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.
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
ef49a11d29601e09e94134975c968e92c0214102 build: allow static or shared but not both (Cory Fields)
36b0adf1b90139a41fdcb94390d0bb06e9224795 build: remove warning until it's reproducible (Cory Fields)
Pull request description:
Continuing from here: https://github.com/bitcoin-core/secp256k1/issues/1224#issuecomment-1460438227
Unfortunately it wasn't really possible to keep a clean diff here because of the nature of the change. I suggest reviewing the lib creation stuff in its entirety, sorry about that :\
Rather than allowing for shared and static libs to be built at the same time like autotools, this PR switches to the CMake convention of allowing only 1.
A new `BUILD_SHARED_LIBS` option is added to match CMake convention, as well as a `SECP256K1_DISABLE_SHARED` option which overrides it. That way even projects which have `BUILD_SHARED_LIBS=1` can opt-into a static libsecp in particular.
Details:
Two object libraries are created: `secp256k1_asm` and `secp256k1_precomputed_objs`. Some tests/benchmarks use the object libraries directly, some link against the real lib: `secp256k1`.
Because the objs don't know what they're going to be linked into, they need to be told how to deal with PIC.
The `DEFINE_SYMBOL` property sets the `DLL_EXPORT` define as necessary (when building a shared lib)
ACKs for top commit:
hebasto:
re-ACK ef49a11d29601e09e94134975c968e92c0214102, only [suggested](https://github.com/bitcoin-core/secp256k1/pull/1230#pullrequestreview-1388191165) changes since my recent [review](https://github.com/bitcoin-core/secp256k1/pull/1230#pullrequestreview-1352125381).
real-or-random:
ACK ef49a11d29601e09e94134975c968e92c0214102
Tree-SHA512: 8870de305176fdb677caff0fdfc6f8c59c0e906489cb72bc9980e551002812685e59e20d731f2a82e33628bdfbb7261eafd6f228038cad3ec83bd74335959600
5bb03c29116409ace8855e64bf2e2b2d45871469 Replace `SECP256K1_ECMULT_TABLE_VERIFY` macro by a function (Hennadii Stepanov)
4429a8c218d7bf7bc6de1de88bc31c834f771385 Suppress `-Wunused-parameter` when building for coverage analysis (Hennadii Stepanov)
Pull request description:
ACKs for top commit:
real-or-random:
utACK 5bb03c29116409ace8855e64bf2e2b2d45871469
jonasnick:
ACK 5bb03c29116409ace8855e64bf2e2b2d45871469
Tree-SHA512: 19a395434ecefea201a03fc45b3f0b88f1520908926ac1207bbc6570034b1141b49c3c98e66819dcd9069dfdd28c7c6fbe957f13fb6bd178fd57ce65bfbb8fbd
