.push_back(x.zero());
      return;
   }
 
   std::vector<BigInt> ws(EC_Point::WORKSPACE_SIZE);
 
   EC_Point x2 = x;
   x2.mult2(ws);
 
   const EC_Point x3(x2.plus(x, ws));
 
   EC_Point y2 = y;
   y2.mult2(ws);
 
   const EC_Point y3(y2.plus(y, ws));
 
   m_M.reserve(15);
 
   m_M.push_back(x);
   m_M.push_back(x2);
   m_M.push_back(x3);
 
   m_M.push_back(y);
   m_M.push_back(y.plus(x, ws));
   m_M.push_back(y.plus(x2, ws));
   m_M.push_back(y.plus(x3, ws));
 
   m_M.push_back(y2);
   m_M.push_back(y2.plus(x, ws));
   m_M.push_back(y2.plus(x2, ws));
   m_M.push_back(y2.plus(x3, ws));
 
   m_M.push_back(y3);
   m_M.push_back(y3.plus(x, ws));
   m_M.push_back(y3.plus(x2, ws));
   m_M.push_back(y3.plus(x3, ws));
 
   bool no_infinity = true;
   for(auto& pt : m_M) {
      if(pt.is_zero()) {
         no_infinity = false;
      }
   }
 
   if(no_infinity) {
      EC_Point::force_all_affine(m_M, ws[0].get_word_vector());
   }
 
   m_no_infinity = no_infinity;
}

References Botan::EC_Point::mult2(), Botan::EC_Point::on_the_curve(), Botan::EC_Point::plus(), and Botan::EC_Point::zero().

Member Function Documentation

multi_exp()

EC_Point Botan::EC_Point_Multi_Point_Precompute::multi_exp	(	const BigInt &	k1,
		const BigInt &	k2 ) const

Definition at line 327 of file point_mul.cpp.

                                                                                            {
   if(m_M.size() == 1) {
      return m_M[0];
   }
 
   std::vector<BigInt> ws(EC_Point::WORKSPACE_SIZE);
 
   const size_t z_bits = round_up(std::max(z1.bits(), z2.bits()), 2);
 
   EC_Point H = m_M[0].zero();
 
   for(size_t i = 0; i != z_bits; i += 2) {
      if(i > 0) {
         H.mult2i(2, ws);
      }
 
      const uint32_t z1_b = z1.get_substring(z_bits - i - 2, 2);
      const uint32_t z2_b = z2.get_substring(z_bits - i - 2, 2);
 
      const uint32_t z12 = (4 * z2_b) + z1_b;
 
      // This function is not intended to be const time
      if(z12) {
         if(m_no_infinity) {
            H.add_affine(m_M[z12 - 1], ws);
         } else {
            H.add(m_M[z12 - 1], ws);
         }
      }
   }
 
   if(z1.is_negative() != z2.is_negative()) {
      H.negate();
   }
 
   return H;
}

References Botan::EC_Point::add(), Botan::EC_Point::add_affine(), Botan::BigInt::bits(), Botan::BigInt::get_substring(), Botan::BigInt::is_negative(), Botan::EC_Point::mult2i(), Botan::EC_Point::negate(), Botan::round_up(), and Botan::EC_Point::zero().

Referenced by Botan::EC_Mul2Table_Data_BN::mul2_vartime(), Botan::EC_Mul2Table_Data_BN::mul2_vartime_x_mod_order_eq(), and Botan::multi_exponentiate().

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The documentation for this class was generated from the following files:

• src/lib/pubkey/ec_group/point_mul.h
• src/lib/pubkey/ec_group/point_mul.cpp