pubkey/ecgdsa/ecgdsa.cpp

/*
* ECGDSA (BSI-TR-03111, version 2.0)
* (C) 2016 René Korthaus
* (C) 2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/ecgdsa.h>
#include <botan/keypair.h>
#include <botan/reducer.h>
#include <botan/internal/pk_ops_impl.h>
#include <botan/internal/point_mul.h>

namespace Botan {

bool ECGDSA_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 {

/**
* ECGDSA signature operation
*/
class ECGDSA_Signature_Operation final : public PK_Ops::Signature_with_EMSA
   {
   public:

      ECGDSA_Signature_Operation(const ECGDSA_PrivateKey& ecgdsa,
                                const std::string& emsa) :
         PK_Ops::Signature_with_EMSA(emsa),
         m_group(ecgdsa.domain()),
         m_x(ecgdsa.private_value())
         {
         }

      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(); }

   private:
      const EC_Group m_group;
      const BigInt& m_x;
      std::vector<BigInt> m_ws;
   };

secure_vector<uint8_t>
ECGDSA_Signature_Operation::raw_sign(const uint8_t msg[], size_t msg_len,
                                     RandomNumberGenerator& rng)
   {
   const BigInt m(msg, msg_len, m_group.get_order_bits());

   const BigInt k = m_group.random_scalar(rng);

   const BigInt r = m_group.mod_order(
      m_group.blinded_base_point_multiply_x(k, rng, m_ws));

   const BigInt kr = m_group.multiply_mod_order(k, r);

   const BigInt s = m_group.multiply_mod_order(m_x, kr - m);

   // With overwhelming probability, a bug rather than actual zero r/s
   if(r.is_zero() || s.is_zero())
      throw Internal_Error("During ECGDSA signature generated zero r/s");

   return BigInt::encode_fixed_length_int_pair(r, s, m_group.get_order_bytes());
   }

/**
* ECGDSA verification operation
*/
class ECGDSA_Verification_Operation final : public PK_Ops::Verification_with_EMSA
   {
   public:

      ECGDSA_Verification_Operation(const ECGDSA_PublicKey& ecgdsa,
                                   const std::string& emsa) :
         PK_Ops::Verification_with_EMSA(emsa),
         m_group(ecgdsa.domain()),
         m_gy_mul(m_group.get_base_point(), ecgdsa.public_point())
         {
         }

      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;
   };

bool ECGDSA_Verification_Operation::verify(const uint8_t msg[], size_t msg_len,
                                           const uint8_t sig[], size_t sig_len)
   {
   if(sig_len != m_group.get_order_bytes() * 2)
      return false;

   const BigInt e(msg, msg_len, m_group.get_order_bits());

   const BigInt r(sig, sig_len / 2);
   const BigInt s(sig + sig_len / 2, sig_len / 2);

   if(r <= 0 || r >= m_group.get_order() || s <= 0 || s >= m_group.get_order())
      return false;

   const BigInt w = m_group.inverse_mod_order(r);

   const BigInt u1 = m_group.multiply_mod_order(e, w);
   const BigInt u2 = m_group.multiply_mod_order(s, w);
   const PointGFp R = m_gy_mul.multi_exp(u1, u2);

   if(R.is_zero())
      return false;

   const BigInt v = m_group.mod_order(R.get_affine_x());
   return (v == r);
   }

}

std::unique_ptr<PK_Ops::Verification>
ECGDSA_PublicKey::create_verification_op(const std::string& params,
                                         const std::string& provider) const
   {
   if(provider == "base" || provider.empty())
      return std::unique_ptr<PK_Ops::Verification>(new ECGDSA_Verification_Operation(*this, params));
   throw Provider_Not_Found(algo_name(), provider);
   }

std::unique_ptr<PK_Ops::Signature>
ECGDSA_PrivateKey::create_signature_op(RandomNumberGenerator& /*rng*/,
                                       const std::string& params,
                                       const std::string& provider) const
   {
   if(provider == "base" || provider.empty())
      return std::unique_ptr<PK_Ops::Signature>(new ECGDSA_Signature_Operation(*this, params));
   throw Provider_Not_Found(algo_name(), provider);
   }

}