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Implement variable-sized windows into multiexp

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Closes https://github.com/serai-dex/serai/issues/17 by using the 
PrimeFieldBits API to do so.

Should greatly speed up small batches, along with batches in the 
hundreds. Saves almost a full second on the cross-group DLEq proof.
This commit is contained in:
Luke Parker
2022-06-30 09:30:24 -04:00
parent 5d115f1e1c
commit 7890827a48
15 changed files with 342 additions and 148 deletions
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26
crypto/dleq/src/cross_group/mod.rs
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@@ -83,7 +83,8 @@ pub struct DLEqProof<G0: PrimeGroup, G1: PrimeGroup> {
poks: (SchnorrPoK<G0>, SchnorrPoK<G1>)
}
impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1> {
impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1>
where G0::Scalar: PrimeFieldBits, G1::Scalar: PrimeFieldBits {
fn initialize_transcript<T: Transcript>(
transcript: &mut T,
generators: (Generators<G0>, Generators<G1>),
@@ -134,13 +135,17 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1> {
}
// TODO: Use multiexp here after https://github.com/serai-dex/serai/issues/17
fn reconstruct_key<G: PrimeGroup>(commitments: impl Iterator<Item = G>) -> G {
fn reconstruct_key<G: PrimeGroup>(
commitments: impl Iterator<Item = G>
) -> G where G::Scalar: PrimeFieldBits {
let mut pow_2 = G::Scalar::one();
commitments.fold(G::identity(), |key, commitment| {
let res = key + (commitment * pow_2);
pow_2 = pow_2.double();
res
})
multiexp::multiexp_vartime(
&commitments.map(|commitment| {
let res = (pow_2, commitment);
pow_2 = pow_2.double();
res
}).collect::<Vec<_>>()
)
}
fn reconstruct_keys(&self) -> (G0, G1) {
@@ -169,10 +174,7 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1> {
transcript: &mut T,
generators: (Generators<G0>, Generators<G1>),
f: G0::Scalar
) -> (
Self,
(G0::Scalar, G1::Scalar)
) where G0::Scalar: PrimeFieldBits, G1::Scalar: PrimeFieldBits {
) -> (Self, (G0::Scalar, G1::Scalar)) {
// At least one bit will be dropped from either field element, making it irrelevant which one
// we get a random element in
let f = scalar_normalize::<_, G1::Scalar>(f);
@@ -262,7 +264,7 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1> {
&self,
transcript: &mut T,
generators: (Generators<G0>, Generators<G1>)
) -> Result<(G0, G1), DLEqError> where G0::Scalar: PrimeFieldBits, G1::Scalar: PrimeFieldBits {
) -> Result<(G0, G1), DLEqError> {
let capacity = G0::Scalar::CAPACITY.min(G1::Scalar::CAPACITY);
if self.bits.len() != capacity.try_into().unwrap() {
return Err(DLEqError::InvalidProofLength);