[FreshEyes] crypto, refactor: add new KeyPair class #15
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The wallet returns an untweaked internal key for taproot outputs. If the output commits to a tree of scripts, this key needs to be tweaked with the merkle root. Even if the output does not commit to a tree of scripts, BIP341/342 recommend commiting to a hash of the public key. Previously, this logic for applying the taptweak was implemented in the ::SignSchnorr method. Move this tweaking and signing logic to a new class, KeyPair, and add a method to CKey for computing a KeyPair, CKey::ComputeKeyPair. This class is a wrapper for the `secp256k1_keypair` type. The motivation is to be able to use the the tweaked internal key outside of signing, e.g. in silent payments when retreiving the private key before ECDH. Having the KeyPair class is also a general improvement in that we almost always convert to `secp256k1_keypair` objects when using taproot private keys with libsecp256k1. Co-authored-by: Cory Fields <cory-nospam-@coryfields.com>
Reuse existing bip340 test vectors.
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There were 36 issue comments left by 4 reviewers for the pull request |
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| * (this is used for key path spending, with specific | ||
| * Merkle root of the script tree). | ||
| */ | ||
| KeyPair ComputeKeyPair(const uint256* merkle_root) const; |
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https://github.com/bitcoin/bitcoin/pull/30051#discussion_r1596806833at 2024/05/10, 14:11:53 UTC - comment link
https://github.com/bitcoin/bitcoin/pull/30051#discussion_r1596979700at 2024/05/10, 16:44:18 UTC.
| // Repeat the same check, but use the KeyPair directly without any merkle tweak | ||
| KeyPair keypair = key.ComputeKeyPair(/*merkle_root=*/nullptr); | ||
| CKey keypair_seckey; | ||
| BOOST_CHECK(keypair.GetKey(keypair_seckey)); |
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https://github.com/bitcoin/bitcoin/pull/30051#discussion_r1598114179at 2024/05/13, 08:55:21 UTC.
| private: | ||
| KeyPair(const CKey& key, const uint256* merkle_root); | ||
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| using KeyType = std::array<unsigned char, 96>; |
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https://github.com/bitcoin/bitcoin/pull/30051#discussion_r1598119960at 2024/05/13, 08:59:33 UTC.
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The author josibake wrote the following PR called crypto, refactor: add new KeyPair class, issue number 30051 in bitcoin/bitcoin cloned by FreshEyes below:
Broken out from
#28201The wallet returns an untweaked internal key for taproot outputs. If the output commits to a tree of scripts, this key needs to be tweaked with the merkle root. Even if the output does not commit to a tree of scripts, BIP341/342 recommend commiting to a hash of the public key.
Previously, this logic for applying the taptweak was implemented in the
CKey::SignSchnorrmethod.This PR moves introduces a KeyPair class which wraps a
secp256k1_keypairtype and refactors SignSchnorr to use this new KeyPair. The KeyPair class is created with an optional merkle_root argument and the logic from BIP341 is applied depending on the state of the merkle_root argument.The motivation for this refactor is to be able to use the tap tweak logic outside of signing, e.g. in silent payments when retrieving the private key (see
#28201).Outside of silent payments, since we almost always convert a
CKeyto asecp256k1_keypairwhen doing anything with taproot keys, it seems generally useful to have a way to model this type in our code base.