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a141deaf36
This helps identify where the various functionalities are used, or rather, not used. The `Ciphersuite` trait present in `patches/ciphersuite`, facilitating the entire FCMP++ tree, only requires the markers _and_ canonical point decoding. I've opened a PR to upstream such a trait into `group` (https://github.com/zkcrypto/group/pull/68). `WrappedGroup` is still justified for as long as `Group::generator` exists. Moving `::generator()` to its own trait, on an independent structure (upstream) would be massively appreciated. @tarcieri also wanted to update from `fn generator()` to `const GENERATOR`, which would encourage further discussion on https://github.com/zkcrypto/group/issues/32 and https://github.com/zkcrypto/group/issues/45, which have been stagnant. The `Id` trait is occasionally used yet really should be first off the chopping block. Finally, `WithPreferredHash` is only actually used around a third of the time, which more than justifies it being a separate trait. --- Updates `dalek_ff_group::Scalar` to directly re-export `curve25519_dalek::Scalar`, as without issue. `dalek_ff_group::RistrettoPoint` also could be replaced with an export of `curve25519_dalek::RistrettoPoint`, yet the coordinator relies on how we implemented `Hash` on it for the hell of it so it isn't worth it at this time. `dalek_ff_group::EdwardsPoint` can't be replaced for an re-export of `curve25519_dalek::SubgroupPoint` as it doesn't implement `zeroize`, `subtle` traits within a released, non-yanked version. Relevance to https://github.com/serai-dex/serai/issues/201 and https://github.com/dalek-cryptography/curve25519-dalek/issues/811#issuecomment-3247732746. Also updates the `Ristretto` ciphersuite to prefer `Blake2b-512` over `SHA2-512`. In order to maintain compliance with FROST's IETF standard, `modular-frost` defines its own ciphersuite for Ristretto which still uses `SHA2-512`.
44 lines
1.2 KiB
Rust
44 lines
1.2 KiB
Rust
use core::ops::Deref;
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use zeroize::{Zeroize, Zeroizing};
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use rand_core::{RngCore, CryptoRng};
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use ciphersuite::{
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group::{ff::PrimeField, Group, GroupEncoding},
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GroupIo,
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};
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use dkg::Participant;
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/// Sample a random, unbiased point on the elliptic curve with an unknown discrete logarithm.
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///
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/// This keeps it simple by using rejection sampling.
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pub(crate) fn sample_point<C: GroupIo>(rng: &mut (impl RngCore + CryptoRng)) -> C::G {
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let mut repr = <C::G as GroupEncoding>::Repr::default();
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loop {
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rng.fill_bytes(repr.as_mut());
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if let Ok(point) = C::read_G(&mut repr.as_ref()) {
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if bool::from(!point.is_identity()) {
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return point;
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}
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}
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}
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}
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pub(super) fn polynomial<F: PrimeField + Zeroize>(
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coefficients: &[Zeroizing<F>],
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l: Participant,
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) -> Zeroizing<F> {
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let l = F::from(u64::from(u16::from(l)));
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// This should never be reached since Participant is explicitly non-zero
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assert!(l != F::ZERO, "zero participant passed to polynomial");
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let mut share = Zeroizing::new(F::ZERO);
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for (idx, coefficient) in coefficients.iter().rev().enumerate() {
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*share += coefficient.deref();
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if idx != (coefficients.len() - 1) {
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*share *= l;
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}
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}
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share
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}
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