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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);
}
}