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 <pubkey.h>
  7  
  8  #include <hash.h>
  9  #include <secp256k1.h>
 10  #include <secp256k1_ellswift.h>
 11  #include <secp256k1_extrakeys.h>
 12  #include <secp256k1_recovery.h>
 13  #include <secp256k1_schnorrsig.h>
 14  #include <span.h>
 15  #include <uint256.h>
 16  #include <util/strencodings.h>
 17  
 18  #include <algorithm>
 19  #include <cassert>
 20  
 21  using namespace util::hex_literals;
 22  
 23  namespace {
 24  
 25  struct Secp256k1SelfTester
 26  {
 27      Secp256k1SelfTester() {
 28          /* Run libsecp256k1 self-test before using the secp256k1_context_static. */
 29          secp256k1_selftest();
 30      }
 31  } SECP256K1_SELFTESTER;
 32  
 33  } // namespace
 34  
 35  /** This function is taken from the libsecp256k1 distribution and implements
 36   *  DER parsing for ECDSA signatures, while supporting an arbitrary subset of
 37   *  format violations.
 38   *
 39   *  Supported violations include negative integers, excessive padding, garbage
 40   *  at the end, and overly long length descriptors. This is safe to use in
 41   *  Bitcoin because since the activation of BIP66, signatures are verified to be
 42   *  strict DER before being passed to this module, and we know it supports all
 43   *  violations present in the blockchain before that point.
 44   */
 45  int ecdsa_signature_parse_der_lax(secp256k1_ecdsa_signature* sig, const unsigned char *input, size_t inputlen) {
 46      size_t rpos, rlen, spos, slen;
 47      size_t pos = 0;
 48      size_t lenbyte;
 49      unsigned char tmpsig[64] = {0};
 50      int overflow = 0;
 51  
 52      /* Hack to initialize sig with a correctly-parsed but invalid signature. */
 53      secp256k1_ecdsa_signature_parse_compact(secp256k1_context_static, sig, tmpsig);
 54  
 55      /* Sequence tag byte */
 56      if (pos == inputlen || input[pos] != 0x30) {
 57          return 0;
 58      }
 59      pos++;
 60  
 61      /* Sequence length bytes */
 62      if (pos == inputlen) {
 63          return 0;
 64      }
 65      lenbyte = input[pos++];
 66      if (lenbyte & 0x80) {
 67          lenbyte -= 0x80;
 68          if (lenbyte > inputlen - pos) {
 69              return 0;
 70          }
 71          pos += lenbyte;
 72      }
 73  
 74      /* Integer tag byte for R */
 75      if (pos == inputlen || input[pos] != 0x02) {
 76          return 0;
 77      }
 78      pos++;
 79  
 80      /* Integer length for R */
 81      if (pos == inputlen) {
 82          return 0;
 83      }
 84      lenbyte = input[pos++];
 85      if (lenbyte & 0x80) {
 86          lenbyte -= 0x80;
 87          if (lenbyte > inputlen - pos) {
 88              return 0;
 89          }
 90          while (lenbyte > 0 && input[pos] == 0) {
 91              pos++;
 92              lenbyte--;
 93          }
 94          static_assert(sizeof(size_t) >= 4, "size_t too small");
 95          if (lenbyte >= 4) {
 96              return 0;
 97          }
 98          rlen = 0;
 99          while (lenbyte > 0) {
100              rlen = (rlen << 8) + input[pos];
101              pos++;
102              lenbyte--;
103          }
104      } else {
105          rlen = lenbyte;
106      }
107      if (rlen > inputlen - pos) {
108          return 0;
109      }
110      rpos = pos;
111      pos += rlen;
112  
113      /* Integer tag byte for S */
114      if (pos == inputlen || input[pos] != 0x02) {
115          return 0;
116      }
117      pos++;
118  
119      /* Integer length for S */
120      if (pos == inputlen) {
121          return 0;
122      }
123      lenbyte = input[pos++];
124      if (lenbyte & 0x80) {
125          lenbyte -= 0x80;
126          if (lenbyte > inputlen - pos) {
127              return 0;
128          }
129          while (lenbyte > 0 && input[pos] == 0) {
130              pos++;
131              lenbyte--;
132          }
133          static_assert(sizeof(size_t) >= 4, "size_t too small");
134          if (lenbyte >= 4) {
135              return 0;
136          }
137          slen = 0;
138          while (lenbyte > 0) {
139              slen = (slen << 8) + input[pos];
140              pos++;
141              lenbyte--;
142          }
143      } else {
144          slen = lenbyte;
145      }
146      if (slen > inputlen - pos) {
147          return 0;
148      }
149      spos = pos;
150  
151      /* Ignore leading zeroes in R */
152      while (rlen > 0 && input[rpos] == 0) {
153          rlen--;
154          rpos++;
155      }
156      /* Copy R value */
157      if (rlen > 32) {
158          overflow = 1;
159      } else {
160          memcpy(tmpsig + 32 - rlen, input + rpos, rlen);
161      }
162  
163      /* Ignore leading zeroes in S */
164      while (slen > 0 && input[spos] == 0) {
165          slen--;
166          spos++;
167      }
168      /* Copy S value */
169      if (slen > 32) {
170          overflow = 1;
171      } else {
172          memcpy(tmpsig + 64 - slen, input + spos, slen);
173      }
174  
175      if (!overflow) {
176          overflow = !secp256k1_ecdsa_signature_parse_compact(secp256k1_context_static, sig, tmpsig);
177      }
178      if (overflow) {
179          /* Overwrite the result again with a correctly-parsed but invalid
180             signature if parsing failed. */
181          memset(tmpsig, 0, 64);
182          secp256k1_ecdsa_signature_parse_compact(secp256k1_context_static, sig, tmpsig);
183      }
184      return 1;
185  }
186  
187  /** Nothing Up My Sleeve (NUMS) point
188   *
189   *  NUMS_H is a point with an unknown discrete logarithm, constructed by taking the sha256 of 'g'
190   *  (uncompressed encoding), which happens to be a point on the curve.
191   *
192   *  For an example script for calculating H, refer to the unit tests in
193   *  ./test/functional/test_framework/crypto/secp256k1.py
194   */
195  constexpr XOnlyPubKey XOnlyPubKey::NUMS_H{
196      // Use immediate lambda to work around GCC-14 bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117966
197      []() consteval { return XOnlyPubKey{"50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0"_hex_u8}; }(),
198  };
199  
200  std::vector<CKeyID> XOnlyPubKey::GetKeyIDs() const
201  {
202      std::vector<CKeyID> out;
203      // For now, use the old full pubkey-based key derivation logic. As it is indexed by
204      // Hash160(full pubkey), we need to return both a version prefixed with 0x02, and one
205      // with 0x03.
206      unsigned char b[33] = {0x02};
207      std::copy(m_keydata.begin(), m_keydata.end(), b + 1);
208      CPubKey fullpubkey;
209      fullpubkey.Set(b, b + 33);
210      out.push_back(fullpubkey.GetID());
211      b[0] = 0x03;
212      fullpubkey.Set(b, b + 33);
213      out.push_back(fullpubkey.GetID());
214      return out;
215  }
216  
217  CPubKey XOnlyPubKey::GetEvenCorrespondingCPubKey() const
218  {
219      unsigned char full_key[CPubKey::COMPRESSED_SIZE] = {0x02};
220      std::copy(begin(), end(), full_key + 1);
221      return CPubKey{full_key};
222  }
223  
224  bool XOnlyPubKey::IsFullyValid() const
225  {
226      secp256k1_xonly_pubkey pubkey;
227      return secp256k1_xonly_pubkey_parse(secp256k1_context_static, &pubkey, m_keydata.data());
228  }
229  
230  bool XOnlyPubKey::VerifySchnorr(const uint256& msg, std::span<const unsigned char> sigbytes) const
231  {
232      assert(sigbytes.size() == 64);
233      secp256k1_xonly_pubkey pubkey;
234      if (!secp256k1_xonly_pubkey_parse(secp256k1_context_static, &pubkey, m_keydata.data())) return false;
235      return secp256k1_schnorrsig_verify(secp256k1_context_static, sigbytes.data(), msg.begin(), 32, &pubkey);
236  }
237  
238  static const HashWriter HASHER_TAPTWEAK{TaggedHash("TapTweak")};
239  
240  uint256 XOnlyPubKey::ComputeTapTweakHash(const uint256* merkle_root) const
241  {
242      if (merkle_root == nullptr) {
243          // We have no scripts. The actual tweak does not matter, but follow BIP341 here to
244          // allow for reproducible tweaking.
245          return (HashWriter{HASHER_TAPTWEAK} << m_keydata).GetSHA256();
246      } else {
247          return (HashWriter{HASHER_TAPTWEAK} << m_keydata << *merkle_root).GetSHA256();
248      }
249  }
250  
251  bool XOnlyPubKey::CheckTapTweak(const XOnlyPubKey& internal, const uint256& merkle_root, bool parity) const
252  {
253      secp256k1_xonly_pubkey internal_key;
254      if (!secp256k1_xonly_pubkey_parse(secp256k1_context_static, &internal_key, internal.data())) return false;
255      uint256 tweak = internal.ComputeTapTweakHash(&merkle_root);
256      return secp256k1_xonly_pubkey_tweak_add_check(secp256k1_context_static, m_keydata.begin(), parity, &internal_key, tweak.begin());
257  }
258  
259  std::optional<std::pair<XOnlyPubKey, bool>> XOnlyPubKey::CreateTapTweak(const uint256* merkle_root) const
260  {
261      secp256k1_xonly_pubkey base_point;
262      if (!secp256k1_xonly_pubkey_parse(secp256k1_context_static, &base_point, data())) return std::nullopt;
263      secp256k1_pubkey out;
264      uint256 tweak = ComputeTapTweakHash(merkle_root);
265      if (!secp256k1_xonly_pubkey_tweak_add(secp256k1_context_static, &out, &base_point, tweak.data())) return std::nullopt;
266      int parity = -1;
267      std::pair<XOnlyPubKey, bool> ret;
268      secp256k1_xonly_pubkey out_xonly;
269      if (!secp256k1_xonly_pubkey_from_pubkey(secp256k1_context_static, &out_xonly, &parity, &out)) return std::nullopt;
270      secp256k1_xonly_pubkey_serialize(secp256k1_context_static, ret.first.begin(), &out_xonly);
271      assert(parity == 0 || parity == 1);
272      ret.second = parity;
273      return ret;
274  }
275  
276  
277  bool CPubKey::Verify(const uint256 &hash, const std::vector<unsigned char>& vchSig) const {
278      if (!IsValid())
279          return false;
280      secp256k1_pubkey pubkey;
281      secp256k1_ecdsa_signature sig;
282      if (!secp256k1_ec_pubkey_parse(secp256k1_context_static, &pubkey, vch, size())) {
283          return false;
284      }
285      if (!ecdsa_signature_parse_der_lax(&sig, vchSig.data(), vchSig.size())) {
286          return false;
287      }
288      /* libsecp256k1's ECDSA verification requires lower-S signatures, which have
289       * not historically been enforced in Bitcoin, so normalize them first. */
290      secp256k1_ecdsa_signature_normalize(secp256k1_context_static, &sig, &sig);
291      return secp256k1_ecdsa_verify(secp256k1_context_static, &sig, hash.begin(), &pubkey);
292  }
293  
294  bool CPubKey::RecoverCompact(const uint256 &hash, const std::vector<unsigned char>& vchSig) {
295      if (vchSig.size() != COMPACT_SIGNATURE_SIZE)
296          return false;
297      int recid = (vchSig[0] - 27) & 3;
298      bool fComp = ((vchSig[0] - 27) & 4) != 0;
299      secp256k1_pubkey pubkey;
300      secp256k1_ecdsa_recoverable_signature sig;
301      if (!secp256k1_ecdsa_recoverable_signature_parse_compact(secp256k1_context_static, &sig, &vchSig[1], recid)) {
302          return false;
303      }
304      if (!secp256k1_ecdsa_recover(secp256k1_context_static, &pubkey, &sig, hash.begin())) {
305          return false;
306      }
307      unsigned char pub[SIZE];
308      size_t publen = SIZE;
309      secp256k1_ec_pubkey_serialize(secp256k1_context_static, pub, &publen, &pubkey, fComp ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
310      Set(pub, pub + publen);
311      return true;
312  }
313  
314  bool CPubKey::IsFullyValid() const {
315      if (!IsValid())
316          return false;
317      secp256k1_pubkey pubkey;
318      return secp256k1_ec_pubkey_parse(secp256k1_context_static, &pubkey, vch, size());
319  }
320  
321  bool CPubKey::Decompress() {
322      if (!IsValid())
323          return false;
324      secp256k1_pubkey pubkey;
325      if (!secp256k1_ec_pubkey_parse(secp256k1_context_static, &pubkey, vch, size())) {
326          return false;
327      }
328      unsigned char pub[SIZE];
329      size_t publen = SIZE;
330      secp256k1_ec_pubkey_serialize(secp256k1_context_static, pub, &publen, &pubkey, SECP256K1_EC_UNCOMPRESSED);
331      Set(pub, pub + publen);
332      return true;
333  }
334  
335  bool CPubKey::Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
336      assert(IsValid());
337      assert((nChild >> 31) == 0);
338      assert(size() == COMPRESSED_SIZE);
339      unsigned char out[64];
340      BIP32Hash(cc, nChild, *begin(), begin()+1, out);
341      memcpy(ccChild.begin(), out+32, 32);
342      secp256k1_pubkey pubkey;
343      if (!secp256k1_ec_pubkey_parse(secp256k1_context_static, &pubkey, vch, size())) {
344          return false;
345      }
346      if (!secp256k1_ec_pubkey_tweak_add(secp256k1_context_static, &pubkey, out)) {
347          return false;
348      }
349      unsigned char pub[COMPRESSED_SIZE];
350      size_t publen = COMPRESSED_SIZE;
351      secp256k1_ec_pubkey_serialize(secp256k1_context_static, pub, &publen, &pubkey, SECP256K1_EC_COMPRESSED);
352      pubkeyChild.Set(pub, pub + publen);
353      return true;
354  }
355  
356  EllSwiftPubKey::EllSwiftPubKey(std::span<const std::byte> ellswift) noexcept
357  {
358      assert(ellswift.size() == SIZE);
359      std::copy(ellswift.begin(), ellswift.end(), m_pubkey.begin());
360  }
361  
362  CPubKey EllSwiftPubKey::Decode() const
363  {
364      secp256k1_pubkey pubkey;
365      secp256k1_ellswift_decode(secp256k1_context_static, &pubkey, UCharCast(m_pubkey.data()));
366  
367      size_t sz = CPubKey::COMPRESSED_SIZE;
368      std::array<uint8_t, CPubKey::COMPRESSED_SIZE> vch_bytes;
369  
370      secp256k1_ec_pubkey_serialize(secp256k1_context_static, vch_bytes.data(), &sz, &pubkey, SECP256K1_EC_COMPRESSED);
371      assert(sz == vch_bytes.size());
372  
373      return CPubKey{vch_bytes.begin(), vch_bytes.end()};
374  }
375  
376  void CExtPubKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
377      code[0] = nDepth;
378      memcpy(code+1, vchFingerprint, 4);
379      WriteBE32(code+5, nChild);
380      memcpy(code+9, chaincode.begin(), 32);
381      assert(pubkey.size() == CPubKey::COMPRESSED_SIZE);
382      memcpy(code+41, pubkey.begin(), CPubKey::COMPRESSED_SIZE);
383  }
384  
385  void CExtPubKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
386      nDepth = code[0];
387      memcpy(vchFingerprint, code+1, 4);
388      nChild = ReadBE32(code+5);
389      memcpy(chaincode.begin(), code+9, 32);
390      pubkey.Set(code+41, code+BIP32_EXTKEY_SIZE);
391      if ((nDepth == 0 && (nChild != 0 || ReadLE32(vchFingerprint) != 0)) || !pubkey.IsFullyValid()) pubkey = CPubKey();
392  }
393  
394  void CExtPubKey::EncodeWithVersion(unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE]) const
395  {
396      memcpy(code, version, 4);
397      Encode(&code[4]);
398  }
399  
400  void CExtPubKey::DecodeWithVersion(const unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE])
401  {
402      memcpy(version, code, 4);
403      Decode(&code[4]);
404  }
405  
406  bool CExtPubKey::Derive(CExtPubKey &out, unsigned int _nChild) const {
407      if (nDepth == std::numeric_limits<unsigned char>::max()) return false;
408      out.nDepth = nDepth + 1;
409      CKeyID id = pubkey.GetID();
410      memcpy(out.vchFingerprint, &id, 4);
411      out.nChild = _nChild;
412      return pubkey.Derive(out.pubkey, out.chaincode, _nChild, chaincode);
413  }
414  
415  /* static */ bool CPubKey::CheckLowS(const std::vector<unsigned char>& vchSig) {
416      secp256k1_ecdsa_signature sig;
417      if (!ecdsa_signature_parse_der_lax(&sig, vchSig.data(), vchSig.size())) {
418          return false;
419      }
420      return (!secp256k1_ecdsa_signature_normalize(secp256k1_context_static, nullptr, &sig));
421  }