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The prior-present `Ciphersuite::hash_to_F` was a sin. Implementations took a DST, yet were not require to securely handle it. It was also biased towards the requirements of `modular-frost` as `ciphersuite` was originally written all those years ago, when `modular-frost` had needs exceeding what `ff`, `group` satisfied. Now, the hash is bound to produce an output which can be converted to a scalar with `ff::FromUniformBytes`. A new `hash_to_F`, which accepts a single argument of the value to hash (removing the potential to insecurely handle the DST by removing the DST entirely). Due to `digest` yielding a `GenericArray`, yet `FromUniformBytes` taking a `const usize`, the `ciphersuite` crate now defines a `FromUniformBytes` trait taking an array (then implemented for all satisfiers of `ff::FromUniformBytes`). In order to get the array type from the `GenericArray`, the output of the hash, `digest` is updated to the `0.11` release candidate which moves to `flexible-array` which solves that problem. The existing, specific `hash_to_F` functions have been moved to `modular-frost` as necessary. `flexible-array` itself is patched to a fork due to https://github.com/RustCrypto/hybrid-array/issues/131.
Schnorr Signatures
A challenge (and therefore HRAm) agnostic Schnorr signature library. This is intended to be used as a primitive by a variety of crates relying on Schnorr signatures, voiding the need to constantly define a Schnorr signature struct with associated functions.
This library provides signatures of the R, s form. Batch verification is
supported via the multiexp crate. Half-aggregation, as defined in
https://eprint.iacr.org/2021/350, is also supported.
This library was audited by Cypher Stack in March 2023, culminating in commit 669d2dbffc1dafb82a09d9419ea182667115df06. Any subsequent changes have not undergone auditing.
This library is usable under no_std, via alloc, when the default features are disabled.