c6cd2b15a007ad0a2d5c4656ae641ba442d8b2fe ci: Add task for static library on Windows + CMake (Hennadii Stepanov)
020bf69a44ba700624d09de0c18ceb867369d24e build: Add extensive docs on visibility issues (Tim Ruffing)
0196e8ade16e2b2d8efadac01d8520205553ee39 build: Introduce `SECP256k1_DLL_EXPORT` macro (Hennadii Stepanov)
9f1b1904a358e4ce7248c6542e8c7ac143ba0e3f refactor: Replace `SECP256K1_API_VAR` with `SECP256K1_API` (Hennadii Stepanov)
ae9db95ceaa2605138fac9c237c640acea3f3bd6 build: Introduce `SECP256K1_STATIC` macro for Windows users (Hennadii Stepanov)
Pull request description:
Previous attempts:
- https://github.com/bitcoin-core/secp256k1/pull/1346
- https://github.com/bitcoin-core/secp256k1/pull/1362
The result is as follows:
1. Simple, concise and extensively documented code.
2. Explicitly documented use cases with no ambiguities.
3. No workarounds for linker warnings.
4. Solves one item in https://github.com/bitcoin-core/secp256k1/issues/1235.
ACKs for top commit:
real-or-random:
utACK c6cd2b15a007ad0a2d5c4656ae641ba442d8b2fe
Tree-SHA512: d58694452d630aefbd047916033249891bc726b7475433aaaa7c3ea2a07ded8f185a598385b67c2ee3440ec5904ff9d9452c97b0961d84dcb2eb2cf46caa171e
The scheme implemented is described below, and largely follows the paper
"SwiftEC: Shallue–van de Woestijne Indifferentiable Function To Elliptic Curves",
by Chavez-Saab, Rodriguez-Henriquez, and Tibouchi
(https://eprint.iacr.org/2022/759).
A new 64-byte public key format is introduced, with the property that *every*
64-byte array is an encoding for a non-infinite curve point. Each curve point
has roughly 2^256 distinct encodings. This permits disguising public keys as
uniformly random bytes.
The new API functions:
* secp256k1_ellswift_encode: convert a normal public key to an ellswift 64-byte
public key, using additional entropy to pick among the many possible
encodings.
* secp256k1_ellswift_decode: convert an ellswift 64-byte public key to a normal
public key.
* secp256k1_ellswift_create: a faster and safer equivalent to calling
secp256k1_ec_pubkey_create + secp256k1_ellswift_encode.
* secp256k1_ellswift_xdh: x-only ECDH directly on ellswift 64-byte public keys,
where the key encodings are fed to the hash function.
The scheme itself is documented in secp256k1_ellswift.h.
