1  // Copyright (c) 2009-2022 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  bool CKey::Negate()
170  {
171      assert(keydata);
172      return secp256k1_ec_seckey_negate(secp256k1_context_sign, keydata->data());
173  }
174  
175  CPrivKey CKey::GetPrivKey() const {
176      assert(keydata);
177      CPrivKey seckey;
178      int ret;
179      size_t seckeylen;
180      seckey.resize(SIZE);
181      seckeylen = SIZE;
182      ret = ec_seckey_export_der(secp256k1_context_sign, seckey.data(), &seckeylen, UCharCast(begin()), fCompressed);
183      assert(ret);
184      seckey.resize(seckeylen);
185      return seckey;
186  }
187  
188  CPubKey CKey::GetPubKey() const {
189      assert(keydata);
190      secp256k1_pubkey pubkey;
191      size_t clen = CPubKey::SIZE;
192      CPubKey result;
193      int ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pubkey, UCharCast(begin()));
194      assert(ret);
195      secp256k1_ec_pubkey_serialize(secp256k1_context_sign, (unsigned char*)result.begin(), &clen, &pubkey, fCompressed ? SECP256K1_EC_COMPRESSED : SECP256K1_EC_UNCOMPRESSED);
196      assert(result.size() == clen);
197      assert(result.IsValid());
198      return result;
199  }
200  
201  // Check that the sig has a low R value and will be less than 71 bytes
202  bool SigHasLowR(const secp256k1_ecdsa_signature* sig)
203  {
204      unsigned char compact_sig[64];
205      secp256k1_ecdsa_signature_serialize_compact(secp256k1_context_sign, compact_sig, sig);
206  
207      // In DER serialization, all values are interpreted as big-endian, signed integers. The highest bit in the integer indicates
208      // its signed-ness; 0 is positive, 1 is negative. When the value is interpreted as a negative integer, it must be converted
209      // to a positive value by prepending a 0x00 byte so that the highest bit is 0. We can avoid this prepending by ensuring that
210      // our highest bit is always 0, and thus we must check that the first byte is less than 0x80.
211      return compact_sig[0] < 0x80;
212  }
213  
214  bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, bool grind, uint32_t test_case) const {
215      if (!keydata)
216          return false;
217      vchSig.resize(CPubKey::SIGNATURE_SIZE);
218      size_t nSigLen = CPubKey::SIGNATURE_SIZE;
219      unsigned char extra_entropy[32] = {0};
220      WriteLE32(extra_entropy, test_case);
221      secp256k1_ecdsa_signature sig;
222      uint32_t counter = 0;
223      int ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, (!grind && test_case) ? extra_entropy : nullptr);
224  
225      // Grind for low R
226      while (ret && !SigHasLowR(&sig) && grind) {
227          WriteLE32(extra_entropy, ++counter);
228          ret = secp256k1_ecdsa_sign(secp256k1_context_sign, &sig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, extra_entropy);
229      }
230      assert(ret);
231      secp256k1_ecdsa_signature_serialize_der(secp256k1_context_sign, vchSig.data(), &nSigLen, &sig);
232      vchSig.resize(nSigLen);
233      // Additional verification step to prevent using a potentially corrupted signature
234      secp256k1_pubkey pk;
235      ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &pk, UCharCast(begin()));
236      assert(ret);
237      ret = secp256k1_ecdsa_verify(secp256k1_context_static, &sig, hash.begin(), &pk);
238      assert(ret);
239      return true;
240  }
241  
242  bool CKey::VerifyPubKey(const CPubKey& pubkey) const {
243      if (pubkey.IsCompressed() != fCompressed) {
244          return false;
245      }
246      unsigned char rnd[8];
247      std::string str = "Bitcoin key verification\n";
248      GetRandBytes(rnd);
249      uint256 hash{Hash(str, rnd)};
250      std::vector<unsigned char> vchSig;
251      Sign(hash, vchSig);
252      return pubkey.Verify(hash, vchSig);
253  }
254  
255  bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
256      if (!keydata)
257          return false;
258      vchSig.resize(CPubKey::COMPACT_SIGNATURE_SIZE);
259      int rec = -1;
260      secp256k1_ecdsa_recoverable_signature rsig;
261      int ret = secp256k1_ecdsa_sign_recoverable(secp256k1_context_sign, &rsig, hash.begin(), UCharCast(begin()), secp256k1_nonce_function_rfc6979, nullptr);
262      assert(ret);
263      ret = secp256k1_ecdsa_recoverable_signature_serialize_compact(secp256k1_context_sign, &vchSig[1], &rec, &rsig);
264      assert(ret);
265      assert(rec != -1);
266      vchSig[0] = 27 + rec + (fCompressed ? 4 : 0);
267      // Additional verification step to prevent using a potentially corrupted signature
268      secp256k1_pubkey epk, rpk;
269      ret = secp256k1_ec_pubkey_create(secp256k1_context_sign, &epk, UCharCast(begin()));
270      assert(ret);
271      ret = secp256k1_ecdsa_recover(secp256k1_context_static, &rpk, &rsig, hash.begin());
272      assert(ret);
273      ret = secp256k1_ec_pubkey_cmp(secp256k1_context_static, &epk, &rpk);
274      assert(ret == 0);
275      return true;
276  }
277  
278  bool CKey::SignSchnorr(const uint256& hash, Span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const
279  {
280      assert(sig.size() == 64);
281      secp256k1_keypair keypair;
282      if (!secp256k1_keypair_create(secp256k1_context_sign, &keypair, UCharCast(begin()))) return false;
283      if (merkle_root) {
284          secp256k1_xonly_pubkey pubkey;
285          if (!secp256k1_keypair_xonly_pub(secp256k1_context_sign, &pubkey, nullptr, &keypair)) return false;
286          unsigned char pubkey_bytes[32];
287          if (!secp256k1_xonly_pubkey_serialize(secp256k1_context_sign, pubkey_bytes, &pubkey)) return false;
288          uint256 tweak = XOnlyPubKey(pubkey_bytes).ComputeTapTweakHash(merkle_root->IsNull() ? nullptr : merkle_root);
289          if (!secp256k1_keypair_xonly_tweak_add(secp256k1_context_static, &keypair, tweak.data())) return false;
290      }
291      bool ret = secp256k1_schnorrsig_sign32(secp256k1_context_sign, sig.data(), hash.data(), &keypair, aux.data());
292      if (ret) {
293          // Additional verification step to prevent using a potentially corrupted signature
294          secp256k1_xonly_pubkey pubkey_verify;
295          ret = secp256k1_keypair_xonly_pub(secp256k1_context_static, &pubkey_verify, nullptr, &keypair);
296          ret &= secp256k1_schnorrsig_verify(secp256k1_context_static, sig.data(), hash.begin(), 32, &pubkey_verify);
297      }
298      if (!ret) memory_cleanse(sig.data(), sig.size());
299      memory_cleanse(&keypair, sizeof(keypair));
300      return ret;
301  }
302  
303  bool CKey::Load(const CPrivKey &seckey, const CPubKey &vchPubKey, bool fSkipCheck=false) {
304      MakeKeyData();
305      if (!ec_seckey_import_der(secp256k1_context_sign, (unsigned char*)begin(), seckey.data(), seckey.size())) {
306          ClearKeyData();
307          return false;
308      }
309      fCompressed = vchPubKey.IsCompressed();
310  
311      if (fSkipCheck)
312          return true;
313  
314      return VerifyPubKey(vchPubKey);
315  }
316  
317  bool CKey::Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const {
318      assert(IsValid());
319      assert(IsCompressed());
320      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
321      if ((nChild >> 31) == 0) {
322          CPubKey pubkey = GetPubKey();
323          assert(pubkey.size() == CPubKey::COMPRESSED_SIZE);
324          BIP32Hash(cc, nChild, *pubkey.begin(), pubkey.begin()+1, vout.data());
325      } else {
326          assert(size() == 32);
327          BIP32Hash(cc, nChild, 0, UCharCast(begin()), vout.data());
328      }
329      memcpy(ccChild.begin(), vout.data()+32, 32);
330      keyChild.Set(begin(), begin() + 32, true);
331      bool ret = secp256k1_ec_seckey_tweak_add(secp256k1_context_sign, (unsigned char*)keyChild.begin(), vout.data());
332      if (!ret) keyChild.ClearKeyData();
333      return ret;
334  }
335  
336  EllSwiftPubKey CKey::EllSwiftCreate(Span<const std::byte> ent32) const
337  {
338      assert(keydata);
339      assert(ent32.size() == 32);
340      std::array<std::byte, EllSwiftPubKey::size()> encoded_pubkey;
341  
342      auto success = secp256k1_ellswift_create(secp256k1_context_sign,
343                                               UCharCast(encoded_pubkey.data()),
344                                               keydata->data(),
345                                               UCharCast(ent32.data()));
346  
347      // Should always succeed for valid keys (asserted above).
348      assert(success);
349      return {encoded_pubkey};
350  }
351  
352  ECDHSecret CKey::ComputeBIP324ECDHSecret(const EllSwiftPubKey& their_ellswift, const EllSwiftPubKey& our_ellswift, bool initiating) const
353  {
354      assert(keydata);
355  
356      ECDHSecret output;
357      // BIP324 uses the initiator as party A, and the responder as party B. Remap the inputs
358      // accordingly:
359      bool success = secp256k1_ellswift_xdh(secp256k1_context_sign,
360                                            UCharCast(output.data()),
361                                            UCharCast(initiating ? our_ellswift.data() : their_ellswift.data()),
362                                            UCharCast(initiating ? their_ellswift.data() : our_ellswift.data()),
363                                            keydata->data(),
364                                            initiating ? 0 : 1,
365                                            secp256k1_ellswift_xdh_hash_function_bip324,
366                                            nullptr);
367      // Should always succeed for valid keys (assert above).
368      assert(success);
369      return output;
370  }
371  
372  CKey GenerateRandomKey(bool compressed) noexcept
373  {
374      CKey key;
375      key.MakeNewKey(/*fCompressed=*/compressed);
376      return key;
377  }
378  
379  bool CExtKey::Derive(CExtKey &out, unsigned int _nChild) const {
380      if (nDepth == std::numeric_limits<unsigned char>::max()) return false;
381      out.nDepth = nDepth + 1;
382      CKeyID id = key.GetPubKey().GetID();
383      memcpy(out.vchFingerprint, &id, 4);
384      out.nChild = _nChild;
385      return key.Derive(out.key, out.chaincode, _nChild, chaincode);
386  }
387  
388  void CExtKey::SetSeed(Span<const std::byte> seed)
389  {
390      static const unsigned char hashkey[] = {'B','i','t','c','o','i','n',' ','s','e','e','d'};
391      std::vector<unsigned char, secure_allocator<unsigned char>> vout(64);
392      CHMAC_SHA512{hashkey, sizeof(hashkey)}.Write(UCharCast(seed.data()), seed.size()).Finalize(vout.data());
393      key.Set(vout.data(), vout.data() + 32, true);
394      memcpy(chaincode.begin(), vout.data() + 32, 32);
395      nDepth = 0;
396      nChild = 0;
397      memset(vchFingerprint, 0, sizeof(vchFingerprint));
398  }
399  
400  CExtPubKey CExtKey::Neuter() const {
401      CExtPubKey ret;
402      ret.nDepth = nDepth;
403      memcpy(ret.vchFingerprint, vchFingerprint, 4);
404      ret.nChild = nChild;
405      ret.pubkey = key.GetPubKey();
406      ret.chaincode = chaincode;
407      return ret;
408  }
409  
410  void CExtKey::Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const {
411      code[0] = nDepth;
412      memcpy(code+1, vchFingerprint, 4);
413      WriteBE32(code+5, nChild);
414      memcpy(code+9, chaincode.begin(), 32);
415      code[41] = 0;
416      assert(key.size() == 32);
417      memcpy(code+42, key.begin(), 32);
418  }
419  
420  void CExtKey::Decode(const unsigned char code[BIP32_EXTKEY_SIZE]) {
421      nDepth = code[0];
422      memcpy(vchFingerprint, code+1, 4);
423      nChild = ReadBE32(code+5);
424      memcpy(chaincode.begin(), code+9, 32);
425      key.Set(code+42, code+BIP32_EXTKEY_SIZE, true);
426      if ((nDepth == 0 && (nChild != 0 || ReadLE32(vchFingerprint) != 0)) || code[41] != 0) key = CKey();
427  }
428  
429  bool ECC_InitSanityCheck() {
430      CKey key = GenerateRandomKey();
431      CPubKey pubkey = key.GetPubKey();
432      return key.VerifyPubKey(pubkey);
433  }
434  
435  void ECC_Start() {
436      assert(secp256k1_context_sign == nullptr);
437  
438      secp256k1_context *ctx = secp256k1_context_create(SECP256K1_CONTEXT_NONE);
439      assert(ctx != nullptr);
440  
441      {
442          // Pass in a random blinding seed to the secp256k1 context.
443          std::vector<unsigned char, secure_allocator<unsigned char>> vseed(32);
444          GetRandBytes(vseed);
445          bool ret = secp256k1_context_randomize(ctx, vseed.data());
446          assert(ret);
447      }
448  
449      secp256k1_context_sign = ctx;
450  }
451  
452  void ECC_Stop() {
453      secp256k1_context *ctx = secp256k1_context_sign;
454      secp256k1_context_sign = nullptr;
455  
456      if (ctx) {
457          secp256k1_context_destroy(ctx);
458      }
459  }