/*

* (C) 2018 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#ifndef BOTAN_MONTY_EXP_H_

#define BOTAN_MONTY_EXP_H_

#include <memory>

#include <botan/bigint.h>

namespace Botan {

class Modular_Reducer;

class Montgomery_Params;

class Montgomery_Exponentation_State;

/*

* Precompute for calculating values g^x mod p

*/

std::shared_ptr<const Montgomery_Exponentation_State>

monty_precompute(std::shared_ptr<const Montgomery_Params> params_p,

                 const BigInt& g,

                 size_t window_bits,

                 bool const_time = true);

/*

* Return g^k mod p

*/

BigInt monty_execute(const Montgomery_Exponentation_State& precomputed_state,

                     const BigInt& k, size_t max_k_bits);

/*

* Return g^k mod p taking variable time depending on k

* @warning only use this if k is public

*/

BigInt monty_execute_vartime(const Montgomery_Exponentation_State& precomputed_state,

                             const BigInt& k);

inline

BigInt monty_exp(std::shared_ptr<const Montgomery_Params> params_p,

                 const BigInt& g, const BigInt& k, size_t max_k_bits)

   {

   auto precomputed = monty_precompute(params_p, g, 4, true);

   return monty_execute(*precomputed, k, max_k_bits);

   }

inline

BigInt monty_exp_vartime(std::shared_ptr<const Montgomery_Params> params_p,

                         const BigInt& g, const BigInt& k)

   {

   auto precomputed = monty_precompute(params_p, g, 4, false);

   return monty_execute_vartime(*precomputed, k);

   }

/**

* Return (x^z1 * y^z2) % p

*/

BigInt monty_multi_exp(std::shared_ptr<const Montgomery_Params> params_p,

                       const BigInt& x,

                       const BigInt& z1,

                       const BigInt& y,

                       const BigInt& z2);

}

#endif