[−][src]Crate zerocaf

What is Zerocaf?

Zerocaf is a pure Rust cryptographic library constructed to define operations for an elliptic curve embedded into the Ristretto scalar field, which allows the construction of prime order groups from an otherwise non prime order curve.

The ultimate purpose of defining operations is for set inclusion proofs - where it is shown, in zero-knowledge, that a private key exists in a set of many public keys.

Additionally, the zero-knowledge proofs use Bulletproofs as the argument for arithmetic circuits that are used to form arbitrary constraint systems.

What can it be used for?

The main goal of the library, as said before, is to be the base of operations over set inclusion proofs and other Zero-Knowledge protocols.

But since Zerocaf is build upon the Doppio Curve using the Ristretto protocol, it allows other devs to build cryptographic protocols over it without needing to take care about the co-factor of the curve.

This, brings to developers, a good mathematical backend library which can be used as a mid-level API for building all kinds of cryptographic protocols over it such as key agreement, signatures, anonymous credentials, rangeproofs...

Usage

To import the library as a dependency of your project, just add on your Cargo.tomls project file:

zerocaf = "0.1.1"

Then import the crate as:

extern crate zerocaf;

Backends.

Zerocaf has been built following the Curve25519-dalek library structure, which allows for multiple backend implementations. All of the works are built to enable modularity.

Currently, Zerocaf has implemented the u64 backend. By default, the u64 backend is the one which is used to perform all of the operations. Additionly, for future works, we would like to implement a u32 backend aswell.

To select a backend type, the following method can be used:

// For unoptimized builds:
cargo build --features "u64_backend"
 
// For optimized/release builds:
cargo build --release --features "u64_backend"

NOTE: If no backend is selected, the compilation will fail!

Security and features of Zerocaf

As is previously mentioned, zerocaf is designed to host the fastest possible curve operations whilst simultaneously avoiding all of the drawbacks associated with having a cofactor such that h > 1.

To achieve this we make use of Ristretto, which is a technique to construct prime order elliptic curve groups. The Ristretto protocol compresses the cofactor by adding a thin abstraction layer to allow small changes in code to ultimately omit the cofactor issues.

This is achieved by having defining the twisted edwards curve over the ristretto scalar field, which means to perform every operation on the curve in modulo L, where L is the order of the ristretto scalar field.

L = 2^252 + 27742317777372353535851937790883648493.

By expounding the operations in this manner, we can benefit from the speed of a non-prime order twisted edwards curve whilst not suffering the pitfalls of a cofactor greater than one.

Performance & Benchmarks

Benchmarks have been implemented using Criterion.rs. To run them just execute cargo bench on the repository root.

All of the operatons have been implemented using bit-shifting techniques to allow better performance and a significant reduction in execution time.

Examples

We are planning to add some examples about tha basics of the Zerocaf library usage.
They will be uploaded to the examples folder.

This is a very basic usage example of the Zerocaf lib:

extern crate zerocaf;
extern crate rand;
 
use zerocaf::field::FieldElement;
use zerocaf::scalar::Scalar;
use zerocaf::edwards::EdwardsPoint;
 
use rand::{Rng, thread_rng};
 
fn main() -> () {
 
    // Let G be an `EdwardsPoint` which is a point over the Twisted Eds Extended Coordinates. 
    let G: EdwardsPoint = EdwardsPoint {
        X: FieldElement([23, 0, 0, 0, 0]),
        Y: FieldElement([1664892896009688, 132583819244870, 812547420185263, 637811013879057, 13284180325998]),
        Z: FieldElement([1, 0, 0, 0, 0]),
        T: FieldElement([4351986304670635, 4020128726404030, 674192131526433, 1158854437106827, 6468984742885])
    };
 
    let scalar: Scalar = rand_scalar_generation();
    println!("{:?}", scalar);
 
    // Perform G*k, Point mul uses the `add_and_double` standard algorithm.
    let P = &G  * &scalar;
    println!("{:?}", P);
}
 
/// Generate a random `Scalar` defined over the sub-group field
/// modulo: `2^249 - 15145038707218910765482344729778085401`
pub fn rand_scalar_generation() -> Scalar {
    // Gen random 32-byte array. 
    let mut bytes = [0u8;32];
 
    // Fill the bytes varible with random bytes. We can use the 32 bytes co give
    // total randomness but then we will need to be aware because we can generate
    // values greater than `L = 2^252 + 27742317777372353535851937790883648493` and
    // the program will panic if we don't catch the error correctly on the 
    // `from_bytes()` Scalar method call.
    thread_rng().try_fill(&mut bytes[..31]).expect("Error getting the random bytes");
 
    Scalar::from_bytes(&bytes)
}

We will also publish some videos talking about how is the library built and the maths that are happening behind the scenes.
Videos can also include programming examples using `Zerocaf` as a dependency.
You can check them on the [Dusk Network Youtube Channel](https://www.youtube.com/channel/UCAfY3VcuaxAelPp44B253Rw).

Modules

backend	This contains the different backend implementations: `u64` and further comming ones. .
constants	Contains the curve-constants needed by different algorithm implementations.
edwards	Edwards Point operations and their implementations are shown with the corresponding definitions. Encoding/decoding process implementations are shown, as is support for all kind of interactions which apply each of the processes.
field	A `FieldElement` represents an element of the finite field modulo `2^252 + 27742317777372353535851937790883648493`.
montgomery	Implementation that provides support for Montgomery Points over the Doppio curve.
scalar	A `Scalar` represents an element of the finite field modulo `2^249 - 15145038707218910765482344729778085401`.
traits	Module for Public Trait implementations.