Crate k256

RustCrypto: secp256k1 (K-256) elliptic curve

secp256k1 (a.k.a. K-256) elliptic curve library written in pure Rust with support for ECDSA signing/verification/public-key recovery, Taproot Schnorr signatures as defined in BIP340, Elliptic Curve Diffie-Hellman (ECDH), and general-purpose secp256k1 elliptic curve group operations which can be used to implement arbitrary group-based protocols.

Uses traits and base types from the elliptic-curve crate.

Optionally includes a secp256k1 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

Security Notes

This crate has been audited by NCC Group, which found a high severity issue in the ECDSA/secp256k1 implementation and another high severity issue in the Schnorr/secp256k1 signature implementation, both of which have since been corrected. We would like to thank Entropy for funding the audit.

This crate has been designed with the goal of ensuring that secret-dependent secp256k1 operations are performed in constant time (using the subtle crate and constant-time formulas). However, it is not suitable for use on processors with a variable-time multiplication operation (e.g. short circuit on multiply-by-zero / multiply-by-one, such as certain 32-bit PowerPC CPUs and some non-ARM microcontrollers).

USE AT YOUR OWN RISK!

Supported Algorithms

• Elliptic Curve Diffie-Hellman (ECDH): gated under the ecdh feature. Note that this is technically ephemeral secp256k1 Diffie-Hellman (a.k.a. ECDHE)
• Elliptic Curve Digital Signature Algorithm (ECDSA): gated under the ecdsa feature. Support for ECDSA/secp256k1 signing and verification, applying low-S normalization (BIP 0062) as used in consensus-critical applications, and additionally supports secp256k1 public-key recovery from ECDSA signatures (as used by e.g. Ethereum)
• Taproot Schnorr signatures (as defined in BIP0340): next-generation signature algorithm based on group operations enabling elegant higher-level constructions like multisignatures.

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.

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

secp256k1 is primarily notable for usage in Bitcoin and other cryptocurrencies, particularly in conjunction with the Elliptic Curve Digital Signature Algorithm (ECDSA). Owing to its wide deployment in these applications, secp256k1 is one of the most popular and commonly used elliptic curves.

Minimum Supported Rust Version

Rust 1.65 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
• MIT license

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.

serde support

When the serde feature of this crate is enabled, Serialize and Deserialize are impl’d for the following types:

• AffinePoint
• Scalar
• ecdsa::VerifyingKey

Please see type-specific documentation for more information.

Re-exports

• pub use elliptic_curve;
• pub use sha2;

Modules

• ecdsa
  Elliptic Curve Digital Signature Algorithm (ECDSA).

Structs

• AffinePoint
  secp256k1 curve point expressed in affine coordinates.
• ProjectivePoint
  A point on the secp256k1 curve in projective coordinates.
• Scalar
  Scalars are elements in the finite field modulo n.
• Secp256k1
  secp256k1 (K-256) elliptic curve.

Type Aliases

• CompressedPoint
  Compressed SEC1-encoded secp256k1 (K-256) curve point.
• EncodedPoint
  SEC1-encoded secp256k1 (K-256) curve point.
• FieldBytes
  secp256k1 (K-256) field element serialized as bytes.
• NonZeroScalar
  Non-zero secp256k1 (K-256) scalar field element.
• PublicKey
  secp256k1 (K-256) public key.
• SecretKey
  secp256k1 (K-256) secret key.
• U256
  256-bit unsigned big integer.
• WideBytes
  Bytes used by a wide reduction: twice the width of FieldBytes.