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MinRoot example improvements (#88)
* support multiple iterations of MinRoot per Nova step * small edits to println * fix declaration
This commit is contained in:
@@ -1,10 +1,8 @@
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//! Demonstrates how to use Nova to produce a recursive proof of the correct execution of
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//! iterations of the MinRoot function, thereby realizing a Nova-based verifiable delay function (VDF).
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//! We currently execute a single iteration of the MinRoot function per step of Nova's recursion.
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//! We execute a configurable number of iterations of the MinRoot function per step of Nova's recursion.
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type G1 = pasta_curves::pallas::Point;
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type G2 = pasta_curves::vesta::Point;
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type S1 = nova_snark::spartan_with_ipa_pc::RelaxedR1CSSNARK<G1>;
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type S2 = nova_snark::spartan_with_ipa_pc::RelaxedR1CSSNARK<G2>;
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use ::bellperson::{gadgets::num::AllocatedNum, ConstraintSystem, SynthesisError};
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use ff::PrimeField;
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use generic_array::typenum::U2;
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@@ -19,8 +17,290 @@ use nova_snark::{
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};
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use num_bigint::BigUint;
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use std::marker::PhantomData;
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use std::time::Instant;
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// A trivial test circuit that we will use on the secondary curve
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#[derive(Clone, Debug)]
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struct MinRootIteration<F: PrimeField> {
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x_i: F,
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y_i: F,
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x_i_plus_1: F,
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y_i_plus_1: F,
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}
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impl<F: PrimeField> MinRootIteration<F> {
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// produces a sample non-deterministic advice, executing one invocation of MinRoot per step
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fn new(num_iters: usize, x_0: &F, y_0: &F, pc: &PoseidonConstants<F, U2>) -> (F, Vec<Self>) {
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// although this code is written generically, it is tailored to Pallas' scalar field
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// (p - 3 / 5)
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let exp = BigUint::parse_bytes(
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b"23158417847463239084714197001737581570690445185553317903743794198714690358477",
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10,
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)
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.unwrap();
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let mut res = Vec::new();
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let mut x_i = *x_0;
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let mut y_i = *y_0;
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for _i in 0..num_iters {
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let x_i_plus_1 = (x_i + y_i).pow_vartime(exp.to_u64_digits()); // computes the fifth root of x_i + y_i
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// sanity check
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let sq = x_i_plus_1 * x_i_plus_1;
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let quad = sq * sq;
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let fifth = quad * x_i_plus_1;
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debug_assert_eq!(fifth, x_i + y_i);
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let y_i_plus_1 = x_i;
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res.push(Self {
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x_i,
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y_i,
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x_i_plus_1,
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y_i_plus_1,
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});
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x_i = x_i_plus_1;
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y_i = y_i_plus_1;
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}
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let z0 = Poseidon::<F, U2>::new_with_preimage(&[*x_0, *y_0], pc).hash();
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(z0, res)
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}
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}
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#[derive(Clone, Debug)]
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struct MinRootCircuit<F: PrimeField> {
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seq: Vec<MinRootIteration<F>>,
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pc: PoseidonConstants<F, U2>,
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}
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impl<F> StepCircuit<F> for MinRootCircuit<F>
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where
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F: PrimeField,
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{
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fn synthesize<CS: ConstraintSystem<F>>(
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&self,
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cs: &mut CS,
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z: AllocatedNum<F>,
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) -> Result<AllocatedNum<F>, SynthesisError> {
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let mut z_out: Result<AllocatedNum<F>, SynthesisError> = Err(SynthesisError::AssignmentMissing);
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for i in 0..self.seq.len() {
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// Allocate four variables for holding non-deterministic advice: x_i, y_i, x_i_plus_1, y_i_plus_1
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let x_i = AllocatedNum::alloc(cs.namespace(|| format!("x_i_iter_{}", i)), || {
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Ok(self.seq[i].x_i)
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})?;
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let y_i = AllocatedNum::alloc(cs.namespace(|| format!("y_i_iter_{}", i)), || {
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Ok(self.seq[i].y_i)
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})?;
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let x_i_plus_1 =
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AllocatedNum::alloc(cs.namespace(|| format!("x_i_plus_1_iter_{}", i)), || {
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Ok(self.seq[i].x_i_plus_1)
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})?;
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// check that z = hash(x_i, y_i), where z is an output from the prior step
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if i == 0 {
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let z_hash = poseidon_hash(
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cs.namespace(|| "input hash"),
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vec![x_i.clone(), y_i.clone()],
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&self.pc,
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)?;
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cs.enforce(
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|| "z =? z_hash",
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|lc| lc + z_hash.get_variable(),
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|lc| lc + CS::one(),
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|lc| lc + z.get_variable(),
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);
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}
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// check the following conditions hold:
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// (i) x_i_plus_1 = (x_i + y_i)^{1/5}, which can be more easily checked with x_i_plus_1^5 = x_i + y_i
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// (ii) y_i_plus_1 = x_i
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// (1) constraints for condition (i) are below
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// (2) constraints for condition (ii) is avoided because we just used x_i wherever y_i_plus_1 is used
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let x_i_plus_1_sq =
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x_i_plus_1.square(cs.namespace(|| format!("x_i_plus_1_sq_iter_{}", i)))?;
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let x_i_plus_1_quad =
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x_i_plus_1_sq.square(cs.namespace(|| format!("x_i_plus_1_quad_{}", i)))?;
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let x_i_plus_1_pow_5 = x_i_plus_1_quad.mul(
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cs.namespace(|| format!("x_i_plus_1_pow_5_{}", i)),
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&x_i_plus_1,
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)?;
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cs.enforce(
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|| format!("x_i_plus_1_pow_5 = x_i + y_i_iter_{}", i),
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|lc| lc + x_i_plus_1_pow_5.get_variable(),
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|lc| lc + CS::one(),
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|lc| lc + x_i.get_variable() + y_i.get_variable(),
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);
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// return hash(x_i_plus_1, y_i_plus_1) since Nova circuits expect a single output
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if i == self.seq.len() - 1 {
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z_out = poseidon_hash(
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cs.namespace(|| "output hash"),
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vec![x_i_plus_1, x_i.clone()],
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&self.pc,
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);
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}
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}
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z_out
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}
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fn compute(&self, z: &F) -> F {
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// sanity check
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let z_hash =
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Poseidon::<F, U2>::new_with_preimage(&[self.seq[0].x_i, self.seq[0].y_i], &self.pc).hash();
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debug_assert_eq!(z, &z_hash);
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// compute output hash using advice
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let iters = self.seq.len();
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Poseidon::<F, U2>::new_with_preimage(
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&[
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self.seq[iters - 1].x_i_plus_1,
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self.seq[iters - 1].y_i_plus_1,
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],
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&self.pc,
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)
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.hash()
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}
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}
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fn main() {
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let num_steps = 10;
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let num_iters_per_step = 10; // number of iterations of MinRoot per Nova's recursive step
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let pc = PoseidonConstants::<<G1 as Group>::Scalar, U2>::new_with_strength(Strength::Standard);
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let circuit_primary = MinRootCircuit {
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seq: vec![
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MinRootIteration {
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x_i: <G1 as Group>::Scalar::zero(),
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y_i: <G1 as Group>::Scalar::zero(),
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x_i_plus_1: <G1 as Group>::Scalar::zero(),
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y_i_plus_1: <G1 as Group>::Scalar::zero(),
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};
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num_iters_per_step
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],
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pc: pc.clone(),
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};
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let circuit_secondary = TrivialTestCircuit {
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_p: Default::default(),
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};
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println!("Nova-based VDF with MinRoot delay function");
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println!("==========================================");
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println!(
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"Proving {} iterations of MinRoot per step",
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num_iters_per_step
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);
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// produce public parameters
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println!("Producing public parameters...");
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let pp = PublicParams::<
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G1,
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G2,
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MinRootCircuit<<G1 as Group>::Scalar>,
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TrivialTestCircuit<<G2 as Group>::Scalar>,
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>::setup(circuit_primary, circuit_secondary.clone());
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println!(
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"Number of constraints per step (primary circuit): {}",
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pp.num_constraints().0
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);
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println!(
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"Number of constraints per step (secondary circuit): {}",
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pp.num_constraints().1
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);
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// produce non-deterministic advice
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let (z0_primary, minroot_iterations) = MinRootIteration::new(
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num_iters_per_step * num_steps,
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&<G1 as Group>::Scalar::zero(),
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&<G1 as Group>::Scalar::one(),
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&pc,
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);
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let minroot_circuits = (0..num_steps)
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.map(|i| MinRootCircuit {
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seq: (0..num_iters_per_step)
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.map(|j| MinRootIteration {
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x_i: minroot_iterations[i * num_iters_per_step + j].x_i,
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y_i: minroot_iterations[i * num_iters_per_step + j].y_i,
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x_i_plus_1: minroot_iterations[i * num_iters_per_step + j].x_i_plus_1,
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y_i_plus_1: minroot_iterations[i * num_iters_per_step + j].y_i_plus_1,
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})
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.collect::<Vec<_>>(),
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pc: pc.clone(),
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})
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.collect::<Vec<_>>();
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let z0_secondary = <G2 as Group>::Scalar::zero();
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type C1 = MinRootCircuit<<G1 as Group>::Scalar>;
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type C2 = TrivialTestCircuit<<G2 as Group>::Scalar>;
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// produce a recursive SNARK
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println!("Generating a RecursiveSNARK...");
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let mut recursive_snark: Option<RecursiveSNARK<G1, G2, C1, C2>> = None;
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for (i, circuit_primary) in minroot_circuits.iter().take(num_steps).enumerate() {
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let start = Instant::now();
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let res = RecursiveSNARK::prove_step(
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&pp,
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recursive_snark,
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circuit_primary.clone(),
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circuit_secondary.clone(),
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z0_primary,
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z0_secondary,
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);
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assert!(res.is_ok());
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println!(
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"RecursiveSNARK::prove_step {}: {:?}, took {:?} ",
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i,
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res.is_ok(),
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start.elapsed()
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);
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recursive_snark = Some(res.unwrap());
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}
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assert!(recursive_snark.is_some());
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let recursive_snark = recursive_snark.unwrap();
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// verify the recursive SNARK
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println!("Verifying a RecursiveSNARK...");
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let start = Instant::now();
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let res = recursive_snark.verify(&pp, num_steps, z0_primary, z0_secondary);
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println!(
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"RecursiveSNARK::verify: {:?}, took {:?}",
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res.is_ok(),
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start.elapsed()
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);
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assert!(res.is_ok());
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// produce a compressed SNARK
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println!("Generating a CompressedSNARK using Spartan with IPA-PC...");
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let start = Instant::now();
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type S1 = nova_snark::spartan_with_ipa_pc::RelaxedR1CSSNARK<G1>;
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type S2 = nova_snark::spartan_with_ipa_pc::RelaxedR1CSSNARK<G2>;
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let res = CompressedSNARK::<_, _, _, _, S1, S2>::prove(&pp, &recursive_snark);
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println!(
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"CompressedSNARK::prove: {:?}, took {:?}",
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res.is_ok(),
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start.elapsed()
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);
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assert!(res.is_ok());
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let compressed_snark = res.unwrap();
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// verify the compressed SNARK
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println!("Verifying a CompressedSNARK...");
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let start = Instant::now();
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let res = compressed_snark.verify(&pp, num_steps, z0_primary, z0_secondary);
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println!(
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"CompressedSNARK::verify: {:?}, took {:?}",
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res.is_ok(),
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start.elapsed()
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);
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assert!(res.is_ok());
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}
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// A trivial test circuit that we use on the secondary curve
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#[derive(Clone, Debug)]
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struct TrivialTestCircuit<F: PrimeField> {
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_p: PhantomData<F>,
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@@ -42,191 +322,3 @@ where
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*z
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}
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}
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#[derive(Clone, Debug)]
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struct MinRootCircuit<F: PrimeField> {
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x_i: F,
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y_i: F,
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x_i_plus_1: F,
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y_i_plus_1: F,
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pc: PoseidonConstants<F, U2>,
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}
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impl<F: PrimeField> MinRootCircuit<F> {
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// produces a sample non-deterministic advice, executing one invocation of MinRoot per step
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fn new(num_steps: usize, x_0: &F, y_0: &F, pc: &PoseidonConstants<F, U2>) -> (F, Vec<Self>) {
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// although this code is written generically, it is tailored to Pallas' scalar field
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// (p - 3 / 5)
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let exp = BigUint::parse_bytes(
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b"23158417847463239084714197001737581570690445185553317903743794198714690358477",
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10,
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)
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.unwrap();
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let mut res = Vec::new();
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let mut x_i = *x_0;
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let mut y_i = *y_0;
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for _i in 0..num_steps {
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let x_i_plus_1 = (x_i + y_i).pow_vartime(exp.to_u64_digits()); // computes the fifth root of x_i + y_i
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// sanity check
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let sq = x_i_plus_1 * x_i_plus_1;
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let quad = sq * sq;
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let fifth = quad * x_i_plus_1;
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debug_assert_eq!(fifth, x_i + y_i);
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let y_i_plus_1 = x_i;
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res.push(Self {
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x_i,
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y_i,
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x_i_plus_1,
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y_i_plus_1,
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pc: pc.clone(),
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});
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x_i = x_i_plus_1;
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y_i = y_i_plus_1;
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}
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let z0 = Poseidon::<F, U2>::new_with_preimage(&[*x_0, *y_0], pc).hash();
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(z0, res)
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}
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}
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impl<F> StepCircuit<F> for MinRootCircuit<F>
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where
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F: PrimeField,
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{
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fn synthesize<CS: ConstraintSystem<F>>(
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&self,
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cs: &mut CS,
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z: AllocatedNum<F>,
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) -> Result<AllocatedNum<F>, SynthesisError> {
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// Allocate four variables for holding non-deterministic advice: x_i, y_i, x_i_plus_1, y_i_plus_1
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let x_i = AllocatedNum::alloc(cs.namespace(|| "x_i"), || Ok(self.x_i))?;
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let y_i = AllocatedNum::alloc(cs.namespace(|| "y_i"), || Ok(self.y_i))?;
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let x_i_plus_1 = AllocatedNum::alloc(cs.namespace(|| "x_i_plus_1"), || Ok(self.x_i_plus_1))?;
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// check that z = hash(x_i, y_i), where z is an output from the prior step
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let z_hash = poseidon_hash(
|
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cs.namespace(|| "input hash"),
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vec![x_i.clone(), y_i.clone()],
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&self.pc,
|
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)?;
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cs.enforce(
|
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|| "z =? z_hash",
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|lc| lc + z_hash.get_variable(),
|
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|lc| lc + CS::one(),
|
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|lc| lc + z.get_variable(),
|
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);
|
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|
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// check the following conditions hold:
|
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// (i) x_i_plus_1 = (x_i + y_i)^{1/5}, which can be more easily checked with x_i_plus_1^5 = x_i + y_i
|
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// (ii) y_i_plus_1 = x_i
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// (1) constraints for condition (i) are below
|
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// (2) constraints for condition (ii) is avoided because we just used x_i wherever y_i_plus_1 is used
|
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let x_i_plus_1_sq = x_i_plus_1.square(cs.namespace(|| "x_i_plus_1_sq"))?;
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let x_i_plus_1_quad = x_i_plus_1_sq.square(cs.namespace(|| "x_i_plus_1_quad"))?;
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let x_i_plus_1_pow_5 = x_i_plus_1_quad.mul(cs.namespace(|| "x_i_plus_1_pow_5"), &x_i_plus_1)?;
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cs.enforce(
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|| "x_i_plus_1_pow_5 = x_i + y_i",
|
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|lc| lc + x_i_plus_1_pow_5.get_variable(),
|
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|lc| lc + CS::one(),
|
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|lc| lc + x_i.get_variable() + y_i.get_variable(),
|
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);
|
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|
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// return hash(x_i_plus_1, y_i_plus_1) since Nova circuits expect a single output
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poseidon_hash(
|
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cs.namespace(|| "output hash"),
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vec![x_i_plus_1, x_i.clone()],
|
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&self.pc,
|
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)
|
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}
|
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|
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fn compute(&self, z: &F) -> F {
|
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// sanity check
|
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let z_hash = Poseidon::<F, U2>::new_with_preimage(&[self.x_i, self.y_i], &self.pc).hash();
|
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debug_assert_eq!(z, &z_hash);
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// compute output hash using advice
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Poseidon::<F, U2>::new_with_preimage(&[self.x_i_plus_1, self.y_i_plus_1], &self.pc).hash()
|
||||
}
|
||||
}
|
||||
|
||||
fn main() {
|
||||
let pc = PoseidonConstants::<<G1 as Group>::Scalar, U2>::new_with_strength(Strength::Standard);
|
||||
|
||||
let circuit_primary = MinRootCircuit {
|
||||
x_i: <G1 as Group>::Scalar::zero(),
|
||||
y_i: <G1 as Group>::Scalar::zero(),
|
||||
x_i_plus_1: <G1 as Group>::Scalar::zero(),
|
||||
y_i_plus_1: <G1 as Group>::Scalar::zero(),
|
||||
pc: pc.clone(),
|
||||
};
|
||||
|
||||
let circuit_secondary = TrivialTestCircuit {
|
||||
_p: Default::default(),
|
||||
};
|
||||
|
||||
// produce public parameters
|
||||
let pp = PublicParams::<
|
||||
G1,
|
||||
G2,
|
||||
MinRootCircuit<<G1 as Group>::Scalar>,
|
||||
TrivialTestCircuit<<G2 as Group>::Scalar>,
|
||||
>::setup(circuit_primary, circuit_secondary.clone());
|
||||
|
||||
// produce non-deterministic advice
|
||||
let num_steps = 3;
|
||||
let (z0_primary, minroot_circuits) = MinRootCircuit::new(
|
||||
num_steps,
|
||||
&<G1 as Group>::Scalar::zero(),
|
||||
&<G1 as Group>::Scalar::one(),
|
||||
&pc,
|
||||
);
|
||||
let z0_secondary = <G2 as Group>::Scalar::zero();
|
||||
|
||||
type C1 = MinRootCircuit<<G1 as Group>::Scalar>;
|
||||
type C2 = TrivialTestCircuit<<G2 as Group>::Scalar>;
|
||||
// produce a recursive SNARK
|
||||
println!("Generating a RecursiveSNARK...");
|
||||
let mut recursive_snark: Option<RecursiveSNARK<G1, G2, C1, C2>> = None;
|
||||
|
||||
for (i, circuit_primary) in minroot_circuits.iter().take(num_steps).enumerate() {
|
||||
let res = RecursiveSNARK::prove_step(
|
||||
&pp,
|
||||
recursive_snark,
|
||||
circuit_primary.clone(),
|
||||
circuit_secondary.clone(),
|
||||
z0_primary,
|
||||
z0_secondary,
|
||||
);
|
||||
assert!(res.is_ok());
|
||||
println!("RecursiveSNARK::prove_step {}: {:?}", i, res.is_ok());
|
||||
recursive_snark = Some(res.unwrap());
|
||||
}
|
||||
|
||||
assert!(recursive_snark.is_some());
|
||||
let recursive_snark = recursive_snark.unwrap();
|
||||
|
||||
// verify the recursive SNARK
|
||||
println!("Verifying a RecursiveSNARK...");
|
||||
let res = recursive_snark.verify(&pp, num_steps, z0_primary, z0_secondary);
|
||||
println!("RecursiveSNARK::verify: {:?}", res.is_ok());
|
||||
assert!(res.is_ok());
|
||||
|
||||
// produce a compressed SNARK
|
||||
println!("Generating a CompressedSNARK...");
|
||||
let res = CompressedSNARK::<_, _, _, _, S1, S2>::prove(&pp, &recursive_snark);
|
||||
println!("CompressedSNARK::prove: {:?}", res.is_ok());
|
||||
assert!(res.is_ok());
|
||||
let compressed_snark = res.unwrap();
|
||||
|
||||
// verify the compressed SNARK
|
||||
println!("Verifying a CompressedSNARK...");
|
||||
let res = compressed_snark.verify(&pp, num_steps, z0_primary, z0_secondary);
|
||||
println!("CompressedSNARK::verify: {:?}", res.is_ok());
|
||||
assert!(res.is_ok());
|
||||
}
|
||||
|
||||
@@ -128,6 +128,14 @@ where
|
||||
_p_c2: Default::default(),
|
||||
}
|
||||
}
|
||||
|
||||
/// Returns the number of constraints in the primary and secondary circuits
|
||||
pub fn num_constraints(&self) -> (usize, usize) {
|
||||
(
|
||||
self.r1cs_shape_primary.num_cons,
|
||||
self.r1cs_shape_secondary.num_cons,
|
||||
)
|
||||
}
|
||||
}
|
||||
|
||||
/// A SNARK that proves the correct execution of an incremental computation
|
||||
|
||||
Reference in New Issue
Block a user