@@ -1,21 +1,32 @@
-# keccak-chain-sonobe
-
-Repo showcasing usage of [Sonobe](https://github.com/privacy-scaling-explorations/sonobe) with [Circom](https://github.com/iden3/circom) circuits.
+# hash-chain-sonobe
 
-Proves a chain of keccak256 hashes, using the [vocdoni/keccak256-circom](https://github.com/vocdoni/keccak256-circom) circuit, with [Nova](https://eprint.iacr.org/2021/370.pdf)+[CycleFold](https://eprint.iacr.org/2023/1192.pdf).
+Repo showcasing usage of [Sonobe](https://github.com/privacy-scaling-explorations/sonobe) with [Arkworks](https://github.com/arkworks-rs) and [Circom](https://github.com/iden3/circom) circuits.
 
 The main idea is to prove $z_n = H(H(...~H(H(H(z_0)))))$, where $n$ is the number of Keccak256 hashes ($H$) that we compute. Proving this in a 'normal' R1CS circuit for a large $n$ would be too costly, but with folding we can manage to prove it in a reasonable time span.
 
 For more info about Sonobe, check out [Sonobe's docs](https://privacy-scaling-explorations.github.io/sonobe-docs).
 
+<p align="center">
+    <img src="https://privacy-scaling-explorations.github.io/sonobe-docs/imgs/folding-main-idea-diagram.png" style="width:70%;" />
+</p>
+
+
 ### Usage
 
+### sha_chain.rs (arkworks circuit)
+Proves a chain of SHA256 hashes, using the [arkworks/sha256](https://github.com/arkworks-rs/crypto-primitives/blob/main/crypto-primitives/src/crh/sha256/constraints.rs) circuit, with [Nova](https://eprint.iacr.org/2021/370.pdf)+[CycleFold](https://eprint.iacr.org/2023/1192.pdf).
+
+- `cargo test --release sha_chain -- --nocapture`
+
+### keccak_chain.rs (circom circuit)
+Proves a chain of keccak256 hashes, using the [vocdoni/keccak256-circom](https://github.com/vocdoni/keccak256-circom) circuit, with [Nova](https://eprint.iacr.org/2021/370.pdf)+[CycleFold](https://eprint.iacr.org/2023/1192.pdf).
+
 Assuming rust and circom have been installed:
-
 - `./compile-circuit.sh`
-- `cargo test --release -- --nocapture`
+- `cargo test --release keccak_chain -- --nocapture`
+
+Note: the Circom variant currently has a bit of extra overhead since at each folding step it uses Circom witness generation to obtain the witness and then it imports it into the arkworks constraint system.
 
 ### Repo structure
-- the Circom circuit to be folded is defined at [./circuit/keccak-chain.circom](https://github.com/arnaucube/keccak-chain-sonobe/blob/main/circuit/keccak-chain.circom)
-- the logic to fold the circuit using Sonobe is defined at [src/lib.rs](https://github.com/arnaucube/keccak-chain-sonobe/blob/main/src/lib.rs)
-	- (it contains some extra sanity check that would not be needed in a real-world use case)
+- the Circom circuit (that defines the keccak-chain) to be folded is defined at [./circuit/keccak-chain.circom](https://github.com/arnaucube/hash-chain-sonobe/blob/main/circuit/keccak-chain.circom)
+- the logic to fold the circuit using Sonobe is defined at [src/{sha_chain, keccak_chain}.rs](https://github.com/arnaucube/hash-chain-sonobe/blob/main/src)

@@ -0,0 +1,237 @@
+///
+/// This example performs the full flow:
+/// - define the circuit to be folded
+/// - fold the circuit with Nova+CycleFold's IVC
+/// - generate a DeciderEthCircuit final proof
+/// - generate the Solidity contract that verifies the proof
+/// - verify the proof in the EVM
+///
+
+#[cfg(test)]
+mod tests {
+    use ark_bn254::{constraints::GVar, Bn254, Fr, G1Projective as G1};
+    use ark_grumpkin::{constraints::GVar as GVar2, Projective as G2};
+
+    use ark_groth16::Groth16;
+
+    use ark_ff::PrimeField;
+
+    use std::path::PathBuf;
+    use std::rc::Rc;
+    use std::time::Instant;
+
+    use folding_schemes::{
+        commitment::{kzg::KZG, pedersen::Pedersen},
+        folding::nova::{
+            decider_eth::{prepare_calldata, Decider as DeciderEth},
+            Nova, PreprocessorParam,
+        },
+        frontend::{circom::CircomFCircuit, FCircuit},
+        transcript::poseidon::poseidon_canonical_config,
+        Decider, Error, FoldingScheme,
+    };
+    use solidity_verifiers::{
+        utils::get_function_selector_for_nova_cyclefold_verifier,
+        verifiers::nova_cyclefold::get_decider_template_for_cyclefold_decider,
+        NovaCycleFoldVerifierKey,
+    };
+
+    use crate::utils::tests::*;
+
+    // function to compute the next state of the folding via rust-native code (not Circom). Used to
+    // check the Circom values.
+    use tiny_keccak::{Hasher, Keccak};
+    fn rust_native_step<F: PrimeField>(
+        _i: usize,
+        z_i: Vec<F>,
+        _external_inputs: Vec<F>,
+    ) -> Result<Vec<F>, Error> {
+        let b = f_vec_bits_to_bytes(z_i.to_vec());
+        let mut h = Keccak::v256();
+        h.update(&b);
+        let mut z_i1 = [0u8; 32];
+        h.finalize(&mut z_i1);
+        bytes_to_f_vec_bits(z_i1.to_vec())
+    }
+
+    #[test]
+    fn full_flow() {
+        // set how many steps of folding we want to compute
+        let n_steps = 1000;
+
+        // set the initial state
+        let z_0_aux: Vec<u32> = vec![0_u32; 32 * 8];
+        let z_0: Vec<Fr> = z_0_aux.iter().map(|v| Fr::from(*v)).collect::<Vec<Fr>>();
+
+        // initialize the Circom circuit
+        let r1cs_path = PathBuf::from("./circuit/keccak-chain.r1cs");
+        let wasm_path = PathBuf::from("./circuit/keccak-chain_js/keccak-chain.wasm");
+
+        let f_circuit_params = (r1cs_path, wasm_path, 32 * 8, 0);
+        let mut f_circuit = CircomFCircuit::<Fr>::new(f_circuit_params).unwrap();
+        // Note (optional): for more speed, we can set a custom rust-native logic, which will be
+        // used for the `step_native` method instead of extracting the values from the circom
+        // witness:
+        f_circuit.set_custom_step_native(Rc::new(rust_native_step));
+
+        // ----------------
+        // Sanity check
+        // check that the f_circuit produces valid R1CS constraints
+        use ark_r1cs_std::alloc::AllocVar;
+        use ark_r1cs_std::fields::fp::FpVar;
+        use ark_r1cs_std::R1CSVar;
+        use ark_relations::r1cs::ConstraintSystem;
+        let cs = ConstraintSystem::<Fr>::new_ref();
+        let z_0_var = Vec::<FpVar<Fr>>::new_witness(cs.clone(), || Ok(z_0.clone())).unwrap();
+        let z_1_var = f_circuit
+            .generate_step_constraints(cs.clone(), 1, z_0_var, vec![])
+            .unwrap();
+        // check z_1_var against the native z_1
+        let z_1_native = f_circuit.step_native(1, z_0.clone(), vec![]).unwrap();
+        assert_eq!(z_1_var.value().unwrap(), z_1_native);
+        // check that the constraint system is satisfied
+        assert!(cs.is_satisfied().unwrap());
+        // ----------------
+
+        // define type aliases to avoid writting the whole type each time
+        pub type N =
+            Nova<G1, GVar, G2, GVar2, CircomFCircuit<Fr>, KZG<'static, Bn254>, Pedersen<G2>, false>;
+        pub type D = DeciderEth<
+            G1,
+            GVar,
+            G2,
+            GVar2,
+            CircomFCircuit<Fr>,
+            KZG<'static, Bn254>,
+            Pedersen<G2>,
+            Groth16<Bn254>,
+            N,
+        >;
+
+        let poseidon_config = poseidon_canonical_config::<Fr>();
+        let mut rng = rand::rngs::OsRng;
+
+        // prepare the Nova prover & verifier params
+        let nova_preprocess_params = PreprocessorParam::new(poseidon_config, f_circuit.clone());
+        let start = Instant::now();
+        let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
+        println!("Nova params generated: {:?}", start.elapsed());
+
+        // initialize the folding scheme engine, in our case we use Nova
+        let mut nova = N::init(&nova_params, f_circuit.clone(), z_0.clone()).unwrap();
+
+        // prepare the Decider prover & verifier params
+        let start = Instant::now();
+        let (decider_pp, decider_vp) = D::preprocess(&mut rng, &nova_params, nova.clone()).unwrap();
+        println!("Decider params generated: {:?}", start.elapsed());
+
+        // run n steps of the folding iteration
+        let start_full = Instant::now();
+        for _ in 0..n_steps {
+            let start = Instant::now();
+            nova.prove_step(rng, vec![], None).unwrap();
+            println!(
+                "Nova::prove_step (keccak256 through Circom) {}: {:?}",
+                nova.i,
+                start.elapsed()
+            );
+        }
+        println!("Nova's all steps time: {:?}", start_full.elapsed());
+
+        // perform the hash chain natively in rust (which uses a rust Keccak256 library)
+        let mut z_i_native = z_0.clone();
+        for i in 0..n_steps {
+            z_i_native = rust_native_step(i, z_i_native.clone(), vec![]).unwrap();
+        }
+        // check that the value of the last folding state (nova.z_i) computed through folding, is
+        // equal to the natively computed hash using the rust_native_step method
+        assert_eq!(nova.z_i, z_i_native);
+
+        // ----------------
+        // Sanity check
+        // The following lines contain a sanity check that checks the IVC proof (before going into
+        // the zkSNARK proof)
+        let (running_instance, incoming_instance, cyclefold_instance) = nova.instances();
+        N::verify(
+            nova_params.1, // Nova's verifier params
+            z_0,
+            nova.z_i.clone(),
+            nova.i,
+            running_instance,
+            incoming_instance,
+            cyclefold_instance,
+        )
+        .unwrap();
+        // ----------------
+
+        let rng = rand::rngs::OsRng;
+        let start = Instant::now();
+        let proof = D::prove(rng, decider_pp, nova.clone()).unwrap();
+        println!("generated Decider proof: {:?}", start.elapsed());
+
+        let verified = D::verify(
+            decider_vp.clone(),
+            nova.i,
+            nova.z_0.clone(),
+            nova.z_i.clone(),
+            &nova.U_i,
+            &nova.u_i,
+            &proof,
+        )
+        .unwrap();
+        assert!(verified);
+        println!("Decider proof verification: {}", verified);
+
+        // generate the Solidity code that verifies this Decider final proof
+        let function_selector =
+            get_function_selector_for_nova_cyclefold_verifier(nova.z_0.len() * 2 + 1);
+
+        let calldata: Vec<u8> = prepare_calldata(
+            function_selector,
+            nova.i,
+            nova.z_0,
+            nova.z_i,
+            &nova.U_i,
+            &nova.u_i,
+            proof,
+        )
+        .unwrap();
+
+        // prepare the setup params for the solidity verifier
+        let nova_cyclefold_vk = NovaCycleFoldVerifierKey::from((decider_vp, f_circuit.state_len()));
+
+        // generate the solidity code
+        let decider_solidity_code = get_decider_template_for_cyclefold_decider(nova_cyclefold_vk);
+
+        /*
+         * Note: since we're proving the Keccak256 (ie. 32 byte size, 256 bits), the number of
+         * inputs is too big for the contract. In a real world use case we would convert the binary
+         * representation into a couple of field elements which would be inputs of the Decider
+         * circuit, and in-circuit we would obtain the binary representation to be used for the
+         * final proof check.
+         *
+         * The following code is commented out for that reason.
+        // verify the proof against the solidity code in the EVM
+        use solidity_verifiers::evm::{compile_solidity, Evm};
+        let nova_cyclefold_verifier_bytecode =
+            compile_solidity(&decider_solidity_code, "NovaDecider");
+        let mut evm = Evm::default();
+        let verifier_address = evm.create(nova_cyclefold_verifier_bytecode);
+        let (_, output) = evm.call(verifier_address, calldata.clone());
+        assert_eq!(*output.last().unwrap(), 1);
+         */
+
+        // save smart contract and the calldata
+        println!("storing nova-verifier.sol and the calldata into files");
+        use std::fs;
+        fs::create_dir_all("./solidity").unwrap();
+        fs::write(
+            "./solidity/nova-verifier.sol",
+            decider_solidity_code.clone(),
+        )
+        .unwrap();
+        fs::write("./solidity/solidity-calldata.calldata", calldata.clone()).unwrap();
+        let s = solidity_verifiers::utils::get_formatted_calldata(calldata.clone());
+        fs::write("./solidity/solidity-calldata.inputs", s.join(",\n")).expect("");
+    }
+}

@@ -1,259 +1,7 @@
 #![allow(non_snake_case)]
 #![allow(non_camel_case_types)]
 #![allow(clippy::upper_case_acronyms)]
-///
-/// This example performs the full flow:
-/// - define the circuit to be folded
-/// - fold the circuit with Nova+CycleFold's IVC
-/// - generate a DeciderEthCircuit final proof
-/// - generate the Solidity contract that verifies the proof
-/// - verify the proof in the EVM
-///
 
-#[cfg(test)]
-mod tests {
-    use ark_bn254::{constraints::GVar, Bn254, Fr, G1Projective as G1};
-    use ark_grumpkin::{constraints::GVar as GVar2, Projective as G2};
-
-    use ark_groth16::Groth16;
-
-    use ark_ff::{BigInteger, BigInteger256, PrimeField};
-
-    use std::path::PathBuf;
-    use std::rc::Rc;
-    use std::time::Instant;
-
-    use folding_schemes::{
-        commitment::{kzg::KZG, pedersen::Pedersen},
-        folding::nova::{
-            decider_eth::{prepare_calldata, Decider as DeciderEth},
-            Nova, PreprocessorParam,
-        },
-        frontend::{circom::CircomFCircuit, FCircuit},
-        transcript::poseidon::poseidon_canonical_config,
-        Decider, Error, FoldingScheme,
-    };
-    use solidity_verifiers::{
-        utils::get_function_selector_for_nova_cyclefold_verifier,
-        verifiers::nova_cyclefold::get_decider_template_for_cyclefold_decider,
-        NovaCycleFoldVerifierKey,
-    };
-
-    fn f_vec_to_bits<F: PrimeField>(v: Vec<F>) -> Vec<bool> {
-        v.iter()
-            .map(|v_i| {
-                if v_i.is_one() {
-                    return true;
-                }
-                false
-            })
-            .collect()
-    }
-    // returns the bytes representation of the given vector of finite field elements that represent
-    // bits
-    fn f_vec_to_bytes<F: PrimeField>(v: Vec<F>) -> Vec<u8> {
-        let b = f_vec_to_bits(v);
-        BigInteger256::from_bits_le(&b).to_bytes_le()
-    }
-    fn bytes_to_f_vec<F: PrimeField>(b: Vec<u8>) -> Result<Vec<F>, Error> {
-        use num_bigint::BigUint;
-        let bi = BigUint::from_bytes_le(&b);
-        let bi = BigInteger256::try_from(bi).unwrap();
-        let bits = bi.to_bits_le();
-        Ok(bits
-            .iter()
-            .map(|&e| if e { F::one() } else { F::zero() })
-            .collect())
-    }
-
-    // function to compute the next state of the folding via rust-native code (not Circom). Used to
-    // check the Circom values.
-    use tiny_keccak::{Hasher, Keccak};
-    fn rust_native_step<F: PrimeField>(
-        _i: usize,
-        z_i: Vec<F>,
-        _external_inputs: Vec<F>,
-    ) -> Result<Vec<F>, Error> {
-        let b = f_vec_to_bytes(z_i.to_vec());
-        let mut h = Keccak::v256();
-        h.update(&b);
-        let mut z_i1 = [0u8; 32];
-        h.finalize(&mut z_i1);
-        bytes_to_f_vec(z_i1.to_vec())
-    }
-
-    #[test]
-    fn full_flow() {
-        // set how many steps of folding we want to compute
-        let n_steps = 10;
-
-        // set the initial state
-        let z_0_aux: Vec<u32> = vec![0_u32; 32 * 8];
-        let z_0: Vec<Fr> = z_0_aux.iter().map(|v| Fr::from(*v)).collect::<Vec<Fr>>();
-
-        // initialize the Circom circuit
-        let r1cs_path = PathBuf::from("./circuit/keccak-chain.r1cs");
-        let wasm_path = PathBuf::from("./circuit/keccak-chain_js/keccak-chain.wasm");
-
-        let f_circuit_params = (r1cs_path, wasm_path, 32 * 8, 0);
-        let mut f_circuit = CircomFCircuit::<Fr>::new(f_circuit_params).unwrap();
-        // Note (optional): for more speed, we can set a custom rust-native logic, which will be
-        // used for the `step_native` method instead of extracting the values from the circom
-        // witness:
-        f_circuit.set_custom_step_native(Rc::new(rust_native_step));
-
-        // ----------------
-        // Sanity check
-        // check that the f_circuit produces valid R1CS constraints
-        use ark_r1cs_std::alloc::AllocVar;
-        use ark_r1cs_std::fields::fp::FpVar;
-        use ark_r1cs_std::R1CSVar;
-        use ark_relations::r1cs::ConstraintSystem;
-        let cs = ConstraintSystem::<Fr>::new_ref();
-        let z_0_var = Vec::<FpVar<Fr>>::new_witness(cs.clone(), || Ok(z_0.clone())).unwrap();
-        let z_1_var = f_circuit
-            .generate_step_constraints(cs.clone(), 1, z_0_var, vec![])
-            .unwrap();
-        // check z_1_var against the native z_1
-        let z_1_native = f_circuit.step_native(1, z_0.clone(), vec![]).unwrap();
-        assert_eq!(z_1_var.value().unwrap(), z_1_native);
-        // check that the constraint system is satisfied
-        assert!(cs.is_satisfied().unwrap());
-        // ----------------
-
-        // define type aliases to avoid writting the whole type each time
-        pub type N =
-            Nova<G1, GVar, G2, GVar2, CircomFCircuit<Fr>, KZG<'static, Bn254>, Pedersen<G2>, false>;
-        pub type D = DeciderEth<
-            G1,
-            GVar,
-            G2,
-            GVar2,
-            CircomFCircuit<Fr>,
-            KZG<'static, Bn254>,
-            Pedersen<G2>,
-            Groth16<Bn254>,
-            N,
-        >;
-
-        let poseidon_config = poseidon_canonical_config::<Fr>();
-        let mut rng = rand::rngs::OsRng;
-
-        // prepare the Nova prover & verifier params
-        let nova_preprocess_params = PreprocessorParam::new(poseidon_config, f_circuit.clone());
-        let start = Instant::now();
-        let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
-        println!("Nova params generated: {:?}", start.elapsed());
-
-        // initialize the folding scheme engine, in our case we use Nova
-        let mut nova = N::init(&nova_params, f_circuit.clone(), z_0.clone()).unwrap();
-
-        // prepare the Decider prover & verifier params
-        let start = Instant::now();
-        let (decider_pp, decider_vp) = D::preprocess(&mut rng, &nova_params, nova.clone()).unwrap();
-        println!("Decider params generated: {:?}", start.elapsed());
-
-        // run n steps of the folding iteration
-        for _ in 0..n_steps {
-            let start = Instant::now();
-            nova.prove_step(rng, vec![], None).unwrap();
-            println!("Nova::prove_step {}: {:?}", nova.i, start.elapsed());
-        }
-
-        // perform the hash chain natively in rust (which uses a rust Keccak256 library)
-        let mut z_i_native = z_0.clone();
-        for i in 0..n_steps {
-            z_i_native = rust_native_step(i, z_i_native.clone(), vec![]).unwrap();
-        }
-        // check that the value of the last folding state (nova.z_i) computed through folding, is
-        // equal to the natively computed hash using the rust_native_step method
-        assert_eq!(nova.z_i, z_i_native);
-
-        // ----------------
-        // Sanity check
-        // The following lines contain a sanity check that checks the IVC proof (before going into
-        // the zkSNARK proof)
-        let (running_instance, incoming_instance, cyclefold_instance) = nova.instances();
-        N::verify(
-            nova_params.1, // Nova's verifier params
-            z_0,
-            nova.z_i.clone(),
-            nova.i,
-            running_instance,
-            incoming_instance,
-            cyclefold_instance,
-        )
-        .unwrap();
-        // ----------------
-
-        let rng = rand::rngs::OsRng;
-        let start = Instant::now();
-        let proof = D::prove(rng, decider_pp, nova.clone()).unwrap();
-        println!("generated Decider proof: {:?}", start.elapsed());
-
-        let verified = D::verify(
-            decider_vp.clone(),
-            nova.i,
-            nova.z_0.clone(),
-            nova.z_i.clone(),
-            &nova.U_i,
-            &nova.u_i,
-            &proof,
-        )
-        .unwrap();
-        assert!(verified);
-        println!("Decider proof verification: {}", verified);
-
-        // generate the Solidity code that verifies this Decider final proof
-        let function_selector =
-            get_function_selector_for_nova_cyclefold_verifier(nova.z_0.len() * 2 + 1);
-
-        let calldata: Vec<u8> = prepare_calldata(
-            function_selector,
-            nova.i,
-            nova.z_0,
-            nova.z_i,
-            &nova.U_i,
-            &nova.u_i,
-            proof,
-        )
-        .unwrap();
-
-        // prepare the setup params for the solidity verifier
-        let nova_cyclefold_vk = NovaCycleFoldVerifierKey::from((decider_vp, f_circuit.state_len()));
-
-        // generate the solidity code
-        let decider_solidity_code = get_decider_template_for_cyclefold_decider(nova_cyclefold_vk);
-
-        /*
-         * Note: since we're proving the Keccak256 (ie. 32 byte size, 256 bits), the number of
-         * inputs is too big for the contract. In a real world use case we would convert the binary
-         * representation into a couple of field elements which would be inputs of the Decider
-         * circuit, and in-circuit we would obtain the binary representation to be used for the
-         * final proof check.
-         *
-         * The following code is commented out for that reason.
-        // verify the proof against the solidity code in the EVM
-        use solidity_verifiers::evm::{compile_solidity, Evm};
-        let nova_cyclefold_verifier_bytecode =
-            compile_solidity(&decider_solidity_code, "NovaDecider");
-        let mut evm = Evm::default();
-        let verifier_address = evm.create(nova_cyclefold_verifier_bytecode);
-        let (_, output) = evm.call(verifier_address, calldata.clone());
-        assert_eq!(*output.last().unwrap(), 1);
-         */
-
-        // save smart contract and the calldata
-        println!("storing nova-verifier.sol and the calldata into files");
-        use std::fs;
-        fs::create_dir_all("./solidity").unwrap();
-        fs::write(
-            "./solidity/nova-verifier.sol",
-            decider_solidity_code.clone(),
-        )
-        .unwrap();
-        fs::write("./solidity/solidity-calldata.calldata", calldata.clone()).unwrap();
-        let s = solidity_verifiers::utils::get_formatted_calldata(calldata.clone());
-        fs::write("./solidity/solidity-calldata.inputs", s.join(",\n")).expect("");
-    }
-}
+mod keccak_chain;
+mod sha_chain;
+mod utils;

@@ -0,0 +1,273 @@
+///
+/// This example performs the full flow:
+/// - define the circuit to be folded
+/// - fold the circuit with Nova+CycleFold's IVC
+/// - generate a DeciderEthCircuit final proof
+/// - generate the Solidity contract that verifies the proof
+/// - verify the proof in the EVM
+///
+
+#[cfg(test)]
+mod tests {
+    use ark_bn254::{constraints::GVar, Bn254, Fr, G1Projective as G1};
+    use ark_grumpkin::{constraints::GVar as GVar2, Projective as G2};
+
+    use ark_groth16::Groth16;
+
+    use ark_ff::PrimeField;
+
+    use std::time::Instant;
+
+    use ark_crypto_primitives::crh::sha256::{constraints::Sha256Gadget, digest::Digest, Sha256};
+    use ark_r1cs_std::fields::fp::FpVar;
+    use ark_r1cs_std::{bits::uint8::UInt8, boolean::Boolean, ToBitsGadget, ToBytesGadget};
+    use ark_relations::r1cs::{ConstraintSystemRef, SynthesisError};
+    use std::marker::PhantomData;
+
+    use folding_schemes::{
+        commitment::{kzg::KZG, pedersen::Pedersen},
+        folding::nova::{
+            decider_eth::{prepare_calldata, Decider as DeciderEth},
+            Nova, PreprocessorParam,
+        },
+        frontend::FCircuit,
+        transcript::poseidon::poseidon_canonical_config,
+        Decider, Error, FoldingScheme,
+    };
+    use solidity_verifiers::{
+        utils::get_function_selector_for_nova_cyclefold_verifier,
+        verifiers::nova_cyclefold::get_decider_template_for_cyclefold_decider,
+        NovaCycleFoldVerifierKey,
+    };
+
+    use crate::utils::tests::*;
+
+    /// Test circuit to be folded
+    #[derive(Clone, Copy, Debug)]
+    pub struct SHA256FoldStepCircuit<F: PrimeField> {
+        _f: PhantomData<F>,
+    }
+    impl<F: PrimeField> FCircuit<F> for SHA256FoldStepCircuit<F> {
+        type Params = ();
+        fn new(_params: Self::Params) -> Result<Self, Error> {
+            Ok(Self { _f: PhantomData })
+        }
+        fn state_len(&self) -> usize {
+            32
+        }
+        fn external_inputs_len(&self) -> usize {
+            0
+        }
+        // function to compute the next state of the folding via rust-native code (not Circom). Used to
+        // check the Circom values.
+        fn step_native(
+            &self,
+            _i: usize,
+            z_i: Vec<F>,
+            _external_inputs: Vec<F>,
+        ) -> Result<Vec<F>, Error> {
+            let b = f_vec_to_bytes(z_i.to_vec());
+            let mut sha256 = Sha256::default();
+            sha256.update(b);
+            let z_i1 = sha256.finalize().to_vec();
+
+            bytes_to_f_vec(z_i1.to_vec())
+        }
+        fn generate_step_constraints(
+            &self,
+            _cs: ConstraintSystemRef<F>,
+            _i: usize,
+            z_i: Vec<FpVar<F>>,
+            _external_inputs: Vec<FpVar<F>>,
+        ) -> Result<Vec<FpVar<F>>, SynthesisError> {
+            let mut sha256_var = Sha256Gadget::default();
+            let z_i_u8: Vec<UInt8<F>> = z_i
+                .iter()
+                .map(|f| UInt8::<F>::from_bits_le(&f.to_bits_le().unwrap()[..8]))
+                .collect::<Vec<_>>();
+            sha256_var.update(&z_i_u8).unwrap();
+            let z_i1_u8 = sha256_var.finalize()?.to_bytes()?;
+            let z_i1: Vec<FpVar<F>> = z_i1_u8
+                .iter()
+                .map(|e| {
+                    let bits = e.to_bits_le().unwrap();
+                    Boolean::<F>::le_bits_to_fp_var(&bits).unwrap()
+                })
+                .collect();
+
+            Ok(z_i1)
+        }
+    }
+
+    #[test]
+    fn full_flow() {
+        // set how many steps of folding we want to compute
+        let n_steps = 100;
+
+        // set the initial state
+        // let z_0_aux: Vec<u32> = vec![0_u32; 32 * 8];
+        let z_0_aux: Vec<u8> = vec![0_u8; 32];
+        let z_0: Vec<Fr> = z_0_aux.iter().map(|v| Fr::from(*v)).collect::<Vec<Fr>>();
+
+        let f_circuit = SHA256FoldStepCircuit::<Fr>::new(()).unwrap();
+
+        // ----------------
+        // Sanity check
+        // check that the f_circuit produces valid R1CS constraints
+        use ark_r1cs_std::alloc::AllocVar;
+        use ark_r1cs_std::fields::fp::FpVar;
+        use ark_r1cs_std::R1CSVar;
+        use ark_relations::r1cs::ConstraintSystem;
+        let cs = ConstraintSystem::<Fr>::new_ref();
+        let z_0_var = Vec::<FpVar<Fr>>::new_witness(cs.clone(), || Ok(z_0.clone())).unwrap();
+        let z_1_var = f_circuit
+            .generate_step_constraints(cs.clone(), 1, z_0_var, vec![])
+            .unwrap();
+        // check z_1_var against the native z_1
+        let z_1_native = f_circuit.step_native(1, z_0.clone(), vec![]).unwrap();
+        assert_eq!(z_1_var.value().unwrap(), z_1_native);
+        // check that the constraint system is satisfied
+        assert!(cs.is_satisfied().unwrap());
+        // ----------------
+
+        // define type aliases to avoid writting the whole type each time
+        pub type N = Nova<
+            G1,
+            GVar,
+            G2,
+            GVar2,
+            SHA256FoldStepCircuit<Fr>,
+            KZG<'static, Bn254>,
+            Pedersen<G2>,
+            false,
+        >;
+        pub type D = DeciderEth<
+            G1,
+            GVar,
+            G2,
+            GVar2,
+            SHA256FoldStepCircuit<Fr>,
+            KZG<'static, Bn254>,
+            Pedersen<G2>,
+            Groth16<Bn254>,
+            N,
+        >;
+
+        let poseidon_config = poseidon_canonical_config::<Fr>();
+        let mut rng = rand::rngs::OsRng;
+
+        // prepare the Nova prover & verifier params
+        let nova_preprocess_params = PreprocessorParam::new(poseidon_config, f_circuit);
+        let start = Instant::now();
+        let nova_params = N::preprocess(&mut rng, &nova_preprocess_params).unwrap();
+        println!("Nova params generated: {:?}", start.elapsed());
+
+        // initialize the folding scheme engine, in our case we use Nova
+        let mut nova = N::init(&nova_params, f_circuit, z_0.clone()).unwrap();
+
+        // prepare the Decider prover & verifier params
+        let start = Instant::now();
+        let (decider_pp, decider_vp) = D::preprocess(&mut rng, &nova_params, nova.clone()).unwrap();
+        println!("Decider params generated: {:?}", start.elapsed());
+
+        // run n steps of the folding iteration
+        let start_full = Instant::now();
+        for _ in 0..n_steps {
+            let start = Instant::now();
+            nova.prove_step(rng, vec![], None).unwrap();
+            println!(
+                "Nova::prove_step (sha256) {}: {:?}",
+                nova.i,
+                start.elapsed()
+            );
+        }
+        println!("Nova's all steps time: {:?}", start_full.elapsed());
+
+        // ----------------
+        // Sanity check
+        // The following lines contain a sanity check that checks the IVC proof (before going into
+        // the zkSNARK proof)
+        let (running_instance, incoming_instance, cyclefold_instance) = nova.instances();
+        N::verify(
+            nova_params.1, // Nova's verifier params
+            z_0,
+            nova.z_i.clone(),
+            nova.i,
+            running_instance,
+            incoming_instance,
+            cyclefold_instance,
+        )
+        .unwrap();
+        // ----------------
+
+        let rng = rand::rngs::OsRng;
+        let start = Instant::now();
+        let proof = D::prove(rng, decider_pp, nova.clone()).unwrap();
+        println!("generated Decider proof: {:?}", start.elapsed());
+
+        let verified = D::verify(
+            decider_vp.clone(),
+            nova.i,
+            nova.z_0.clone(),
+            nova.z_i.clone(),
+            &nova.U_i,
+            &nova.u_i,
+            &proof,
+        )
+        .unwrap();
+        assert!(verified);
+        println!("Decider proof verification: {}", verified);
+
+        // generate the Solidity code that verifies this Decider final proof
+        let function_selector =
+            get_function_selector_for_nova_cyclefold_verifier(nova.z_0.len() * 2 + 1);
+
+        let calldata: Vec<u8> = prepare_calldata(
+            function_selector,
+            nova.i,
+            nova.z_0,
+            nova.z_i,
+            &nova.U_i,
+            &nova.u_i,
+            proof,
+        )
+        .unwrap();
+
+        // prepare the setup params for the solidity verifier
+        let nova_cyclefold_vk = NovaCycleFoldVerifierKey::from((decider_vp, f_circuit.state_len()));
+
+        // generate the solidity code
+        let decider_solidity_code = get_decider_template_for_cyclefold_decider(nova_cyclefold_vk);
+
+        /*
+         * Note: since we're proving the SHA256 (ie. 32 byte size, 256 bits), the number of inputs
+         * is too big for the contract. In a real world use case we would convert the binary
+         * representation into a couple of field elements which would be inputs of the Decider
+         * circuit, and in-circuit we would obtain the binary representation to be used for the
+         * final proof check.
+         *
+         * The following code is commented out for that reason.
+        // verify the proof against the solidity code in the EVM
+        use solidity_verifiers::evm::{compile_solidity, Evm};
+        let nova_cyclefold_verifier_bytecode =
+            compile_solidity(&decider_solidity_code, "NovaDecider");
+        let mut evm = Evm::default();
+        let verifier_address = evm.create(nova_cyclefold_verifier_bytecode);
+        let (_, output) = evm.call(verifier_address, calldata.clone());
+        assert_eq!(*output.last().unwrap(), 1);
+         */
+
+        // save smart contract and the calldata
+        println!("storing nova-verifier.sol and the calldata into files");
+        use std::fs;
+        fs::create_dir_all("./solidity").unwrap();
+        fs::write(
+            "./solidity/nova-verifier.sol",
+            decider_solidity_code.clone(),
+        )
+        .unwrap();
+        fs::write("./solidity/solidity-calldata.calldata", calldata.clone()).unwrap();
+        let s = solidity_verifiers::utils::get_formatted_calldata(calldata.clone());
+        fs::write("./solidity/solidity-calldata.inputs", s.join(",\n")).expect("");
+    }
+}

@@ -0,0 +1,49 @@
+#[cfg(test)]
+pub(crate) mod tests {
+    use ark_ff::{BigInteger, BigInteger256, PrimeField};
+    use folding_schemes::Error;
+
+    /// interprets the vector of finite field elements as a vector of bytes
+    pub(crate) fn f_vec_to_bytes<F: PrimeField>(b: Vec<F>) -> Vec<u8> {
+        b.iter()
+            .map(|e| {
+                let bytes: Vec<u8> = e.into_bigint().to_bytes_le();
+                bytes[0]
+            })
+            .collect()
+    }
+    /// for a given byte array, returns the bytes representation in finite field elements
+    pub(crate) fn bytes_to_f_vec<F: PrimeField>(b: Vec<u8>) -> Result<Vec<F>, Error> {
+        Ok(b.iter()
+            .map(|&e| F::from_le_bytes_mod_order(&[e]))
+            .collect::<Vec<F>>())
+    }
+    /// returns the bytes representation of the given vector of finite field elements that represent
+    /// bits
+    pub(crate) fn f_vec_bits_to_bytes<F: PrimeField>(v: Vec<F>) -> Vec<u8> {
+        let b = f_vec_to_bits(v);
+        BigInteger256::from_bits_le(&b).to_bytes_le()
+    }
+    /// for a given byte array, returns its bits representation in finite field elements
+    pub(crate) fn bytes_to_f_vec_bits<F: PrimeField>(b: Vec<u8>) -> Result<Vec<F>, Error> {
+        use num_bigint::BigUint;
+        let bi = BigUint::from_bytes_le(&b);
+        let bi = BigInteger256::try_from(bi).unwrap();
+        let bits = bi.to_bits_le();
+        Ok(bits
+            .iter()
+            .map(|&e| if e { F::one() } else { F::zero() })
+            .collect())
+    }
+    /// interprets the given vector of finite field elements as a vector of bits
+    pub(crate) fn f_vec_to_bits<F: PrimeField>(v: Vec<F>) -> Vec<bool> {
+        v.iter()
+            .map(|v_i| {
+                if v_i.is_one() {
+                    return true;
+                }
+                false
+            })
+            .collect()
+    }
+}