ecc_key.cpp

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/*
* ECC Key implemenation
* (C) 2007 Manuel Hartl, FlexSecure GmbH
*          Falko Strenzke, FlexSecure GmbH
*     2008-2010 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/ecc_key.h>
#include <botan/numthry.h>
#include <botan/der_enc.h>
#include <botan/ber_dec.h>
#include <botan/secmem.h>
#include <botan/point_gfp.h>
#include <botan/workfactor.h>

namespace Botan {

size_t EC_PublicKey::key_length() const
   {
   return domain().get_p_bits();
   }

size_t EC_PublicKey::estimated_strength() const
   {
   return ecp_work_factor(key_length());
   }

EC_PublicKey::EC_PublicKey(const EC_Group& dom_par,
                           const PointGFp& pub_point) :
   m_domain_params(dom_par), m_public_key(pub_point)
   {
   if (!dom_par.get_curve_oid().empty())
      m_domain_encoding = EC_DOMPAR_ENC_OID;
   else
      m_domain_encoding = EC_DOMPAR_ENC_EXPLICIT;

#if 0
   if(domain().get_curve() != public_point().get_curve())
      throw Invalid_Argument("EC_PublicKey: curve mismatch in constructor");
#endif
   }

EC_PublicKey::EC_PublicKey(const AlgorithmIdentifier& alg_id,
                           const std::vector<uint8_t>& key_bits) :
   m_domain_params{EC_Group(alg_id.get_parameters())},
   m_public_key{domain().OS2ECP(key_bits)}
   {
   if (!domain().get_curve_oid().empty())
      m_domain_encoding = EC_DOMPAR_ENC_OID;
   else
      m_domain_encoding = EC_DOMPAR_ENC_EXPLICIT;
   }

bool EC_PublicKey::check_key(RandomNumberGenerator& rng,
                             bool) const
   {
   return m_domain_params.verify_group(rng) &&
          m_domain_params.verify_public_element(public_point());
   }


AlgorithmIdentifier EC_PublicKey::algorithm_identifier() const
   {
   return AlgorithmIdentifier(get_oid(), DER_domain());
   }

std::vector<uint8_t> EC_PublicKey::public_key_bits() const
   {
   return public_point().encode(point_encoding());
   }

void EC_PublicKey::set_point_encoding(PointGFp::Compression_Type enc)
   {
   if(enc != PointGFp::COMPRESSED &&
      enc != PointGFp::UNCOMPRESSED &&
      enc != PointGFp::HYBRID)
      throw Invalid_Argument("Invalid point encoding for EC_PublicKey");

   m_point_encoding = enc;
   }

void EC_PublicKey::set_parameter_encoding(EC_Group_Encoding form)
   {
   if(form != EC_DOMPAR_ENC_EXPLICIT &&
      form != EC_DOMPAR_ENC_IMPLICITCA &&
      form != EC_DOMPAR_ENC_OID)
      throw Invalid_Argument("Invalid encoding form for EC-key object specified");

   if((form == EC_DOMPAR_ENC_OID) && (m_domain_params.get_curve_oid().empty()))
      throw Invalid_Argument("Invalid encoding form OID specified for "
                             "EC-key object whose corresponding domain "
                             "parameters are without oid");

   m_domain_encoding = form;
   }

const BigInt& EC_PrivateKey::private_value() const
   {
   if(m_private_key == 0)
      throw Invalid_State("EC_PrivateKey::private_value - uninitialized");

   return m_private_key;
   }

/**
* EC_PrivateKey constructor
*/
EC_PrivateKey::EC_PrivateKey(RandomNumberGenerator& rng,
                             const EC_Group& ec_group,
                             const BigInt& x,
                             bool with_modular_inverse)
   {
   m_domain_params = ec_group;
   if (!ec_group.get_curve_oid().empty())
      m_domain_encoding = EC_DOMPAR_ENC_OID;
   else
      m_domain_encoding = EC_DOMPAR_ENC_EXPLICIT;

   if(x == 0)
      {
      m_private_key = ec_group.random_scalar(rng);
      }
   else
      {
      m_private_key = x;
      }

   std::vector<BigInt> ws;

   if(with_modular_inverse)
      {
      // ECKCDSA
      m_public_key = domain().blinded_base_point_multiply(
         m_domain_params.inverse_mod_order(m_private_key), rng, ws);
      }
   else
      {
      m_public_key = domain().blinded_base_point_multiply(m_private_key, rng, ws);
      }

   BOTAN_ASSERT(m_public_key.on_the_curve(),
                "Generated public key point was on the curve");
   }

secure_vector<uint8_t> EC_PrivateKey::private_key_bits() const
   {
   return DER_Encoder()
      .start_cons(SEQUENCE)
         .encode(static_cast<size_t>(1))
         .encode(BigInt::encode_1363(m_private_key, m_private_key.bytes()), OCTET_STRING)
         .start_cons(ASN1_Tag(1), PRIVATE)
            .encode(m_public_key.encode(PointGFp::Compression_Type::UNCOMPRESSED), BIT_STRING)
         .end_cons()
      .end_cons()
      .get_contents();
   }

EC_PrivateKey::EC_PrivateKey(const AlgorithmIdentifier& alg_id,
                             const secure_vector<uint8_t>& key_bits,
                             bool with_modular_inverse)
   {
   m_domain_params = EC_Group(alg_id.get_parameters());
   m_domain_encoding = EC_DOMPAR_ENC_EXPLICIT;

   if (!domain().get_curve_oid().empty())
      m_domain_encoding = EC_DOMPAR_ENC_OID;
   else
      m_domain_encoding = EC_DOMPAR_ENC_EXPLICIT;

   OID key_parameters;
   secure_vector<uint8_t> public_key_bits;

   BER_Decoder(key_bits)
      .start_cons(SEQUENCE)
         .decode_and_check<size_t>(1, "Unknown version code for ECC key")
         .decode_octet_string_bigint(m_private_key)
         .decode_optional(key_parameters, ASN1_Tag(0), PRIVATE)
         .decode_optional_string(public_key_bits, BIT_STRING, 1, PRIVATE)
      .end_cons();

   if(public_key_bits.empty())
      {
      if(with_modular_inverse)
         {
         // ECKCDSA
         m_public_key = domain().get_base_point() * m_domain_params.inverse_mod_order(m_private_key);
         }
      else
         {
         m_public_key = domain().get_base_point() * m_private_key;
         }

      BOTAN_ASSERT(m_public_key.on_the_curve(),
                   "Public point derived from loaded key was on the curve");
      }
   else
      {
      m_public_key = domain().OS2ECP(public_key_bits);
      // OS2ECP verifies that the point is on the curve
      }
   }

}