/*

* ECDH implemenation

* (C) 2007 Manuel Hartl, FlexSecure GmbH

*     2007 Falko Strenzke, FlexSecure GmbH

*     2008-2010 Jack Lloyd

*

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

*/

#include <botan/ecdh.h>

#include <botan/numthry.h>

#include <botan/internal/pk_ops_impl.h>

namespace Botan {

std::unique_ptr<Public_Key> ECDH_PrivateKey::public_key() const {

   return std::make_unique<ECDH_PublicKey>(domain(), public_point());

}

namespace {

/**

* ECDH operation

*/

class ECDH_KA_Operation final : public PK_Ops::Key_Agreement_with_KDF {

   public:

      ECDH_KA_Operation(const ECDH_PrivateKey& key, std::string_view kdf, RandomNumberGenerator& rng) :

            PK_Ops::Key_Agreement_with_KDF(kdf), m_group(key.domain()), m_rng(rng) {

         m_l_times_priv = m_group.inverse_mod_order(m_group.get_cofactor()) * key.private_value();

      }

      size_t agreed_value_size() const override { return m_group.get_p_bytes(); }

      secure_vector<uint8_t> raw_agree(const uint8_t w[], size_t w_len) override {

         EC_Point input_point = m_group.get_cofactor() * m_group.OS2ECP(w, w_len);

         input_point.randomize_repr(m_rng);

         const EC_Point S = m_group.blinded_var_point_multiply(input_point, m_l_times_priv, m_rng, m_ws);

         if(S.on_the_curve() == false) {

            throw Internal_Error("ECDH agreed value was not on the curve");

         }

         return BigInt::encode_1363(S.get_affine_x(), m_group.get_p_bytes());

      }

   private:

      const EC_Group m_group;

      BigInt m_l_times_priv;

      RandomNumberGenerator& m_rng;

      std::vector<BigInt> m_ws;

};

}  // namespace

std::unique_ptr<Private_Key> ECDH_PublicKey::generate_another(RandomNumberGenerator& rng) const {

   return std::make_unique<ECDH_PrivateKey>(rng, domain());

}

std::unique_ptr<PK_Ops::Key_Agreement> ECDH_PrivateKey::create_key_agreement_op(RandomNumberGenerator& rng,

                                                                                std::string_view params,

                                                                                std::string_view provider) const {

   if(provider == "base" || provider.empty()) {

      return std::make_unique<ECDH_KA_Operation>(*this, params, rng);

   }

   throw Provider_Not_Found(algo_name(), provider);

}

}  // namespace Botan