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Unify the cross-group DLEq challenges

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This does reduce the strength of the challenges to that of the weaker 
field, yet that doesn't have any impact on whether or not this is ZK due 
to the key being shared across fields.

Saves ~8kb.
This commit is contained in:
Luke Parker
2022-06-30 11:23:13 -04:00
parent 7890827a48
commit 4eafbe2a09
3 changed files with 16 additions and 18 deletions
Download Patch File Download Diff File Expand all files Collapse all files

23
crypto/dleq/src/cross_group/mod.rs
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@@ -8,7 +8,7 @@ use group::{ff::{Field, PrimeField, PrimeFieldBits}, prime::PrimeGroup};
use crate::{Generators, challenge};
pub mod scalar;
use scalar::scalar_normalize;
use scalar::{scalar_normalize, scalar_convert};
pub(crate) mod schnorr;
use schnorr::SchnorrPoK;
@@ -32,7 +32,7 @@ pub(crate) fn read_point<R: Read, G: PrimeGroup>(r: &mut R) -> std::io::Result<G
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct Bit<G0: PrimeGroup, G1: PrimeGroup> {
commitments: (G0, G1),
e: (G0::Scalar, G1::Scalar),
e: G0::Scalar,
s: [(G0::Scalar, G1::Scalar); 2]
}
@@ -41,8 +41,7 @@ impl<G0: PrimeGroup, G1: PrimeGroup> Bit<G0, G1> {
pub fn serialize<W: Write>(&self, w: &mut W) -> std::io::Result<()> {
w.write_all(self.commitments.0.to_bytes().as_ref())?;
w.write_all(self.commitments.1.to_bytes().as_ref())?;
w.write_all(self.e.0.to_repr().as_ref())?;
w.write_all(self.e.1.to_repr().as_ref())?;
w.write_all(self.e.to_repr().as_ref())?;
for i in 0 .. 2 {
w.write_all(self.s[i].0.to_repr().as_ref())?;
w.write_all(self.s[i].1.to_repr().as_ref())?;
@@ -55,7 +54,7 @@ impl<G0: PrimeGroup, G1: PrimeGroup> Bit<G0, G1> {
Ok(
Bit {
commitments: (read_point(r)?, read_point(r)?),
e: (read_scalar(r)?, read_scalar(r)?),
e: read_scalar(r)?,
s: [
(read_scalar(r)?, read_scalar(r)?),
(read_scalar(r)?, read_scalar(r)?)
@@ -71,6 +70,8 @@ pub enum DLEqError {
InvalidProofOfKnowledge,
#[error("invalid proof length")]
InvalidProofLength,
#[error("invalid challenge")]
InvalidChallenge,
#[error("invalid proof")]
InvalidProof
}
@@ -117,7 +118,7 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1>
fn nonces<T: Transcript>(mut transcript: T, nonces: (G0, G1)) -> (G0::Scalar, G1::Scalar) {
transcript.append_message(b"nonce_0", nonces.0.to_bytes().as_ref());
transcript.append_message(b"nonce_1", nonces.1.to_bytes().as_ref());
(challenge(&mut transcript, b"challenge_G"), challenge(&mut transcript, b"challenge_H"))
scalar_normalize(challenge(&mut transcript))
}
#[allow(non_snake_case)]
@@ -134,7 +135,6 @@ 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 where G::Scalar: PrimeFieldBits {
@@ -240,9 +240,9 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1>
bits.push(
if *bit {
Bit { commitments, e: e_0, s: [s_1, s_0] }
Bit { commitments, e: e_0.0, s: [s_1, s_0] }
} else {
Bit { commitments, e: e_1, s: [s_0, s_1] }
Bit { commitments, e: e_1.0, s: [s_0, s_1] }
}
);
@@ -282,7 +282,8 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1>
for (i, bit) in self.bits.iter().enumerate() {
Self::transcript_bit(transcript, i, bit.commitments);
if bit.e != Self::R_nonces(
let bit_e = (bit.e, scalar_convert(bit.e).ok_or(DLEqError::InvalidChallenge)?);
if bit_e != Self::R_nonces(
transcript.clone(),
generators,
bit.s[0],
@@ -295,7 +296,7 @@ impl<G0: PrimeGroup, G1: PrimeGroup> DLEqProof<G0, G1>
generators,
bit.s[1],
bit.commitments,
bit.e
bit_e
)
) {
return Err(DLEqError::InvalidProof);