Poseidon

Poseidon is a cryptographic hash function optimized for efficiency in ZK. Circom comes with an implementation of Poseidon that can be used in your circuits.

The Poseidon sponge construction takes inputs from a prime field and produces a single output element from the same field. In this example, we process two field elements for the BN-254 curve and condense them into a single element, with both inputs originating from the same party.

To quickly get started, we provide a bash script that runs the Poseidon circuit using co-circom. After cloning the repository, navigate to the /co-circom/examples directory and execute the following command:

sh run_full_poseidon.sh

The script will execute all the necessary steps to generate a proof for the Poseidon circuit. We can inspect the script to understand the steps involved in generating a proof for the Poseidon circuit.

# split input into shares
cargo run --release --bin co-circom -- split-input --circuit test_vectors/poseidon/circuit.circom --input test_vectors/poseidon/input.json --protocol REP3 --curve BN254 --out-dir test_vectors/poseidon --config test_vectors/poseidon/config.toml
# run witness extension in MPC
cargo run --release --bin co-circom -- generate-witness --input test_vectors/poseidon/input.json.0.shared --circuit test_vectors/poseidon/circuit.circom --protocol REP3 --curve BN254 --config configs/party1.toml --out test_vectors/poseidon/witness.wtns.0.shared &
cargo run --release --bin co-circom -- generate-witness --input test_vectors/poseidon/input.json.1.shared --circuit test_vectors/poseidon/circuit.circom --protocol REP3 --curve BN254 --config configs/party2.toml --out test_vectors/poseidon/witness.wtns.1.shared &
cargo run --release --bin co-circom -- generate-witness --input test_vectors/poseidon/input.json.2.shared --circuit test_vectors/poseidon/circuit.circom --protocol REP3 --curve BN254 --config configs/party3.toml --out test_vectors/poseidon/witness.wtns.2.shared
# run proving in MPC
cargo run --release --bin co-circom -- generate-proof groth16 --witness test_vectors/poseidon/witness.wtns.0.shared --zkey test_vectors/poseidon/poseidon.zkey --protocol REP3 --curve BN254 --config configs/party1.toml --out proof.0.json --public-input public_input.json &
cargo run --release --bin co-circom -- generate-proof groth16 --witness test_vectors/poseidon/witness.wtns.1.shared --zkey test_vectors/poseidon/poseidon.zkey --protocol REP3 --curve BN254 --config configs/party2.toml --out proof.1.json &
cargo run --release --bin co-circom -- generate-proof groth16 --witness test_vectors/poseidon/witness.wtns.2.shared --zkey test_vectors/poseidon/poseidon.zkey --protocol REP3 --curve BN254 --config configs/party3.toml --out proof.2.json
# verify proof
cargo run --release --bin co-circom -- verify groth16  --proof proof.0.json --vk test_vectors/poseidon/verification_key.json --public-input public_input.json --curve BN254