# RustCrypto: secp256k1 (K-256) elliptic curve
[![crate][crate-image]][crate-link]
[![Docs][docs-image]][docs-link]
![Apache2/MIT licensed][license-image]
![Rust Version][rustc-image]
[![Build Status][build-image]][build-link]
[secp256k1] (a.k.a. K-256) elliptic curve library written in pure Rust with
support for [ECDSA] signing/verification (including Ethereum-style signatures
with public-key recovery), Elliptic Curve Diffie-Hellman (ECDH), and general
purpose arithmetic which can be used to implement arbitrary protocols.
Uses traits and base types from the [`elliptic-curve`] crate.
Optionally includes an [`arithmetic`] feature providing scalar and
point types (projective/affine) with support for constant-time scalar
multiplication. Additionally, implements traits from the [`group`] crate
which can be used to generically construct group-based protocols.
[Documentation][docs-link]
## ⚠️ Security Warning
The elliptic curve arithmetic contained in this crate has never been
independently audited!
This crate has been designed with the goal of ensuring that secret-dependent
operations are performed in constant time (using the `subtle` crate and
constant-time formulas). However, it has not been thoroughly assessed to ensure
that generated assembly is constant time on common CPU architectures.
USE AT YOUR OWN RISK!
## Supported Algorithms
- [Elliptic Curve Diffie-Hellman (ECDH)][ECDH]: gated under the `ecdh` feature.
- [Elliptic Curve Digital Signature Algorithm (ECDSA)][ECDSA]: gated under the
`ecdsa` feature. Supports low-S normalized ECDSA signing and verification
as used in consensus-critical applications, and additionally supports
public key recovery from ECDSA signatures (as used by e.g. Ethereum).
## About secp256k1 (K-256)
[secp256k1] is a Koblitz curve commonly used in cryptocurrency applications.
The "K-256" name follows NIST notation where P = prime fields,
B = binary fields, and K = Koblitz curves (defined over F₂).
The curve is specified as `secp256k1` by Certicom's SECG in
"SEC 2: Recommended Elliptic Curve Domain Parameters":
<https://www.secg.org/sec2-v2.pdf>
It's primarily notable for usage in Bitcoin and other cryptocurrencies,
particularly in conjunction with the
[Elliptic Curve Digital Signature Algorithm (ECDSA)][ECDSA].
## Minimum Supported Rust Version
Rust **1.44** or higher.
Minimum supported Rust version can be changed in the future, but it will be
done with a minor version bump.
## SemVer Policy
- All on-by-default features of this library are covered by SemVer
- MSRV is considered exempt from SemVer as noted above
## License
All crates licensed under either of
* [Apache License, Version 2.0](http://www.apache.org/licenses/LICENSE-2.0)
* [MIT license](http://opensource.org/licenses/MIT)
at your option.
### Contribution
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.
[//]: # (badges)
[crate-image]: https://img.shields.io/crates/v/k256.svg
[crate-link]: https://crates.io/crates/k256
[docs-image]: https://docs.rs/k256/badge.svg
[docs-link]: https://docs.rs/k256/
[license-image]: https://img.shields.io/badge/license-Apache2.0/MIT-blue.svg
[rustc-image]: https://img.shields.io/badge/rustc-1.44+-blue.svg
[build-image]: https://github.com/RustCrypto/elliptic-curves/workflows/k256/badge.svg?branch=master&event=push
[build-link]: https://github.com/RustCrypto/elliptic-curves/actions?query=workflow%3Ak256
[//]: # (general links)
[secp256k1]: https://en.bitcoin.it/wiki/Secp256k1
[`elliptic-curve`]: https://github.com/RustCrypto/traits/tree/master/elliptic-curve
[`arithmetic`]: https://docs.rs/k256/latest/k256/arithmetic/index.html
[`group`]: https://github.com/zkcrypto/group
[ECDH]: https://en.wikipedia.org/wiki/Elliptic-curve_Diffie-Hellman
[ECDSA]: https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm