eckcdsa.cpp

Go to the documentation of this file.

/*
* ECKCDSA (ISO/IEC 14888-3:2006/Cor.2:2009)
* (C) 2016 René Korthaus, Sirrix AG
* (C) 2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/eckcdsa.h>
#include <botan/internal/pk_ops_impl.h>
#include <botan/internal/point_mul.h>
#include <botan/internal/keypair.h>
#include <botan/reducer.h>
#include <botan/internal/emsa.h>
#include <botan/hash.h>
#include <botan/rng.h>
 
namespace Botan {
 
std::unique_ptr<Public_Key> ECKCDSA_PrivateKey::public_key() const
   {
   return std::make_unique<ECKCDSA_PublicKey>(domain(), public_point());
   }
 
bool ECKCDSA_PrivateKey::check_key(RandomNumberGenerator& rng,
                                   bool strong) const
   {
   if(!public_point().on_the_curve())
      {
      return false;
      }
 
   if(!strong)
      {
      return true;
      }
 
   return KeyPair::signature_consistency_check(rng, *this, "EMSA1(SHA-256)");
   }
 
namespace {
 
/**
* ECKCDSA signature operation
*/
class ECKCDSA_Signature_Operation final : public PK_Ops::Signature_with_EMSA
   {
   public:
 
      ECKCDSA_Signature_Operation(const ECKCDSA_PrivateKey& eckcdsa,
                                  const std::string& emsa) :
         PK_Ops::Signature_with_EMSA(emsa),
         m_group(eckcdsa.domain()),
         m_x(eckcdsa.private_value()),
         m_prefix()
         {
         const BigInt public_point_x = eckcdsa.public_point().get_affine_x();
         const BigInt public_point_y = eckcdsa.public_point().get_affine_y();
 
         const size_t order_bytes = m_group.get_order_bytes();
 
         m_prefix.resize(2*order_bytes);
         BigInt::encode_1363(&m_prefix[0], order_bytes, public_point_x);
         BigInt::encode_1363(&m_prefix[order_bytes], order_bytes, public_point_y);
 
         const size_t block_size = HashFunction::create(hash_for_signature())->hash_block_size();
         // Either truncate or zero-extend to match the hash block size
         m_prefix.resize(block_size);
         }
 
      secure_vector<uint8_t> raw_sign(const uint8_t msg[], size_t msg_len,
                                      RandomNumberGenerator& rng) override;
 
      size_t signature_length() const override { return 2*m_group.get_order_bytes(); }
      size_t max_input_bits() const override { return m_group.get_order_bits(); }
 
      bool has_prefix() override { return true; }
      secure_vector<uint8_t> message_prefix() const override { return m_prefix; }
 
   private:
      const EC_Group m_group;
      const BigInt& m_x;
      secure_vector<uint8_t> m_prefix;
      std::vector<BigInt> m_ws;
   };
 
secure_vector<uint8_t>
ECKCDSA_Signature_Operation::raw_sign(const uint8_t msg[], size_t /*msg_len*/,
                                      RandomNumberGenerator& rng)
   {
   const BigInt k = m_group.random_scalar(rng);
   const BigInt k_times_P_x = m_group.blinded_base_point_multiply_x(k, rng, m_ws);
 
   secure_vector<uint8_t> to_be_hashed(k_times_P_x.bytes());
   k_times_P_x.binary_encode(to_be_hashed.data());
 
   std::unique_ptr<EMSA> emsa = this->clone_emsa();
   emsa->update(to_be_hashed.data(), to_be_hashed.size());
   secure_vector<uint8_t> c = emsa->raw_data();
   c = emsa->encoding_of(c, max_input_bits(), rng);
 
   const BigInt r(c.data(), c.size());
 
   xor_buf(c, msg, c.size());
   BigInt w(c.data(), c.size());
   w = m_group.mod_order(w);
 
   const BigInt s = m_group.multiply_mod_order(m_x, k - w);
   if(s.is_zero())
      throw Internal_Error("During ECKCDSA signature generation created zero s");
 
   secure_vector<uint8_t> output = BigInt::encode_1363(r, c.size());
   output += BigInt::encode_1363(s, m_group.get_order_bytes());
   return output;
   }
 
/**
* ECKCDSA verification operation
*/
class ECKCDSA_Verification_Operation final : public PK_Ops::Verification_with_EMSA
   {
   public:
 
      ECKCDSA_Verification_Operation(const ECKCDSA_PublicKey& eckcdsa,
                                     const std::string& emsa) :
         PK_Ops::Verification_with_EMSA(emsa),
         m_group(eckcdsa.domain()),
         m_gy_mul(m_group.get_base_point(), eckcdsa.public_point()),
         m_prefix()
         {
         const BigInt public_point_x = eckcdsa.public_point().get_affine_x();
         const BigInt public_point_y = eckcdsa.public_point().get_affine_y();
 
         const size_t order_bytes = m_group.get_order_bytes();
 
         m_prefix.resize(2*order_bytes);
         BigInt::encode_1363(&m_prefix[0], order_bytes, public_point_x);
         BigInt::encode_1363(&m_prefix[order_bytes], order_bytes, public_point_y);
 
         const size_t block_size = HashFunction::create(hash_for_signature())->hash_block_size();
         // Either truncate or zero-extend to match the hash block size
         m_prefix.resize(block_size);
         }
 
      bool has_prefix() override { return true; }
      secure_vector<uint8_t> message_prefix() const override { return m_prefix; }
 
      size_t max_input_bits() const override { return m_group.get_order_bits(); }
 
      bool with_recovery() const override { return false; }
 
      bool verify(const uint8_t msg[], size_t msg_len,
                  const uint8_t sig[], size_t sig_len) override;
   private:
      const EC_Group m_group;
      const PointGFp_Multi_Point_Precompute m_gy_mul;
      secure_vector<uint8_t> m_prefix;
   };
 
bool ECKCDSA_Verification_Operation::verify(const uint8_t msg[], size_t /*msg_len*/,
                                            const uint8_t sig[], size_t sig_len)
   {
   const std::unique_ptr<HashFunction> hash = HashFunction::create(hash_for_signature());
   //calculate size of r
 
   const size_t order_bytes = m_group.get_order_bytes();
 
   const size_t size_r = std::min(hash -> output_length(), order_bytes);
   if(sig_len != size_r + order_bytes)
      {
      return false;
      }
 
   secure_vector<uint8_t> r(sig, sig + size_r);
 
   // check that 0 < s < q
   const BigInt s(sig + size_r, order_bytes);
 
   if(s <= 0 || s >= m_group.get_order())
      {
      return false;
      }
 
   secure_vector<uint8_t> r_xor_e(r);
   xor_buf(r_xor_e, msg, r.size());
   BigInt w(r_xor_e.data(), r_xor_e.size());
   w = m_group.mod_order(w);
 
   const PointGFp q = m_gy_mul.multi_exp(w, s);
   if(q.is_zero())
      {
      return false;
      }
 
   const BigInt q_x = q.get_affine_x();
   secure_vector<uint8_t> c(q_x.bytes());
   q_x.binary_encode(c.data());
   std::unique_ptr<EMSA> emsa = this->clone_emsa();
   emsa->update(c.data(), c.size());
   secure_vector<uint8_t> v = emsa->raw_data();
   Null_RNG rng;
   v = emsa->encoding_of(v, max_input_bits(), rng);
 
   return (v == r);
   }
 
}
 
std::unique_ptr<PK_Ops::Verification>
ECKCDSA_PublicKey::create_verification_op(const std::string& params,
                                          const std::string& provider) const
   {
   if(provider == "base" || provider.empty())
      return std::make_unique<ECKCDSA_Verification_Operation>(*this, params);
   throw Provider_Not_Found(algo_name(), provider);
   }
 
std::unique_ptr<PK_Ops::Signature>
ECKCDSA_PrivateKey::create_signature_op(RandomNumberGenerator& /*rng*/,
                                        const std::string& params,
                                        const std::string& provider) const
   {
   if(provider == "base" || provider.empty())
      return std::make_unique<ECKCDSA_Signature_Operation>(*this, params);
   throw Provider_Not_Found(algo_name(), provider);
   }
 
}