1<h1 align="center">ZEXE (Zero knowledge EXEcution)</h1>
  2
  3<p align="center">
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 10
 11
 12___ZEXE___ (pronounced */zeksē/*) is a Rust library for decentralized private computation.
 13
 14
 15This library was initially developed as part of the paper *"[ZEXE: Enabling Decentralized Private Computation][zexe]"*, and it is released under the MIT License and the Apache v2 License (see [License](#license)).
 16
 17**WARNING:** This is an academic proof-of-concept prototype, and in particular has not received careful code review. This implementation is NOT ready for production use.
 18
 19## Overview
 20
 21This library implements a ledger-based system that enables users to execute offline computations and subsequently produce publicly-verifiable transactions that attest to the correctness of these offline executions. The transactions contain *zero-knowledge succinct arguments* (zkSNARKs) attesting to the correctness of the offline computations, and provide strong notions of privacy and succinctness.
 22
 23- **Privacy** - transactions reveal no information about the offline computation.
 24- **Succinctness** - transactions can be validated in time that is independent of the offline computation.
 25- **Application isolation** - malicious applications cannot affect the execution of honest applications.
 26- **Application interaction** -  applications can safely communicate with each other.
 27
 28Informally, the library provides the ability to create transactions that run arbitrary (Turing-complete) scripts on hidden data stored on the ledger. In more detail, the library implements a cryptographic primitive known as *decentralized private computation* (DPC) schemes, which are described in detail in the [ZEXE paper][zexe].
 29
 30## Directory structure
 31
 32This repository contains several Rust crates that implement the different building blocks of ZEXE. The high-level structure of the repository is as follows.
 33
 34* [`algebra`](algebra): Rust crate that provides finite fields and elliptic curves
 35* [`crypto-primitives`](crypto-primitives): Rust crate that implements some useful cryptographic primitives (and constraints for them)
 36* [`dpc`](dpc): Rust crate that implements DPC schemes (the main cryptographic primitive in this repository)
 37* [`ff-fft`](ff-fft): Rust crate that provides efficient finite field polynomial arithmetic based on finite field FFTs
 38* [`r1cs-core`](r1cs-core): Rust crate that defines core interfaces for a Rank-1 Constraint System (R1CS)
 39* [`r1cs-std`](r1cs-std): Rust crate that provides various gadgets used to construct R1CS
 40* [`gm17`](gm17): Rust crate that implements the zkSNARK of [Groth and Maller][GM17]
 41* [`groth16`](groth16): Rust crate that implements the zkSNARK of [Groth][Groth16]
 42
 43
 44In addition, there is a  [`bench-utils`](bench-utils) crate which contains infrastructure for benchmarking. This crate includes macros for timing code segments and is used for profiling the building blocks of ZEXE.
 45
 46[GM17]: https://ia.cr/2017/540
 47[Groth16]: https://ia.cr/2016/260
 48
 49
 50## Build guide
 51
 52The library compiles on the `stable` toolchain of the Rust compiler. To install the latest version of Rust, first install `rustup` by following the instructions [here](https://rustup.rs/), or via your platform's package manager. Once `rustup` is installed, install the Rust toolchain by invoking:
 53```bash
 54rustup install stable
 55```
 56
 57After that, use `cargo`, the standard Rust build tool, to build the library:
 58```bash
 59git clone https://github.com/scipr-lab/zexe.git
 60cd zexe/dpc
 61cargo build --release
 62```
 63
 64This library comes with unit tests for each of the provided crates. Run the tests with:
 65```bash
 66cargo test
 67```
 68
 69This library comes with benchmarks for the following crates:
 70
 71- [`algebra`](algebra)
 72- [`dpc`](dpc)
 73
 74These benchmarks require the nightly Rust toolchain; to install this, run `rustup install nightly`. Then, to run benchmarks, run the following command:
 75```bash
 76cargo +nightly bench
 77```
 78
 79Compiling with `adcxq`, `adoxq` and `mulxq` instructions can lead to a 30-70% speedup. These are available on most `x86_64` platforms (Broadwell onwards for Intel and Ryzen onwards for AMD). Run the following command:
 80```bash
 81RUSTFLAGS="-C target-feature=+bmi2,+adx" cargo +nightly test/build/bench --features asm
 82```
 83Tip: If optimising for performance, your mileage may vary with passing `--emit=asm` to `RUSTFLAGS`.
 84
 85To bench `algebra-benches` with greater accuracy, especially for functions with execution times on the order of nanoseconds, use the `n_fold` feature to run selected functions 1000x per iteration. To run with multiple features, make sure to double quote the features.
 86```bash
 87cargo +nightly bench --features "n_fold bls12_381"
 88```
 89
 90
 91## License
 92
 93ZEXE is licensed under either of the following licenses, at your discretion.
 94
 95 * Apache License Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
 96 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
 97
 98Unless you explicitly state otherwise, any contribution submitted for inclusion in ZEXE by you shall be dual licensed as above (as defined in the Apache v2 License), without any additional terms or conditions.
 99
100[zexe]: https://ia.cr/2018/962
101
102## Reference paper
103
104[_ZEXE: Enabling Decentralized Private Computation_][zexe]    
105[Sean Bowe](https://www.github.com/ebfull), Alessandro Chiesa, Matthew Green, Ian Miers, [Pratyush Mishra](https://www.github.com/pratyush), [Howard Wu](https://www.github.com/howardwu)    
106*IEEE S&P 2020* (*IACR ePrint Report 2018/962*)
107
108## Acknowledgements
109
110This work was supported by:
111a Google Faculty Award;
112the National Science Foundation;
113the UC Berkeley Center for Long-Term Cybersecurity;
114and donations from the Ethereum Foundation, the Interchain Foundation, and Qtum.
115
116Some parts of the finite field arithmetic, elliptic curve arithmetic, FFTs, and multi-threading infrastructure in the `algebra` crate have been adapted from code in the [`ff`](https://github.com/zkcrypto/ff), [`pairing`](https://github.com/zkcrypto/pairing), and [`bellman`](https://github.com/zkcrypto/bellman) crates, developed by [Sean Bowe](https://www.github.com/ebfull) and others from Zcash.