text: // Copyright (c) 2009-2016 The Bitcoin Core developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #include "key.h"
  
  #include "arith_uint256.h"
  #include "crypto/common.h"
  #include "crypto/hmac_sha512.h"
  #include "pubkey.h"
  #include "random.h"
  
  #include <secp256k1.h>
  #include <secp256k1_recovery.h>
  
  static secp256k1_context* secp256k1_context_sign = nullptr;
  
  /** These functions are taken from the libsecp256k1 distribution and are very ugly. */
  static int ec_privkey_import_der(const secp256k1_context* ctx, unsigned char* out32, const unsigned char* privkey, size_t privkeylen)
  {
      const unsigned char* end = privkey + privkeylen;
      int lenb = 0;
      int len = 0;
      memset(out32, 0, 32);
      /* sequence header */
      if (end < privkey + 1 || *privkey != 0x30) {
          return 0;
      }
      privkey++;
      /* sequence length constructor */
      if (end < privkey + 1 || !(*privkey & 0x80)) {
          return 0;
      }
      lenb = *privkey & ~0x80;
      privkey++;
      if (lenb < 1 || lenb > 2) {
          return 0;
      }
      if (end < privkey + lenb) {
          return 0;
      }
      /* sequence length */
      len = privkey[lenb - 1] | (lenb > 1 ? privkey[lenb - 2] << 8 : 0);
      privkey += lenb;
      if (end < privkey + len) {
          return 0;
      }
      /* sequence element 0: version number (=1) */
      if (end < privkey + 3 || privkey[0] != 0x02 || privkey[1] != 0x01 || privkey[2] != 0x01) {
          return 0;
      }
      privkey += 3;
      /* sequence element 1: octet string, up to 32 bytes */
      if (end < privkey + 2 || privkey[0] != 0x04 || privkey[1] > 0x20 || end < privkey + 2 + privkey[1]) {
          return 0;
      }
      memcpy(out32 + 32 - privkey[1], privkey + 2, privkey[1]);
      if (!secp256k1_ec_seckey_verify(ctx, out32)) {
          memset(out32, 0, 32);
          return 0;
      }
      return 1;
  }
  
  static int ec_privkey_export_der(const secp256k1_context* ctx, unsigned char* privkey, size_t* privkeylen, const unsigned char* key32, int compressed)
  {
      secp256k1_pubkey pubkey;
      size_t pubkeylen = 0;
      if (!secp256k1_ec_pubkey_create(ctx, &pubkey, key32)) {
          *privkeylen = 0;
          return 0;
      }
      if (compressed) {
          static const unsigned char begin[] = {
              0x30, 0x81, 0xD3, 0x02, 0x01, 0x01, 0x04, 0x20};
          static const unsigned char middle[] = {
              0xA0, 0x81, 0x85, 0x30, 0x81, 0x82, 0x02, 0x01, 0x01, 0x30, 0x2C, 0x06, 0x07, 0x2A, 0x86, 0x48,
              0xCE, 0x3D, 0x01, 0x01, 0x02, 0x21, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
              0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
              0xFF, 0xFF, 0xFE, 0xFF, 0xFF, 0xFC, 0x2F, 0x30, 0x06, 0x04, 0x01, 0x00, 0x04, 0x01, 0x07, 0x04,
              0x21, 0x02, 0x79, 0xBE, 0x66, 0x7E, 0xF9, 0xDC, 0xBB, 0xAC, 0x55, 0xA0, 0x62, 0x95, 0xCE, 0x87,
              0x0B, 0x07, 0x02, 0x9B, 0xFC, 0xDB, 0x2D, 0xCE, 0x28, 0xD9, 0x59, 0xF2, 0x81, 0x5B, 0x16, 0xF8,
              0x17, 0x98, 0x02, 0x21, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
              0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xBA, 0xAE, 0xDC, 0xE6, 0xAF, 0x48, 0xA0, 0x3B, 0xBF, 0xD2, 0x5E,
              0x8C, 0xD0, 0x36, 0x41, 0x41, 0x02, 0x01, 0x01, 0xA1, 0x24, 0x03, 0x22, 0x00};
          unsigned char* ptr = privkey;
          memcpy(ptr, begin, sizeof(begin));
          ptr += sizeof(begin);
          memcpy(ptr, key32, 32);
          ptr += 32;
          memcpy(ptr, middle, sizeof(middle));
          ptr += sizeof(middle);
          pubkeylen = 33;
          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED);
          ptr += pubkeylen;
          *privkeylen = ptr - privkey;
      } else {
          static const unsigned char begin[] = {
              0x30, 0x82, 0x01, 0x13, 0x02, 0x01, 0x01, 0x04, 0x20};
          static const unsigned char middle[] = {
              0xA0, 0x81, 0xA5, 0x30, 0x81, 0xA2, 0x02, 0x01, 0x01, 0x30, 0x2C, 0x06, 0x07, 0x2A, 0x86, 0x48,
              0xCE, 0x3D, 0x01, 0x01, 0x02, 0x21, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
              0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
              0xFF, 0xFF, 0xFE, 0xFF, 0xFF, 0xFC, 0x2F, 0x30, 0x06, 0x04, 0x01, 0x00, 0x04, 0x01, 0x07, 0x04,
              0x41, 0x04, 0x79, 0xBE, 0x66, 0x7E, 0xF9, 0xDC, 0xBB, 0xAC, 0x55, 0xA0, 0x62, 0x95, 0xCE, 0x87,
              0x0B, 0x07, 0x02, 0x9B, 0xFC, 0xDB, 0x2D, 0xCE, 0x28, 0xD9, 0x59, 0xF2, 0x81, 0x5B, 0x16, 0xF8,
              0x17, 0x98, 0x48, 0x3A, 0xDA, 0x77, 0x26, 0xA3, 0xC4, 0x65, 0x5D, 0xA4, 0xFB, 0xFC, 0x0E, 0x11,
              0x08, 0xA8, 0xFD, 0x17, 0xB4, 0x48, 0xA6, 0x85, 0x54, 0x19, 0x9C, 0x47, 0xD0, 0x8F, 0xFB, 0x10,
              0xD4, 0xB8, 0x02, 0x21, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
              0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xBA, 0xAE, 0xDC, 0xE6, 0xAF, 0x48, 0xA0, 0x3B, 0xBF, 0xD2, 0x5E,
              0x8C, 0xD0, 0x36, 0x41, 0x41, 0x02, 0x01, 0x01, 0xA1, 0x44, 0x03, 0x42, 0x00};
          unsigned char* ptr = privkey;
          memcpy(ptr, begin, sizeof(begin));
          ptr += sizeof(begin);
          memcpy(ptr, key32, 32);
          ptr += 32;
          memcpy(ptr, middle, sizeof(middle));
          ptr += sizeof(middle);
          pubkeylen = 65;
          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
          ptr += pubkeylen;
          *privkeylen = ptr - privkey;
      }
      return 1;
  }
  
  bool CKey::Check(const unsigned char* vch)
  {
      return secp256k1_ec_seckey_verify(secp256k1_context_sign, vch);
  }
  
  void CKey::MakeNewKey(bool fCompressedIn)
  {
      do {
          GetStrongRandBytes(keydata.data(), keydata.size());
      } while (!Check(keydata.data()));
      fValid = true;
      fCompressed = fCompressedIn;
  }
  
  CPrivKey CKey::GetPrivKey() const
  {
      assert(fValid);
      CPrivKey privkey;
      int ret;
      size_t privkeylen;
      privkey.resize(279);
      privkeylen = 279;
      ret = ec_privkey_export_der(secp256k1_context_sign, (unsigned char*)privkey.data(), &privkeylen, begin(), fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
      assert(ret);
      privkey.resize(privkeylen);
      return privkey;
  }
  
  CPubKey CKey::GetPubKey() const
  {
      assert(fValid);
      secp256k1_pubkey pubkey;
      size_t clen = 65;
      CPubKey result;
      int ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pubkey, begin());
      assert(ret);
      secp256k1_ec_pubkey_serialize(secp256k1_context_sign, (unsigned char*)result.begin(), &clen, &pubkey, fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
      assert(result.size() == clen);
      assert(result.IsValid());
      return result;
  }
  
  bool CKey::Sign(const uint256& hash, std::vector<unsigned char>& vchSig, uint32_t test_case) const
  {
      if (!fValid)
          return false;
      vchSig.resize(72);
      size_t nSigLen = 72;
      unsigned char extra_entropy[32] = {0};
      WriteLE32(extra_entropy, test_case);
      secp256k1_ecdsa_signature sig;
      int ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), begin(), secp256k1_nonce_function_rfc6979, test_case ? extra_entropy : nullptr);
      assert(ret);
      secp256k1_ecdsa_signature_serialize_der(secp256k1_context_sign, (unsigned char*)vchSig.data(), &nSigLen, &sig);
      vchSig.resize(nSigLen);
      return true;
  }
  
  bool CKey::VerifyPubKey(const CPubKey& pubkey) const
  {
      if (pubkey.IsCompressed() != fCompressed) {
          return false;
      }
      unsigned char rnd[8];
      std::string str = "BitcoinBridge key verification\n";
      GetRandBytes(rnd, sizeof(rnd));
      uint256 hash;
      CHash256().Write((unsigned char*)str.data(), str.size()).Write(rnd, sizeof(rnd)).Finalize(hash.begin());
      std::vector<unsigned char> vchSig;
      Sign(hash, vchSig);
      return pubkey.Verify(hash, vchSig);
  }
  
  bool CKey::SignCompact(const uint256& hash, std::vector<unsigned char>& vchSig) const
  {
      if (!fValid)
          return false;
      vchSig.resize(65);
      int rec = -1;
      secp256k1_ecdsa_recoverable_signature sig;
      int ret = secp256k1_ecdsa_sign_recoverable(secp256k1_context_sign, &sig, hash.begin(), begin(), secp256k1_nonce_function_rfc6979, nullptr);
      assert(ret);
      secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_context_sign, (unsigned char*)&vchSig[1], &rec, &sig);
      assert(ret);
      assert(rec != -1);
      vchSig[0] = 27 + rec + (fCompressed ? 4 : 0);
      return true;
  }
  
  bool CKey::Load(CPrivKey& privkey, CPubKey& vchPubKey, bool fSkipCheck = false)
  {
      if (!ec_privkey_import_der(secp256k1_context_sign, (unsigned char*)begin(), privkey.data(), privkey.size()))
          return false;
      fCompressed = vchPubKey.IsCompressed();
      fValid = true;
  
      if (fSkipCheck)
          return true;
  
      return VerifyPubKey(vchPubKey);
  }
  
  bool CKey::Derive(CKey& keyChild, ChainCode& ccChild, unsigned int nChild, const ChainCode& cc) const
  {
      assert(IsValid());
      assert(IsCompressed());
      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
      if ((nChild >> 31) == 0) {
          CPubKey pubkey = GetPubKey();
          assert(pubkey.begin() + 33 == pubkey.end());
          BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin() + 1, vout.data());
      } else {
          assert(begin() + 32 == end());
          BIP32Hash(cc, nChild, 0, begin(), vout.data());
      }
      memcpy(ccChild.begin(), vout.data() + 32, 32);
      memcpy((unsigned char*)keyChild.begin(), begin(), 32);
      bool ret = secp256k1_ec_privkey_tweak_add(secp256k1_context_sign, (unsigned char*)keyChild.begin(), vout.data());
      keyChild.fCompressed = true;
      keyChild.fValid = ret;
      return ret;
  }
  
  bool CExtKey::Derive(CExtKey& out, unsigned int _nChild) const
  {
      out.nDepth = nDepth + 1;
      CKeyID id = key.GetPubKey().GetID();
      memcpy(&out.vchFingerprint[0], &id, 4);
      out.nChild = _nChild;
      return key.Derive(out.key, out.chaincode, _nChild, chaincode);
  }
  
  void CExtKey::SetMaster(const unsigned char* seed, unsigned int nSeedLen)
  {
      static const unsigned char hashkey[] = {'B', 'i', 't', 'c', 'o', 'i', 'n', ' ', 's', 'e', 'e', 'd'};
      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
      CHMAC_SHA512(hashkey, sizeof(hashkey)).Write(seed, nSeedLen).Finalize(vout.data());
      key.Set(vout.data(), vout.data() + 32, true);
      memcpy(chaincode.begin(), vout.data() + 32, 32);
      nDepth = 0;
      nChild = 0;
      memset(vchFingerprint, 0, sizeof(vchFingerprint));
  }
  
  CExtPubKey CExtKey::Neuter() const
  {
      CExtPubKey ret;
      ret.nDepth = nDepth;
      memcpy(&ret.vchFingerprint[0], &vchFingerprint[0], 4);
      ret.nChild = nChild;
      ret.pubkey = key.GetPubKey();
      ret.chaincode = chaincode;
      return ret;
  }
  
  void CExtKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const
  {
      code[0] = nDepth;
      memcpy(code + 1, vchFingerprint, 4);
      code[5] = (nChild >> 24) & 0xFF;
      code[6] = (nChild >> 16) & 0xFF;
      code[7] = (nChild >> 8) & 0xFF;
      code[8] = (nChild >> 0) & 0xFF;
      memcpy(code + 9, chaincode.begin(), 32);
      code[41] = 0;
      assert(key.size() == 32);
      memcpy(code + 42, key.begin(), 32);
  }
  
  void CExtKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE])
  {
      nDepth = code[0];
      memcpy(vchFingerprint, code + 1, 4);
      nChild = (code[5] << 24) | (code[6] << 16) | (code[7] << 8) | code[8];
      memcpy(chaincode.begin(), code + 9, 32);
      key.Set(code + 42, code + BIP32_EXTKEY_SIZE, true);
  }
  
  bool ECC_InitSanityCheck()
  {
      CKey key;
      key.MakeNewKey(true);
      CPubKey pubkey = key.GetPubKey();
      return key.VerifyPubKey(pubkey);
  }
  
  void ECC_Start()
  {
      assert(secp256k1_context_sign == nullptr);
  
      secp256k1_context* ctx = secp256k1_context_create(SECP256K1_CONTEXT_SIGN);
      assert(ctx != nullptr);
  
      {
          // Pass in a random blinding seed to the secp256k1 context.
          std::vector<unsigned char, secure_allocator<unsigned char>> vseed(32);
          GetRandBytes(vseed.data(), 32);
          bool ret = secp256k1_context_randomize(ctx, vseed.data());
          assert(ret);
      }
  
      secp256k1_context_sign = ctx;
  }
  
  void ECC_Stop()
  {
      secp256k1_context* ctx = secp256k1_context_sign;
      secp256k1_context_sign = nullptr;
  
      if (ctx) {
          secp256k1_context_destroy(ctx);
      }
  }
  