From 43131a0afbad775c42da874cf2aac6774e5cae7d Mon Sep 17 00:00:00 2001
From: chancharles92 <chancharles92@gmail.com>
Date: Thu, 14 Jul 2022 12:19:10 -0700
Subject: [PATCH] product check APIs (#41)

---
 poly-iop/src/lib.rs            |   2 +
 poly-iop/src/prod_check/mod.rs | 114 +++++++++++++++++++++++++++++++++
 2 files changed, 116 insertions(+)
 create mode 100644 poly-iop/src/prod_check/mod.rs

diff --git a/poly-iop/src/lib.rs b/poly-iop/src/lib.rs
index 319f06d..57f83f5 100644
--- a/poly-iop/src/lib.rs
+++ b/poly-iop/src/lib.rs
@@ -4,6 +4,7 @@ use std::marker::PhantomData;
 mod errors;
 mod hyperplonk;
 mod perm_check;
+mod prod_check;
 mod structs;
 mod sum_check;
 mod transcript;
@@ -17,6 +18,7 @@ pub use perm_check::{
     util::{identity_permutation_mle, random_permutation_mle},
     PermutationCheck,
 };
+pub use prod_check::ProductCheck;
 pub use sum_check::SumCheck;
 pub use transcript::IOPTranscript;
 pub use utils::*;
diff --git a/poly-iop/src/prod_check/mod.rs b/poly-iop/src/prod_check/mod.rs
new file mode 100644
index 0000000..7f3ff33
--- /dev/null
+++ b/poly-iop/src/prod_check/mod.rs
@@ -0,0 +1,114 @@
+//! Main module for the Permutation Check protocol
+
+use crate::{errors::PolyIOPErrors, transcript::IOPTranscript, VirtualPolynomial, ZeroCheck};
+use ark_ff::PrimeField;
+use ark_poly::DenseMultilinearExtension;
+
+/// A ProductCheck is derived from ZeroCheck.
+///
+/// A ProductCheck IOP takes the following steps:
+///
+/// Inputs:
+/// - f(x)
+///
+/// Prover steps:
+/// 1. `compute_product_poly` to build `prod(x0, ..., x_n)` from virtual
+/// polynomial f
+/// 2. push commitments of `f(x)`, `prod(x)` to the transcript
+/// (done by the snark caller)
+/// 3. `generate_challenge` from current transcript (generate alpha)
+/// 4. `prove` to generate the zerocheck proof for the virtual polynomial
+///     prod(1, x) - prod(x, 0) * prod(x, 1) + alpha * (f(x) - prod(0, x))
+///
+/// Verifier steps:
+/// 1. Extract commitments of `f(x)`, `prod(x)` from the proof, push them to the
+/// transcript (done by the snark caller)
+/// 2. `generate_challenge` from current transcript (generate alpha)
+/// 3. `verify` to verify the zerocheck proof and generate the subclaim for
+/// polynomial evaluations
+pub trait ProductCheck<F: PrimeField>: ZeroCheck<F> {
+    type ProductCheckSubClaim;
+    type ProductCheckChallenge;
+
+    /// Initialize the system with a transcript
+    ///
+    /// This function is optional -- in the case where a ProductCheck is
+    /// an building block for a more complex protocol, the transcript
+    /// may be initialized by this complex protocol, and passed to the
+    /// ProductCheck prover/verifier.
+    fn init_transcript() -> Self::Transcript;
+
+    /// Generate random challenge `alpha` from a transcript.
+    fn generate_challenge(
+        transcript: &mut Self::Transcript,
+    ) -> Result<Self::ProductCheckChallenge, PolyIOPErrors>;
+
+    /// Compute the product polynomial `prod(x)` where
+    ///
+    ///  - `prod(0,x) := prod(0, x1, …, xn)` is the MLE over the
+    /// evaluations of `f(x)` on the boolean hypercube {0,1}^n
+    ///
+    /// - `prod(1,x)` is a MLE over the evaluations of `prod(x, 0) * prod(x, 1)`
+    /// on the boolean hypercube {0,1}^n
+    ///
+    /// The caller needs to check num_vars matches in f
+    /// Cost: linear in N.
+    fn compute_product_poly(
+        fx: &VirtualPolynomial<F>,
+    ) -> Result<DenseMultilinearExtension<F>, PolyIOPErrors>;
+
+    /// Initialize the prover to argue that for a virtual polynomial f(x),
+    /// it holds that `s = \prod_{x \in {0,1}^n} f(x)`
+    ///
+    /// Inputs:
+    /// - fx: the virtual polynomial
+    /// - prod_x: the product polynomial
+    /// - transcript: a transcript that is used to generate the challenges alpha
+    /// - claimed_product: the claimed product value
+    ///
+    /// Cost: O(N)
+    fn prove(
+        fx: &VirtualPolynomial<F>,
+        prod_x: &DenseMultilinearExtension<F>,
+        transcript: &mut IOPTranscript<F>,
+        claimed_product: F,
+    ) -> Result<Self::Proof, PolyIOPErrors>;
+
+    /// Verify that for a witness virtual polynomial f(x),
+    /// it holds that `s = \prod_{x \in {0,1}^n} f(x)`
+    fn verify(
+        proof: &Self::Proof,
+        aux_info: &Self::VPAuxInfo,
+        transcript: &mut Self::Transcript,
+        claimed_product: F,
+    ) -> Result<Self::ProductCheckSubClaim, PolyIOPErrors>;
+}
+
+/// A product check subclaim consists of
+/// - A zero check IOP subclaim for
+/// `Q(x) = prod(1, x) - prod(x, 0) * prod(x, 1) + alpha * (f(x) - prod(0, x)`
+/// is 0, consists of the following:
+///   - the SubClaim from the SumCheck
+///   - the initial challenge r which is used to build eq(x, r) in ZeroCheck
+/// - A final query for `prod(1, ..., 1, 0) = claimed_product`.
+// Note that this final query is in fact a constant that
+// is independent from the proof. So we should avoid
+// (de)serialize it.
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct ProductCheckSubClaim<F: PrimeField, ZC: ZeroCheck<F>> {
+    // the SubClaim from the ZeroCheck
+    zero_check_sub_claim: ZC::ZeroCheckSubClaim,
+    // final query which consists of
+    // - the vector `(1, ..., 1, 0)`
+    // - the evaluation `claimed_product`
+    final_query: (Vec<F>, F),
+}
+
+/// The random challenges in a product check protocol
+#[allow(dead_code)]
+pub struct ProductCheckChallenge<F: PrimeField> {
+    alpha: F,
+}
+
+#[cfg(test)]
+mod test {}