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Dedicated crate for the Schnorr contract

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This commit is contained in:
Luke Parker
2024-09-15 00:41:16 -04:00
parent bdf89f5350
commit 1c5bc2259e
20 changed files with 389 additions and 222 deletions
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102
processor/ethereum/ethereum-serai/src/crypto.rs
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@@ -62,56 +62,6 @@ pub fn deterministically_sign(tx: &TxLegacy) -> Signed<TxLegacy> {
}
}
/// The public key for a Schnorr-signing account.
#[allow(non_snake_case)]
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub struct PublicKey {
pub(crate) A: ProjectivePoint,
pub(crate) px: Scalar,
}
impl PublicKey {
/// Construct a new `PublicKey`.
///
/// This will return None if the provided point isn't eligible to be a public key (due to
/// bounds such as parity).
#[allow(non_snake_case)]
pub fn new(A: ProjectivePoint) -> Option<PublicKey> {
let affine = A.to_affine();
// Only allow even keys to save a word within Ethereum
let is_odd = bool::from(affine.y_is_odd());
if is_odd {
None?;
}
let x_coord = affine.x();
let x_coord_scalar = <Scalar as Reduce<KU256>>::reduce_bytes(&x_coord);
// Return None if a reduction would occur
// Reductions would be incredibly unlikely and shouldn't be an issue, yet it's one less
// headache/concern to have
// This does ban a trivial amoount of public keys
if x_coord_scalar.to_repr() != x_coord {
None?;
}
Some(PublicKey { A, px: x_coord_scalar })
}
pub fn point(&self) -> ProjectivePoint {
self.A
}
pub fn eth_repr(&self) -> [u8; 32] {
self.px.to_repr().into()
}
pub fn from_eth_repr(repr: [u8; 32]) -> Option<Self> {
#[allow(non_snake_case)]
let A = Option::<AffinePoint>::from(AffinePoint::decompress(&repr.into(), 0.into()))?.into();
Option::from(Scalar::from_repr(repr.into())).map(|px| PublicKey { A, px })
}
}
/// The HRAm to use for the Schnorr contract.
#[derive(Clone, Default)]
pub struct EthereumHram {}
@@ -128,58 +78,6 @@ impl Hram<Secp256k1> for EthereumHram {
}
}
/// A signature for the Schnorr contract.
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub struct Signature {
pub(crate) c: Scalar,
pub(crate) s: Scalar,
}
impl Signature {
pub fn verify(&self, public_key: &PublicKey, message: &[u8]) -> bool {
#[allow(non_snake_case)]
let R = (Secp256k1::generator() * self.s) - (public_key.A * self.c);
EthereumHram::hram(&R, &public_key.A, message) == self.c
}
/// Construct a new `Signature`.
///
/// This will return None if the signature is invalid.
pub fn new(
public_key: &PublicKey,
message: &[u8],
signature: SchnorrSignature<Secp256k1>,
) -> Option<Signature> {
let c = EthereumHram::hram(&signature.R, &public_key.A, message);
if !signature.verify(public_key.A, c) {
None?;
}
let res = Signature { c, s: signature.s };
assert!(res.verify(public_key, message));
Some(res)
}
pub fn c(&self) -> Scalar {
self.c
}
pub fn s(&self) -> Scalar {
self.s
}
pub fn to_bytes(&self) -> [u8; 64] {
let mut res = [0; 64];
res[.. 32].copy_from_slice(self.c.to_repr().as_ref());
res[32 ..].copy_from_slice(self.s.to_repr().as_ref());
res
}
pub fn from_bytes(bytes: [u8; 64]) -> std::io::Result<Self> {
let mut reader = bytes.as_slice();
let c = Secp256k1::read_F(&mut reader)?;
let s = Secp256k1::read_F(&mut reader)?;
Ok(Signature { c, s })
}
}
impl From<&Signature> for AbiSignature {
fn from(sig: &Signature) -> AbiSignature {
let c: [u8; 32] = sig.c.to_repr().into();