/*

* ECDSA implemenation

* (C) 2007 Manuel Hartl, FlexSecure GmbH

*     2007 Falko Strenzke, FlexSecure GmbH

*     2008-2010,2015,2016,2018 Jack Lloyd

*     2016 René Korthaus

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/ecdsa.h>

#include <botan/reducer.h>

#include <botan/internal/keypair.h>

#include <botan/internal/pk_ops_impl.h>

#include <botan/internal/point_mul.h>

#if defined(BOTAN_HAS_RFC6979_GENERATOR)

   #include <botan/internal/rfc6979.h>

#endif

namespace Botan {

namespace {

EC_Point recover_ecdsa_public_key(

   const EC_Group& group, const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s, uint8_t v) {

   if(group.get_cofactor() != 1) {

      throw Invalid_Argument("ECDSA public key recovery only supported for prime order groups");

   }

   if(v >= 4) {

      throw Invalid_Argument("Unexpected v param for ECDSA public key recovery");

   }

   const BigInt& group_order = group.get_order();

   if(r <= 0 || r >= group_order || s <= 0 || s >= group_order) {

      throw Invalid_Argument("Out of range r/s cannot recover ECDSA public key");

   }

   const uint8_t y_odd = v % 2;

   const uint8_t add_order = v >> 1;

   const size_t p_bytes = group.get_p_bytes();

   try {

      const BigInt e = BigInt::from_bytes_with_max_bits(msg.data(), msg.size(), group.get_order_bits());

      const BigInt r_inv = group.inverse_mod_order(r);

      BigInt x = r + add_order * group_order;

      std::vector<uint8_t> X(p_bytes + 1);

      X[0] = 0x02 | y_odd;

      x.serialize_to(std::span{X}.subspan(1));

      const EC_Point R = group.OS2ECP(X);

      if((R * group_order).is_zero() == false) {

         throw Decoding_Error("Unable to recover ECDSA public key");

      }

      // Compute r_inv * (s*R - eG)

      EC_Point_Multi_Point_Precompute RG_mul(R, group.get_base_point());

      const BigInt ne = group.mod_order(group_order - e);

      return r_inv * RG_mul.multi_exp(s, ne);

   } catch(...) {

      // continue on and throw

   }

   throw Decoding_Error("Failed to recover ECDSA public key from signature/msg pair");

}

}  // namespace

ECDSA_PublicKey::ECDSA_PublicKey(

   const EC_Group& group, const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s, uint8_t v) :

      EC_PublicKey(group, recover_ecdsa_public_key(group, msg, r, s, v)) {}

Unexecuted instantiation: Botan::ECDSA_PublicKey::ECDSA_PublicKey(Botan::EC_Group const&, std::__1::vector<unsigned char, std::__1::allocator<unsigned char> > const&, Botan::BigInt const&, Botan::BigInt const&, unsigned char)

Unexecuted instantiation: Botan::ECDSA_PublicKey::ECDSA_PublicKey(Botan::EC_Group const&, std::__1::vector<unsigned char, std::__1::allocator<unsigned char> > const&, Botan::BigInt const&, Botan::BigInt const&, unsigned char)

std::unique_ptr<Private_Key> ECDSA_PublicKey::generate_another(RandomNumberGenerator& rng) const {

   return std::make_unique<ECDSA_PrivateKey>(rng, domain());

}

uint8_t ECDSA_PublicKey::recovery_param(const std::vector<uint8_t>& msg, const BigInt& r, const BigInt& s) const {

   for(uint8_t v = 0; v != 4; ++v) {

      try {

         EC_Point R = recover_ecdsa_public_key(this->domain(), msg, r, s, v);

         if(R == this->public_point()) {

            return v;

         }

      } catch(Decoding_Error&) {

         // try the next v

      }

   }

   throw Internal_Error("Could not determine ECDSA recovery parameter");

}

std::unique_ptr<Public_Key> ECDSA_PrivateKey::public_key() const {

   return std::make_unique<ECDSA_PublicKey>(domain(), public_point());

}

bool ECDSA_PrivateKey::check_key(RandomNumberGenerator& rng, bool strong) const {

   if(!EC_PrivateKey::check_key(rng, strong)) {

      return false;

   }

   if(!strong) {

      return true;

   }

   return KeyPair::signature_consistency_check(rng, *this, "SHA-256");

}

namespace {

/**

* ECDSA signature operation

*/

class ECDSA_Signature_Operation final : public PK_Ops::Signature_with_Hash {

   public:

      ECDSA_Signature_Operation(const ECDSA_PrivateKey& ecdsa, std::string_view padding, RandomNumberGenerator& rng) :

            PK_Ops::Signature_with_Hash(padding), m_group(ecdsa.domain()), m_x(ecdsa.private_value()) {

#if defined(BOTAN_HAS_RFC6979_GENERATOR)

         m_rfc6979 = std::make_unique<RFC6979_Nonce_Generator>(this->rfc6979_hash_function(), m_group.get_order(), m_x);

#endif

         m_b = m_group.random_scalar(rng);

         m_b_inv = m_group.inverse_mod_order(m_b);

      }

      size_t signature_length() const override { return 2 * m_group.get_order_bytes(); }

      secure_vector<uint8_t> raw_sign(const uint8_t msg[], size_t msg_len, RandomNumberGenerator& rng) override;

      AlgorithmIdentifier algorithm_identifier() const override;

   private:

      const EC_Group m_group;

      const BigInt m_x;

#if defined(BOTAN_HAS_RFC6979_GENERATOR)

      std::unique_ptr<RFC6979_Nonce_Generator> m_rfc6979;

#endif

      std::vector<BigInt> m_ws;

      BigInt m_b, m_b_inv;

};

AlgorithmIdentifier ECDSA_Signature_Operation::algorithm_identifier() const {

   const std::string full_name = "ECDSA/" + hash_function();

   const OID oid = OID::from_string(full_name);

   return AlgorithmIdentifier(oid, AlgorithmIdentifier::USE_EMPTY_PARAM);

}

secure_vector<uint8_t> ECDSA_Signature_Operation::raw_sign(const uint8_t msg[],

                                                           size_t msg_len,

                                                           RandomNumberGenerator& rng) {

   BigInt m = m_group.mod_order(BigInt::from_bytes_with_max_bits(msg, msg_len, m_group.get_order_bits()));

#if defined(BOTAN_HAS_RFC6979_GENERATOR)

   const BigInt k = m_rfc6979->nonce_for(m);

#else

   const BigInt k = m_group.random_scalar(rng);

#endif

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

   const BigInt k_inv = m_group.inverse_mod_order(k);

   /*

   * Blind the input message and compute x*r+m as (x*r*b + m*b)/b

   */

   m_b = m_group.square_mod_order(m_b);

   m_b_inv = m_group.square_mod_order(m_b_inv);

   m = m_group.multiply_mod_order(m_b, m_group.mod_order(m));

   const BigInt xr_m = m_group.mod_order(m_group.multiply_mod_order(m_x, m_b, r) + m);

   const BigInt s = m_group.multiply_mod_order(k_inv, xr_m, m_b_inv);

   // With overwhelming probability, a bug rather than actual zero r/s

   if(r.is_zero() || s.is_zero()) {

      throw Internal_Error("During ECDSA signature generated zero r/s");

   }

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

}

/**

* ECDSA verification operation

*/

class ECDSA_Verification_Operation final : public PK_Ops::Verification_with_Hash {

   public:

      ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa, std::string_view padding) :

            PK_Ops::Verification_with_Hash(padding),

            m_group(ecdsa.domain()),

            m_gy_mul(m_group.get_base_point(), ecdsa.public_point()) {}

      ECDSA_Verification_Operation(const ECDSA_PublicKey& ecdsa, const AlgorithmIdentifier& alg_id) :

            PK_Ops::Verification_with_Hash(alg_id, "ECDSA", true),

            m_group(ecdsa.domain()),

            m_gy_mul(m_group.get_base_point(), ecdsa.public_point()) {}

      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 EC_Point_Multi_Point_Precompute m_gy_mul;

};

bool ECDSA_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 = BigInt::from_bytes_with_max_bits(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);

   // Cannot be negative here since we just decoded from binary

   if(r.is_zero() || s.is_zero()) {

      return false;

   }

   if(r >= m_group.get_order() || s >= m_group.get_order()) {

      return false;

   }

   const BigInt w = m_group.inverse_mod_order(s);

   const BigInt u1 = m_group.multiply_mod_order(m_group.mod_order(e), w);

   const BigInt u2 = m_group.multiply_mod_order(r, w);

   const EC_Point 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);

}

}  // namespace

std::unique_ptr<PK_Ops::Verification> ECDSA_PublicKey::create_verification_op(std::string_view params,

                                                                              std::string_view provider) const {

   if(provider == "base" || provider.empty()) {

      return std::make_unique<ECDSA_Verification_Operation>(*this, params);

   }

   throw Provider_Not_Found(algo_name(), provider);

}

std::unique_ptr<PK_Ops::Verification> ECDSA_PublicKey::create_x509_verification_op(

   const AlgorithmIdentifier& signature_algorithm, std::string_view provider) const {

   if(provider == "base" || provider.empty()) {

      return std::make_unique<ECDSA_Verification_Operation>(*this, signature_algorithm);

   }

   throw Provider_Not_Found(algo_name(), provider);

}

std::unique_ptr<PK_Ops::Signature> ECDSA_PrivateKey::create_signature_op(RandomNumberGenerator& rng,

                                                                         std::string_view params,

                                                                         std::string_view provider) const {

   if(provider == "base" || provider.empty()) {

      return std::make_unique<ECDSA_Signature_Operation>(*this, params, rng);

   }

   throw Provider_Not_Found(algo_name(), provider);

}

}  // namespace Botan