* 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 `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>
`zeroize` is WASM-friendly as it has no dependencies on C compilers.
Instead uses Rust's own volatile write semantics and compiler fences to
ensure zeroization is not elided by the compiler.
This begins to attempt to restructure the source tree so that the common parts
are common and the different parts are different.
The backend is now split into two parts:
- serial (containing the implementation using serial formulas and mixed-model arithmetic).
- vector (containing the implementation using parallel formulas and single-model arithmetic).
The serial scalar_mul tree is now under backend::serial::scalar_mul.
The avx2 scalar_mul tree is now under backend::avx2::scalar_mul.
