Zapper

Zapper is a privacy-focused smart contract system that hides the processed data and the identity of its users by leveraging encryption and non-interactive zero-knowledge proofs (specifically, zk-SNARKs). This repository contains an implementation of the Zapper system, which is described in the following research paper:

Samuel Steffen, Benjamin Bichsel, and Martin Vechev. 2022. Zapper: Smart Contracts with Data and Identity Privacy. In Proceedings of CCS ’22.

Warning / Security Disclaimer

Zapper is a research project and its implementation should not be considered secure (e.g., it may contain bugs and has not undergone any security review)! Do not use Zapper in a productive system or to process sensitive confidential data.

Installation and Usage

We recommend using Zapper via its Docker image.

To this end, install docker in rootless mode (as an alternative to rootless mode, you can use sudo to run docker). Further, you will need the following general-purpose dependencies:

sudo apt-get install build-essential rsync

Then, running the following command will enter a shell inside a docker container with zapper installed.

cd docker
make run  # use `sudo make run` if you cannot run docker in rootless mode

Unit tests

To check if your installation was successful, you can run Zapper's unit tests:

pytest --import-mode=importlib

Run

To create a new application, follow the existing examples. Then, you can compile it and run a specific scenario by following the existing evaluation script.

CCS 2022 Evaluation

The original artifact evaluated in the CCS 2022 paper can be found under the tag ccs2022. The evaluation consists of two parts: a main evaluation for fixed system parameters (folder ./frontend/eval) and microbenchmarks for varying system parameters (folder ./microbench).

Reproduce Plots from Reference Data

This repository contains the reference data (see ./frontend/eval/results/reference and ./microbench/*-results.log) resulting from running the experiments on our machine and used to create the plots in the CCS 2022 paper. To reproduce these plots, run the following commands:

cd frontend/eval
python ./analyze_results.py
cd ../..
cd microbench
python ./analyze.py
cd ..

These commands produce the following outputs:

• in stdout: LaTex-friendly text containing key numbers and tables
• a PDF plot ./frontend/eval/circuit-components-plot.pdf
• a PDF plot ./microbench/one-dim-params-plot.pdf

If you want to copy files from your docker container to your host system, you can use docker cp (from outside docker):

docker cp zapper:/zapper ./zapper-copied-from-docker-image  # copy all files to host

Reproduce Results

To reproduce the evaluation results, run the following commands:

cd ./frontend
bash ./run-eval.sh           # main results
cd -
cd ./microbench
python ./run_microbench.py   # results for varying system parameters
cd -

Note: The second command may take a long time to execute (several hours).

These commands produce the following outputs:

• a folder ./frontend/eval/results/<datetime>_<id> containing JSON-formatted data in the *_data.log and *_backend_data.log files
• a file ./microbench/grid-results.log containing data used for the least-squares fit of circuit size estimation coefficients
• a file ./microbench/line-results.log containing data used to generate the microbenchmarking plots

Development

To set up Zapper for development, we recommend using miniconda.

To this end, install miniconda.

Then, install Zapper using

./install-conda.sh

To enter the installed Zapper environment, run:

conda activate zapper

Citing this Work

You are encouraged to cite the following research paper if you use Zapper for academic research.

@inproceedings{steffen2022zapper,
    author = {Steffen, Samuel and Bichsel, Benjamin and Vechev, Martin},
    title = {Zapper: Smart Contracts with Data and Identity Privacy},
    year = {2022},
    publisher = {Association for Computing Machinery},
    booktitle = {Proceedings of the 2022 ACM SIGSAC Conference on Computer and Communications Security},
    location = {Los Angeles, U.S.A.},
    series = {CCS ’22}
}