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#![allow(non_snake_case)]
use crate::utilities::ErrorReason;
use curv::arithmetic::traits::Modulo;
use curv::arithmetic::traits::Samplable;
use curv::arithmetic::{traits::*, BigInt};
use serde::{Deserialize, Serialize};
use utilities::{compute_rsa_modulus, h_g, hash_to_prime};
const BIT_LENGTH: usize = 4096;
const SEED_LENGTH: usize = 256;
pub mod utilities;
pub struct ElGamal;
pub struct ExponentElGamal;
#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct SolvedVDF {
vdf_instance: UnsolvedVDF,
pub y: BigInt,
pub pi: BigInt,
}
#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct SetupForVDF {
pub t: BigInt,
pub N: BigInt,
}
#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
pub struct UnsolvedVDF {
pub x: BigInt,
pub setup: SetupForVDF,
}
impl SetupForVDF {
pub fn public_setup(t: &BigInt) -> Self {
let N = compute_rsa_modulus(BIT_LENGTH);
SetupForVDF { t: t.clone(), N }
}
pub fn pick_challenge(setup: &SetupForVDF) -> UnsolvedVDF {
let x = BigInt::sample(SEED_LENGTH);
UnsolvedVDF {
x,
setup: setup.clone(),
}
}
}
impl UnsolvedVDF {
pub fn eval(unsolved_vdf: &UnsolvedVDF) -> SolvedVDF {
let N = unsolved_vdf.setup.N.clone();
let x = unsolved_vdf.x.clone();
let t = unsolved_vdf.setup.t.clone();
let g = h_g(&N, &x);
let mut y = g.clone();
let mut i = BigInt::zero();
while i < t {
y = BigInt::mod_mul(&y, &y, &N);
i = i + BigInt::one();
}
let l = hash_to_prime(&unsolved_vdf.setup, &g, &y);
let mut i = BigInt::zero();
let mut b: BigInt;
let mut r = BigInt::one();
let mut r2: BigInt;
let two = BigInt::from(2);
let mut pi = BigInt::one();
let mut g_b: BigInt;
while i < t {
r2 = &r * &two;
b = r2.div_floor(&l);
r = r2.mod_floor(&l);
g_b = BigInt::mod_pow(&g, &b, &N);
pi = BigInt::mod_mul(&pi, &pi, &N);
pi = BigInt::mod_mul(&pi, &g_b, &N);
i = i + BigInt::one();
}
let vdf = SolvedVDF {
vdf_instance: unsolved_vdf.clone(),
y,
pi,
};
vdf
}
}
impl SolvedVDF {
pub fn verify(&self, unsolved_vdf: &UnsolvedVDF) -> Result<(), ErrorReason> {
if &self.vdf_instance != unsolved_vdf {
return Err(ErrorReason::MisMatchedVDF);
}
let N = self.vdf_instance.setup.N.clone();
let g = h_g(&self.vdf_instance.setup.N, &self.vdf_instance.x);
if &self.y >= &N || &self.pi >= &N {
return Err(ErrorReason::VDFVerifyError);
}
let l = hash_to_prime(&self.vdf_instance.setup, &g, &self.y);
let r = BigInt::mod_pow(&BigInt::from(2), &self.vdf_instance.setup.t, &l);
let pi_l = BigInt::mod_pow(&self.pi, &l, &N);
let g_r = BigInt::mod_pow(&g, &r, &N);
let pi_l_g_r = BigInt::mod_mul(&pi_l, &g_r, &N);
match pi_l_g_r == self.y {
true => return Ok(()),
false => return Err(ErrorReason::VDFVerifyError),
}
}
}
#[cfg(test)]
mod tests {
use super::SetupForVDF;
use super::UnsolvedVDF;
use curv::arithmetic::traits::Samplable;
use curv::BigInt;
use std::time::Instant;
#[test]
fn test_vdf_valid_proof() {
let t = BigInt::sample(13);
let setup = SetupForVDF::public_setup(&t);
let mut i = 0;
while i < 10 {
let unsolved_vdf = SetupForVDF::pick_challenge(&setup);
let start = Instant::now();
let solved_vdf = UnsolvedVDF::eval(&unsolved_vdf);
let duration1 = start.elapsed();
let start = Instant::now();
let res = solved_vdf.verify(&unsolved_vdf);
let duration2 = start.elapsed();
i = i + 1;
println!("eval time: {:?}", duration1);
println!("verify time: {:?}", duration2);
assert!(res.is_ok());
}
}
}