text: // Copyright (c) 2017, The Monero Project
  // 
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  // permitted provided that the following conditions are met:
  // 
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  //    conditions and the following disclaimer.
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  // 2. Redistributions in binary form must reproduce the above copyright notice, this list
  //    of conditions and the following disclaimer in the documentation and/or other
  //    materials provided with the distribution.
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  //    used to endorse or promote products derived from this software without specific
  //    prior written permission.
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  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
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  // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #include <unordered_set>
  #include "include_base_utils.h"
  #include "crypto/crypto.h"
  #include "ringct/rctOps.h"
  #include "cryptonote_basic/account.h"
  #include "cryptonote_basic/cryptonote_format_utils.h"
  #include "multisig.h"
  
  #undef EARTH_DEFAULT_LOG_CATEGORY
  #define EARTH_DEFAULT_LOG_CATEGORY "multisig"
  
  using namespace std;
  
  static const rct::key multisig_salt = { {'M', 'u', 'l', 't' , 'i', 's', 'i', 'g', 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } };
  
  namespace cryptonote
  {
    //-----------------------------------------------------------------
    crypto::secret_key get_multisig_blinded_secret_key(const crypto::secret_key &key)
    {
      rct::keyV data;
      data.push_back(rct::sk2rct(key));
      data.push_back(multisig_salt);
      return rct::rct2sk(rct::hash_to_scalar(data));
    }
    //-----------------------------------------------------------------
    void generate_multisig_N_N(const account_keys &keys, const std::vector<crypto::public_key> &spend_keys, std::vector<crypto::secret_key> &multisig_keys, rct::key &spend_skey, rct::key &spend_pkey)
    {
      // the multisig spend public key is the sum of all spend public keys
      multisig_keys.clear();
      const crypto::secret_key spend_secret_key = get_multisig_blinded_secret_key(keys.m_spend_secret_key);
      CHECK_AND_ASSERT_THROW_MES(crypto::secret_key_to_public_key(spend_secret_key, (crypto::public_key&)spend_pkey), "Failed to derive public key");
      for (const auto &k: spend_keys)
        rct::addKeys(spend_pkey, spend_pkey, rct::pk2rct(k));
      multisig_keys.push_back(spend_secret_key);
      spend_skey = rct::sk2rct(spend_secret_key);
    }
    //-----------------------------------------------------------------
    void generate_multisig_N1_N(const account_keys &keys, const std::vector<crypto::public_key> &spend_keys, std::vector<crypto::secret_key> &multisig_keys, rct::key &spend_skey, rct::key &spend_pkey)
    {
      multisig_keys.clear();
      spend_pkey = rct::identity();
      spend_skey = rct::zero();
  
      // create all our composite private keys
      crypto::secret_key blinded_skey = get_multisig_blinded_secret_key(keys.m_spend_secret_key);
      for (const auto &k: spend_keys)
      {
        rct::key sk = rct::scalarmultKey(rct::pk2rct(k), rct::sk2rct(blinded_skey));
        crypto::secret_key msk = get_multisig_blinded_secret_key(rct::rct2sk(sk));
        multisig_keys.push_back(msk);
        sc_add(spend_skey.bytes, spend_skey.bytes, (const unsigned char*)msk.data);
      }
    }
    //-----------------------------------------------------------------
    crypto::secret_key generate_multisig_view_secret_key(const crypto::secret_key &skey, const std::vector<crypto::secret_key> &skeys)
    {
      rct::key view_skey = rct::sk2rct(get_multisig_blinded_secret_key(skey));
      for (const auto &k: skeys)
        sc_add(view_skey.bytes, view_skey.bytes, rct::sk2rct(k).bytes);
      return rct::rct2sk(view_skey);
    }
    //-----------------------------------------------------------------
    crypto::public_key generate_multisig_N1_N_spend_public_key(const std::vector<crypto::public_key> &pkeys)
    {
      rct::key spend_public_key = rct::identity();
      for (const auto &pk: pkeys)
      {
        rct::addKeys(spend_public_key, spend_public_key, rct::pk2rct(pk));
      }
      return rct::rct2pk(spend_public_key);
    }
    //-----------------------------------------------------------------
    bool generate_multisig_key_image(const account_keys &keys, size_t multisig_key_index, const crypto::public_key& out_key, crypto::key_image& ki)
    {
      if (multisig_key_index >= keys.m_multisig_keys.size())
        return false;
      crypto::generate_key_image(out_key, keys.m_multisig_keys[multisig_key_index], ki);
      return true;
    }
    //-----------------------------------------------------------------
    void generate_multisig_LR(const crypto::public_key pkey, const crypto::secret_key &k, crypto::public_key &L, crypto::public_key &R)
    {
      rct::scalarmultBase((rct::key&)L, rct::sk2rct(k));
      crypto::generate_key_image(pkey, k, (crypto::key_image&)R);
    }
    //-----------------------------------------------------------------
    bool generate_multisig_composite_key_image(const account_keys &keys, const std::unordered_map<crypto::public_key, subaddress_index>& subaddresses, const crypto::public_key& out_key, const crypto::public_key &tx_public_key, const std::vector<crypto::public_key>& additional_tx_public_keys, size_t real_output_index, const std::vector<crypto::key_image> &pkis, crypto::key_image &ki)
    {
      cryptonote::keypair in_ephemeral;
      if (!cryptonote::generate_key_image_helper(keys, subaddresses, out_key, tx_public_key, additional_tx_public_keys, real_output_index, in_ephemeral, ki))
        return false;
      std::unordered_set<crypto::key_image> used;
      for (size_t m = 0; m < keys.m_multisig_keys.size(); ++m)
      {
        crypto::key_image pki;
        bool r = cryptonote::generate_multisig_key_image(keys, m, out_key, pki);
        if (!r)
          return false;
        used.insert(pki);
      }
      for (const auto &pki: pkis)
      {
        if (used.find(pki) == used.end())
        {
          used.insert(pki);
          rct::addKeys((rct::key&)ki, rct::ki2rct(ki), rct::ki2rct(pki));
        }
      }
      return true;
    }
    //-----------------------------------------------------------------
  }
  