text: /*
  * 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::unique_ptr<Public_Key>(new 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();
  
           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);
     }
  
  }
  