* 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
The `from_slice` methods on `CompressedEdwardsY` and
`CompressedRistretto` both previously panicked if the slice was the
wrong length.
This changes them to be fallible, returning `TryFromSliceError` in the
event the slice is the wrong length.
It also adds a `TryFrom<&[u8]>` impl for each of these types which calls
the corresponding `from_slice` method.
This is the name we adopted for a similar feature in @RustCrypto.
It's a bit less jargony and also leaves the door open in the future to
other types of precomputed tables.
* 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.
Crate features are intended to be additive, whereas only 1-of-N possible
backends can be selected.
Features can also be activated by transitive dependencies, which leads
to a problem of different dependences selecting conflicting backends.
Using `--cfg` instead moves all backend selection control to the
toplevel executable.
This commit switches to the following RUSTFLAGS to enable backends:
- `--cfg curve25519_dalek_backend="fiat"`: uses `fiat-crypto`
- `--cfg curve25519_dalek_backend="simd"`: uses nightly-only SIMD
As proposed in #442 this makes `digest` an
optional feature that is not covered by the
SemVer public API stability guarantees.
Co-authored-by: Michael Rosenberg <michael@mrosenberg.pub>
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>
* Deprecated `EdwardsPoint::hash_from_bytes` and renamed to
`EdwardsPoint::nonspec_map_to_curve`
* Added KAT test vectors for `RistrettoPoint::from_uniform_bytes`
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.
This is useful for programs/protocol which can do some heuristics or
learning-based approach towards optimising the table size based on the number of
uses of e.g. a public key, the second basepoint in a Pedersen commitment, etc.,
i.e. the first time a public key is used to verify a signature, the usual
variable-time basepoint multiscalar multiplication is used, however after 1000
verifications, the table size is upgraded, and again after 10000 verifications,
etc.
This implements a macro for implementing the BasepointTable trait, and
uses the macro to create basepoint table types. The default table
still uses radix-16 representation and is ~30KB in size. The new
table types, and their memory usage and additions required per
basepoint multiplication are:
* `EdwardsBasepointTableRadix64`: ~120KB, 43 additions
* `EdwardsBasepointTableRadix128`: ~240KB, 37 additions
* `EdwardsBasepointTableRadix256`: ~480KB, 32 additions
We due this in lieu of implementing `TryFrom` to allow for API
consumers to use the `?` operator to convert potential `None`s into
their own `Result<T, CustomError>` types for better error handling
with less boilerplate.
Note that this is a breaking API change.
