diff --git a/Cargo.toml b/Cargo.toml
index abb006638..a51b6a1a5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,6 +11,7 @@ members = [
     "compiler",
     "pilgen",
     "halo2",
+    "backend",
 ]
 
 [patch."https://github.com/privacy-scaling-explorations/halo2.git"]
diff --git a/backend/Cargo.toml b/backend/Cargo.toml
new file mode 100644
index 000000000..1bb686ed4
--- /dev/null
+++ b/backend/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "backend"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+halo2 = { path = "../halo2" }
+pil_analyzer = { path = "../pil_analyzer" }
+number = { path = "../number" }
+strum = { version = "0.24.1", features = ["derive"] }
diff --git a/backend/src/lib.rs b/backend/src/lib.rs
new file mode 100644
index 000000000..5f78c76c9
--- /dev/null
+++ b/backend/src/lib.rs
@@ -0,0 +1,66 @@
+use number::FieldElement;
+use pil_analyzer::Analyzed;
+use std::io;
+use strum::{Display, EnumString, EnumVariantNames};
+
+#[derive(Clone, EnumString, EnumVariantNames, Display)]
+pub enum Backend {
+    #[strum(serialize = "halo2")]
+    Halo2,
+    #[strum(serialize = "halo2-mock")]
+    Halo2Mock,
+}
+
+/// Create a proof for a given PIL, fixed column values and witness column values
+/// using the chosen backend.
+
+pub type Proof = Vec<u8>;
+pub type Params = Vec<u8>;
+
+pub trait ProverWithParams {
+    fn prove<T: FieldElement, R: io::Read>(
+        pil: &Analyzed<T>,
+        fixed: Vec<(&str, Vec<T>)>,
+        witness: Vec<(&str, Vec<T>)>,
+        params: R,
+    ) -> Option<Proof>;
+
+    fn generate_params<T: FieldElement>(size: usize) -> Params;
+}
+
+pub trait ProverWithoutParams {
+    fn prove<T: FieldElement>(
+        pil: &Analyzed<T>,
+        fixed: Vec<(&str, Vec<T>)>,
+        witness: Vec<(&str, Vec<T>)>,
+    ) -> Option<Proof>;
+}
+
+pub struct Halo2Backend;
+pub struct Halo2MockBackend;
+
+impl ProverWithParams for Halo2Backend {
+    fn prove<T: FieldElement, R: io::Read>(
+        pil: &Analyzed<T>,
+        fixed: Vec<(&str, Vec<T>)>,
+        witness: Vec<(&str, Vec<T>)>,
+        params: R,
+    ) -> Option<Proof> {
+        Some(halo2::prove_ast_read_params(pil, fixed, witness, params))
+    }
+
+    fn generate_params<T: FieldElement>(size: usize) -> Params {
+        halo2::generate_params::<T>(size)
+    }
+}
+
+impl ProverWithoutParams for Halo2MockBackend {
+    fn prove<T: FieldElement>(
+        pil: &Analyzed<T>,
+        fixed: Vec<(&str, Vec<T>)>,
+        witness: Vec<(&str, Vec<T>)>,
+    ) -> Option<Proof> {
+        halo2::mock_prove(pil, fixed, witness);
+        None
+    }
+}
diff --git a/compiler/Cargo.toml b/compiler/Cargo.toml
index 37f0f548c..2065a0248 100644
--- a/compiler/Cargo.toml
+++ b/compiler/Cargo.toml
@@ -4,6 +4,7 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+backend = { path = "../backend" }
 itertools = "^0.10"
 log = "0.4.17"
 mktemp = "0.5.0"
@@ -14,4 +15,4 @@ executor = { path = "../executor" }
 pilgen = { path = "../pilgen" }
 pil_analyzer = { path = "../pil_analyzer" }
 halo2 = { path = "../halo2" }
-strum = { version = "0.24.1", features = ["derive"] }
\ No newline at end of file
+json = "^0.12"
\ No newline at end of file
diff --git a/compiler/src/backends.rs b/compiler/src/backends.rs
deleted file mode 100644
index 0c0a5dda9..000000000
--- a/compiler/src/backends.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-use strum::{Display, EnumString, EnumVariantNames};
-
-#[derive(Clone, EnumString, EnumVariantNames, Display)]
-pub enum Backend {
-    #[strum(serialize = "halo2")]
-    Halo2,
-}
diff --git a/compiler/src/lib.rs b/compiler/src/lib.rs
index 08076b9fe..1b8c9a016 100644
--- a/compiler/src/lib.rs
+++ b/compiler/src/lib.rs
@@ -3,15 +3,18 @@
 use std::ffi::OsStr;
 use std::fs;
 use std::io::BufWriter;
+use std::io::Write;
 use std::path::Path;
 use std::time::Instant;
 
-mod backends;
+use json::JsonValue;
+
+pub mod util;
 mod verify;
 
-pub use backends::Backend;
+pub use backend::{Backend, Proof};
 use number::write_polys_file;
-use pil_analyzer::json_exporter;
+use pil_analyzer::{json_exporter, Analyzed};
 pub use verify::{compile_asm_string_temp, verify, verify_asm_string};
 
 use executor::constant_evaluator;
@@ -32,7 +35,7 @@ pub fn compile_pil_or_asm<T: FieldElement>(
     prove_with: Option<Backend>,
 ) {
     if file_name.ends_with(".asm") {
-        compile_asm(file_name, inputs, output_dir, force_overwrite, prove_with)
+        compile_asm(file_name, inputs, output_dir, force_overwrite, prove_with);
     } else {
         compile_pil(
             Path::new(file_name),
@@ -40,7 +43,11 @@ pub fn compile_pil_or_asm<T: FieldElement>(
             Some(inputs_to_query_callback(inputs)),
             prove_with,
         );
-    };
+    }
+}
+
+pub fn analyze_pil<T: FieldElement>(pil_file: &Path) -> Analyzed<T> {
+    pil_analyzer::analyze(pil_file)
 }
 
 /// Compiles a .pil file to its json form and also tries to generate
@@ -159,43 +166,29 @@ where
     let (constants, degree) = constant_evaluator::generate(analyzed);
     log::info!("Took {}", start.elapsed().as_secs_f32());
     if analyzed.constant_count() == constants.len() {
-        write_polys_file(
-            &mut BufWriter::new(&mut fs::File::create(output_dir.join("constants.bin")).unwrap()),
-            degree,
-            &constants,
-        );
-        log::info!("Wrote constants.bin.");
+        write_constants_to_fs(&constants, output_dir, degree);
+        log::info!("Generated constants.");
+
         log::info!("Deducing witness columns...");
         let commits = executor::witgen::generate(analyzed, degree, &constants, query_callback);
-        write_polys_file(
-            &mut BufWriter::new(&mut fs::File::create(output_dir.join("commits.bin")).unwrap()),
-            degree,
-            &commits,
-        );
-        log::info!("Wrote commits.bin.");
+        write_commits_to_fs(&commits, output_dir, degree);
+        log::info!("Generated witness.");
+
+        // TODO the fs and params stuff needs to be refactored out of here
         if let Some(Backend::Halo2) = prove_with {
-            use std::io::Write;
-            let proof = halo2::prove_ast(analyzed, constants, commits);
-            let mut proof_file = fs::File::create(output_dir.join("proof.bin")).unwrap();
-            let mut proof_writer = BufWriter::new(&mut proof_file);
-            proof_writer.write_all(&proof).unwrap();
-            proof_writer.flush().unwrap();
-            log::info!("Wrote proof.bin.");
+            let degree = usize::BITS - degree.leading_zeros() + 1;
+            let params = halo2::kzg_params(degree as usize);
+            let proof = halo2::prove_ast(analyzed, constants, commits, params);
+            write_proof_to_fs(&proof, output_dir);
+            log::info!("Generated proof.");
         }
     } else {
         log::warn!("Not writing constants.bin because not all declared constants are defined (or there are none).");
         success = false;
     }
     let json_out = json_exporter::export(analyzed);
-    let json_file = {
-        let mut file = file_name.to_os_string();
-        file.push(".json");
-        file
-    };
-    json_out
-        .write(&mut fs::File::create(output_dir.join(&json_file)).unwrap())
-        .unwrap();
-    log::info!("Wrote {}.", json_file.to_string_lossy());
+    write_compiled_json_to_fs(&json_out, file_name, output_dir);
+    log::info!("Compiled PIL source code.");
 
     success
 }
@@ -222,3 +215,49 @@ pub fn inputs_to_query_callback<T: FieldElement>(inputs: Vec<T>) -> impl Fn(&str
         }
     }
 }
+
+fn write_constants_to_fs<T: FieldElement>(
+    commits: &Vec<(&str, Vec<T>)>,
+    output_dir: &Path,
+    degree: u64,
+) {
+    write_polys_file(
+        &mut BufWriter::new(&mut fs::File::create(output_dir.join("constants.bin")).unwrap()),
+        degree,
+        commits,
+    );
+    log::info!("Wrote constants.bin.");
+}
+
+fn write_commits_to_fs<T: FieldElement>(
+    commits: &Vec<(&str, Vec<T>)>,
+    output_dir: &Path,
+    degree: u64,
+) {
+    write_polys_file(
+        &mut BufWriter::new(&mut fs::File::create(output_dir.join("commits.bin")).unwrap()),
+        degree,
+        commits,
+    );
+    log::info!("Wrote commits.bin.");
+}
+
+fn write_proof_to_fs(proof: &Proof, output_dir: &Path) {
+    let mut proof_file = fs::File::create(output_dir.join("proof.bin")).unwrap();
+    let mut proof_writer = BufWriter::new(&mut proof_file);
+    proof_writer.write_all(proof).unwrap();
+    proof_writer.flush().unwrap();
+    log::info!("Wrote proof.bin.");
+}
+
+fn write_compiled_json_to_fs(json_out: &JsonValue, file_name: &OsStr, output_dir: &Path) {
+    let json_file = {
+        let mut file = file_name.to_os_string();
+        file.push(".json");
+        file
+    };
+    json_out
+        .write(&mut fs::File::create(output_dir.join(&json_file)).unwrap())
+        .unwrap();
+    log::info!("Wrote {}.", json_file.to_string_lossy());
+}
diff --git a/compiler/src/util.rs b/compiler/src/util.rs
new file mode 100644
index 000000000..4747e854e
--- /dev/null
+++ b/compiler/src/util.rs
@@ -0,0 +1,35 @@
+use number::{read_polys_file, DegreeType, FieldElement};
+use pil_analyzer::Analyzed;
+use std::{fs::File, path::Path};
+
+pub fn read_fixed<'a, T: FieldElement>(
+    pil: &'a Analyzed<T>,
+    dir: &Path,
+) -> (Vec<(&'a str, Vec<T>)>, DegreeType) {
+    let fixed_columns: Vec<&str> = pil
+        .constant_polys_in_source_order()
+        .iter()
+        .map(|(poly, _)| poly.absolute_name.as_str())
+        .collect();
+
+    read_polys_file(
+        &mut File::open(dir.join("constants").with_extension("bin")).unwrap(),
+        &fixed_columns,
+    )
+}
+
+pub fn read_witness<'a, T: FieldElement>(
+    pil: &'a Analyzed<T>,
+    dir: &Path,
+) -> (Vec<(&'a str, Vec<T>)>, DegreeType) {
+    let witness_columns: Vec<&str> = pil
+        .committed_polys_in_source_order()
+        .iter()
+        .map(|(poly, _)| poly.absolute_name.as_str())
+        .collect();
+
+    read_polys_file(
+        &mut File::open(dir.join("commits").with_extension("bin")).unwrap(),
+        &witness_columns,
+    )
+}
diff --git a/halo2/src/lib.rs b/halo2/src/lib.rs
index 3e4fa0cd7..1c6cc7f2a 100644
--- a/halo2/src/lib.rs
+++ b/halo2/src/lib.rs
@@ -4,4 +4,4 @@ pub(crate) mod mock_prover;
 pub(crate) mod prover;
 
 pub use mock_prover::mock_prove;
-pub use prover::prove_ast;
+pub use prover::*;
diff --git a/halo2/src/mock_prover.rs b/halo2/src/mock_prover.rs
index eee4eb98c..eded1267c 100644
--- a/halo2/src/mock_prover.rs
+++ b/halo2/src/mock_prover.rs
@@ -1,6 +1,3 @@
-use std::{fs::File, path::Path};
-
-use number::read_polys_file;
 use pil_analyzer::Analyzed;
 use polyexen::plaf::PlafDisplayBaseTOML;
 
@@ -8,44 +5,15 @@ use super::circuit_builder::analyzed_to_circuit;
 use halo2_proofs::{dev::MockProver, halo2curves::bn256::Fr};
 use number::{BigInt, FieldElement};
 
-pub fn mock_prove<T: FieldElement>(file: &Path, dir: &Path) {
-    let analyzed: Analyzed<T> = pil_analyzer::analyze(file);
-
-    if polyexen::expr::get_field_p::<Fr>() != T::modulus().to_arbitrary_integer() {
-        panic!("powdr modulus doesn't match halo2 modulus. Make sure you are using Bn254");
-    }
-
-    let fixed_columns: Vec<&str> = analyzed
-        .constant_polys_in_source_order()
-        .iter()
-        .map(|(poly, _)| poly.absolute_name.as_str())
-        .collect();
-
-    let witness_columns: Vec<&str> = analyzed
-        .committed_polys_in_source_order()
-        .iter()
-        .map(|(poly, _)| poly.absolute_name.as_str())
-        .collect();
-
-    let (fixed, fixed_degree) = read_polys_file(
-        &mut File::open(dir.join("constants").with_extension("bin")).unwrap(),
-        &fixed_columns,
-    );
-    let (witness, witness_degree) = read_polys_file(
-        &mut File::open(dir.join("commits").with_extension("bin")).unwrap(),
-        &witness_columns,
-    );
-
-    assert_eq!(fixed_degree, witness_degree);
-
-    mock_prove_ast(&analyzed, fixed, witness)
-}
-
-fn mock_prove_ast<T: FieldElement>(
+pub fn mock_prove<T: FieldElement>(
     pil: &Analyzed<T>,
     fixed: Vec<(&str, Vec<T>)>,
     witness: Vec<(&str, Vec<T>)>,
 ) {
+    if polyexen::expr::get_field_p::<Fr>() != T::modulus().to_arbitrary_integer() {
+        panic!("powdr modulus doesn't match halo2 modulus. Make sure you are using Bn254");
+    }
+
     let circuit = analyzed_to_circuit(pil, fixed, witness);
 
     // double the row count in order to make space for the cells introduced by the backend
@@ -110,7 +78,7 @@ mod test {
         let (fixed, degree) = executor::constant_evaluator::generate(&analyzed);
         let witness = executor::witgen::generate(&analyzed, degree, &fixed, Some(query_callback));
 
-        mock_prove_ast(&analyzed, fixed, witness);
+        mock_prove(&analyzed, fixed, witness);
     }
 
     #[test]
@@ -122,7 +90,7 @@ mod test {
         let query_callback = |_: &str| -> Option<Bn254Field> { None };
 
         let witness = executor::witgen::generate(&analyzed, degree, &fixed, Some(query_callback));
-        mock_prove_ast(&analyzed, fixed, witness);
+        mock_prove(&analyzed, fixed, witness);
     }
 
     #[test]
diff --git a/halo2/src/prover.rs b/halo2/src/prover.rs
index 86a469ffb..cbb92e906 100644
--- a/halo2/src/prover.rs
+++ b/halo2/src/prover.rs
@@ -2,7 +2,7 @@ use halo2_proofs::{
     halo2curves::bn256::{Bn256, Fr, G1Affine},
     plonk::{create_proof, keygen_pk, keygen_vk, verify_proof},
     poly::{
-        commitment::ParamsProver,
+        commitment::{Params, ParamsProver},
         kzg::{
             commitment::{KZGCommitmentScheme, ParamsKZG},
             multiopen::{ProverGWC, VerifierGWC},
@@ -17,13 +17,34 @@ use polyexen::plaf::PlafDisplayBaseTOML;
 use rand::{rngs::StdRng, SeedableRng};
 
 use crate::circuit_builder::analyzed_to_circuit;
+use std::io;
 
 /// Create a halo2 proof for a given PIL, fixed column values and witness column values
 /// We use KZG ([GWC variant](https://eprint.iacr.org/2019/953)) and Keccak256
+
+pub fn prove_ast_read_params<T: FieldElement, R: io::Read>(
+    pil: &Analyzed<T>,
+    fixed: Vec<(&str, Vec<T>)>,
+    witness: Vec<(&str, Vec<T>)>,
+    mut params: R,
+) -> Vec<u8> {
+    if polyexen::expr::get_field_p::<Fr>() != T::modulus().to_arbitrary_integer() {
+        panic!("powdr modulus doesn't match halo2 modulus. Make sure you are using Bn254");
+    }
+
+    prove_ast(
+        pil,
+        fixed,
+        witness,
+        ParamsKZG::<Bn256>::read(&mut params).unwrap(),
+    )
+}
+
 pub fn prove_ast<T: FieldElement>(
     pil: &Analyzed<T>,
     fixed: Vec<(&str, Vec<T>)>,
     witness: Vec<(&str, Vec<T>)>,
+    params: ParamsKZG<Bn256>,
 ) -> Vec<u8> {
     if polyexen::expr::get_field_p::<Fr>() != T::modulus().to_arbitrary_integer() {
         panic!("powdr modulus doesn't match halo2 modulus. Make sure you are using Bn254");
@@ -31,15 +52,10 @@ pub fn prove_ast<T: FieldElement>(
 
     let circuit = analyzed_to_circuit(pil, fixed, witness);
 
-    let circuit_row_count_log = usize::BITS - circuit.plaf.info.num_rows.leading_zeros();
-
-    let expanded_row_count_log = circuit_row_count_log + 1;
-
     log::debug!("{}", PlafDisplayBaseTOML(&circuit.plaf));
 
     let inputs = vec![];
 
-    let params = ParamsKZG::<Bn256>::new(expanded_row_count_log);
     let vk = keygen_vk(&params, &circuit).unwrap();
     let pk = keygen_pk(&params, vk.clone(), &circuit).unwrap();
     let mut transcript: Keccak256Write<
@@ -73,3 +89,19 @@ pub fn prove_ast<T: FieldElement>(
 
     proof
 }
+
+pub fn kzg_params(size: usize) -> ParamsKZG<Bn256> {
+    ParamsKZG::<Bn256>::new(size as u32)
+}
+
+pub fn generate_params<T: FieldElement>(size: usize) -> Vec<u8> {
+    if polyexen::expr::get_field_p::<Fr>() != T::modulus().to_arbitrary_integer() {
+        panic!("powdr modulus doesn't match halo2 modulus. Make sure you are using Bn254");
+    }
+
+    let params = kzg_params(size);
+    let mut data = vec![];
+    ParamsKZG::<Bn256>::write(&params, &mut data).unwrap();
+
+    data
+}
diff --git a/powdr_cli/Cargo.toml b/powdr_cli/Cargo.toml
index 9ae50be4e..dc169fd67 100644
--- a/powdr_cli/Cargo.toml
+++ b/powdr_cli/Cargo.toml
@@ -12,6 +12,7 @@ parser = { path = "../parser" }
 riscv = { path = "../riscv" }
 number = { path = "../number" }
 halo2 = { path = "../halo2" }
+backend = { path = "../backend" }
 strum = { version = "0.24.1", features = ["derive"] }
 
 [[bin]]
diff --git a/powdr_cli/src/main.rs b/powdr_cli/src/main.rs
index e521a2139..e3f256f26 100644
--- a/powdr_cli/src/main.rs
+++ b/powdr_cli/src/main.rs
@@ -2,6 +2,7 @@
 
 mod util;
 
+use backend::{self, ProverWithParams, ProverWithoutParams, *};
 use clap::{Parser, Subcommand};
 use compiler::{compile_pil_or_asm, Backend};
 use env_logger::{Builder, Target};
@@ -11,6 +12,8 @@ use riscv::{compile_riscv_asm, compile_rust};
 use std::{borrow::Cow, fs, io::Write, path::Path};
 use strum::{Display, EnumString, EnumVariantNames};
 
+use std::io::{BufWriter, Cursor};
+
 #[derive(Clone, EnumString, EnumVariantNames, Display)]
 pub enum FieldArgument {
     #[strum(serialize = "gl")]
@@ -130,10 +133,7 @@ enum Commands {
         prove_with: Option<Backend>,
     },
 
-    /// Apply the Halo2 workflow on an input file and prover values over the Bn254 field
-    /// That means parsing, analysis, witness generation,
-    /// and Halo2 mock proving.
-    Halo2MockProver {
+    Prove {
         /// Input PIL file
         file: String,
 
@@ -141,6 +141,42 @@ enum Commands {
         #[arg(short, long)]
         #[arg(default_value_t = String::from("."))]
         dir: String,
+
+        /// The field to use
+        #[arg(long)]
+        #[arg(default_value_t = FieldArgument::Gl)]
+        #[arg(value_parser = clap_enum_variants!(FieldArgument))]
+        field: FieldArgument,
+
+        /// Generate a proof with a given backend.
+        #[arg(short, long)]
+        #[arg(value_parser = clap_enum_variants!(Backend))]
+        backend: Backend,
+
+        /// File containing previously generated setup parameters.
+        #[arg(short, long)]
+        params: Option<String>,
+    },
+
+    Setup {
+        /// Size of the parameters
+        size: usize,
+
+        /// Directory to output the generated parameters
+        #[arg(short, long)]
+        #[arg(default_value_t = String::from("."))]
+        dir: String,
+
+        /// The field to use
+        #[arg(long)]
+        #[arg(default_value_t = FieldArgument::Gl)]
+        #[arg(value_parser = clap_enum_variants!(FieldArgument))]
+        field: FieldArgument,
+
+        /// Generate a proof with a given backend.
+        #[arg(short, long)]
+        #[arg(value_parser = clap_enum_variants!(Backend))]
+        backend: Backend,
     },
 
     /// Parses and prints the PIL file on stdout.
@@ -235,8 +271,79 @@ fn main() {
             force,
             prove_with
         ),
-        Commands::Halo2MockProver { file, dir } => {
-            halo2::mock_prove::<Bn254Field>(Path::new(&file), Path::new(&dir));
+        Commands::Prove {
+            file,
+            dir,
+            field,
+            backend,
+            params,
+        } => {
+            let pil = Path::new(&file);
+            let dir = Path::new(&dir);
+
+            let proof = call_with_field!(read_and_prove, field, pil, dir, backend, params);
+
+            if let Some(proof) = proof {
+                let mut proof_file = fs::File::create(dir.join("proof.bin")).unwrap();
+                let mut proof_writer = BufWriter::new(&mut proof_file);
+                proof_writer.write_all(&proof).unwrap();
+                proof_writer.flush().unwrap();
+                log::info!("Wrote proof.bin.");
+            }
+        }
+        Commands::Setup {
+            size,
+            dir,
+            field,
+            backend,
+        } => {
+            setup(size, dir, field, backend);
         }
     }
 }
+
+fn setup(size: usize, dir: String, field: FieldArgument, backend: Backend) {
+    let dir = Path::new(&dir);
+    let params = match (field, &backend) {
+        (FieldArgument::Bn254, Backend::Halo2) => Halo2Backend::generate_params::<Bn254Field>(size),
+        (_, Backend::Halo2) => panic!("Backend halo2 requires field Bn254"),
+        _ => panic!("Backend {} does not accept params.", backend),
+    };
+    write_params_to_fs(&params, dir);
+}
+
+fn write_params_to_fs(params: &[u8], output_dir: &Path) {
+    let mut params_file = fs::File::create(output_dir.join("params.bin")).unwrap();
+    let mut params_writer = BufWriter::new(&mut params_file);
+    params_writer.write_all(params).unwrap();
+    params_writer.flush().unwrap();
+    log::info!("Wrote params.bin.");
+}
+
+fn read_and_prove<T: FieldElement>(
+    file: &Path,
+    dir: &Path,
+    backend: Backend,
+    params: Option<String>,
+) -> Option<Vec<u8>> {
+    let pil = compiler::analyze_pil::<T>(file);
+    let fixed = compiler::util::read_fixed(&pil, dir);
+    let witness = compiler::util::read_witness(&pil, dir);
+
+    assert_eq!(fixed.1, witness.1);
+
+    match (backend, params) {
+        (Backend::Halo2, Some(params)) => {
+            let params = fs::File::open(dir.join(params)).unwrap();
+            Halo2Backend::prove(&pil, fixed.0, witness.0, params)
+        }
+        (Backend::Halo2, None) => {
+            let degree = usize::BITS - fixed.1.leading_zeros() + 1;
+            let params = Halo2Backend::generate_params::<Bn254Field>(degree as usize);
+            write_params_to_fs(&params, dir);
+            Halo2Backend::prove(&pil, fixed.0, witness.0, Cursor::new(params))
+        }
+        (Backend::Halo2Mock, Some(_)) => panic!("Backend Halo2Mock does not accept params"),
+        (Backend::Halo2Mock, None) => Halo2MockBackend::prove(&pil, fixed.0, witness.0),
+    }
+}