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use crate::{PublicKey, SecretKey};
use bls12_381_plus::{
multi_miller_loop, ExpandMsgXmd, G1Affine, G1Projective, G2Affine, G2Prepared,
};
use core::{
fmt::{self, Display},
ops::Neg,
};
use ff::Field;
use group::{Curve, Group};
use serde::{Deserialize, Deserializer, Serialize, Serializer};
use subtle::{Choice, CtOption};
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct ProofOfPossession(pub(crate) G1Projective);
impl Default for ProofOfPossession {
fn default() -> Self {
Self(G1Projective::identity())
}
}
impl Display for ProofOfPossession {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.0.fmt(f)
}
}
impl Serialize for ProofOfPossession {
fn serialize<S>(&self, s: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
self.0.serialize(s)
}
}
impl<'de> Deserialize<'de> for ProofOfPossession {
fn deserialize<D>(d: D) -> Result<Self, D::Error>
where
D: Deserializer<'de>,
{
let p = G1Projective::deserialize(d)?;
Ok(Self(p))
}
}
impl ProofOfPossession {
pub const BYTES: usize = 48;
const DST: &'static [u8] = b"BLS_POP_BLS12381G1_XMD:SHA-256_SSWU_RO_POP_";
pub fn new(sk: &SecretKey) -> Option<Self> {
if sk.0.is_zero() {
return None;
}
let pk = PublicKey::from(sk);
let a = G1Projective::hash::<ExpandMsgXmd<sha2::Sha256>>(&pk.to_bytes(), Self::DST);
Some(Self(a * sk.0))
}
pub fn verify(&self, pk: PublicKey) -> Choice {
if pk.0.is_identity().unwrap_u8() == 1 {
return Choice::from(0);
}
let a = G1Projective::hash::<ExpandMsgXmd<sha2::Sha256>>(&pk.to_bytes(), Self::DST);
let g2 = G2Affine::generator().neg();
multi_miller_loop(&[
(&a.to_affine(), &G2Prepared::from(pk.0.to_affine())),
(&self.0.to_affine(), &G2Prepared::from(g2)),
])
.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> {
let mut t = [0u8; Self::BYTES];
t.copy_from_slice(bytes);
G1Affine::from_compressed(&t).map(|p| Self(G1Projective::from(&p)))
}
}
#[test]
fn pop_works() {
use crate::MockRng;
use rand_core::SeedableRng;
let seed = [2u8; 16];
let mut rng = MockRng::from_seed(seed);
let sk = SecretKey::random(&mut rng).unwrap();
let pop = ProofOfPossession::new(&sk).unwrap();
let pk = PublicKey::from(&sk);
assert_eq!(pop.verify(pk).unwrap_u8(), 1);
}