text: // Copyright (c) 2009-2017 The Bitcoin developers
  // Copyright (c) 2017-2020 The PIVX developers
  // Copyright (c) 2020 The CLEARCOIN 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 "uint256.h"
  #include "crypto/common.h"
  #include "crypto/hmac_sha512.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. */
  
  /**
   * This parses a format loosely based on a DER encoding of the ECPrivateKey type from
   * section C.4 of SEC 1 <http://www.secg.org/sec1-v2.pdf>, with the following caveats:
   *
   * * The octet-length of the SEQUENCE must be encoded as 1 or 2 octets. It is not
   *   required to be encoded as one octet if it is less than 256, as DER would require.
   * * The octet-length of the SEQUENCE must not be greater than the remaining
   *   length of the key encoding, but need not match it (i.e. the encoding may contain
   *   junk after the encoded SEQUENCE).
   * * The privateKey OCTET STRING is zero-filled on the left to 32 octets.
   * * Anything after the encoding of the privateKey OCTET STRING is ignored, whether
   *   or not it is validly encoded DER.
   *
   * out32 must point to an output buffer of length at least 32 bytes.
   */
  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;
      memset(out32, 0, 32);
      /* sequence header */
      if (end - privkey < 1 || *privkey != 0x30u) {
          return 0;
      }
      privkey++;
      /* sequence length constructor */
      if (end - privkey < 1 || !(*privkey & 0x80u)) {
          return 0;
      }
      ptrdiff_t lenb = *privkey & ~0x80u; privkey++;
      if (lenb < 1 || lenb > 2) {
          return 0;
      }
      if (end - privkey < lenb) {
          return 0;
      }
      /* sequence length */
      ptrdiff_t len = privkey[lenb-1] | (lenb > 1 ? privkey[lenb-2] << 8 : 0u);
      privkey += lenb;
      if (end - privkey < len) {
          return 0;
      }
      /* sequence element 0: version number (=1) */
      if (end - privkey < 3 || privkey[0] != 0x02u || privkey[1] != 0x01u || privkey[2] != 0x01u) {
          return 0;
      }
      privkey += 3;
      /* sequence element 1: octet string, up to 32 bytes */
      if (end - privkey < 2 || privkey[0] != 0x04u) {
          return 0;
      }
      ptrdiff_t oslen = privkey[1];
      privkey += 2;
      if (oslen > 32 || end - privkey < oslen) {
          return 0;
      }
      memcpy(out32 + (32 - oslen), privkey, oslen);
      if (!secp256k1_ec_seckey_verify(ctx, out32)) {
          memset(out32, 0, 32);
          return 0;
      }
      return 1;
  }
  
  /**
   * This serializes to a DER encoding of the ECPrivateKey type from section C.4 of SEC 1
   * <http://www.secg.org/sec1-v2.pdf>. The optional parameters and publicKey fields are
   * included.
   *
   * privkey must point to an output buffer of length at least CKey::PRIVATE_KEY_SIZE bytes.
   * privkeylen must initially be set to the size of the privkey buffer. Upon return it
   * will be set to the number of bytes used in the buffer.
   * key32 must point to a 32-byte raw private key.
   */
  static int ec_privkey_export_der(const secp256k1_context *ctx, unsigned char *privkey, size_t *privkeylen, const unsigned char *key32, int compressed) {
      assert(*privkeylen >= CKey::PRIVATE_KEY_SIZE);
      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 = CPubKey::COMPRESSED_PUBLIC_KEY_SIZE;
          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED);
          ptr += pubkeylen;
          *privkeylen = ptr - privkey;
          assert(*privkeylen == CKey::COMPRESSED_PRIVATE_KEY_SIZE);
      } 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 = CPubKey::PUBLIC_KEY_SIZE;
          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
          ptr += pubkeylen;
          *privkeylen = ptr - privkey;
          assert(*privkeylen == CKey::PRIVATE_KEY_SIZE);
      }
      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;
  }
  
  bool CKey::SetPrivKey(const CPrivKey& privkey, bool fCompressedIn)
  {
      if (!ec_privkey_import_der(secp256k1_context_sign, (unsigned char*)begin(), &privkey[0], privkey.size()))
          return false;
      fCompressed = fCompressedIn;
      fValid = true;
      return true;
  }
  
  uint256 CKey::GetPrivKey_256()
  {
      void* key = keydata.data();
      uint256* key_256 = (uint256*)key;
  
      return *key_256;
  }
  
  CPrivKey CKey::GetPrivKey() const
  {
      assert(fValid);
      CPrivKey privkey;
      size_t privkeylen;
      privkey.resize(PRIVATE_KEY_SIZE);
      privkeylen = PRIVATE_KEY_SIZE;
      int ret = ec_privkey_export_der(secp256k1_context_sign, (unsigned char*)&privkey[0], &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;
      CPubKey result;
      size_t clen = 65;
      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(CPubKey::SIGNATURE_SIZE);
      size_t nSigLen = CPubKey::SIGNATURE_SIZE;
      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 = "Bitcoin 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(CPubKey::COMPACT_SIGNATURE_SIZE);
      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(const CPrivKey& privkey, const 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.size() == CPubKey::COMPRESSED_PUBLIC_KEY_SIZE);
          BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, vout.data());
      } else {
          assert(size() == 32);
          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::SetSeed(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);
      }
  }
  