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/ber_dec.h>
#include <botan/der_enc.h>
#include <botan/ec_point.h>
#include <botan/numthry.h>
#include <botan/secmem.h>
#include <botan/internal/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());
}
 
namespace {
 
EC_Group_Encoding default_encoding_for(EC_Group& group) {
   if(group.get_curve_oid().empty()) {
      return EC_Group_Encoding::Explicit;
   } else {
      return EC_Group_Encoding::NamedCurve;
   }
}
 
}  // namespace
 
EC_PublicKey::EC_PublicKey(const EC_Group& dom_par, const EC_Point& pub_point) :
      m_domain_params(dom_par), m_public_key(pub_point), m_domain_encoding(default_encoding_for(m_domain_params)) {}
 
EC_PublicKey::EC_PublicKey(const AlgorithmIdentifier& alg_id, std::span<const uint8_t> key_bits) :
      m_domain_params{EC_Group(alg_id.parameters())},
      m_public_key{domain().OS2ECP(key_bits)},
      m_domain_encoding(default_encoding_for(m_domain_params)) {}
 
bool EC_PublicKey::check_key(RandomNumberGenerator& rng, bool /*strong*/) const {
   return m_domain_params.verify_group(rng) && m_domain_params.verify_public_element(public_point());
}
 
AlgorithmIdentifier EC_PublicKey::algorithm_identifier() const {
   return AlgorithmIdentifier(object_identifier(), DER_domain());
}
 
std::vector<uint8_t> EC_PublicKey::public_key_bits() const {
   return public_point().encode(point_encoding());
}
 
void EC_PublicKey::set_point_encoding(EC_Point_Format enc) {
   if(enc != EC_Point_Format::Compressed && enc != EC_Point_Format::Uncompressed && enc != EC_Point_Format::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_Group_Encoding::NamedCurve && m_domain_params.get_curve_oid().empty()) {
      throw Invalid_Argument("Cannot used NamedCurve encoding for a curve without an 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;
   m_domain_encoding = default_encoding_for(m_domain_params);
 
   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::raw_private_key_bits() const {
   return BigInt::encode_locked(m_private_key);
}
 
secure_vector<uint8_t> EC_PrivateKey::private_key_bits() const {
   return DER_Encoder()
      .start_sequence()
      .encode(static_cast<size_t>(1))
      .encode(BigInt::encode_1363(m_private_key, m_private_key.bytes()), ASN1_Type::OctetString)
      .start_explicit_context_specific(1)
      .encode(m_public_key.encode(EC_Point_Format::Uncompressed), ASN1_Type::BitString)
      .end_cons()
      .end_cons()
      .get_contents();
}
 
EC_PrivateKey::EC_PrivateKey(const AlgorithmIdentifier& alg_id,
                             std::span<const uint8_t> key_bits,
                             bool with_modular_inverse) {
   m_domain_params = EC_Group(alg_id.parameters());
   m_domain_encoding = default_encoding_for(m_domain_params);
 
   OID key_parameters;
   secure_vector<uint8_t> public_key_bits;
 
   BER_Decoder(key_bits)
      .start_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_Type(0), ASN1_Class::ExplicitContextSpecific)
      .decode_optional_string(public_key_bits, ASN1_Type::BitString, 1, ASN1_Class::ExplicitContextSpecific)
      .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
   }
}
 
const BigInt& EC_PublicKey::get_int_field(std::string_view field) const {
   if(field == "public_x") {
      BOTAN_ASSERT_NOMSG(this->public_point().is_affine());
      return this->public_point().get_x();
   } else if(field == "public_y") {
      BOTAN_ASSERT_NOMSG(this->public_point().is_affine());
      return this->public_point().get_y();
   } else if(field == "base_x") {
      return this->domain().get_g_x();
   } else if(field == "base_y") {
      return this->domain().get_g_y();
   } else if(field == "p") {
      return this->domain().get_p();
   } else if(field == "a") {
      return this->domain().get_a();
   } else if(field == "b") {
      return this->domain().get_b();
   } else if(field == "cofactor") {
      return this->domain().get_cofactor();
   } else if(field == "order") {
      return this->domain().get_order();
   } else {
      return Public_Key::get_int_field(field);
   }
}
 
const BigInt& EC_PrivateKey::get_int_field(std::string_view field) const {
   if(field == "x") {
      return this->private_value();
   } else {
      return EC_PublicKey::get_int_field(field);
   }
}
 
}  // namespace Botan