1  // Copyright (c) 2009-present The Bitcoin Core developers
  2  // Copyright (c) 2017 The Zcash developers
  3  // Distributed under the MIT software license, see the accompanying
  4  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  5  
  6  #include <key.h>
  7  
  8  #include <crypto/common.h>
  9  #include <crypto/hmac_sha512.h>
 10  #include <hash.h>
 11  #include <random.h>
 12  
 13  #include <secp256k1.h>
 14  #include <secp256k1_ellswift.h>
 15  #include <secp256k1_extrakeys.h>
 16  #include <secp256k1_recovery.h>
 17  #include <secp256k1_schnorrsig.h>
 18  
 19  static secp256k1_context* secp256k1_context_sign = nullptr;
 20  
 21  /** These functions are taken from the libsecp256k1 distribution and are very ugly. */
 22  
 23  /**
 24   * This parses a format loosely based on a DER encoding of the ECPrivateKey type from
 25   * section C.4 of SEC 1 <https://www.secg.org/sec1-v2.pdf>, with the following caveats:
 26   *
 27   * * The octet-length of the SEQUENCE must be encoded as 1 or 2 octets. It is not
 28   *   required to be encoded as one octet if it is less than 256, as DER would require.
 29   * * The octet-length of the SEQUENCE must not be greater than the remaining
 30   *   length of the key encoding, but need not match it (i.e. the encoding may contain
 31   *   junk after the encoded SEQUENCE).
 32   * * The privateKey OCTET STRING is zero-filled on the left to 32 octets.
 33   * * Anything after the encoding of the privateKey OCTET STRING is ignored, whether
 34   *   or not it is validly encoded DER.
 35   *
 36   * out32 must point to an output buffer of length at least 32 bytes.
 37   */
 38  int ec_seckey_import_der(const secp256k1_context* ctx, unsigned char *out32, const unsigned char *seckey, size_t seckeylen) {
 39      const unsigned char *end = seckey + seckeylen;
 40      memset(out32, 0, 32);
 41      /* sequence header */
 42      if (end - seckey < 1 || *seckey != 0x30u) {
 43          return 0;
 44      }
 45      seckey++;
 46      /* sequence length constructor */
 47      if (end - seckey < 1 || !(*seckey & 0x80u)) {
 48          return 0;
 49      }
 50      ptrdiff_t lenb = *seckey & ~0x80u; seckey++;
 51      if (lenb < 1 || lenb > 2) {
 52          return 0;
 53      }
 54      if (end - seckey < lenb) {
 55          return 0;
 56      }
 57      /* sequence length */
 58      ptrdiff_t len = seckey[lenb-1] | (lenb > 1 ? seckey[lenb-2] << 8 : 0u);
 59      seckey += lenb;
 60      if (end - seckey < len) {
 61          return 0;
 62      }
 63      /* sequence element 0: version number (=1) */
 64      if (end - seckey < 3 || seckey[0] != 0x02u || seckey[1] != 0x01u || seckey[2] != 0x01u) {
 65          return 0;
 66      }
 67      seckey += 3;
 68      /* sequence element 1: octet string, up to 32 bytes */
 69      if (end - seckey < 2 || seckey[0] != 0x04u) {
 70          return 0;
 71      }
 72      ptrdiff_t oslen = seckey[1];
 73      seckey += 2;
 74      if (oslen > 32 || end - seckey < oslen) {
 75          return 0;
 76      }
 77      memcpy(out32 + (32 - oslen), seckey, oslen);
 78      if (!secp256k1_ec_seckey_verify(ctx, out32)) {
 79          memset(out32, 0, 32);
 80          return 0;
 81      }
 82      return 1;
 83  }
 84  
 85  /**
 86   * This serializes to a DER encoding of the ECPrivateKey type from section C.4 of SEC 1
 87   * <https://www.secg.org/sec1-v2.pdf>. The optional parameters and publicKey fields are
 88   * included.
 89   *
 90   * seckey must point to an output buffer of length at least CKey::SIZE bytes.
 91   * seckeylen must initially be set to the size of the seckey buffer. Upon return it
 92   * will be set to the number of bytes used in the buffer.
 93   * key32 must point to a 32-byte raw private key.
 94   */
 95  int ec_seckey_export_der(const secp256k1_context *ctx, unsigned char *seckey, size_t *seckeylen, const unsigned char *key32, bool compressed) {
 96      assert(*seckeylen >= CKey::SIZE);
 97      secp256k1_pubkey pubkey;
 98      size_t pubkeylen = 0;
 99      if (!secp256k1_ec_pubkey_create(ctx, &pubkey, key32)) {
100          *seckeylen = 0;
101          return 0;
102      }
103      if (compressed) {
104          static const unsigned char begin[] = {
105              0x30,0x81,0xD3,0x02,0x01,0x01,0x04,0x20
106          };
107          static const unsigned char middle[] = {
108              0xA0,0x81,0x85,0x30,0x81,0x82,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
109              0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
110              0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
111              0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
112              0x21,0x02,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
113              0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
114              0x17,0x98,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
115              0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
116              0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x24,0x03,0x22,0x00
117          };
118          unsigned char *ptr = seckey;
119          memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
120          memcpy(ptr, key32, 32); ptr += 32;
121          memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
122          pubkeylen = CPubKey::COMPRESSED_SIZE;
123          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED);
124          ptr += pubkeylen;
125          *seckeylen = ptr - seckey;
126          assert(*seckeylen == CKey::COMPRESSED_SIZE);
127      } else {
128          static const unsigned char begin[] = {
129              0x30,0x82,0x01,0x13,0x02,0x01,0x01,0x04,0x20
130          };
131          static const unsigned char middle[] = {
132              0xA0,0x81,0xA5,0x30,0x81,0xA2,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
133              0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
134              0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
135              0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
136              0x41,0x04,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
137              0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
138              0x17,0x98,0x48,0x3A,0xDA,0x77,0x26,0xA3,0xC4,0x65,0x5D,0xA4,0xFB,0xFC,0x0E,0x11,
139              0x08,0xA8,0xFD,0x17,0xB4,0x48,0xA6,0x85,0x54,0x19,0x9C,0x47,0xD0,0x8F,0xFB,0x10,
140              0xD4,0xB8,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
141              0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
142              0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x44,0x03,0x42,0x00
143          };
144          unsigned char *ptr = seckey;
145          memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
146          memcpy(ptr, key32, 32); ptr += 32;
147          memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
148          pubkeylen = CPubKey::SIZE;
149          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
150          ptr += pubkeylen;
151          *seckeylen = ptr - seckey;
152          assert(*seckeylen == CKey::SIZE);
153      }
154      return 1;
155  }
156  
157  bool CKey::Check(const unsigned char *vch) {
158      return secp256k1_ec_seckey_verify(secp256k1_context_sign, vch);
159  }
160  
161  void CKey::MakeNewKey(bool fCompressedIn) {
162      MakeKeyData();
163      do {
164          GetStrongRandBytes(*keydata);
165      } while (!Check(keydata->data()));
166      fCompressed = fCompressedIn;
167  }
168  
169  CPrivKey CKey::GetPrivKey() const {
170      assert(keydata);
171      CPrivKey seckey;
172      int ret;
173      size_t seckeylen;
174      seckey.resize(SIZE);
175      seckeylen = SIZE;
176      ret = ec_seckey_export_der(secp256k1_context_sign, seckey.data(), &seckeylen, UCharCast(begin()), fCompressed);
177      assert(ret);
178      seckey.resize(seckeylen);
179      return seckey;
180  }
181  
182  CPubKey CKey::GetPubKey() const {
183      assert(keydata);
184      secp256k1_pubkey pubkey;
185      size_t clen = CPubKey::SIZE;
186      CPubKey result;
187      int ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pubkey, UCharCast(begin()));
188      assert(ret);
189      secp256k1_ec_pubkey_serialize(secp256k1_context_sign, (unsigned char*)result.begin(), &clen, &pubkey, fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
190      assert(result.size() == clen);
191      assert(result.IsValid());
192      return result;
193  }
194  
195  // Check that the sig has a low R value and will be less than 71 bytes
196  bool SigHasLowR(const secp256k1_ecdsa_signature* sig)
197  {
198      unsigned char compact_sig[64];
199      secp256k1_ecdsa_signature_serialize_compact(secp256k1_context_sign, compact_sig, sig);
200  
201      // In DER serialization, all values are interpreted as big-endian, signed integers. The highest bit in the integer indicates
202      // its signed-ness; 0 is positive, 1 is negative. When the value is interpreted as a negative integer, it must be converted
203      // to a positive value by prepending a 0x00 byte so that the highest bit is 0. We can avoid this prepending by ensuring that
204      // our highest bit is always 0, and thus we must check that the first byte is less than 0x80.
205      return compact_sig[0] < 0x80;
206  }
207  
208  bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, bool grind, uint32_t test_case) const {
209      if (!keydata)
210          return false;
211      vchSig.resize(CPubKey::SIGNATURE_SIZE);
212      size_t nSigLen = CPubKey::SIGNATURE_SIZE;
213      unsigned char extra_entropy[32] = {0};
214      WriteLE32(extra_entropy, test_case);
215      secp256k1_ecdsa_signature sig;
216      uint32_t counter = 0;
217      int ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, (!grind && test_case) ? extra_entropy : nullptr);
218  
219      // Grind for low R
220      while (ret && !SigHasLowR(&sig) && grind) {
221          WriteLE32(extra_entropy, ++counter);
222          ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, extra_entropy);
223      }
224      assert(ret);
225      secp256k1_ecdsa_signature_serialize_der(secp256k1_context_sign, vchSig.data(), &nSigLen, &sig);
226      vchSig.resize(nSigLen);
227      // Additional verification step to prevent using a potentially corrupted signature
228      secp256k1_pubkey pk;
229      ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pk, UCharCast(begin()));
230      assert(ret);
231      ret = secp256k1_ecdsa_verify(secp256k1_context_static, &sig, hash.begin(), &pk);
232      assert(ret);
233      return true;
234  }
235  
236  bool CKey::VerifyPubKey(const CPubKey& pubkey) const {
237      if (pubkey.IsCompressed() != fCompressed) {
238          return false;
239      }
240      unsigned char rnd[8];
241      std::string str = "Bitcoin key verification\n";
242      GetRandBytes(rnd);
243      uint256 hash{Hash(str, rnd)};
244      std::vector<unsigned char> vchSig;
245      Sign(hash, vchSig);
246      return pubkey.Verify(hash, vchSig);
247  }
248  
249  bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
250      if (!keydata)
251          return false;
252      vchSig.resize(CPubKey::COMPACT_SIGNATURE_SIZE);
253      int rec = -1;
254      secp256k1_ecdsa_recoverable_signature rsig;
255      int ret = secp256k1_ecdsa_sign_recoverable(secp256k1_context_sign, &rsig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, nullptr);
256      assert(ret);
257      ret = secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_context_sign, &vchSig[1], &rec, &rsig);
258      assert(ret);
259      assert(rec != -1);
260      vchSig[0] = 27 + rec + (fCompressed ? 4 : 0);
261      // Additional verification step to prevent using a potentially corrupted signature
262      secp256k1_pubkey epk, rpk;
263      ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &epk, UCharCast(begin()));
264      assert(ret);
265      ret = secp256k1_ecdsa_recover(secp256k1_context_static, &rpk, &rsig, hash.begin());
266      assert(ret);
267      ret = secp256k1_ec_pubkey_cmp(secp256k1_context_static, &epk, &rpk);
268      assert(ret == 0);
269      return true;
270  }
271  
272  bool CKey::SignSchnorr(const uint256& hash, std::span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const
273  {
274      KeyPair kp = ComputeKeyPair(merkle_root);
275      return kp.SignSchnorr(hash, sig, aux);
276  }
277  
278  bool CKey::Load(const CPrivKey &seckey, const CPubKey &vchPubKey, bool fSkipCheck=false) {
279      MakeKeyData();
280      if (!ec_seckey_import_der(secp256k1_context_sign, (unsigned char*)begin(), seckey.data(), seckey.size())) {
281          ClearKeyData();
282          return false;
283      }
284      fCompressed = vchPubKey.IsCompressed();
285  
286      if (fSkipCheck)
287          return true;
288  
289      return VerifyPubKey(vchPubKey);
290  }
291  
292  bool CKey::Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
293      assert(IsValid());
294      assert(IsCompressed());
295      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
296      if ((nChild >> 31) == 0) {
297          CPubKey pubkey = GetPubKey();
298          assert(pubkey.size() == CPubKey::COMPRESSED_SIZE);
299          BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, vout.data());
300      } else {
301          assert(size() == 32);
302          BIP32Hash(cc, nChild, 0, UCharCast(begin()), vout.data());
303      }
304      memcpy(ccChild.begin(), vout.data()+32, 32);
305      keyChild.Set(begin(), begin() + 32, true);
306      bool ret = secp256k1_ec_seckey_tweak_add(secp256k1_context_sign, (unsigned char*)keyChild.begin(), vout.data());
307      if (!ret) keyChild.ClearKeyData();
308      return ret;
309  }
310  
311  EllSwiftPubKey CKey::EllSwiftCreate(std::span<const std::byte> ent32) const
312  {
313      assert(keydata);
314      assert(ent32.size() == 32);
315      std::array<std::byte, EllSwiftPubKey::size()> encoded_pubkey;
316  
317      auto success = secp256k1_ellswift_create(secp256k1_context_sign,
318                                               UCharCast(encoded_pubkey.data()),
319                                               keydata->data(),
320                                               UCharCast(ent32.data()));
321  
322      // Should always succeed for valid keys (asserted above).
323      assert(success);
324      return {encoded_pubkey};
325  }
326  
327  ECDHSecret CKey::ComputeBIP324ECDHSecret(const EllSwiftPubKey& their_ellswift, const EllSwiftPubKey& our_ellswift, bool initiating) const
328  {
329      assert(keydata);
330  
331      ECDHSecret output;
332      // BIP324 uses the initiator as party A, and the responder as party B. Remap the inputs
333      // accordingly:
334      bool success = secp256k1_ellswift_xdh(secp256k1_context_sign,
335                                            UCharCast(output.data()),
336                                            UCharCast(initiating ? our_ellswift.data() : their_ellswift.data()),
337                                            UCharCast(initiating ? their_ellswift.data() : our_ellswift.data()),
338                                            keydata->data(),
339                                            initiating ? 0 : 1,
340                                            secp256k1_ellswift_xdh_hash_function_bip324,
341                                            nullptr);
342      // Should always succeed for valid keys (assert above).
343      assert(success);
344      return output;
345  }
346  
347  KeyPair CKey::ComputeKeyPair(const uint256* merkle_root) const
348  {
349      return KeyPair(*this, merkle_root);
350  }
351  
352  CKey GenerateRandomKey(bool compressed) noexcept
353  {
354      CKey key;
355      key.MakeNewKey(/*fCompressed=*/compressed);
356      return key;
357  }
358  
359  bool CExtKey::Derive(CExtKey &out, unsigned int _nChild) const {
360      if (nDepth == std::numeric_limits<unsigned char>::max()) return false;
361      out.nDepth = nDepth + 1;
362      CKeyID id = key.GetPubKey().GetID();
363      memcpy(out.vchFingerprint, &id, 4);
364      out.nChild = _nChild;
365      return key.Derive(out.key, out.chaincode, _nChild, chaincode);
366  }
367  
368  void CExtKey::SetSeed(std::span<const std::byte> seed)
369  {
370      static const unsigned char hashkey[] = {'B','i','t','c','o','i','n',' ','s','e','e','d'};
371      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
372      CHMAC_SHA512{hashkey, sizeof(hashkey)}.Write(UCharCast(seed.data()), seed.size()).Finalize(vout.data());
373      key.Set(vout.data(), vout.data() + 32, true);
374      memcpy(chaincode.begin(), vout.data() + 32, 32);
375      nDepth = 0;
376      nChild = 0;
377      memset(vchFingerprint, 0, sizeof(vchFingerprint));
378  }
379  
380  CExtPubKey CExtKey::Neuter() const {
381      CExtPubKey ret;
382      ret.nDepth = nDepth;
383      memcpy(ret.vchFingerprint, vchFingerprint, 4);
384      ret.nChild = nChild;
385      ret.pubkey = key.GetPubKey();
386      ret.chaincode = chaincode;
387      return ret;
388  }
389  
390  void CExtKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
391      code[0] = nDepth;
392      memcpy(code+1, vchFingerprint, 4);
393      WriteBE32(code+5, nChild);
394      memcpy(code+9, chaincode.begin(), 32);
395      code[41] = 0;
396      assert(key.size() == 32);
397      memcpy(code+42, key.begin(), 32);
398  }
399  
400  void CExtKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
401      nDepth = code[0];
402      memcpy(vchFingerprint, code+1, 4);
403      nChild = ReadBE32(code+5);
404      memcpy(chaincode.begin(), code+9, 32);
405      key.Set(code+42, code+BIP32_EXTKEY_SIZE, true);
406      if ((nDepth == 0 && (nChild != 0 || ReadLE32(vchFingerprint) != 0)) || code[41] != 0) key = CKey();
407  }
408  
409  KeyPair::KeyPair(const CKey& key, const uint256* merkle_root)
410  {
411      static_assert(std::tuple_size<KeyType>() == sizeof(secp256k1_keypair));
412      MakeKeyPairData();
413      auto keypair = reinterpret_cast<secp256k1_keypair*>(m_keypair->data());
414      bool success = secp256k1_keypair_create(secp256k1_context_sign, keypair, UCharCast(key.data()));
415      if (success && merkle_root) {
416          secp256k1_xonly_pubkey pubkey;
417          unsigned char pubkey_bytes[32];
418          assert(secp256k1_keypair_xonly_pub(secp256k1_context_sign, &pubkey, nullptr, keypair));
419          assert(secp256k1_xonly_pubkey_serialize(secp256k1_context_sign, pubkey_bytes, &pubkey));
420          uint256 tweak = XOnlyPubKey(pubkey_bytes).ComputeTapTweakHash(merkle_root->IsNull() ? nullptr : merkle_root);
421          success = secp256k1_keypair_xonly_tweak_add(secp256k1_context_static, keypair, tweak.data());
422      }
423      if (!success) ClearKeyPairData();
424  }
425  
426  bool KeyPair::SignSchnorr(const uint256& hash, std::span<unsigned char> sig, const uint256& aux) const
427  {
428      assert(sig.size() == 64);
429      if (!IsValid()) return false;
430      auto keypair = reinterpret_cast<const secp256k1_keypair*>(m_keypair->data());
431      bool ret = secp256k1_schnorrsig_sign32(secp256k1_context_sign, sig.data(), hash.data(), keypair, aux.data());
432      if (ret) {
433          // Additional verification step to prevent using a potentially corrupted signature
434          secp256k1_xonly_pubkey pubkey_verify;
435          ret = secp256k1_keypair_xonly_pub(secp256k1_context_static, &pubkey_verify, nullptr, keypair);
436          ret &= secp256k1_schnorrsig_verify(secp256k1_context_static, sig.data(), hash.begin(), 32, &pubkey_verify);
437      }
438      if (!ret) memory_cleanse(sig.data(), sig.size());
439      return ret;
440  }
441  
442  bool ECC_InitSanityCheck() {
443      CKey key = GenerateRandomKey();
444      CPubKey pubkey = key.GetPubKey();
445      return key.VerifyPubKey(pubkey);
446  }
447  
448  /** Initialize the elliptic curve support. May not be called twice without calling ECC_Stop first. */
449  static void ECC_Start() {
450      assert(secp256k1_context_sign == nullptr);
451  
452      secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
453      assert(ctx != nullptr);
454  
455      {
456          // Pass in a random blinding seed to the secp256k1 context.
457          std::vector<unsigned char, secure_allocator<unsigned char>> vseed(32);
458          GetRandBytes(vseed);
459          bool ret = secp256k1_context_randomize(ctx, vseed.data());
460          assert(ret);
461      }
462  
463      secp256k1_context_sign = ctx;
464  }
465  
466  /** Deinitialize the elliptic curve support. No-op if ECC_Start wasn't called first. */
467  static void ECC_Stop() {
468      secp256k1_context *ctx = secp256k1_context_sign;
469      secp256k1_context_sign = nullptr;
470  
471      if (ctx) {
472          secp256k1_context_destroy(ctx);
473      }
474  }
475  
476  ECC_Context::ECC_Context()
477  {
478      ECC_Start();
479  }
480  
481  ECC_Context::~ECC_Context()
482  {
483      ECC_Stop();
484  }