text: /*
  * GOST 34.10-2001 implemenation
  * (C) 2007 Falko Strenzke, FlexSecure GmbH
  *          Manuel Hartl, FlexSecure GmbH
  * (C) 2008-2010,2015,2018 Jack Lloyd
  *
  * Botan is released under the Simplified BSD License (see license.txt)
  */
  
  #include <botan/gost_3410.h>
  #include <botan/internal/pk_ops_impl.h>
  #include <botan/internal/point_mul.h>
  #include <botan/reducer.h>
  #include <botan/der_enc.h>
  #include <botan/ber_dec.h>
  
  namespace Botan {
  
  std::vector<uint8_t> GOST_3410_PublicKey::public_key_bits() const
     {
     const BigInt x = public_point().get_affine_x();
     const BigInt y = public_point().get_affine_y();
  
     size_t part_size = std::max(x.bytes(), y.bytes());
  
     std::vector<uint8_t> bits(2*part_size);
  
     x.binary_encode(&bits[part_size - x.bytes()]);
     y.binary_encode(&bits[2*part_size - y.bytes()]);
  
     // Keys are stored in little endian format (WTF)
     for(size_t i = 0; i != part_size / 2; ++i)
        {
        std::swap(bits[i], bits[part_size-1-i]);
        std::swap(bits[part_size+i], bits[2*part_size-1-i]);
        }
  
     std::vector<uint8_t> output;
     DER_Encoder(output).encode(bits, OCTET_STRING);
     return output;
     }
  
  AlgorithmIdentifier GOST_3410_PublicKey::algorithm_identifier() const
     {
     std::vector<uint8_t> params;
  
     DER_Encoder(params)
        .start_cons(SEQUENCE)
           .encode(domain().get_curve_oid())
        .end_cons();
  
     return AlgorithmIdentifier(get_oid(), params);
     }
  
  GOST_3410_PublicKey::GOST_3410_PublicKey(const AlgorithmIdentifier& alg_id,
                                           const std::vector<uint8_t>& key_bits)
     {
     OID ecc_param_id;
  
     // The parameters also includes hash and cipher OIDs
     BER_Decoder(alg_id.get_parameters()).start_cons(SEQUENCE).decode(ecc_param_id);
  
     m_domain_params = EC_Group(ecc_param_id);
  
     secure_vector<uint8_t> bits;
     BER_Decoder(key_bits).decode(bits, OCTET_STRING);
  
     const size_t part_size = bits.size() / 2;
  
     // Keys are stored in little endian format (WTF)
     for(size_t i = 0; i != part_size / 2; ++i)
        {
        std::swap(bits[i], bits[part_size-1-i]);
        std::swap(bits[part_size+i], bits[2*part_size-1-i]);
        }
  
     BigInt x(bits.data(), part_size);
     BigInt y(&bits[part_size], part_size);
  
     m_public_key = domain().point(x, y);
  
     BOTAN_ASSERT(m_public_key.on_the_curve(),
                  "Loaded GOST 34.10 public key is on the curve");
     }
  
  namespace {
  
  BigInt decode_le(const uint8_t msg[], size_t msg_len)
     {
     secure_vector<uint8_t> msg_le(msg, msg + msg_len);
  
     for(size_t i = 0; i != msg_le.size() / 2; ++i)
        std::swap(msg_le[i], msg_le[msg_le.size()-1-i]);
  
     return BigInt(msg_le.data(), msg_le.size());
     }
  
  /**
  * GOST-34.10 signature operation
  */
  class GOST_3410_Signature_Operation final : public PK_Ops::Signature_with_EMSA
     {
     public:
        GOST_3410_Signature_Operation(const GOST_3410_PrivateKey& gost_3410,
                                      const std::string& emsa) :
           PK_Ops::Signature_with_EMSA(emsa),
           m_group(gost_3410.domain()),
           m_x(gost_3410.private_value())
           {}
  
        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(); }
  
        secure_vector<uint8_t> raw_sign(const uint8_t msg[], size_t msg_len,
                                        RandomNumberGenerator& rng) override;
  
     private:
        const EC_Group m_group;
        const BigInt& m_x;
        std::vector<BigInt> m_ws;
     };
  
  secure_vector<uint8_t>
  GOST_3410_Signature_Operation::raw_sign(const uint8_t msg[], size_t msg_len,
                                          RandomNumberGenerator& rng)
     {
     const BigInt k = m_group.random_scalar(rng);
  
     BigInt e = decode_le(msg, msg_len);
  
     e = m_group.mod_order(e);
     if(e == 0)
        e = 1;
  
     const BigInt r = m_group.mod_order(
        m_group.blinded_base_point_multiply_x(k, rng, m_ws));
  
     const BigInt s = m_group.mod_order(
        m_group.multiply_mod_order(r, m_x) +
        m_group.multiply_mod_order(k, e));
  
     if(r == 0 || s == 0)
        throw Internal_Error("GOST 34.10 signature generation failed, r/s equal to zero");
  
     return BigInt::encode_fixed_length_int_pair(s, r, m_group.get_order_bytes());
     }
  
  /**
  * GOST-34.10 verification operation
  */
  class GOST_3410_Verification_Operation final : public PK_Ops::Verification_with_EMSA
     {
     public:
  
        GOST_3410_Verification_Operation(const GOST_3410_PublicKey& gost,
                                         const std::string& emsa) :
           PK_Ops::Verification_with_EMSA(emsa),
           m_group(gost.domain()),
           m_gy_mul(m_group.get_base_point(), gost.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 GOST_3410_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 s(sig, sig_len / 2);
     const BigInt r(sig + sig_len / 2, sig_len / 2);
  
     const BigInt& order = m_group.get_order();
  
     if(r <= 0 || r >= order || s <= 0 || s >= order)
        return false;
  
     BigInt e = decode_le(msg, msg_len);
     e = m_group.mod_order(e);
     if(e == 0)
        e = 1;
  
     const BigInt v = m_group.inverse_mod_order(e);
  
     const BigInt z1 = m_group.multiply_mod_order(s, v);
     const BigInt z2 = m_group.multiply_mod_order(-r, v);
  
     const PointGFp R = m_gy_mul.multi_exp(z1, z2);
  
     if(R.is_zero())
       return false;
  
     return (R.get_affine_x() == r);
     }
  
  }
  
  std::unique_ptr<PK_Ops::Verification>
  GOST_3410_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 GOST_3410_Verification_Operation(*this, params));
     throw Provider_Not_Found(algo_name(), provider);
     }
  
  std::unique_ptr<PK_Ops::Signature>
  GOST_3410_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 GOST_3410_Signature_Operation(*this, params));
     throw Provider_Not_Found(algo_name(), provider);
     }
  
  }
  