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use crate::partial_signature_vt::PARTIAL_SIGNATURE_VT_BYTES;
use crate::{PartialSignatureVt, PublicKeyVt, SecretKey};
use bls12_381_plus::{
multi_miller_loop, ExpandMsgXmd, G1Affine, G2Affine, G2Prepared, G2Projective, Scalar,
};
use core::{
fmt::{self, Display},
ops::Neg,
};
use ff::Field;
use group::{Curve, Group};
use serde::{Deserialize, Deserializer, Serialize, Serializer};
use subtle::{Choice, CtOption};
use vsss_rs::{Error, Shamir, Share};
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct SignatureVt(pub(crate) G2Projective);
impl Display for SignatureVt {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.0.fmt(f)
}
}
impl Default for SignatureVt {
fn default() -> Self {
Self(G2Projective::identity())
}
}
impl Serialize for SignatureVt {
fn serialize<S>(&self, s: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
self.0.serialize(s)
}
}
impl<'de> Deserialize<'de> for SignatureVt {
fn deserialize<D>(d: D) -> Result<Self, D::Error>
where
D: Deserializer<'de>,
{
let p = G2Projective::deserialize(d)?;
Ok(Self(p))
}
}
impl SignatureVt {
pub const BYTES: usize = 96;
const DST: &'static [u8] = b"BLS_SIG_BLS12381G2_XMD:SHA-256_SSWU_RO_POP_";
pub fn new<B: AsRef<[u8]>>(sk: &SecretKey, msg: B) -> Option<Self> {
if sk.0.is_zero() {
return None;
}
let a = Self::hash_msg(msg.as_ref());
Some(Self(a * sk.0))
}
pub(crate) fn hash_msg(msg: &[u8]) -> G2Projective {
G2Projective::hash::<ExpandMsgXmd<sha2::Sha256>>(msg, Self::DST)
}
pub fn verify<B: AsRef<[u8]>>(&self, pk: PublicKeyVt, msg: B) -> Choice {
if pk.0.is_identity().unwrap_u8() == 1 || self.0.is_identity().unwrap_u8() == 1 {
return Choice::from(0);
}
let a = Self::hash_msg(msg.as_ref());
let g1 = G1Affine::generator().neg();
multi_miller_loop(&[
(&pk.0.to_affine(), &G2Prepared::from(a.to_affine())),
(&g1, &G2Prepared::from(self.0.to_affine())),
])
.final_exponentiation()
.is_identity()
}
pub fn to_bytes(self) -> [u8; Self::BYTES] {
self.0.to_affine().to_compressed()
}
pub fn from_bytes(bytes: &[u8; Self::BYTES]) -> CtOption<Self> {
G2Affine::from_compressed(bytes).map(|p| Self(G2Projective::from(&p)))
}
pub fn from_partials<const T: usize, const N: usize>(
partials: &[PartialSignatureVt],
) -> Result<Self, Error> {
if T > partials.len() {
return Err(Error::SharingLimitLessThanThreshold);
}
let mut pp = [Share::<PARTIAL_SIGNATURE_VT_BYTES>::default(); T];
for i in 0..T {
pp[i] = partials[i].0;
}
let point = Shamir::<T, N>::combine_shares_group::<
Scalar,
G2Projective,
PARTIAL_SIGNATURE_VT_BYTES,
>(&pp)?;
Ok(Self(point))
}
}
#[test]
fn signature_vt_works() {
use crate::MockRng;
use rand_core::{RngCore, SeedableRng};
let seed = [2u8; 16];
let mut rng = MockRng::from_seed(seed);
let sk = SecretKey::random(&mut rng).unwrap();
let mut msg = [0u8; 12];
rng.fill_bytes(&mut msg);
let sig = SignatureVt::new(&sk, msg).unwrap();
let pk = PublicKeyVt::from(&sk);
assert_eq!(sig.verify(pk, msg).unwrap_u8(), 1);
}
#[test]
fn threshold_works() {
use crate::MockRng;
use rand_core::{RngCore, SeedableRng};
let seed = [3u8; 16];
let mut rng = MockRng::from_seed(seed);
let sk = SecretKey::random(&mut rng).unwrap();
let pk = PublicKeyVt::from(&sk);
let res_shares = sk.split::<MockRng, 2, 3>(&mut rng);
assert!(res_shares.is_ok());
let shares = res_shares.unwrap();
let mut msg = [0u8; 12];
rng.fill_bytes(&mut msg);
let mut sigs = [PartialSignatureVt::default(); 3];
for (i, share) in shares.iter().enumerate() {
let opt = PartialSignatureVt::new(share, &msg);
assert!(opt.is_some());
sigs[i] = opt.unwrap();
}
for i in 0..3 {
for j in 0..3 {
if i == j {
continue;
}
let res = SignatureVt::from_partials::<2, 3>(&[sigs[i], sigs[j]]);
assert!(res.is_ok());
let sig = res.unwrap();
assert_eq!(sig.verify(pk, msg).unwrap_u8(), 1);
}
}
}