This also makes the order in which module options are processed
consistent between CMake and autotools (the reverse order of the listing
printed to stdout).
It is a non-Libtool-specific way to explicitly specify the user's
intention to consume a static `libseck256k1`.
This change allows to get rid of MSVC linker warnings LNK4217 and
LNK4286. Also, it makes possible to merge the `SECP256K1_API` and
`SECP256K1_API_VAR` into one.
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.
This warns on certain identifiers reserved by the C standard, namely
* identifiers that begin with an underscore followed by an uppercase
letter, and
* identifiers in the global namespace that begin with an underscore.
We had used such identifiers in the past for macros in include guards,
and we should make sure that we don't reintroduce such identifiers
going forward.
Note that C reserves more identifiers for "future library directions",
e.g., identifiers that begin with "str" followed by a lowercase letter.
But even the C standards committee has decided that this is somewhat
silly and adopted a proposal [1] for C23 that removes the restriction
that programs using these identifiers have UB. Instead, these
identifiers are now "potentially reserved", which is not a normative
restriction but simply an informative warning that the identifiers
may become fully reserved in the future.
[1] https://www.open-std.org/jtc1/sc22/WG14/www/docs/n2625.pdf
This change eases the use of alternate build systems by moving
the variables in `src/libsecp256k1-config.h` to compiler macros
for each invocation, preventing duplication of these variables
for each build system.
Co-authored-by: Ali Sherief <ali@notatether.com>
There are plenty of unreleased variants of libsecp256k1 version 0.1.0
(libsecp256k1.so.0.0.0) in the wild. We choose a new version number to allow a
clear distinction.
There are variants of 0.1.0 that are incompatible with the initial release,
hence we increase the minor version to arrive at version number 0.2.0. For the
same reason, we increase the LIB_VERSION_CURRENT and keep AGE at 0.
The changelog for 0.2.0 consists of the relevant changes since 2021-12-25, which
is the date when the initial release process PR was merged (and the library
version was set to a pre-release, see 423b6d19d373f1224fd671a982584d7e7900bc93).
This is somewhat arbitrary but at least points readers to relevant changes.
41e8704b484652cf5bbb2b7ecc27feedc3cf0ae1 build: Enable some modules by default (Tim Ruffing)
Pull request description:
This has been discussed in https://github.com/bitcoin-core/secp256k1/issues/817#issuecomment-693198323 and I agree with the arguments brought up there.
Alternatively, we could not enable them and add a discussion to the readme why we discourage people from using the modules. I believe enabling ECDH is not very controversial. But what about recovery? Do we want to leave it off and instead give a reason?
ACKs for top commit:
sipa:
ACK 41e8704b484652cf5bbb2b7ecc27feedc3cf0ae1
jonasnick:
ACK 41e8704b484652cf5bbb2b7ecc27feedc3cf0ae1
Tree-SHA512: 1dd21037043f2b2c94a92cd2f31e69b505ba5b43119897bc0934966d9ccd84fc4fc20e7509af634f1c3a096710db1a2253090f5f1f107b9d258945a5546e9ba4
