8794a4b3ae QA: add test for HKDF HMAC_SHA256 L32 (Jonas Schnelli)
551d489416 Add HKDF HMAC_SHA256 L=32 implementations (Jonas Schnelli)
3b64f852e4 QA: add test for CKey::Negate() (Jonas Schnelli)
463921bb64 CKey: add method to negate the key (Jonas Schnelli)
Pull request description:
This adds a limited implementation of `HKDF` (defined by rfc5869) that supports only HMAC-SHA256 and length output of 32 bytes (will be required for v2 transport protocol).
This PR also includes a method to negate a private key which is useful to enforce public keys starting with 0x02 (or 0x03) (a requirement for the v2 transport protocol). The new `CKey::Negate()` method is pretty much a wrapper around `secp256k1_ec_privkey_negate()`.
Including tests.
This is a subset of #14032 and a pre-requirement for the v2 transport protocol.
ACKs for commit 8794a4:
Tree-SHA512: 5341929dfa29f5da766ec3612784baec6a3ad69972f08b5a985a8aafdae4dae36f104a2b888d1f5d1f33561456bd111f960d7e32c2cc4fd18e48358468f26c1a
376638afcf