Circom wrapper's helper function

.gitignore

@@ -1,2 +1,5 @@
 /target
-Cargo.lock
+Cargo.lock
+# Circom generated files
+/src/frontend/circom/test_folder/test_circuit.r1cs
+/src/frontend/circom/test_folder/test_circuit_js/

Cargo.toml

@@ -4,25 +4,28 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-ark-ec = "0.4.2"
+ark-ec = "^0.4.0"
 ark-ff = "^0.4.0"
 ark-poly = "^0.4.0"
 ark-std = "^0.4.0"
 ark-crypto-primitives = { version = "^0.4.0", default-features = false, features = ["r1cs", "sponge", "crh"] }
 ark-relations = { version = "^0.4.0", default-features = false }
 ark-r1cs-std = { version = "^0.4.0", default-features = false }
+ark-circom = { git = "https://github.com/gakonst/ark-circom.git" }
 thiserror = "1.0"
 rayon = "1.7.0"
+num-bigint = "0.4"
+color-eyre = "=0.6.2"
 
 # tmp imports for espresso's sumcheck
-ark-serialize = "0.4.2"
+ark-serialize = "^0.4.0"
 espresso_subroutines = {git="https://github.com/EspressoSystems/hyperplonk", package="subroutines"}
 espresso_transcript = {git="https://github.com/EspressoSystems/hyperplonk", package="transcript"}
 
-
 [dev-dependencies]
 ark-pallas = {version="0.4.0", features=["r1cs"]}
 ark-vesta = {version="0.4.0"}
+ark-bn254 = "0.4.0"
 
 [features]
 default = ["parallel", "nova", "hypernova"]

src/frontend/circom/mod.rs

@@ -0,0 +1,234 @@
+use std::{error::Error, fs::File, io::BufReader, marker::PhantomData, path::PathBuf};
+
+use color_eyre::Result;
+use num_bigint::BigInt;
+
+use ark_circom::{circom::r1cs_reader, WitnessCalculator};
+use ark_ec::pairing::Pairing;
+use ark_ff::PrimeField;
+
+use crate::ccs::r1cs::R1CS;
+use crate::utils::vec::SparseMatrix;
+
+// Define the sparse matrices on PrimeFiled.
+pub type Constraints<F> = (ConstraintVec<F>, ConstraintVec<F>, ConstraintVec<F>);
+pub type ConstraintVec<F> = Vec<(usize, F)>;
+pub type ExtractedConstraintsResult<F> =
+    Result<(Vec<Constraints<F>>, usize, usize), Box<dyn Error>>;
+
+// A struct that wraps Circom functionalities, allowing for extraction of R1CS and witnesses
+// based on file paths to Circom's .r1cs and .wasm.
+pub struct CircomWrapper<E: Pairing> {
+    r1cs_filepath: PathBuf,
+    wasm_filepath: PathBuf,
+    _marker: PhantomData<E>,
+}
+
+impl<E: Pairing> CircomWrapper<E> {
+    // Creates a new instance of the CircomWrapper with the file paths.
+    pub fn new(r1cs_filepath: PathBuf, wasm_filepath: PathBuf) -> Self {
+        CircomWrapper {
+            r1cs_filepath,
+            wasm_filepath,
+            _marker: PhantomData,
+        }
+    }
+
+    // Aggregates multiple functions to obtain R1CS and Z as defined in folding-schemes from Circom.
+    pub fn extract_r1cs_and_z(
+        &self,
+        inputs: &[(String, Vec<BigInt>)],
+    ) -> Result<(R1CS<E::ScalarField>, Vec<E::ScalarField>), Box<dyn Error>> {
+        let (constraints, pub_io_len, num_variables) = self.extract_constraints_from_r1cs()?;
+        let witness = self.calculate_witness(inputs)?;
+        self.circom_to_folding_schemes_r1cs_and_z(constraints, &witness, pub_io_len, num_variables)
+    }
+
+    // Extracts constraints from the r1cs file.
+    pub fn extract_constraints_from_r1cs(&self) -> ExtractedConstraintsResult<E::ScalarField>
+    where
+        E: Pairing,
+    {
+        // Opens the .r1cs file and create a reader.
+        let file = File::open(&self.r1cs_filepath)?;
+        let reader = BufReader::new(file);
+
+        // Reads the R1CS file and extract the constraints directly.
+        let r1cs_file = r1cs_reader::R1CSFile::<E>::new(reader)?;
+        let pub_io_len = (r1cs_file.header.n_pub_in + r1cs_file.header.n_pub_out) as usize;
+        let r1cs = r1cs_reader::R1CS::<E>::from(r1cs_file);
+        let num_variables = r1cs.num_variables;
+        let constraints: Vec<Constraints<E::ScalarField>> = r1cs.constraints;
+
+        Ok((constraints, pub_io_len, num_variables))
+    }
+
+    // Converts a set of constraints from ark-circom into R1CS format of folding-schemes.
+    pub fn convert_to_folding_schemes_r1cs<F>(
+        &self,
+        constraints: Vec<Constraints<F>>,
+        pub_io_len: usize,
+        num_variables: usize,
+    ) -> R1CS<F>
+    where
+        F: PrimeField,
+    {
+        let mut a_matrix: Vec<Vec<(F, usize)>> = Vec::new();
+        let mut b_matrix: Vec<Vec<(F, usize)>> = Vec::new();
+        let mut c_matrix: Vec<Vec<(F, usize)>> = Vec::new();
+
+        let n_rows = constraints.len();
+
+        for (ai, bi, ci) in constraints {
+            a_matrix.push(
+                ai.into_iter()
+                    .map(|(index, scalar)| (scalar, index))
+                    .collect(),
+            );
+            b_matrix.push(
+                bi.into_iter()
+                    .map(|(index, scalar)| (scalar, index))
+                    .collect(),
+            );
+            c_matrix.push(
+                ci.into_iter()
+                    .map(|(index, scalar)| (scalar, index))
+                    .collect(),
+            );
+        }
+
+        let l = pub_io_len;
+        let n_cols = num_variables;
+
+        let A = SparseMatrix {
+            n_rows,
+            n_cols,
+            coeffs: a_matrix,
+        };
+        let B = SparseMatrix {
+            n_rows,
+            n_cols,
+            coeffs: b_matrix,
+        };
+        let C = SparseMatrix {
+            n_rows,
+            n_cols,
+            coeffs: c_matrix,
+        };
+
+        R1CS::<F> { l, A, B, C }
+    }
+
+    // Calculates the witness given the Wasm filepath and inputs.
+    pub fn calculate_witness(&self, inputs: &[(String, Vec<BigInt>)]) -> Result<Vec<BigInt>> {
+        let mut calculator = WitnessCalculator::new(&self.wasm_filepath)?;
+        calculator.calculate_witness(inputs.to_vec().into_iter(), true)
+    }
+
+    // Converts a num_bigint input to `PrimeField`'s BigInt.
+    pub fn num_bigint_to_ark_bigint<F: PrimeField>(
+        &self,
+        value: &BigInt,
+    ) -> Result<F::BigInt, Box<dyn Error>> {
+        let big_uint = value
+            .to_biguint()
+            .ok_or_else(|| "BigInt is negative".to_string())?;
+        F::BigInt::try_from(big_uint).map_err(|_| "BigInt conversion failed".to_string().into())
+    }
+
+    // Converts R1CS constraints and witness from ark-circom format
+    // into folding-schemes R1CS and z format.
+    pub fn circom_to_folding_schemes_r1cs_and_z<F>(
+        &self,
+        constraints: Vec<Constraints<F>>,
+        witness: &[BigInt],
+        pub_io_len: usize,
+        num_variables: usize,
+    ) -> Result<(R1CS<F>, Vec<F>), Box<dyn Error>>
+    where
+        F: PrimeField,
+    {
+        let folding_schemes_r1cs =
+            self.convert_to_folding_schemes_r1cs(constraints, pub_io_len, num_variables);
+
+        let z: Result<Vec<F>, _> = witness
+            .iter()
+            .map(|big_int| {
+                let ark_big_int = self.num_bigint_to_ark_bigint::<F>(big_int)?;
+                F::from_bigint(ark_big_int).ok_or_else(|| {
+                    "Failed to convert bigint to field element"
+                        .to_string()
+                        .into()
+                })
+            })
+            .collect();
+
+        z.map(|z| (folding_schemes_r1cs, z))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::frontend::circom::CircomWrapper;
+    use ark_bn254::Bn254;
+    use num_bigint::BigInt;
+    use std::{env, process::Command};
+
+    // Compiles the .circom file to generate the .r1cs and .wasm files.
+    fn compile_circom_to_r1cs_and_wasm(base_path: &std::path::Path) {
+        let script_path = base_path.join("compile.sh");
+
+        let status = Command::new("bash")
+            .arg(script_path)
+            .status()
+            .expect("Failed to execute circom compilation script.");
+
+        assert!(status.success(), "Circom compilation script failed.");
+    }
+
+    /*
+    test_circuit represents 35 = x^3 + x + 5 in test_folder/test_circuit.circom.
+    In the test_circom_conversion_success function, x is assigned the value 3, which satisfies the R1CS correctly.
+    In the test_circom_conversion_failure function, x is assigned the value 6, which doesn't satisfy the R1CS.
+    */
+
+    fn test_circom_conversion_logic(expect_success: bool, inputs: Vec<(String, Vec<BigInt>)>) {
+        let current_dir = env::current_dir().unwrap();
+        let base_path = current_dir.join("src/frontend/circom/test_folder");
+
+        compile_circom_to_r1cs_and_wasm(&base_path);
+
+        let r1cs_filepath = base_path.join("test_circuit.r1cs");
+        let wasm_filepath = base_path.join("test_circuit_js/test_circuit.wasm");
+
+        assert!(r1cs_filepath.exists());
+        assert!(wasm_filepath.exists());
+
+        let circom_wrapper = CircomWrapper::<Bn254>::new(r1cs_filepath, wasm_filepath);
+
+        let (r1cs, z) = circom_wrapper
+            .extract_r1cs_and_z(&inputs)
+            .expect("Error processing input");
+
+        // Checks the relationship of R1CS.
+        let check_result = std::panic::catch_unwind(|| {
+            r1cs.check_relation(&z).unwrap();
+        });
+
+        match (expect_success, check_result) {
+            (true, Ok(_)) => {}
+            (false, Err(_)) => {}
+            (true, Err(_)) => panic!("Expected success but got a failure."),
+            (false, Ok(_)) => panic!("Expected a failure but got success."),
+        }
+    }
+
+    #[test]
+    fn test_circom_conversion() {
+        // expect it to pass for correct inputs.
+        test_circom_conversion_logic(true, vec![("step_in".to_string(), vec![BigInt::from(3)])]);
+
+        // expect it to fail for incorrect inputs.
+        test_circom_conversion_logic(false, vec![("step_in".to_string(), vec![BigInt::from(7)])]);
+    }
+}

src/frontend/circom/test_folder/compile.sh

@@ -0,0 +1,2 @@
+#!/bin/bash
+circom ./src/frontend/circom/test_folder/test_circuit.circom --r1cs --wasm --prime bn128 --output ./src/frontend/circom/test_folder/

src/frontend/circom/test_folder/test_circuit.circom

@@ -0,0 +1,13 @@
+pragma circom 2.0.3;
+
+template Example () {
+    signal input step_in;
+    signal output step_out;   
+    signal temp;
+
+    temp <== step_in * step_in;
+    step_out <== temp * step_in + step_in + 5;
+    step_out === 35; 
+}
+
+component main = Example();

src/frontend/mod.rs

@@ -1 +1,2 @@
 pub mod arkworks;
+pub mod circom;