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.
bef448f9af248dba016883401de07b431f3e686e cmake: Fix library ABI versioning (Hennadii Stepanov)
Pull request description:
This change emulates Libtool to make sure Libtool and CMake agree on the ABI version.
To test, one needs to simulate a release with backward-compatible API changes, which means the following changes in `configure.ac` and `CMakeLists.txt`:
- incrementing of `*_LIB_VERSION_CURRENT`
- setting `*_LIB_VERSION_REVISION` to zero
- incrementing of `*_LIB_VERSION_AGE`
ACKs for top commit:
real-or-random:
ACK bef448f9af248dba016883401de07b431f3e686e diff looks good and I tested on Linux
Tree-SHA512: f7551fc7377ea50c8bc32d14108a034a1f91ebbb63d5fec562e5cc28416637834b9a4dcba3692df1780adcd1212ad4f238dc0219ab5add68bd88a5a458572ee5
An executable target in the `COMMAND` option will automatically be
replaced by the location of the executable created at build time.
This change fixes tests for Windows binaries using Wine.
71f746c057a66d5ae0dfdb5d439bc49592c0d16e cmake: Include `include` directory for subtree builds (Hennadii Stepanov)
5431b9decdbbdf30c5c5f2aed4b59662f5c681a2 cmake: Make `SECP256K1_INSTALL` default depend on `PROJECT_IS_TOP_LEVEL` (Hennadii Stepanov)
162608cc982538906e775d0c549aff2de5dee413 cmake: Emulate `PROJECT_IS_TOP_LEVEL` for CMake<3.21 (Hennadii Stepanov)
Pull request description:
This PR:
1. Emulates [`PROJECT_IS_TOP_LEVEL`](https://cmake.org/cmake/help/latest/variable/PROJECT_IS_TOP_LEVEL.html) variable for CMake versions where it is not available.
2. Makes the `SECP256K1_INSTALL` option dependent on `PROJECT_IS_TOP_LEVEL` (a [follow up](https://github.com/bitcoin-core/secp256k1/pull/1263#issuecomment-1516564300) of https://github.com/bitcoin-core/secp256k1/pull/1263).
3. Makes integration of this project as a subtree easier. A top project can `#include <secp256k1.h>` with no additional `target_include_directories()` commands. For example, see https://github.com/hebasto/secp256k1-CMake-example/tree/subtree.
ACKs for top commit:
theuni:
utACK 71f746c057a66d5ae0dfdb5d439bc49592c0d16e.
Tree-SHA512: 8ccdbcc94b26f36e772611ebaab0f2846debd6ad20f9e361be31a8d2128a14273acb692b0631026e12cc6cdef6d445dce0fd3beb4f71af47b46dfcf840a18879
