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#![cfg_attr(not(feature = "std"), no_std)]
use rand_core::{RngCore, CryptoRng};
use zeroize::Zeroize;
use transcript::Transcript;
use ff::{Field, PrimeField};
use group::prime::PrimeGroup;
#[cfg(feature = "serialize")]
use std::io::{self, ErrorKind, Error, Read, Write};
#[cfg(feature = "experimental")]
pub mod cross_group;
#[cfg(test)]
mod tests;
pub(crate) fn challenge<T: Transcript, F: PrimeField>(transcript: &mut T) -> F {
let target = ((usize::try_from(F::NUM_BITS).unwrap() + 7) / 8) * 2;
let mut challenge_bytes = transcript.challenge(b"challenge").as_ref().to_vec();
while challenge_bytes.len() < target {
challenge_bytes.extend(transcript.challenge(b"challenge_extension").as_ref());
}
challenge_bytes.truncate(target);
let mut challenge = F::zero();
for b in challenge_bytes {
for _ in 0 .. 8 {
challenge = challenge.double();
}
challenge += F::from(u64::from(b));
}
challenge
}
#[cfg(feature = "serialize")]
fn read_scalar<R: Read, F: PrimeField>(r: &mut R) -> io::Result<F> {
let mut repr = F::Repr::default();
r.read_exact(repr.as_mut())?;
let scalar = F::from_repr(repr);
if scalar.is_none().into() {
Err(Error::new(ErrorKind::Other, "invalid scalar"))?;
}
Ok(scalar.unwrap())
}
#[derive(Debug)]
pub enum DLEqError {
InvalidProof,
}
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub struct DLEqProof<G: PrimeGroup> {
c: G::Scalar,
s: G::Scalar,
}
#[allow(non_snake_case)]
impl<G: PrimeGroup> DLEqProof<G> {
fn transcript<T: Transcript>(transcript: &mut T, generator: G, nonce: G, point: G) {
transcript.append_message(b"generator", generator.to_bytes().as_ref());
transcript.append_message(b"nonce", nonce.to_bytes().as_ref());
transcript.append_message(b"point", point.to_bytes().as_ref());
}
pub fn prove<R: RngCore + CryptoRng, T: Transcript>(
rng: &mut R,
transcript: &mut T,
generators: &[G],
mut scalar: G::Scalar,
) -> DLEqProof<G>
where
G::Scalar: Zeroize,
{
let mut r = G::Scalar::random(rng);
transcript.domain_separate(b"dleq");
for generator in generators {
Self::transcript(transcript, *generator, *generator * r, *generator * scalar);
}
let c = challenge(transcript);
let s = r + (c * scalar);
scalar.zeroize();
r.zeroize();
DLEqProof { c, s }
}
pub fn verify<T: Transcript>(
&self,
transcript: &mut T,
generators: &[G],
points: &[G],
) -> Result<(), DLEqError> {
if generators.len() != points.len() {
Err(DLEqError::InvalidProof)?;
}
transcript.domain_separate(b"dleq");
for (generator, point) in generators.iter().zip(points) {
Self::transcript(transcript, *generator, (*generator * self.s) - (*point * self.c), *point);
}
if self.c != challenge(transcript) {
Err(DLEqError::InvalidProof)?;
}
Ok(())
}
#[cfg(feature = "serialize")]
pub fn serialize<W: Write>(&self, w: &mut W) -> io::Result<()> {
w.write_all(self.c.to_repr().as_ref())?;
w.write_all(self.s.to_repr().as_ref())
}
#[cfg(feature = "serialize")]
pub fn deserialize<R: Read>(r: &mut R) -> io::Result<DLEqProof<G>> {
Ok(DLEqProof { c: read_scalar(r)?, s: read_scalar(r)? })
}
}