/*

* 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/keypair.h>

#include <botan/reducer.h>

#include <botan/emsa.h>

#include <botan/hash.h>

#include <botan/rng.h>

namespace Botan {

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();

         m_prefix.resize(public_point_x.bytes() + public_point_y.bytes());

         public_point_x.binary_encode(m_prefix.data());

         public_point_y.binary_encode(&m_prefix[public_point_x.bytes()]);

         m_prefix.resize(HashFunction::create(hash_for_signature())->hash_block_size()); // use only the "hash input block size" leftmost bits

         }

      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,

                                     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();

         m_prefix.resize(public_point_x.bytes() + public_point_y.bytes());

         public_point_x.binary_encode(&m_prefix[0]);

         public_point_y.binary_encode(&m_prefix[public_point_x.bytes()]);

         m_prefix.resize(HashFunction::create(hash_for_signature())->hash_block_size()); // use only the "hash input block size" leftmost bits

         }

      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,

                                           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);

   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::unique_ptr<PK_Ops::Verification>(new 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::unique_ptr<PK_Ops::Signature>(new ECKCDSA_Signature_Operation(*this, params));

   throw Provider_Not_Found(algo_name(), provider);

   }

}