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https://github.com/poanetwork/threshold_crypto

A pairing-based threshold cryptosystem for collaborative decryption and signatures used in HoneybadgerBFT implementation
https://github.com/poanetwork/threshold_crypto

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A pairing-based threshold cryptosystem for collaborative decryption and signatures used in HoneybadgerBFT implementation

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# threshold_crypto



[![crates.io](https://img.shields.io/crates/v/threshold_crypto.svg)](https://crates.io/crates/threshold_crypto)

[![Documentation](https://docs.rs/threshold_crypto/badge.svg)](https://docs.rs/threshold_crypto)

[![Build Status](https://travis-ci.org/poanetwork/threshold_crypto.svg?branch=master)](https://travis-ci.org/poanetwork/threshold_crypto)



A pairing-based threshold cryptosystem for collaborative decryption and signatures.



The `threshold_crypto` crate provides cryptographic keys with methods for signing and encrypting messages, as well as key sets for _threshold_ signatures and threshold encryption.



The threshold signature scheme is described in [Threshold Signatures, Multisignatures and Blind Signatures Based on the Gap-Diffie-Hellman-Group Signature Scheme](https://www.iacr.org/archive/pkc2003/25670031/25670031.pdf) by Alexandra Boldyreva. This paper extends [Boneh-Lynn-Shacham](https://www.iacr.org/archive/asiacrypt2001/22480516.pdf) signatures to the threshold setting. Message encryption uses the [scheme by Baek and Zhang](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.119.1717&rep=rep1&type=pdf).

Our implementation is based on the [`pairing`](https://crates.io/crates/pairing) elliptic curve library.



In a network environment, messages are signed and encrypted, and key and signature shares are distributed to network participants. A message can be decrypted and authenticated only with cooperation from at least `threshold +

1` nodes.



## Security Audit



An [official security audit](https://github.com/poanetwork/wiki/wiki/Threshold-Crypto-Audit) has been completed on `threshold_crypto` by [Jean-Philippe Aumasson](https://aumasson.jp/). No exploitable security issues were found, and potential improvements have been addressed. Outdated dependencies mentioned in the audit were updated in commit [54026f5](https://github.com/poanetwork/threshold_crypto/commit/54026f5fe7e0b5a52e446ac01a50469da1f15a71).



## Usage



`Cargo.toml`:



```toml

[dependencies]

threshold_crypto = { version = "0.4", git = "https://github.com/poanetwork/threshold_crypto" }

```



`main.rs`:



```rust

extern crate rand;

extern crate threshold_crypto;



use threshold_crypto::SecretKey;



/// Very basic secret key usage.

fn main() {

    let sk0 = SecretKey::random();

    let sk1 = SecretKey::random();



    let pk0 = sk0.public_key();



    let msg0 = b"Real news";

    let msg1 = b"Fake news";



    assert!(pk0.verify(&sk0.sign(msg0), msg0));

    assert!(!pk0.verify(&sk1.sign(msg0), msg0)); // Wrong key.

    assert!(!pk0.verify(&sk0.sign(msg1), msg0)); // Wrong message.

}

```



### Testing



Run tests with:



```

$ cargo test

```



### Examples



Run examples from the [`examples`](examples) directory using:



```

$ cargo run --example 

```



Also see the

[distributed_key_generation](https://github.com/poanetwork/threshold_crypto/blob/d81953b55d181311c2a4eed2b6c34059fcf3fdae/src/poly.rs#L967)

test.



## Application Details



The basic usage outline is:

* choose a threshold value `t`

* create a key set

* distribute `N` secret key shares among the participants

* publish the public master key



A third party can now encrypt a message to the public master key

and any set of `t + 1` participants *(but no fewer!)* can collaborate to

decrypt it. Also, any set of `t + 1` participants can collaborate to sign a message,

producing a signature that is verifiable with the public master key.



In this system, a signature is unique and independent of

the set of participants that produced it. If `S1` and `S2` are

signatures for the same message, produced by two different sets of `t + 1`

secret key share holders, both signatures will be valid AND

equal. This is useful in some applications, for example a message signature can serve as a pseudorandom number unknown to anyone until `t + 1` participants agree to reveal it.



In its simplest form, threshold_crypto requires a trusted dealer to

produce and distribute the secret key shares. However, keys can be produced so that only the corresponding participant knows their secret in the end.  This crate

includes the basic tools to implement such a *Distributed Key Generation*

scheme.



A major application for this library is within a distributed network that

must tolerate up to `t` adversarial (malicious or faulty) nodes. Because `t +

1` nodes are required to sign or reveal information, messages can be trusted

by third-parties as representing the consensus of the network.



### Documentation



* [crate documentation](https://docs.rs/threshold_crypto/)

* [crates.io package](https://crates.io/crates/threshold_crypto) 



## Performance



Benchmarking functionality is kept in the [`benches` directory](benches). You

can run the benchmarks with the following command:



```

$ RUSTFLAGS="-C target_cpu=native" cargo bench

```



We use the [`criterion`](https://crates.io/crates/criterion) benchmarking library.



### Mock cryptography



To speed up automatic tests of crates depending on `threshold_crypto`, the `use-insecure-test-only-mock-crypto` feature is available. **Activating this feature will effectively disable encryption and should only be used during tests!** Essentially, the underlying elliptic curves will be replaced by small finite fields, yielding a 10-200X speed-up in execution. The resulting ciphers can be trivially broken in a number of ways and should never be used in production.



## License



Licensed under either of:



* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)

* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)



at your option.



## Contributing



See the [CONTRIBUTING](CONTRIBUTING.md) document for contribution, testing and

pull request protocol.



Unless you explicitly state otherwise, any contribution intentionally

submitted for inclusion in the work by you, as defined in the Apache-2.0

license, shall be dual licensed as above, without any additional terms or

conditions.