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Downstream the eVRF libraries from FCMP++

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Also adds no-std support to secq256k1 and embedwards25519.
This commit is contained in:
Luke Parker
2025-01-29 22:29:40 -05:00
parent 19422de231
commit 2bc880e372
35 changed files with 456 additions and 340 deletions
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14
crypto/evrf/ec-gadgets/Cargo.toml
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@@ -3,19 +3,25 @@ name = "generalized-bulletproofs-ec-gadgets"
version = "0.1.0"
description = "Gadgets for working with an embedded Elliptic Curve in a Generalized Bulletproofs circuit"
license = "MIT"
repository = "https://github.com/serai-dex/serai/tree/develop/crypto/evrf/ec-gadgets"
repository = "https://github.com/serai-dex/serai/tree/develop/crypto/fcmps/ec-gadgets"
authors = ["Luke Parker <lukeparker5132@gmail.com>"]
keywords = ["bulletproofs", "circuit", "divisors"]
edition = "2021"
rust-version = "1.80"
rust-version = "1.69"
[package.metadata.docs.rs]
all-features = true
rustdoc-args = ["--cfg", "docsrs"]
[dependencies]
std-shims = { path = "../../../common/std-shims", version = "^0.1.1", default-features = false }
generic-array = { version = "1", default-features = false, features = ["alloc"] }
ciphersuite = { path = "../../ciphersuite", version = "0.4", default-features = false, features = ["std"] }
ciphersuite = { path = "../../ciphersuite", version = "0.4", default-features = false }
generalized-bulletproofs-circuit-abstraction = { path = "../circuit-abstraction" }
generalized-bulletproofs-circuit-abstraction = { path = "../circuit-abstraction", default-features = false }
[features]
std = ["std-shims/std", "ciphersuite/std", "generalized-bulletproofs-circuit-abstraction/std"]
default = ["std"]

31
crypto/evrf/ec-gadgets/src/dlog.rs
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@@ -1,4 +1,5 @@
use core::fmt;
use std_shims::{vec, vec::Vec};
use ciphersuite::{
group::ff::{Field, PrimeField, BatchInverter},
@@ -10,11 +11,6 @@ use generalized_bulletproofs_circuit_abstraction::*;
use crate::*;
/// Parameters for a discrete logarithm proof.
///
/// This isn't required to be implemented by the Field/Group/Ciphersuite, solely a struct, to
/// enable parameterization of discrete log proofs to the bitlength of the discrete logarithm.
/// While that may be F::NUM_BITS, a discrete log proof a for a full scalar, it could also be 64,
/// a discrete log proof for a u64 (such as if opening a Pedersen commitment in-circuit).
pub trait DiscreteLogParameters {
/// The amount of bits used to represent a scalar.
type ScalarBits: ArrayLength;
@@ -30,8 +26,8 @@ pub trait DiscreteLogParameters {
/// The amount of y x**i coefficients in a divisor.
///
/// This is the amount of points in a divisor (the amount of bits in a scalar, plus one) plus
/// one, divided by two, minus two.
/// This is the amount of points in a divisor (the amount of bits in a scalar, plus one) divided
/// by two, minus two.
type YxCoefficients: ArrayLength;
}
@@ -106,8 +102,6 @@ pub struct Divisor<Parameters: DiscreteLogParameters> {
/// exceeding trivial complexity.
pub y: Variable,
/// The coefficients for the `y**1 x**i` terms of the polynomial.
// This subtraction enforces the divisor to have at least 4 points which is acceptable.
// TODO: Double check these constants
pub yx: GenericArray<Variable, Parameters::YxCoefficients>,
/// The coefficients for the `x**i` terms of the polynomial, skipping x**1.
///
@@ -324,7 +318,7 @@ pub trait EcDlogGadgets<C: Ciphersuite> {
&self,
transcript: &mut T,
curve: &CurveSpec<C::F>,
generators: &[GeneratorTable<C::F, Parameters>],
generators: &[&GeneratorTable<C::F, Parameters>],
) -> (DiscreteLogChallenge<C::F, Parameters>, Vec<ChallengedGenerator<C::F, Parameters>>);
/// Prove this point has the specified discrete logarithm over the specified generator.
@@ -355,12 +349,14 @@ impl<C: Ciphersuite> EcDlogGadgets<C> for Circuit<C> {
&self,
transcript: &mut T,
curve: &CurveSpec<C::F>,
generators: &[GeneratorTable<C::F, Parameters>],
generators: &[&GeneratorTable<C::F, Parameters>],
) -> (DiscreteLogChallenge<C::F, Parameters>, Vec<ChallengedGenerator<C::F, Parameters>>) {
// Get the challenge points
// TODO: Implement a proper hash to curve
let sign_of_points = transcript.challenge_bytes();
let sign_of_point_0 = (sign_of_points[0] & 1) == 1;
let sign_of_point_1 = ((sign_of_points[0] >> 1) & 1) == 1;
let (c0_x, c0_y) = loop {
let c0_x: C::F = transcript.challenge();
let c0_x = transcript.challenge::<C>();
let Some(c0_y) =
Option::<C::F>::from(((c0_x.square() * c0_x) + (curve.a * c0_x) + curve.b).sqrt())
else {
@@ -368,17 +364,16 @@ impl<C: Ciphersuite> EcDlogGadgets<C> for Circuit<C> {
};
// Takes the even y coordinate as to not be dependent on whatever root the above sqrt
// happens to returns
// TODO: Randomly select which to take
break (c0_x, if bool::from(c0_y.is_odd()) { -c0_y } else { c0_y });
break (c0_x, if bool::from(c0_y.is_odd()) != sign_of_point_0 { -c0_y } else { c0_y });
};
let (c1_x, c1_y) = loop {
let c1_x: C::F = transcript.challenge();
let c1_x = transcript.challenge::<C>();
let Some(c1_y) =
Option::<C::F>::from(((c1_x.square() * c1_x) + (curve.a * c1_x) + curve.b).sqrt())
else {
continue;
};
break (c1_x, if bool::from(c1_y.is_odd()) { -c1_y } else { c1_y });
break (c1_x, if bool::from(c1_y.is_odd()) != sign_of_point_1 { -c1_y } else { c1_y });
};
// mmadd-1998-cmo
@@ -483,7 +478,7 @@ impl<C: Ciphersuite> EcDlogGadgets<C> for Circuit<C> {
let arg_iter = arg_iter.chain(dlog.iter());
for variable in arg_iter {
debug_assert!(
matches!(variable, Variable::CG { .. } | Variable::CH { .. } | Variable::V(_)),
matches!(variable, Variable::CG { .. } | Variable::V(_)),
"discrete log proofs requires all arguments belong to commitments",
);
}

1
crypto/evrf/ec-gadgets/src/lib.rs
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@@ -1,5 +1,6 @@
#![cfg_attr(docsrs, feature(doc_auto_cfg))]
#![doc = include_str!("../README.md")]
#![cfg_attr(not(feature = "std"), no_std)]
#![deny(missing_docs)]
#![allow(non_snake_case)]