Step‑by‑Step Guide to Run the co‑snarks tools

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1. Prerequisites – Install Required Software

Tool / Library	Installation Command (Linux/macOS)	Notes
Rust toolchain (stable)	```bash\ncurl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs	sh\nsource $HOME/.cargo/env\n```
Git	bash\nsudo apt-get install -y git # Debian/Ubuntu\n# or\nbrew install git # macOS\n	Needed to clone the repo.
Node.js & npm (v20+)	```bash\ncurl -fsSL https://deb.nodesource.com/setup_20.x	sudo -E bash -\nsudo apt-get install -y nodejs # Debian/Ubuntu\n# or\nbrew install node # macOS\n```
circom (circuit compiler)	bash\nnpm install -g circom\n
snarkjs (proof verifier)	bash\nnpm install -g snarkjs\n
Python 3.9+ (optional helpers)	bash\nsudo apt-get install -y python3 python3-pip # Debian/Ubuntu\n
OpenSSL development headers	bash\nsudo apt-get install -y libssl-dev # Debian/Ubuntu\n	Needed for some Rust crates.
Build‑essential tools (gcc, make, etc.)	bash\nsudo apt-get install -y build-essential # Debian/Ubuntu\n	macOS users need Xcode Command Line Tools (xcode-select --install).

Verify installations:

rustc --version   # e.g., rustc 1.78.0
cargo --version
node -v
npm -v
circom --version
snarkjs --version

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2. Clone the Repository

git clone https://github.com/0xgetz/co-snarks.git
cd co-snarks

The repo layout (relevant parts):

co-snarks/
├─ coCircom/
│   ├─ co-circom/          # Rust binary for Circom‑based MPC
│   └─ circom-mpc-vm/      # VM implementation
├─ coNoir/
│   └─ co-noir/            # Rust binary for Noir‑based MPC
├─ mpc-core/
└─ mpc-net/

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3. Build the Binaries

3.1. Build co‑circom

cd coCircom/co-circom
cargo build --release

The compiled binary will be at target/release/co-circom. Add it to your PATH for convenience:

export PATH=$PWD/target/release:$PATH   # add to ~/.bashrc or ~/.zshrc for persistence

3.2. Build co‑noir

cd ../../coNoir/co-noir
cargo build --release

Again, add the binary to your PATH:

export PATH=$PWD/target/release:$PATH

Tip: If you plan to call these binaries from other languages (Python, Go, etc.), you can also build a shared library (cd … && cargo build --release --features python) – see the repo’s README for optional features.

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4. Prepare a Sample Circuit (Circom)

Create a simple multiplication circuit example.circom:

pragma circom 2.0.0;

template Multiplier() {
    signal input a;
    signal input b;
    signal output c;

    c <== a * b;
}

component main = Multiplier();

Compile it with circom:

circom example.circom --r1cs --wasm --sym

You will obtain:

• example.r1cs – the arithmetic circuit
• example.wasm – witness generator
• example.sym – symbol file (optional)

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5. Convert the Circuit to a co‑SNARK (Distributed Setup)

Run the co-circom setup command on the generated R1CS file:

co-circom setup example.r1cs

What happens:

1. The tool splits the witness generation into shares for each participant.
2. It creates key shares (proving and verification keys) that can be distributed.
3. Output files (e.g., example.co.r1cs, vk_*.json, pk_*.json) are placed in the same folder.

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6. Run a Multi‑Party Computation (MPC) Session

co-circom provides two binary modes:

• coordinator – optional central node that only forwards messages.
• participant – each party that holds a private input share.

You can run a simple 2‑party demo locally.

6.1. Start the Coordinator (optional)

co-circom coordinator --port 9000 &
COORD_PID=$!

The coordinator just relays encrypted messages between participants.

6.2. Launch Participant 1

co-circom participant \
    --host localhost \
    --port 9000 \
    --id 1 \
    --input a=5,b=7 &

6.3. Launch Participant 2

co-circom participant \
    --host localhost \
    --port 9000 \
    --id 2 \
    --input a=5,b=7 &

Both participants will:

1. Generate their share of the witness using the example.wasm file.
2. Run the MPC‑VM to compute the multiplication securely.
3. Produce a SNARK proof (e.g., Groth16 or PLONK, depending on the setup).
4. Write proof files (proof.json, public.json) to the working directory.

6.4. Verify the Proof

You can verify with either snarkjs or the built‑in verifier:

snarkjs verify verification_key.json proof.json public.json
# or
co-circom verify \
    --vk verification_key.json \
    --proof proof.json \
    --public public.json

A successful verification prints true.

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7. End‑to‑End Bash Script (2‑Party Demo)

Save the following as run_cosnark_demo.sh and make it executable (chmod +x run_cosnark_demo.sh).

#!/usr/bin/env bash
set -e

# 1. Compile the circuit
circom example.circom --r1cs --wasm --sym

# 2. Distributed setup
co-circom setup example.r1cs

# 3. Start coordinator (background)
co-circom coordinator --port 9000 &
COORD_PID=$!

# 4. Participant 1 (background)
co-circom participant --host localhost --port 9000 --id 1 --input a=3,b=4 &
P1_PID=$!

# 5. Participant 2 (background)
co-circom participant --host localhost --port 9000 --id 2 --input a=3,b=4 &
P2_PID=$!

# 6. Wait for both participants to finish
wait $P1_PID $P2_PID

# 7. Verify the generated proof
snarkjs verify verification_key.json proof.json public.json

# 8. Clean up coordinator process
kill $COORD_PID

Run it:

./run_cosnark_demo.sh

If everything works, you’ll see true at the verification step.

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8. Using co‑noir (Noir Circuits)

8.1. Write a Noir circuit (example.nr)

fn main(a: Field, b: Field) -> Field {
    a * b
}

8.2. Compile with Noir CLI

cargo install noir   # if you haven’t installed it yet
noir compile example.nr

This produces example.circuit (or similar) and a proving key.

8.3. Distributed setup with co-noir

co-noir setup example.circuit

The rest of the flow (coordinator → participants → verify) mirrors the co-circom steps, just swapping the binary name.

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9. Common Pitfalls & Troubleshooting

Symptom	Likely Cause	Fix
cargo: command not found	$HOME/.cargo/bin not in $PATH	Add export PATH=$HOME/.cargo/bin:$PATH to your shell rc file.
Build fails with openssl errors