* Replace `unwrap_u8` with `into`
Leverages the `From<Choice>` impl for `bool` where applicable instead,
which results in clearer logic which more closely matches `bool`.
* Removed Scalar::{from_bits, from_bytes_clamped}; all constructible scalars are now reduced mod l
* Made Scalar::reduce() not pub; fixed test warning
* Added benches for scalar add/sub/mul
* Docs
* Added EdwardsPoint::mul_base_clamped and gated Scalar::from_bits behind legacy_compatibility
* Added unit test for Mul impl on unreduced Scalars
* Added Montgomery::mul_base_clamped
* Added BasepointTable::mul_base_clamped
* Removed invalid scalar arithmetic test; this functionality is no longer supported
* Made clamp_integer() const
* Updated readme and changelog
* Added BasepointTable::mul_base_clamped to tests
* Added proper deprecation notice to Scalar::from_bits; added legacy_compatibility to Makefile and docsrs flags
* Fixed-based Montgomery scalar multiplication
Adds `MontgomeryPoint::mul_base` as an API for fixed-base scalar
multiplication which allows for potential future optimizations.
As a baseline implementation, it uses the variable base scalar
multiplication implementation.
This follows the existing `EdwardsPoint::mul_base` and
`RistrettoPoint::mul_base` APIs.
* Added Montgomery mul_base bench
* Switched MontgomeryPoint::mul_base to use EdwardsPoint::mul_base
---------
Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>
* Add `basepoint-tables` crate feature
Feature-gates the inclusion of basepoint tables under a
`basepoint-tables` feature, with the goal of reducing code size for e.g.
embedded applications.
* Add `mul_base` method to `EdwardsPoint` and `RistrettoPoint`
Provides fixed-base scalar multiplication which optionally uses
precomputed basepoint tables when the `basepoint-tables` feature is
enabled, providing 4X better performance.
Falls back on variable-base scalar multiplication in the event the
feature is disabled.
Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>
* Make basepoint table constants static references
This ensures they have a fixed address and aren't duplicated across
compilation units.
Since they were already always borrowed, this changes the static values
to be `&'static` addresses to ensure they're always borrowed rather than
potentially copied.
* rustfmt
* Make `zeroize` an optional dependency
The `zeroize` crate provides a defense against memory read oracles which
typically arise from memory unsafety.
Pure Rust programs may not benefit from `zeroize`, and in certain cases
the unsafe code used by `zeroize` may be more concerning.
This commit makes `zeroize` into an optional feature so users may elect
to disable it if they so desire.
* Added zeroize feature flag to README
Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>
For the field element types `FieldElement` and `Scalar`, use inherent
constants instead of (non-const) functions to return these constant
values.
It's likely the original functions predate support for inherent
constants, but now that they're available, they're a better fit for
these sort of constant values.
Previously `cargo test --no-default-features` would succeed but with
warnings. This commit fixes all of those warnings and tests
`--no-default-features` in CI to ensure that in perpetuity.
As proposed in #442 this makes `rand_core` an
optional feature that is not covered by the
SemVer public API stability guarantees.
Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>
This implementation:
- is agnostic on the hash used to pick a field element, even though SHA512 is commonly used,
- follows https://tools.ietf.org/id/draft-irtf-cfrg-hash-to-curve-10.html closely
- tests the outputs of the function using libsignal's implementation.
The functionality we were using is now contained in the `rand_core` crate, which
we already depend upon. As far as testing code goes, only benchmarks still
depend upon `rand`, as they use `thread_rng`.
This was more useful at the time when we were determining, e.g., optimal lookup
table sizes and could regenerate them more easily, but it came at a massive
complexity cost. It also meant that we were unable to implement backend
autoselection. This commit removes the `build.rs` entirely. In the future, a
different `build.rs` could be added that auto-selects a backend, but it seems
like the current default-u64 setup has been working fine.
This change provides a common convention for using allocator-dependent
features with:
#![cfg(feature = "alloc")]
When available, `Vec` is imported consistently as `prelude::Vec`, which
means modules that need access to `Vec` can simply do:
use prelude::*;
and if an allocator is available, `Vec` will be in the crate prelude.
This allows all `alloc` vs `std` gating to be handled in `lib.rs`,
`build.rs`, and `prelude.rs` so the rest of the codebase doesn't have to
do any gating whatsoever.
Since Criterion can only benchmark public API, these changes just drop
all internal benchmarks (e.g., benchmarks for field operations). But
those are usually microbenchmarks whose meaning is kind of questionable
anyways, so I don't think this is a big loss.
The `bench` feature disappears, since Criterion works on stable Rust.
