text: // Copyright (c) 2014 The ShadowCoin developers
  // Copyright (c) 2014-2015 The OKCash developers
  // Copyright (c) 2015 The Tellurion developers
  // Distributed under the MIT/X11 software license, see the accompanying
  // file license.txt or http://www.opensource.org/licenses/mit-license.php.
  
  #include "stealth.h"
  #include "base58.h"
  
  
  #include <openssl/rand.h>
  #include <openssl/ec.h>
  #include <openssl/ecdsa.h>
  #include <openssl/obj_mac.h>
  
  //const uint8_t stealth_version_byte = 0x2a;
  const uint8_t stealth_version_byte = 0x28;
  
  
  bool CStealthAddress::SetEncoded(const std::string& encodedAddress)
  {
      data_chunk raw;
      
      if (!DecodeBase58(encodedAddress, raw))
      {
          if (fDebug)
              printf("CStealthAddress::SetEncoded DecodeBase58 falied.\n");
          return false;
      };
      
      if (!VerifyChecksum(raw))
      {
          if (fDebug)
              printf("CStealthAddress::SetEncoded verify_checksum falied.\n");
          return false;
      };
      
      if (raw.size() < 1 + 1 + 33 + 1 + 33 + 1 + 1 + 4)
      {
          if (fDebug)
              printf("CStealthAddress::SetEncoded() too few bytes provided.\n");
          return false;
      };
      
      
      uint8_t* p = &raw[0];
      uint8_t version = *p++;
      
      if (version != stealth_version_byte)
      {
          printf("CStealthAddress::SetEncoded version mismatch 0x%x != 0x%x.\n", version, stealth_version_byte);
          return false;
      };
      
      options = *p++;
      
      scan_pubkey.resize(33);
      memcpy(&scan_pubkey[0], p, 33);
      p += 33;
      //uint8_t spend_pubkeys = *p++;
      p++;
      
      spend_pubkey.resize(33);
      memcpy(&spend_pubkey[0], p, 33);
      
      return true;
  };
  
  std::string CStealthAddress::Encoded() const
  {
      // https://wiki.unsystem.net/index.php/DarkWallet/Stealth#Address_format
      // [version] [options] [scan_key] [N] ... [Nsigs] [prefix_length] ...
      
      data_chunk raw;
      raw.push_back(stealth_version_byte);
      
      raw.push_back(options);
      
      raw.insert(raw.end(), scan_pubkey.begin(), scan_pubkey.end());
      raw.push_back(1); // number of spend pubkeys
      raw.insert(raw.end(), spend_pubkey.begin(), spend_pubkey.end());
      raw.push_back(0); // number of signatures
      raw.push_back(0); // ?
      
      AppendChecksum(raw);
      
      return EncodeBase58(raw);
  };
  
  
  uint32_t BitcoinChecksum(uint8_t* p, uint32_t nBytes)
  {
      if (!p || nBytes == 0)
          return 0;
      
      uint8_t hash1[32];
      SHA256(p, nBytes, (uint8_t*)hash1);
      uint8_t hash2[32];
      SHA256((uint8_t*)hash1, sizeof(hash1), (uint8_t*)hash2);
      
      // -- checksum is the 1st 4 bytes of the hash
      uint32_t checksum = from_little_endian<uint32_t>(&hash2[0]);
      
      return checksum;
  };
  
  void AppendChecksum(data_chunk& data)
  {
      uint32_t checksum = BitcoinChecksum(&data[0], data.size());
      
      // -- to_little_endian
      std::vector<uint8_t> tmp(4);
      
      //memcpy(&tmp[0], &checksum, 4);
      for (int i = 0; i < 4; ++i)
      {
          tmp[i] = checksum & 0xFF;
          checksum >>= 8;
      };
      
      data.insert(data.end(), tmp.begin(), tmp.end());
  };
  
  bool VerifyChecksum(const data_chunk& data)
  {
      if (data.size() < 4)
          return false;
      
      uint32_t checksum = from_little_endian<uint32_t>(data.end() - 4);
      
      return BitcoinChecksum((uint8_t*)&data[0], data.size()-4) == checksum;
  };
  
  
  int GenerateRandomSecret(ec_secret& out)
  {
      RandAddSeedPerfmon();
      
      static uint256 max("FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364140");
      static uint256 min(16000); // increase? min valid key is 1
      
      uint256 test;
      
      int i;
      // -- check max, try max 32 times
      for (i = 0; i < 32; ++i)
      {
          RAND_bytes((unsigned char*) test.begin(), 32);
          if (test > min && test < max)
          {
              memcpy(&out.e[0], test.begin(), 32);
              break;
          };
      };
      
      if (i > 31)
      {
          printf("Error: GenerateRandomSecret failed to generate a valid key.\n");
          return 1;
      };
      
      return 0;
  };
  
  int SecretToPublicKey(const ec_secret& secret, ec_point& out)
  {
      // -- public key = private * G
      int rv = 0;
      
      EC_GROUP *ecgrp = EC_GROUP_new_by_curve_name(NID_secp256k1);
      
      if (!ecgrp)
      {
          printf("SecretToPublicKey(): EC_GROUP_new_by_curve_name failed.\n");
          return 1;
      };
  
      BIGNUM* bnIn = BN_bin2bn(&secret.e[0], ec_secret_size, BN_new());
      if (!bnIn)
      {
          EC_GROUP_free(ecgrp);
          printf("SecretToPublicKey(): BN_bin2bn failed\n");
          return 1;
      };
      
      EC_POINT* pub = EC_POINT_new(ecgrp);
      
      
      EC_POINT_mul(ecgrp, pub, bnIn, NULL, NULL, NULL);
      
      BIGNUM* bnOut = EC_POINT_point2bn(ecgrp, pub, POINT_CONVERSION_COMPRESSED, BN_new(), NULL);
      if (!bnOut)
      {
          printf("SecretToPublicKey(): point2bn failed\n");
          rv = 1;
      } else
      {
          out.resize(ec_compressed_size);
          if (BN_num_bytes(bnOut) != (int) ec_compressed_size
              || BN_bn2bin(bnOut, &out[0]) != (int) ec_compressed_size)
          {
              printf("SecretToPublicKey(): bnOut incorrect length.\n");
              rv = 1;
          };
          
          BN_free(bnOut);
      };
      
      EC_GROUP_free(ecgrp);
      BN_free(bnIn);
      EC_POINT_free(pub);
  
      return rv;
  };
  
  
  int StealthSecret(ec_secret& secret, ec_point& pubkey, const ec_point& pkSpend, ec_secret& sharedSOut, ec_point& pkOut)
  {
      /*
      
      send:
          secret = ephem_secret, pubkey = scan_pubkey
      
      receive:
          secret = scan_secret, pubkey = ephem_pubkey
          c = H(dP)
      
      Q = public scan key (EC point, 33 bytes)
      d = private scan key (integer, 32 bytes)
      R = public spend key
      f = private spend key
  
      Q = dG
      R = fG
      
      Sender (has Q and R, not d or f):
      
      P = eG
  
      c = H(eQ) = H(dP)
      R' = R + cG
      
      
      Recipient gets R' and P
      
      test 0 and infinity?
      */
      
      int rv = 0;
      std::vector<uint8_t> vchOutQ;
      
      BN_CTX* bnCtx   = NULL;
      BIGNUM* bnEphem = NULL;
      BIGNUM* bnQ     = NULL;
      EC_POINT* Q     = NULL;
      BIGNUM* bnOutQ  = NULL;
      BIGNUM* bnc     = NULL;
      EC_POINT* C     = NULL;
      BIGNUM* bnR     = NULL;
      EC_POINT* R     = NULL;
      EC_POINT* Rout  = NULL;
      BIGNUM* bnOutR  = NULL;
      
      EC_GROUP* ecgrp = EC_GROUP_new_by_curve_name(NID_secp256k1);
      
      if (!ecgrp)
      {
          printf("StealthSecret(): EC_GROUP_new_by_curve_name failed.\n");
          return 1;
      };
      
      if (!(bnCtx = BN_CTX_new()))
      {
          printf("StealthSecret(): BN_CTX_new failed.\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnEphem = BN_bin2bn(&secret.e[0], ec_secret_size, BN_new())))
      {
          printf("StealthSecret(): bnEphem BN_bin2bn failed.\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnQ = BN_bin2bn(&pubkey[0], pubkey.size(), BN_new())))
      {
          printf("StealthSecret(): bnQ BN_bin2bn failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(Q = EC_POINT_bn2point(ecgrp, bnQ, NULL, bnCtx)))
      {
          printf("StealthSecret(): Q EC_POINT_bn2point failed\n");
          rv = 1;
          goto End;
      };
      
      // -- eQ
      // EC_POINT_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *n, const EC_POINT *q, const BIGNUM *m, BN_CTX *ctx);
      // EC_POINT_mul calculates the value generator * n + q * m and stores the result in r. The value n may be NULL in which case the result is just q * m. 
      if (!EC_POINT_mul(ecgrp, Q, NULL, Q, bnEphem, bnCtx))
      {
          printf("StealthSecret(): eQ EC_POINT_mul failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnOutQ = EC_POINT_point2bn(ecgrp, Q, POINT_CONVERSION_COMPRESSED, BN_new(), bnCtx)))
      {
          printf("StealthSecret(): Q EC_POINT_bn2point failed\n");
          rv = 1;
          goto End;
      };
      
      
      vchOutQ.resize(ec_compressed_size);
      if (BN_num_bytes(bnOutQ) != (int) ec_compressed_size
          || BN_bn2bin(bnOutQ, &vchOutQ[0]) != (int) ec_compressed_size)
      {
          printf("StealthSecret(): bnOutQ incorrect length.\n");
          rv = 1;
          goto End;
      };
      
      SHA256(&vchOutQ[0], vchOutQ.size(), &sharedSOut.e[0]);
      
      if (!(bnc = BN_bin2bn(&sharedSOut.e[0], ec_secret_size, BN_new())))
      {
          printf("StealthSecret(): BN_bin2bn failed\n");
          rv = 1;
          goto End;
      };
      
      // -- cG
      if (!(C = EC_POINT_new(ecgrp)))
      {
          printf("StealthSecret(): C EC_POINT_new failed\n");
          rv = 1;
          goto End;
      };
      
      if (!EC_POINT_mul(ecgrp, C, bnc, NULL, NULL, bnCtx))
      {
          printf("StealthSecret(): C EC_POINT_mul failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnR = BN_bin2bn(&pkSpend[0], pkSpend.size(), BN_new())))
      {
          printf("StealthSecret(): bnR BN_bin2bn failed\n");
          rv = 1;
          goto End;
      };
      
      
      if (!(R = EC_POINT_bn2point(ecgrp, bnR, NULL, bnCtx)))
      {
          printf("StealthSecret(): R EC_POINT_bn2point failed\n");
          rv = 1;
          goto End;
      };
      
      if (!EC_POINT_mul(ecgrp, C, bnc, NULL, NULL, bnCtx))
      {
          printf("StealthSecret(): C EC_POINT_mul failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(Rout = EC_POINT_new(ecgrp)))
      {
          printf("StealthSecret(): Rout EC_POINT_new failed\n");
          rv = 1;
          goto End;
      };
      
      if (!EC_POINT_add(ecgrp, Rout, R, C, bnCtx))
      {
          printf("StealthSecret(): Rout EC_POINT_add failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnOutR = EC_POINT_point2bn(ecgrp, Rout, POINT_CONVERSION_COMPRESSED, BN_new(), bnCtx)))
      {
          printf("StealthSecret(): Rout EC_POINT_bn2point failed\n");
          rv = 1;
          goto End;
      };
      
      
      pkOut.resize(ec_compressed_size);
      if (BN_num_bytes(bnOutR) != (int) ec_compressed_size
          || BN_bn2bin(bnOutR, &pkOut[0]) != (int) ec_compressed_size)
      {
          printf("StealthSecret(): pkOut incorrect length.\n");
          rv = 1;
          goto End;
      };
      
      End:
      if (bnOutR)     BN_free(bnOutR);
      if (Rout)       EC_POINT_free(Rout);
      if (R)          EC_POINT_free(R);
      if (bnR)        BN_free(bnR);
      if (C)          EC_POINT_free(C);
      if (bnc)        BN_free(bnc);
      if (bnOutQ)     BN_free(bnOutQ);
      if (Q)          EC_POINT_free(Q);
      if (bnQ)        BN_free(bnQ);
      if (bnEphem)    BN_free(bnEphem);
      if (bnCtx)      BN_CTX_free(bnCtx);
      EC_GROUP_free(ecgrp);
      
      return rv;
  };
  
  
  int StealthSecretSpend(ec_secret& scanSecret, ec_point& ephemPubkey, ec_secret& spendSecret, ec_secret& secretOut)
  {
      /*
      
      c  = H(dP)
      R' = R + cG     [without decrypting wallet]
         = (f + c)G   [after decryption of wallet]
           Remember: mod curve.order, pad with 0x00s where necessary?
      */
      
      int rv = 0;
      std::vector<uint8_t> vchOutP;
      
      BN_CTX* bnCtx           = NULL;
      BIGNUM* bnScanSecret    = NULL;
      BIGNUM* bnP             = NULL;
      EC_POINT* P             = NULL;
      BIGNUM* bnOutP          = NULL;
      BIGNUM* bnc             = NULL;
      BIGNUM* bnOrder         = NULL;
      BIGNUM* bnSpend         = NULL;
      
      EC_GROUP* ecgrp = EC_GROUP_new_by_curve_name(NID_secp256k1);
      
      if (!ecgrp)
      {
          printf("StealthSecretSpend(): EC_GROUP_new_by_curve_name failed.\n");
          return 1;
      };
      
      if (!(bnCtx = BN_CTX_new()))
      {
          printf("StealthSecretSpend(): BN_CTX_new failed.\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnScanSecret = BN_bin2bn(&scanSecret.e[0], ec_secret_size, BN_new())))
      {
          printf("StealthSecretSpend(): bnScanSecret BN_bin2bn failed.\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnP = BN_bin2bn(&ephemPubkey[0], ephemPubkey.size(), BN_new())))
      {
          printf("StealthSecretSpend(): bnP BN_bin2bn failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(P = EC_POINT_bn2point(ecgrp, bnP, NULL, bnCtx)))
      {
          printf("StealthSecretSpend(): P EC_POINT_bn2point failed\n");
          rv = 1;
          goto End;
      };
      
      // -- dP
      if (!EC_POINT_mul(ecgrp, P, NULL, P, bnScanSecret, bnCtx))
      {
          printf("StealthSecretSpend(): dP EC_POINT_mul failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnOutP = EC_POINT_point2bn(ecgrp, P, POINT_CONVERSION_COMPRESSED, BN_new(), bnCtx)))
      {
          printf("StealthSecretSpend(): P EC_POINT_bn2point failed\n");
          rv = 1;
          goto End;
      };
      
      
      vchOutP.resize(ec_compressed_size);
      if (BN_num_bytes(bnOutP) != (int) ec_compressed_size
          || BN_bn2bin(bnOutP, &vchOutP[0]) != (int) ec_compressed_size)
      {
          printf("StealthSecretSpend(): bnOutP incorrect length.\n");
          rv = 1;
          goto End;
      };
      
      uint8_t hash1[32];
      SHA256(&vchOutP[0], vchOutP.size(), (uint8_t*)hash1);
      
      
      if (!(bnc = BN_bin2bn(&hash1[0], 32, BN_new())))
      {
          printf("StealthSecretSpend(): BN_bin2bn failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnOrder = BN_new())
          || !EC_GROUP_get_order(ecgrp, bnOrder, bnCtx))
      {
          printf("StealthSecretSpend(): EC_GROUP_get_order failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnSpend = BN_bin2bn(&spendSecret.e[0], ec_secret_size, BN_new())))
      {
          printf("StealthSecretSpend(): bnSpend BN_bin2bn failed.\n");
          rv = 1;
          goto End;
      };
      
      //if (!BN_add(r, a, b)) return 0;
      //return BN_nnmod(r, r, m, ctx);
      if (!BN_mod_add(bnSpend, bnSpend, bnc, bnOrder, bnCtx))
      {
          printf("StealthSecretSpend(): bnSpend BN_mod_add failed.\n");
          rv = 1;
          goto End;
      };
      
      if (BN_is_zero(bnSpend)) // possible?
      {
          printf("StealthSecretSpend(): bnSpend is zero.\n");
          rv = 1;
          goto End;
      };
      
      if (BN_num_bytes(bnSpend) != (int) ec_secret_size
          || BN_bn2bin(bnSpend, &secretOut.e[0]) != (int) ec_secret_size)
      {
          printf("StealthSecretSpend(): bnSpend incorrect length.\n");
          rv = 1;
          goto End;
      };
      
      End:
      if (bnSpend)        BN_free(bnSpend);
      if (bnOrder)        BN_free(bnOrder);
      if (bnc)            BN_free(bnc);
      if (bnOutP)         BN_free(bnOutP);
      if (P)              EC_POINT_free(P);
      if (bnP)            BN_free(bnP);
      if (bnScanSecret)   BN_free(bnScanSecret);
      if (bnCtx)          BN_CTX_free(bnCtx);
      EC_GROUP_free(ecgrp);
      
      return rv;
  };
  
  
  int StealthSharedToSecretSpend(ec_secret& sharedS, ec_secret& spendSecret, ec_secret& secretOut)
  {
      
      int rv = 0;
      std::vector<uint8_t> vchOutP;
      
      BN_CTX* bnCtx           = NULL;
      BIGNUM* bnc             = NULL;
      BIGNUM* bnOrder         = NULL;
      BIGNUM* bnSpend         = NULL;
      
      EC_GROUP* ecgrp = EC_GROUP_new_by_curve_name(NID_secp256k1);
      
      if (!ecgrp)
      {
          printf("StealthSecretSpend(): EC_GROUP_new_by_curve_name failed.\n");
          return 1;
      };
      
      if (!(bnCtx = BN_CTX_new()))
      {
          printf("StealthSecretSpend(): BN_CTX_new failed.\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnc = BN_bin2bn(&sharedS.e[0], ec_secret_size, BN_new())))
      {
          printf("StealthSecretSpend(): BN_bin2bn failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnOrder = BN_new())
          || !EC_GROUP_get_order(ecgrp, bnOrder, bnCtx))
      {
          printf("StealthSecretSpend(): EC_GROUP_get_order failed\n");
          rv = 1;
          goto End;
      };
      
      if (!(bnSpend = BN_bin2bn(&spendSecret.e[0], ec_secret_size, BN_new())))
      {
          printf("StealthSecretSpend(): bnSpend BN_bin2bn failed.\n");
          rv = 1;
          goto End;
      };
      
      //if (!BN_add(r, a, b)) return 0;
      //return BN_nnmod(r, r, m, ctx);
      if (!BN_mod_add(bnSpend, bnSpend, bnc, bnOrder, bnCtx))
      {
          printf("StealthSecretSpend(): bnSpend BN_mod_add failed.\n");
          rv = 1;
          goto End;
      };
      
      if (BN_is_zero(bnSpend)) // possible?
      {
          printf("StealthSecretSpend(): bnSpend is zero.\n");
          rv = 1;
          goto End;
      };
      
      if (BN_num_bytes(bnSpend) != (int) ec_secret_size
          || BN_bn2bin(bnSpend, &secretOut.e[0]) != (int) ec_secret_size)
      {
          printf("StealthSecretSpend(): bnSpend incorrect length.\n");
          rv = 1;
          goto End;
      };
      
      End:
      if (bnSpend)        BN_free(bnSpend);
      if (bnOrder)        BN_free(bnOrder);
      if (bnc)            BN_free(bnc);
      if (bnCtx)          BN_CTX_free(bnCtx);
      EC_GROUP_free(ecgrp);
      
      return rv;
  };
  
  bool IsStealthAddress(const std::string& encodedAddress)
  {
      data_chunk raw;
      
      if (!DecodeBase58(encodedAddress, raw))
      {
          //printf("IsStealthAddress DecodeBase58 falied.\n");
          return false;
      };
      
      if (!VerifyChecksum(raw))
      {
          //printf("IsStealthAddress verify_checksum falied.\n");
          return false;
      };
      
      if (raw.size() < 1 + 1 + 33 + 1 + 33 + 1 + 1 + 4)
      {
          //printf("IsStealthAddress too few bytes provided.\n");
          return false;
      };
      
      
      uint8_t* p = &raw[0];
      uint8_t version = *p++;
      
      if (version != stealth_version_byte)
      {
          //printf("IsStealthAddress version mismatch 0x%x != 0x%x.\n", version, stealth_version_byte);
          return false;
      };
      
      return true;
  };
  