ec973dd197 refactor: remove un-tested early returns (josibake)
72a5822d43 tests: add tests for KeyPair (josibake)
cebb08b121 refactor: move SignSchnorr to KeyPair (josibake)
c39fd39ba8 crypto: add KeyPair wrapper class (josibake)
5d507a0091 tests: add key tweak smoke test (josibake)
f14900b6e4 bench: add benchmark for signing with a taptweak (josibake)
Pull request description:
Broken out from #28201
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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 `CKey::SignSchnorr` method.
This PR moves introduces a KeyPair class which wraps a `secp256k1_keypair` type 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 `CKey` to a `secp256k1_keypair` when doing anything with taproot keys, it seems generally useful to have a way to model this type in our code base.
ACKs for top commit:
paplorinc:
ACK ec973dd197 - will happily reack if you decide to apply @ismaelsadeeq's suggestions
ismaelsadeeq:
Code review ACK ec973dd197
itornaza:
trACK ec973dd197
theStack:
Code-review ACK ec973dd197
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