ecdh.cpp

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/*
* 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>

#if defined(BOTAN_HAS_OPENSSL)
  #include <botan/internal/openssl.h>
#endif

namespace Botan {

namespace {

/**
* ECDH operation
*/
class ECDH_KA_Operation final : public PK_Ops::Key_Agreement_with_KDF
   {
   public:

      ECDH_KA_Operation(const ECDH_PrivateKey& key, const std::string& 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
         {
         PointGFp input_point = m_group.get_cofactor() * m_group.OS2ECP(w, w_len);
         input_point.randomize_repr(m_rng);

         const PointGFp 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;
   };

}

std::unique_ptr<PK_Ops::Key_Agreement>
ECDH_PrivateKey::create_key_agreement_op(RandomNumberGenerator& rng,
                                         const std::string& params,
                                         const std::string& provider) const
   {
#if defined(BOTAN_HAS_OPENSSL)
   if(provider == "openssl" || provider.empty())
      {
      try
         {
         return make_openssl_ecdh_ka_op(*this, params);
         }
      catch(Lookup_Error&)
         {
         if(provider == "openssl")
            throw;
         }
      }
#endif

   if(provider == "base" || provider.empty())
      return std::unique_ptr<PK_Ops::Key_Agreement>(new ECDH_KA_Operation(*this, params, rng));

   throw Provider_Not_Found(algo_name(), provider);
   }


}