Details
- Reviewers
deadalnix jasonbcox - Group Reviewers
Restricted Project - Maniphest Tasks
- T527: Add Schnorr support to OP_CHECKSIG and OP_CHECKDATASIG
- Commits
- rSTAGINGa8fdf6bf4c9e: Add CKey::SignSchnorr and CPubKey::VerifySchnorr
rABCa8fdf6bf4c9e: Add CKey::SignSchnorr and CPubKey::VerifySchnorr
- Tests added that mimic those used for SignECDSA/VerifyECDSA.
- Test that nonce reuse does not occur for ECDSA and Schnorr.
Diff Detail
- Repository
- rABC Bitcoin ABC
- Branch
- markmerge2
- Lint
Lint Passed - Unit
No Test Coverage - Build Status
Buildable 4730 Build 7523: Bitcoin ABC Buildbot (legacy) Build 7522: arc lint + arc unit
Event Timeline
| src/key.cpp | ||
|---|---|---|
| 207 ↗ | (On Diff #6754) | Braces |
| 219 ↗ | (On Diff #6754) | Is there a reason why the nonce generation function is passed explicitly ? Reusing k between ECDSA and Schnorr would leak the private key, so we we should have a test case that sign with both ECDSA and schnorr and ensure they private key extraction fails. |
| 220 ↗ | (On Diff #6754) | I'm not sure wy these assert rather than return false. |
| src/key.cpp | ||
|---|---|---|
| 207 ↗ | (On Diff #6754) | k :-) |
| 219 ↗ | (On Diff #6754) | Just copying SignECDSA(). No other reason, indeed it doesn't seem necessary. Yes, the reused-k check is indirectly done in the last two tests of deterministic signing. You can see that for the same key signing the same message, ECDSA deterministically produces r=c6ab5f8acfccc114da39dd5ad0b1ef4d39df6a721e824c22e00b7bc7944a1f78 and Schnorr produces r=e7167ae0afbba6019b4c7fcfe6de79165d555e8295bd72da1b8aa1a5b5430588. But this can definitely be tested more explicitly. |
| 220 ↗ | (On Diff #6754) | Yep, I dunno, just copying SignECDSA() :-) |
| src/test/key_tests.cpp | ||
|---|---|---|
| 46 ↗ | (On Diff #6756) | You should use .data() here rather than .begin() . |
| src/test/key_tests.cpp | ||
|---|---|---|
| 46 ↗ | (On Diff #6756) | OK, changed -- I'm curious what's the reasoning by the way? It sounds like most C++ people prefer iterators to pointers. e.g. https://stackoverflow.com/questions/25393431/c-vector-iterators-vs-pointers (My C++ is very rusty, I haven't used it in like 15 years.) |
| src/test/key_tests.cpp | ||
|---|---|---|
| 46 ↗ | (On Diff #6756) | Iterators have better null safety. "not found" situations tend to return container::end() rather than null. |
| src/test/key_tests.cpp | ||
|---|---|---|
| 46 ↗ | (On Diff #6756) | data provides you a pointer to the storage. begin provides you an iterator, that can anything. For completeness, &sig[0] is undefined when sig.size() == 0 . But actually in that case you aren't using memcpy or anything, so iterators are the way to go with std::copy. |
OK so I was an idiot and begin is the way to go with std::copy. Most of the code use memcpy so I was confused. Either way it's fine as std::copy knows about pointers.
rebase & fix
- remove pubkey generation from SignSchnorr()
- switch from data() to begin() in key_tests
Note: this python code reproduces the first Schnorr deterministic signature
#!/usr/bin/env python3 # Reproduce Bitcoin ABC's deterministic Schnorr signature near end of key_tests.cpp from ecdsa.numbertheory import jacobi from ecdsa import SECP256k1 import hashlib import hmac G = SECP256k1.generator p = SECP256k1.curve.p() n = SECP256k1.order def sha(b): return hashlib.sha256(b).digest() msg = b"Very deterministic message" msghash = sha(sha(msg)) assert msghash == bytes.fromhex("5255683da567900bfd3e786ed8836a4e7763c221bf1ac20ece2a5171b9199e8a") print("msg = "+repr(msg)) print("msghash = "+msghash.hex()) # 5HxWvvfubhXpYYpS3tJkw6fq9jE9j18THftkZjHHfmFiWtmAbrj # Kwr371tjA9u2rFSMZjTNun2PXXP3WPZu2afRHTcta6KxEUdm1vEw privkey = 0x12b004fff7f4b69ef8650e767f18f11ede158148b425660723b9f9a66e61f747 print("privkey = "+hex(privkey)) # pubkey point P = privkey*G comppub = (b'\x03' if (P.y()&1) else b'\x02') + P.x().to_bytes(32,'big') assert comppub == bytes.fromhex("030b4c866585dd868a9d62348a9cd008d6a312937048fff31670e7e920cfc7a744") ### Validate the signature found in the code sig = bytes.fromhex("2c56731ac2f7a7e7f11518fc7722a166b02438924ca9d8b4d1113" "47b81d0717571846de67ad3d913a8fdf9d8f3f73161a4c48ae81c" "b183b214765feb86e255ce") r = int.from_bytes(sig[:32],'big') s = int.from_bytes(sig[32:],'big') print("sig.r = " + hex(r)) print("sig.s = " + hex(s)) e = int.from_bytes(sha(r.to_bytes(32, 'big') + comppub + msghash), 'big') % n print("e = " + hex(e)) checkR = s*G + (n-e)*P print("chk.rx = " + hex(checkR.x())) print("chk.ry = " + hex(checkR.y())) print("jacobi(chk.y) = %+d"%(jacobi(checkR.y(),p))) assert checkR.x() == r ### Now try to reconstruct the deterministic nonce # see secp256k1_schnorr_sig_generate_k() in schnorr_impl.h # and nonce_function_rfc6979() in secp256k1.c algo16 = b"Schnorr+SHA256 " ndata = b'' V = b'\x01'*32 K = b'\x00'*32 buf = privkey.to_bytes(32,'big') + msghash + ndata + algo16 # initialize K = hmac.HMAC(K, V+b'\x00'+buf, 'sha256').digest() V = hmac.HMAC(K, V, 'sha256').digest() K = hmac.HMAC(K, V+b'\x01'+buf, 'sha256').digest() V = hmac.HMAC(K, V, 'sha256').digest() # generate once V = hmac.HMAC(K, V, 'sha256').digest() T = b'' k = int.from_bytes(V, 'big') print("nonce k = " + hex(k)) R = k*G print(" (kG).x = " + hex(R.x())) print("+(kG).y = " + hex(R.y())) print("jacobi((kG).y) = %+d"%(jacobi(R.y(),p))) print("-(kG).y = " + hex(p-R.y()))