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_musig.h>
 17  #include <secp256k1_recovery.h>
 18  #include <secp256k1_schnorrsig.h>
 19  
 20  static secp256k1_context* secp256k1_context_sign = nullptr;
 21  
 22  /** These functions are taken from the libsecp256k1 distribution and are very ugly. */
 23  
 24  /**
 25   * This parses a format loosely based on a DER encoding of the ECPrivateKey type from
 26   * section C.4 of SEC 1 <https://www.secg.org/sec1-v2.pdf>, with the following caveats:
 27   *
 28   * * The octet-length of the SEQUENCE must be encoded as 1 or 2 octets. It is not
 29   *   required to be encoded as one octet if it is less than 256, as DER would require.
 30   * * The octet-length of the SEQUENCE must not be greater than the remaining
 31   *   length of the key encoding, but need not match it (i.e. the encoding may contain
 32   *   junk after the encoded SEQUENCE).
 33   * * The privateKey OCTET STRING is zero-filled on the left to 32 octets.
 34   * * Anything after the encoding of the privateKey OCTET STRING is ignored, whether
 35   *   or not it is validly encoded DER.
 36   *
 37   * out32 must point to an output buffer of length at least 32 bytes.
 38   */
 39  int ec_seckey_import_der(const secp256k1_context* ctx, unsigned char *out32, const unsigned char *seckey, size_t seckeylen) {
 40      const unsigned char *end = seckey + seckeylen;
 41      memset(out32, 0, 32);
 42      /* sequence header */
 43      if (end - seckey < 1 || *seckey != 0x30u) {
 44          return 0;
 45      }
 46      seckey++;
 47      /* sequence length constructor */
 48      if (end - seckey < 1 || !(*seckey & 0x80u)) {
 49          return 0;
 50      }
 51      ptrdiff_t lenb = *seckey & ~0x80u; seckey++;
 52      if (lenb < 1 || lenb > 2) {
 53          return 0;
 54      }
 55      if (end - seckey < lenb) {
 56          return 0;
 57      }
 58      /* sequence length */
 59      ptrdiff_t len = seckey[lenb-1] | (lenb > 1 ? seckey[lenb-2] << 8 : 0u);
 60      seckey += lenb;
 61      if (end - seckey < len) {
 62          return 0;
 63      }
 64      /* sequence element 0: version number (=1) */
 65      if (end - seckey < 3 || seckey[0] != 0x02u || seckey[1] != 0x01u || seckey[2] != 0x01u) {
 66          return 0;
 67      }
 68      seckey += 3;
 69      /* sequence element 1: octet string, up to 32 bytes */
 70      if (end - seckey < 2 || seckey[0] != 0x04u) {
 71          return 0;
 72      }
 73      ptrdiff_t oslen = seckey[1];
 74      seckey += 2;
 75      if (oslen > 32 || end - seckey < oslen) {
 76          return 0;
 77      }
 78      memcpy(out32 + (32 - oslen), seckey, oslen);
 79      if (!secp256k1_ec_seckey_verify(ctx, out32)) {
 80          memset(out32, 0, 32);
 81          return 0;
 82      }
 83      return 1;
 84  }
 85  
 86  /**
 87   * This serializes to a DER encoding of the ECPrivateKey type from section C.4 of SEC 1
 88   * <https://www.secg.org/sec1-v2.pdf>. The optional parameters and publicKey fields are
 89   * included.
 90   *
 91   * seckey must point to an output buffer of length at least CKey::SIZE bytes.
 92   * seckeylen must initially be set to the size of the seckey buffer. Upon return it
 93   * will be set to the number of bytes used in the buffer.
 94   * key32 must point to a 32-byte raw private key.
 95   */
 96  int ec_seckey_export_der(const secp256k1_context *ctx, unsigned char *seckey, size_t *seckeylen, const unsigned char *key32, bool compressed) {
 97      assert(*seckeylen >= CKey::SIZE);
 98      secp256k1_pubkey pubkey;
 99      size_t pubkeylen = 0;
100      if (!secp256k1_ec_pubkey_create(ctx, &pubkey, key32)) {
101          *seckeylen = 0;
102          return 0;
103      }
104      if (compressed) {
105          static const unsigned char begin[] = {
106              0x30,0x81,0xD3,0x02,0x01,0x01,0x04,0x20
107          };
108          static const unsigned char middle[] = {
109              0xA0,0x81,0x85,0x30,0x81,0x82,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
110              0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
111              0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
112              0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
113              0x21,0x02,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
114              0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
115              0x17,0x98,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
116              0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
117              0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x24,0x03,0x22,0x00
118          };
119          unsigned char *ptr = seckey;
120          memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
121          memcpy(ptr, key32, 32); ptr += 32;
122          memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
123          pubkeylen = CPubKey::COMPRESSED_SIZE;
124          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_COMPRESSED);
125          ptr += pubkeylen;
126          *seckeylen = ptr - seckey;
127          assert(*seckeylen == CKey::COMPRESSED_SIZE);
128      } else {
129          static const unsigned char begin[] = {
130              0x30,0x82,0x01,0x13,0x02,0x01,0x01,0x04,0x20
131          };
132          static const unsigned char middle[] = {
133              0xA0,0x81,0xA5,0x30,0x81,0xA2,0x02,0x01,0x01,0x30,0x2C,0x06,0x07,0x2A,0x86,0x48,
134              0xCE,0x3D,0x01,0x01,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
135              0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
136              0xFF,0xFF,0xFE,0xFF,0xFF,0xFC,0x2F,0x30,0x06,0x04,0x01,0x00,0x04,0x01,0x07,0x04,
137              0x41,0x04,0x79,0xBE,0x66,0x7E,0xF9,0xDC,0xBB,0xAC,0x55,0xA0,0x62,0x95,0xCE,0x87,
138              0x0B,0x07,0x02,0x9B,0xFC,0xDB,0x2D,0xCE,0x28,0xD9,0x59,0xF2,0x81,0x5B,0x16,0xF8,
139              0x17,0x98,0x48,0x3A,0xDA,0x77,0x26,0xA3,0xC4,0x65,0x5D,0xA4,0xFB,0xFC,0x0E,0x11,
140              0x08,0xA8,0xFD,0x17,0xB4,0x48,0xA6,0x85,0x54,0x19,0x9C,0x47,0xD0,0x8F,0xFB,0x10,
141              0xD4,0xB8,0x02,0x21,0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
142              0xFF,0xFF,0xFF,0xFF,0xFE,0xBA,0xAE,0xDC,0xE6,0xAF,0x48,0xA0,0x3B,0xBF,0xD2,0x5E,
143              0x8C,0xD0,0x36,0x41,0x41,0x02,0x01,0x01,0xA1,0x44,0x03,0x42,0x00
144          };
145          unsigned char *ptr = seckey;
146          memcpy(ptr, begin, sizeof(begin)); ptr += sizeof(begin);
147          memcpy(ptr, key32, 32); ptr += 32;
148          memcpy(ptr, middle, sizeof(middle)); ptr += sizeof(middle);
149          pubkeylen = CPubKey::SIZE;
150          secp256k1_ec_pubkey_serialize(ctx, ptr, &pubkeylen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
151          ptr += pubkeylen;
152          *seckeylen = ptr - seckey;
153          assert(*seckeylen == CKey::SIZE);
154      }
155      return 1;
156  }
157  
158  bool CKey::Check(const unsigned char *vch) {
159      return secp256k1_ec_seckey_verify(secp256k1_context_static, vch);
160  }
161  
162  void CKey::MakeNewKey(bool fCompressedIn) {
163      MakeKeyData();
164      do {
165          GetStrongRandBytes(*keydata);
166      } while (!Check(keydata->data()));
167      fCompressed = fCompressedIn;
168  }
169  
170  CPrivKey CKey::GetPrivKey() const {
171      assert(keydata);
172      CPrivKey seckey;
173      int ret;
174      size_t seckeylen;
175      seckey.resize(SIZE);
176      seckeylen = SIZE;
177      ret = ec_seckey_export_der(secp256k1_context_sign, seckey.data(), &seckeylen, UCharCast(begin()), fCompressed);
178      assert(ret);
179      seckey.resize(seckeylen);
180      return seckey;
181  }
182  
183  CPubKey CKey::GetPubKey() const {
184      assert(keydata);
185      secp256k1_pubkey pubkey;
186      size_t clen = CPubKey::SIZE;
187      CPubKey result;
188      int ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pubkey, UCharCast(begin()));
189      assert(ret);
190      secp256k1_ec_pubkey_serialize(secp256k1_context_static, (unsigned char*)result.begin(), &clen, &pubkey, fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
191      assert(result.size() == clen);
192      assert(result.IsValid());
193      return result;
194  }
195  
196  // Check that the sig has a low R value and will be less than 71 bytes
197  bool SigHasLowR(const secp256k1_ecdsa_signature* sig)
198  {
199      unsigned char compact_sig[64];
200      secp256k1_ecdsa_signature_serialize_compact(secp256k1_context_static, compact_sig, sig);
201  
202      // In DER serialization, all values are interpreted as big-endian, signed integers. The highest bit in the integer indicates
203      // its signed-ness; 0 is positive, 1 is negative. When the value is interpreted as a negative integer, it must be converted
204      // to a positive value by prepending a 0x00 byte so that the highest bit is 0. We can avoid this prepending by ensuring that
205      // our highest bit is always 0, and thus we must check that the first byte is less than 0x80.
206      return compact_sig[0] < 0x80;
207  }
208  
209  bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, bool grind, uint32_t test_case) const {
210      if (!keydata)
211          return false;
212      vchSig.resize(CPubKey::SIGNATURE_SIZE);
213      size_t nSigLen = CPubKey::SIGNATURE_SIZE;
214      unsigned char extra_entropy[32] = {0};
215      WriteLE32(extra_entropy, test_case);
216      secp256k1_ecdsa_signature sig;
217      uint32_t counter = 0;
218      int ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, (!grind && test_case) ? extra_entropy : nullptr);
219  
220      // Grind for low R
221      while (ret && !SigHasLowR(&sig) && grind) {
222          WriteLE32(extra_entropy, ++counter);
223          ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, extra_entropy);
224      }
225      assert(ret);
226      secp256k1_ecdsa_signature_serialize_der(secp256k1_context_static, vchSig.data(), &nSigLen, &sig);
227      vchSig.resize(nSigLen);
228      // Additional verification step to prevent using a potentially corrupted signature
229      secp256k1_pubkey pk;
230      ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pk, UCharCast(begin()));
231      assert(ret);
232      ret = secp256k1_ecdsa_verify(secp256k1_context_static, &sig, hash.begin(), &pk);
233      assert(ret);
234      return true;
235  }
236  
237  bool CKey::VerifyPubKey(const CPubKey& pubkey) const {
238      if (pubkey.IsCompressed() != fCompressed) {
239          return false;
240      }
241      unsigned char rnd[8];
242      std::string str = "Bitcoin key verification\n";
243      GetRandBytes(rnd);
244      uint256 hash{Hash(str, rnd)};
245      std::vector<unsigned char> vchSig;
246      Sign(hash, vchSig);
247      return pubkey.Verify(hash, vchSig);
248  }
249  
250  bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
251      if (!keydata)
252          return false;
253      vchSig.resize(CPubKey::COMPACT_SIGNATURE_SIZE);
254      int rec = -1;
255      secp256k1_ecdsa_recoverable_signature rsig;
256      int ret = secp256k1_ecdsa_sign_recoverable(secp256k1_context_sign, &rsig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, nullptr);
257      assert(ret);
258      ret = secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_context_static, &vchSig[1], &rec, &rsig);
259      assert(ret);
260      assert(rec != -1);
261      vchSig[0] = 27 + rec + (fCompressed ? 4 : 0);
262      // Additional verification step to prevent using a potentially corrupted signature
263      secp256k1_pubkey epk, rpk;
264      ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &epk, UCharCast(begin()));
265      assert(ret);
266      ret = secp256k1_ecdsa_recover(secp256k1_context_static, &rpk, &rsig, hash.begin());
267      assert(ret);
268      ret = secp256k1_ec_pubkey_cmp(secp256k1_context_static, &epk, &rpk);
269      assert(ret == 0);
270      return true;
271  }
272  
273  bool CKey::SignSchnorr(const uint256& hash, std::span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const
274  {
275      KeyPair kp = ComputeKeyPair(merkle_root);
276      return kp.SignSchnorr(hash, sig, aux);
277  }
278  
279  bool CKey::Load(const CPrivKey &seckey, const CPubKey &vchPubKey, bool fSkipCheck=false) {
280      MakeKeyData();
281      if (!ec_seckey_import_der(secp256k1_context_static, (unsigned char*)begin(), seckey.data(), seckey.size())) {
282          ClearKeyData();
283          return false;
284      }
285      fCompressed = vchPubKey.IsCompressed();
286  
287      if (fSkipCheck)
288          return true;
289  
290      return VerifyPubKey(vchPubKey);
291  }
292  
293  bool CKey::Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
294      assert(IsValid());
295      assert(IsCompressed());
296      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
297      if ((nChild >> 31) == 0) {
298          CPubKey pubkey = GetPubKey();
299          assert(pubkey.size() == CPubKey::COMPRESSED_SIZE);
300          BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, vout.data());
301      } else {
302          assert(size() == 32);
303          BIP32Hash(cc, nChild, 0, UCharCast(begin()), vout.data());
304      }
305      memcpy(ccChild.begin(), vout.data()+32, 32);
306      keyChild.Set(begin(), begin() + 32, true);
307      bool ret = secp256k1_ec_seckey_tweak_add(secp256k1_context_static, (unsigned char*)keyChild.begin(), vout.data());
308      if (!ret) keyChild.ClearKeyData();
309      return ret;
310  }
311  
312  EllSwiftPubKey CKey::EllSwiftCreate(std::span<const std::byte> ent32) const
313  {
314      assert(keydata);
315      assert(ent32.size() == 32);
316      std::array<std::byte, EllSwiftPubKey::size()> encoded_pubkey;
317  
318      auto success = secp256k1_ellswift_create(secp256k1_context_sign,
319                                               UCharCast(encoded_pubkey.data()),
320                                               keydata->data(),
321                                               UCharCast(ent32.data()));
322  
323      // Should always succeed for valid keys (asserted above).
324      assert(success);
325      return {encoded_pubkey};
326  }
327  
328  ECDHSecret CKey::ComputeBIP324ECDHSecret(const EllSwiftPubKey& their_ellswift, const EllSwiftPubKey& our_ellswift, bool initiating) const
329  {
330      assert(keydata);
331  
332      ECDHSecret output;
333      // BIP324 uses the initiator as party A, and the responder as party B. Remap the inputs
334      // accordingly:
335      bool success = secp256k1_ellswift_xdh(secp256k1_context_static,
336                                            UCharCast(output.data()),
337                                            UCharCast(initiating ? our_ellswift.data() : their_ellswift.data()),
338                                            UCharCast(initiating ? their_ellswift.data() : our_ellswift.data()),
339                                            keydata->data(),
340                                            initiating ? 0 : 1,
341                                            secp256k1_ellswift_xdh_hash_function_bip324,
342                                            nullptr);
343      // Should always succeed for valid keys (assert above).
344      assert(success);
345      return output;
346  }
347  
348  KeyPair CKey::ComputeKeyPair(const uint256* merkle_root) const
349  {
350      return KeyPair(*this, merkle_root);
351  }
352  
353  std::vector<uint8_t> CKey::CreateMuSig2Nonce(MuSig2SecNonce& secnonce, const uint256& sighash, const CPubKey& aggregate_pubkey, const std::vector<CPubKey>& pubkeys)
354  {
355      // Get the keyagg cache and aggregate pubkey
356      secp256k1_musig_keyagg_cache keyagg_cache;
357      if (!MuSig2AggregatePubkeys(pubkeys, keyagg_cache, aggregate_pubkey)) return {};
358  
359      // Parse participant pubkey
360      CPubKey our_pubkey = GetPubKey();
361      secp256k1_pubkey pubkey;
362      if (!secp256k1_ec_pubkey_parse(secp256k1_context_static, &pubkey, our_pubkey.data(), our_pubkey.size())) {
363          return {};
364      }
365  
366      // Generate randomness for nonce
367      uint256 rand;
368      GetStrongRandBytes(rand);
369  
370      // Generate nonce
371      secp256k1_musig_pubnonce pubnonce;
372      if (!secp256k1_musig_nonce_gen(secp256k1_context_sign, secnonce.Get(), &pubnonce, rand.data(), UCharCast(begin()), &pubkey, sighash.data(), &keyagg_cache, nullptr)) {
373          return {};
374      }
375  
376      // Serialize pubnonce
377      std::vector<uint8_t> out;
378      out.resize(MUSIG2_PUBNONCE_SIZE);
379      if (!secp256k1_musig_pubnonce_serialize(secp256k1_context_static, out.data(), &pubnonce)) {
380          return {};
381      }
382  
383      return out;
384  }
385  
386  std::optional<uint256> CKey::CreateMuSig2PartialSig(const uint256& sighash, const CPubKey& aggregate_pubkey, const std::vector<CPubKey>& pubkeys, const std::map<CPubKey, std::vector<uint8_t>>& pubnonces, MuSig2SecNonce& secnonce, const std::vector<std::pair<uint256, bool>>& tweaks)
387  {
388      secp256k1_keypair keypair;
389      if (!secp256k1_keypair_create(secp256k1_context_sign, &keypair, UCharCast(begin()))) return std::nullopt;
390  
391      // Get the keyagg cache and aggregate pubkey
392      secp256k1_musig_keyagg_cache keyagg_cache;
393      if (!MuSig2AggregatePubkeys(pubkeys, keyagg_cache, aggregate_pubkey)) return std::nullopt;
394  
395      // Check that there are enough pubnonces
396      if (pubnonces.size() != pubkeys.size()) return std::nullopt;
397  
398      // Parse the pubnonces
399      std::vector<std::pair<secp256k1_pubkey, secp256k1_musig_pubnonce>> signers_data;
400      std::vector<const secp256k1_musig_pubnonce*> pubnonce_ptrs;
401      std::optional<size_t> our_pubkey_idx;
402      CPubKey our_pubkey = GetPubKey();
403      for (const CPubKey& part_pk : pubkeys) {
404          const auto& pn_it = pubnonces.find(part_pk);
405          if (pn_it == pubnonces.end()) return std::nullopt;
406          const std::vector<uint8_t> pubnonce = pn_it->second;
407          if (pubnonce.size() != MUSIG2_PUBNONCE_SIZE) return std::nullopt;
408          if (part_pk == our_pubkey) {
409              our_pubkey_idx = signers_data.size();
410          }
411  
412          auto& [secp_pk, secp_pn] = signers_data.emplace_back();
413  
414          if (!secp256k1_ec_pubkey_parse(secp256k1_context_static, &secp_pk, part_pk.data(), part_pk.size())) {
415              return std::nullopt;
416          }
417  
418          if (!secp256k1_musig_pubnonce_parse(secp256k1_context_static, &secp_pn, pubnonce.data())) {
419              return std::nullopt;
420          }
421      }
422      if (our_pubkey_idx == std::nullopt) {
423          return std::nullopt;
424      }
425      pubnonce_ptrs.reserve(signers_data.size());
426      for (auto& [_, pn] : signers_data) {
427          pubnonce_ptrs.push_back(&pn);
428      }
429  
430      // Aggregate nonces
431      secp256k1_musig_aggnonce aggnonce;
432      if (!secp256k1_musig_nonce_agg(secp256k1_context_static, &aggnonce, pubnonce_ptrs.data(), pubnonce_ptrs.size())) {
433          return std::nullopt;
434      }
435  
436      // Apply tweaks
437      for (const auto& [tweak, xonly] : tweaks) {
438          if (xonly) {
439              if (!secp256k1_musig_pubkey_xonly_tweak_add(secp256k1_context_static, nullptr, &keyagg_cache, tweak.data())) {
440                  return std::nullopt;
441              }
442          } else if (!secp256k1_musig_pubkey_ec_tweak_add(secp256k1_context_static, nullptr, &keyagg_cache, tweak.data())) {
443              return std::nullopt;
444          }
445      }
446  
447      // Create musig_session
448      secp256k1_musig_session session;
449      if (!secp256k1_musig_nonce_process(secp256k1_context_static, &session, &aggnonce, sighash.data(), &keyagg_cache)) {
450          return std::nullopt;
451      }
452  
453      // Create partial signature
454      secp256k1_musig_partial_sig psig;
455      if (!secp256k1_musig_partial_sign(secp256k1_context_static, &psig, secnonce.Get(), &keypair, &keyagg_cache, &session)) {
456          return std::nullopt;
457      }
458      // The secnonce must be deleted after signing to prevent nonce reuse.
459      secnonce.Invalidate();
460  
461      // Verify partial signature
462      if (!secp256k1_musig_partial_sig_verify(secp256k1_context_static, &psig, &(signers_data.at(*our_pubkey_idx).second), &(signers_data.at(*our_pubkey_idx).first), &keyagg_cache, &session)) {
463          return std::nullopt;
464      }
465  
466      // Serialize
467      uint256 sig;
468      if (!secp256k1_musig_partial_sig_serialize(secp256k1_context_static, sig.data(), &psig)) {
469          return std::nullopt;
470      }
471  
472      return sig;
473  }
474  
475  CKey GenerateRandomKey(bool compressed) noexcept
476  {
477      CKey key;
478      key.MakeNewKey(/*fCompressed=*/compressed);
479      return key;
480  }
481  
482  bool CExtKey::Derive(CExtKey &out, unsigned int _nChild) const {
483      if (nDepth == std::numeric_limits<unsigned char>::max()) return false;
484      out.nDepth = nDepth + 1;
485      CKeyID id = key.GetPubKey().GetID();
486      memcpy(out.vchFingerprint, &id, 4);
487      out.nChild = _nChild;
488      return key.Derive(out.key, out.chaincode, _nChild, chaincode);
489  }
490  
491  void CExtKey::SetSeed(std::span<const std::byte> seed)
492  {
493      static const unsigned char hashkey[] = {'B','i','t','c','o','i','n',' ','s','e','e','d'};
494      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
495      CHMAC_SHA512{hashkey, sizeof(hashkey)}.Write(UCharCast(seed.data()), seed.size()).Finalize(vout.data());
496      key.Set(vout.data(), vout.data() + 32, true);
497      memcpy(chaincode.begin(), vout.data() + 32, 32);
498      nDepth = 0;
499      nChild = 0;
500      memset(vchFingerprint, 0, sizeof(vchFingerprint));
501  }
502  
503  CExtPubKey CExtKey::Neuter() const {
504      CExtPubKey ret;
505      ret.nDepth = nDepth;
506      memcpy(ret.vchFingerprint, vchFingerprint, 4);
507      ret.nChild = nChild;
508      ret.pubkey = key.GetPubKey();
509      ret.chaincode = chaincode;
510      return ret;
511  }
512  
513  void CExtKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
514      code[0] = nDepth;
515      memcpy(code+1, vchFingerprint, 4);
516      WriteBE32(code+5, nChild);
517      memcpy(code+9, chaincode.begin(), 32);
518      code[41] = 0;
519      assert(key.size() == 32);
520      memcpy(code+42, key.begin(), 32);
521  }
522  
523  void CExtKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
524      nDepth = code[0];
525      memcpy(vchFingerprint, code+1, 4);
526      nChild = ReadBE32(code+5);
527      memcpy(chaincode.begin(), code+9, 32);
528      key.Set(code+42, code+BIP32_EXTKEY_SIZE, true);
529      if ((nDepth == 0 && (nChild != 0 || ReadLE32(vchFingerprint) != 0)) || code[41] != 0) key = CKey();
530  }
531  
532  KeyPair::KeyPair(const CKey& key, const uint256* merkle_root)
533  {
534      static_assert(std::tuple_size<KeyType>() == sizeof(secp256k1_keypair));
535      MakeKeyPairData();
536      auto keypair = reinterpret_cast<secp256k1_keypair*>(m_keypair->data());
537      bool success = secp256k1_keypair_create(secp256k1_context_sign, keypair, UCharCast(key.data()));
538      if (success && merkle_root) {
539          secp256k1_xonly_pubkey pubkey;
540          unsigned char pubkey_bytes[32];
541          assert(secp256k1_keypair_xonly_pub(secp256k1_context_static, &pubkey, nullptr, keypair));
542          assert(secp256k1_xonly_pubkey_serialize(secp256k1_context_static, pubkey_bytes, &pubkey));
543          uint256 tweak = XOnlyPubKey(pubkey_bytes).ComputeTapTweakHash(merkle_root->IsNull() ? nullptr : merkle_root);
544          success = secp256k1_keypair_xonly_tweak_add(secp256k1_context_static, keypair, tweak.data());
545      }
546      if (!success) ClearKeyPairData();
547  }
548  
549  bool KeyPair::SignSchnorr(const uint256& hash, std::span<unsigned char> sig, const uint256& aux) const
550  {
551      assert(sig.size() == 64);
552      if (!IsValid()) return false;
553      auto keypair = reinterpret_cast<const secp256k1_keypair*>(m_keypair->data());
554      bool ret = secp256k1_schnorrsig_sign32(secp256k1_context_sign, sig.data(), hash.data(), keypair, aux.data());
555      if (ret) {
556          // Additional verification step to prevent using a potentially corrupted signature
557          secp256k1_xonly_pubkey pubkey_verify;
558          ret = secp256k1_keypair_xonly_pub(secp256k1_context_static, &pubkey_verify, nullptr, keypair);
559          ret &= secp256k1_schnorrsig_verify(secp256k1_context_static, sig.data(), hash.begin(), 32, &pubkey_verify);
560      }
561      if (!ret) memory_cleanse(sig.data(), sig.size());
562      return ret;
563  }
564  
565  bool ECC_InitSanityCheck() {
566      CKey key = GenerateRandomKey();
567      CPubKey pubkey = key.GetPubKey();
568      return key.VerifyPubKey(pubkey);
569  }
570  
571  /** Initialize the elliptic curve support. May not be called twice without calling ECC_Stop first. */
572  static void ECC_Start() {
573      assert(secp256k1_context_sign == nullptr);
574  
575      secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
576      assert(ctx != nullptr);
577  
578      {
579          // Pass in a random blinding seed to the secp256k1 context.
580          std::vector<unsigned char, secure_allocator<unsigned char>> vseed(32);
581          GetRandBytes(vseed);
582          bool ret = secp256k1_context_randomize(ctx, vseed.data());
583          assert(ret);
584      }
585  
586      secp256k1_context_sign = ctx;
587  }
588  
589  /** Deinitialize the elliptic curve support. No-op if ECC_Start wasn't called first. */
590  static void ECC_Stop() {
591      secp256k1_context *ctx = secp256k1_context_sign;
592      secp256k1_context_sign = nullptr;
593  
594      if (ctx) {
595          secp256k1_context_destroy(ctx);
596      }
597  }
598  
599  ECC_Context::ECC_Context()
600  {
601      ECC_Start();
602  }
603  
604  ECC_Context::~ECC_Context()
605  {
606      ECC_Stop();
607  }