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use crate::traits::{KeyImageGen, Link, Sign, Verify};
use alloc::vec::Vec;
use curve25519_dalek::constants;
use curve25519_dalek::ristretto::RistrettoPoint;
use curve25519_dalek::scalar::Scalar;
use digest::generic_array::typenum::U64;
use digest::Digest;
use rand_core::{CryptoRng, RngCore};
pub struct BLSAG {
challenge: Scalar,
responses: Vec<Scalar>,
ring: Vec<RistrettoPoint>,
key_image: RistrettoPoint,
}
impl KeyImageGen<Scalar, RistrettoPoint> for BLSAG {
fn generate_key_image<Hash: Digest<OutputSize = U64> + Clone + Default>(
k: Scalar,
) -> RistrettoPoint {
let k_point: RistrettoPoint = k * constants::RISTRETTO_BASEPOINT_POINT;
let key_image: RistrettoPoint =
k * RistrettoPoint::from_hash(Hash::default().chain(k_point.compress().as_bytes()));
return key_image;
}
}
impl Sign<Scalar, Vec<RistrettoPoint>> for BLSAG {
fn sign<
Hash: Digest<OutputSize = U64> + Clone + Default,
CSPRNG: CryptoRng + RngCore + Default,
>(
k: Scalar,
mut ring: Vec<RistrettoPoint>,
message: &Vec<u8>,
) -> BLSAG {
let mut csprng = CSPRNG::default();
let k_point: RistrettoPoint = k * constants::RISTRETTO_BASEPOINT_POINT;
let key_image: RistrettoPoint = BLSAG::generate_key_image::<Hash>(k);
let n = ring.len() + 1;
let secret_index = (csprng.next_u32() % n as u32) as usize;
ring.insert(secret_index, k_point);
let a: Scalar = Scalar::random(&mut csprng);
let mut rs: Vec<Scalar> = (0..n).map(|_| Scalar::random(&mut csprng)).collect();
let mut cs: Vec<Scalar> = (0..n).map(|_| Scalar::zero()).collect();
let mut message_hash = Hash::default();
message_hash.input(message);
let mut hashes: Vec<Hash> = (0..n).map(|_| message_hash.clone()).collect();
hashes[(secret_index + 1) % n].input(
(a * constants::RISTRETTO_BASEPOINT_POINT)
.compress()
.as_bytes(),
);
hashes[(secret_index + 1) % n].input(
(a * RistrettoPoint::from_hash(Hash::default().chain(k_point.compress().as_bytes())))
.compress()
.as_bytes(),
);
cs[(secret_index + 1) % n] = Scalar::from_hash(hashes[(secret_index + 1) % n].clone());
let mut i = (secret_index + 1) % n;
loop {
hashes[(i + 1) % n].input(
((rs[i % n] * constants::RISTRETTO_BASEPOINT_POINT) + (cs[i % n] * ring[i % n]))
.compress()
.as_bytes(),
);
hashes[(i + 1) % n].input(
((rs[i % n]
* RistrettoPoint::from_hash(
Hash::default().chain(ring[i % n].compress().as_bytes()),
))
+ (cs[i % n] * key_image))
.compress()
.as_bytes(),
);
cs[(i + 1) % n] = Scalar::from_hash(hashes[(i + 1) % n].clone());
if secret_index >= 1 && i % n == (secret_index - 1) % n {
break;
} else if secret_index == 0 && i % n == n - 1 {
break;
} else {
i = (i + 1) % n;
}
}
rs[secret_index] = a - (cs[secret_index] * k);
return BLSAG {
challenge: cs[0],
responses: rs,
ring: ring,
key_image: key_image,
};
}
}
impl Verify for BLSAG {
fn verify<Hash: Digest<OutputSize = U64> + Clone + Default>(
signature: BLSAG,
message: &Vec<u8>,
) -> bool {
let mut reconstructed_c: Scalar = signature.challenge;
let n = signature.ring.len();
for j in 0..n {
let mut h: Hash = Hash::default();
h.input(message);
h.input(
((signature.responses[j] * constants::RISTRETTO_BASEPOINT_POINT)
+ (reconstructed_c * signature.ring[j]))
.compress()
.as_bytes(),
);
h.input(
(signature.responses[j]
* RistrettoPoint::from_hash(
Hash::default().chain(signature.ring[j].compress().as_bytes()),
)
+ (reconstructed_c * signature.key_image))
.compress()
.as_bytes(),
);
reconstructed_c = Scalar::from_hash(h);
}
return signature.challenge == reconstructed_c;
}
}
impl Link for BLSAG {
fn link(signature_1: BLSAG, signature_2: BLSAG) -> bool {
return signature_1.key_image == signature_2.key_image;
}
}
#[cfg(test)]
mod test {
extern crate blake2;
extern crate rand;
extern crate sha2;
extern crate sha3;
use super::*;
use blake2::Blake2b;
use curve25519_dalek::ristretto::RistrettoPoint;
use curve25519_dalek::scalar::Scalar;
use rand::rngs::OsRng;
use sha2::Sha512;
use sha3::Keccak512;
#[test]
fn blsag() {
let mut csprng = OsRng::default();
let k: Scalar = Scalar::random(&mut csprng);
let n = 2;
let ring: Vec<RistrettoPoint> = (0..(n - 1))
.map(|_| RistrettoPoint::random(&mut csprng))
.collect();
let message: Vec<u8> = b"This is the message".iter().cloned().collect();
{
let signature = BLSAG::sign::<Sha512, OsRng>(k, ring.clone(), &message);
let result = BLSAG::verify::<Sha512>(signature, &message);
assert!(result);
}
{
let signature = BLSAG::sign::<Keccak512, OsRng>(k, ring.clone(), &message);
let result = BLSAG::verify::<Keccak512>(signature, &message);
assert!(result);
}
{
let signature = BLSAG::sign::<Blake2b, OsRng>(k, ring.clone(), &message);
let result = BLSAG::verify::<Blake2b>(signature, &message);
assert!(result);
}
let another_ring: Vec<RistrettoPoint> =
(0..(n - 1))
.map(|_| RistrettoPoint::random(&mut csprng))
.collect();
let another_message: Vec<u8> = b"This is another message".iter().cloned().collect();
let signature_1 = BLSAG::sign::<Blake2b, OsRng>(k, another_ring.clone(), &another_message);
let signature_2 = BLSAG::sign::<Blake2b, OsRng>(k, ring.clone(), &message);
let result = BLSAG::link(signature_1, signature_2);
assert!(result);
}
}