circom-ecdsa

Implementation of ECDSA operations in circom.

Project overview

This repository provides proof-of-concept implementations of ECDSA operations in circom. These implementations are for demonstration purposes only. These circuits are not audited, and this is not intended to be used as a library for production-grade applications.

Circuits can be found in circuits. scripts contains various utility scripts (most importantly, scripts for building a few example zkSNARKs using the ECDSA circuit primitives). test contains some unit tests for the circuits, mostly for witness generation.

Install dependencies

Run yarn at the top level to install npm dependencies (snarkjs and circomlib).
You'll also need circom version >= 2.0.2 on your system. Installation instructions here.
If you want to build the pubkeygen, eth_addr, and groupsig circuits, you'll need to download a Powers of Tau file with 2^22 constraints and copy it into the circuits subdirectory of the project, with the name pot22_final.ptau. We do not provide such a file in this repo due to its large size. You can download and copy Powers of Tau files from the Hermez trusted setup from this repository.
If you want to build the verify circuits, you'll also need a Powers of Tau file that can support at least 2^24 constraints (place it in the same directory as above with the same naming convention).

Building keys and witness generation files

We provide examples of four circuits using the ECDSA primitives implemented here:

pubkeygen: Prove knowledge of a private key corresponding to a ECDSA public key.
eth_addr: Prove knowledge of a private key corresponding to an Ethereum address.
groupsig: Prove knowledge of a private key corresponding to one of three Ethereum addresses, and attest to a specific message.
verify: Prove that a ECDSA verification ran properly on a provided signature and message. Note that this circuit does not verify that the public key itself is valid. This must be done separately by the user.

Run yarn build:pubkeygen, yarn build:eth_addr, yarn build:groupsig, yarn build:verify at the top level to compile each respective circuit and keys.

Each of these will create a subdirectory inside a build directory at the top level (which will be created if it doesn't already exist). Inside this directory, the build process will create r1cs and wasm files for witness generation, as well as a zkey file (proving and verifying keys). Note that this process will take several minutes (see full benchmarks below). Building verify requires 56G of RAM.

This process will also generate and verify a proof for a dummy input in the respective scripts/[circuit_name] subdirectory, as a smoke test.

Benchmarks

All benchmarks were run on a 20-core 3.3GHz, 64G RAM machine. Building verify requires 56G of RAM.

	pubkeygen	eth_addr	groupsig	verify
Constraints	416883	5688823	571721	9480361
Circuit compilation	90s	115s	116s	324s
Witness generation	8s	7s	8s	150s
Trusted setup phase 2 key generation	150s	167s	164s	5569s
Trusted setup phase 2 contribution	28s	47s	47s	767s
Proving key size	254M	347M	349M	5.8G
Proving key verification	157s	185s	184s	6211s
Proving time	12s	17s	16s	239s
Proof verification time	<1s	<1s	<1s	<1s

Testing

Run yarn test at the top level to run tests. Note that these tests only test correctness of witness generation. They do not check that circuits are properly constrained, i.e. that only valid witnesses satisfy the constraints. This is a much harder problem that we're currently working on!

Circuit unit tests are written in typescript, in the test directory using chai, mocha, and circom_tester. Running all tests takes about 1 hour on our 3.3GHz, 64G RAM test machine. To run a subset of the tests, use yarn test --grep [test_str] to run all tests whose description matches [test_str].

Groupsig CLI Demo

You can run a CLI demo of a zkSNARK-enabled group signature generator once you've built the groupsig keys. Simply run yarn groupsig-demo at the top level and follow the instructions in your terminal.

Acknowledgments

This project was built during 0xPARC's Applied ZK Learning Group #1.

We use a circom implementation of keccak from Vocdoni. We also use some circom utilities for converting an ECDSA public key to an Ethereum address implemented by lsankar4033, jefflau, and veronicaz41 for another ZK Learning Group project in the same cohort. We use an optimization for big integer multiplication from xJsnark.

kevjue/circom-ecdsa