diff --git a/src/lib.rs b/src/lib.rs index a682ef0..19a0b6d 100644 --- a/src/lib.rs +++ b/src/lib.rs @@ -10,21 +10,240 @@ #![no_std] #![cfg_attr(feature = "nightly", feature(test))] -#![cfg_attr(feature = "nightly", feature(external_doc))] #![cfg_attr(feature = "nightly", feature(doc_cfg))] #![cfg_attr(feature = "simd_backend", feature(stdsimd))] -// Refuse to compile if documentation is missing, but only on nightly. -// -// This means that missing docs will still fail CI, but means we can use -// README.md as the crate documentation. -#![cfg_attr(feature = "nightly", deny(missing_docs))] -#![cfg_attr(feature = "nightly", doc(include = "../README.md"))] +// Refuse to compile if documentation is missing. +#![deny(missing_docs)] + #![doc(html_logo_url = "https://doc.dalek.rs/assets/dalek-logo-clear.png")] #![doc(html_root_url = "https://docs.rs/curve25519-dalek/2.1.2")] -//! Note that docs will only build on nightly Rust until -//! [RFC 1990 stabilizes](https://github.com/rust-lang/rust/issues/44732). +//! # curve25519-dalek [![](https://img.shields.io/crates/v/curve25519-dalek.svg)](https://crates.io/crates/curve25519-dalek) [![](https://img.shields.io/badge/dynamic/json.svg?label=docs&uri=https%3A%2F%2Fcrates.io%2Fapi%2Fv1%2Fcrates%2Fcurve25519-dalek%2Fversions&query=%24.versions%5B0%5D.num&colorB=4F74A6)](https://doc.dalek.rs) [![](https://travis-ci.org/dalek-cryptography/curve25519-dalek.svg?branch=master)](https://travis-ci.org/dalek-cryptography/curve25519-dalek) +//! +//! +//! +//! **A pure-Rust implementation of group operations on Ristretto and Curve25519.** +//! +//! `curve25519-dalek` is a library providing group operations on the Edwards and +//! Montgomery forms of Curve25519, and on the prime-order Ristretto group. +//! +//! `curve25519-dalek` is not intended to provide implementations of any particular +//! crypto protocol. Rather, implementations of those protocols (such as +//! [`x25519-dalek`][x25519-dalek] and [`ed25519-dalek`][ed25519-dalek]) should use +//! `curve25519-dalek` as a library. +//! +//! `curve25519-dalek` is intended to provide a clean and safe _mid-level_ API for use +//! implementing a wide range of ECC-based crypto protocols, such as key agreement, +//! signatures, anonymous credentials, rangeproofs, and zero-knowledge proof +//! systems. +//! +//! In particular, `curve25519-dalek` implements Ristretto, which constructs a +//! prime-order group from a non-prime-order Edwards curve. This provides the +//! speed and safety benefits of Edwards curve arithmetic, without the pitfalls of +//! cofactor-related abstraction mismatches. +//! +//! # Documentation +//! +//! The semver-stable, public-facing `curve25519-dalek` API is documented +//! [here][docs-external]. In addition, the unstable internal implementation +//! details are documented [here][docs-internal]. +//! +//! The `curve25519-dalek` documentation requires a custom HTML header to include +//! KaTeX for math support. Unfortunately `cargo doc` does not currently support +//! this, but docs can be built using +//! ```sh +//! make doc +//! make doc-internal +//! ``` +//! +//! # Use +//! +//! To import `curve25519-dalek`, add the following to the dependencies section of +//! your project's `Cargo.toml`: +//! ```toml +//! curve25519-dalek = "3" +//! ``` +//! +//! The sole breaking change in the `3.x` series was an update to the `digest` +//! version, and in terms of non-breaking changes it includes: +//! +//! * support for using `alloc` instead of `std` on stable Rust, +//! * the Elligator2 encoding for Edwards points, +//! * a fix to use `packed_simd2`, +//! * various documentation fixes and improvements, +//! * support for configurably-sized, precomputed lookup tables for basepoint scalar +//! multiplication, +//! * two new formally-verified field arithmetic backends which use the Fiat Crypto +//! Rust code, which is generated from proofs of functional correctness checked by +//! the Coq theorem proving system, and +//! * support for explicitly calling the `zeroize` traits for all point types. +//! +//! The `2.x` series has API almost entirely unchanged from the `1.x` series, +//! except that: +//! +//! * an error in the data modeling for the (optional) `serde` feature was +//! corrected, so that when the `2.x`-series `serde` implementation is used +//! with `serde-bincode`, the derived serialization matches the usual X/Ed25519 +//! formats; +//! * the `rand` version was updated. +//! +//! See `CHANGELOG.md` for more details. +//! +//! # Backends and Features +//! +//! The `nightly` feature enables features available only when using a Rust nightly +//! compiler. In particular, it is required for rendering documentation and for +//! the SIMD backends. +//! +//! Curve arithmetic is implemented using one of the following backends: +//! +//! * a `u32` backend using serial formulas and `u64` products; +//! * a `u64` backend using serial formulas and `u128` products; +//! * an `avx2` backend using [parallel formulas][parallel_doc] and `avx2` instructions (sets speed records); +//! * an `ifma` backend using [parallel formulas][parallel_doc] and `ifma` instructions (sets speed records); +//! +//! By default the `u64` backend is selected. To select a specific backend, use: +//! ```sh +//! cargo build --no-default-features --features "std u32_backend" +//! cargo build --no-default-features --features "std u64_backend" +//! # Requires nightly, RUSTFLAGS="-C target_feature=+avx2" to use avx2 +//! cargo build --no-default-features --features "std simd_backend" +//! # Requires nightly, RUSTFLAGS="-C target_feature=+avx512ifma" to use ifma +//! cargo build --no-default-features --features "std simd_backend" +//! ``` +//! Crates using `curve25519-dalek` can either select a backend on behalf of their +//! users, or expose feature flags that control the `curve25519-dalek` backend. +//! +//! The `std` feature is enabled by default, but it can be disabled for no-`std` +//! builds using `--no-default-features`. Note that this requires explicitly +//! selecting an arithmetic backend using one of the `_backend` features. +//! If no backend is selected, compilation will fail. +//! +//! # Safety +//! +//! The `curve25519-dalek` types are designed to make illegal states +//! unrepresentable. For example, any instance of an `EdwardsPoint` is +//! guaranteed to hold a point on the Edwards curve, and any instance of a +//! `RistrettoPoint` is guaranteed to hold a valid point in the Ristretto +//! group. +//! +//! All operations are implemented using constant-time logic (no +//! secret-dependent branches, no secret-dependent memory accesses), +//! unless specifically marked as being variable-time code. +//! We believe that our constant-time logic is lowered to constant-time +//! assembly, at least on `x86_64` targets. +//! +//! As an additional guard against possible future compiler optimizations, +//! the `subtle` crate places an optimization barrier before every +//! conditional move or assignment. More details can be found in [the +//! documentation for the `subtle` crate][subtle_doc]. +//! +//! Some functionality (e.g., multiscalar multiplication or batch +//! inversion) requires heap allocation for temporary buffers. All +//! heap-allocated buffers of potentially secret data are explicitly +//! zeroed before release. +//! +//! However, we do not attempt to zero stack data, for two reasons. +//! First, it's not possible to do so correctly: we don't have control +//! over stack allocations, so there's no way to know how much data to +//! wipe. Second, because `curve25519-dalek` provides a mid-level API, +//! the correct place to start zeroing stack data is likely not at the +//! entrypoints of `curve25519-dalek` functions, but at the entrypoints of +//! functions in other crates. +//! +//! The implementation is memory-safe, and contains no significant +//! `unsafe` code. The SIMD backend uses `unsafe` internally to call SIMD +//! intrinsics. These are marked `unsafe` only because invoking them on an +//! inappropriate CPU would cause `SIGILL`, but the entire backend is only +//! compiled with appropriate `target_feature`s, so this cannot occur. +//! +//! # Performance +//! +//! Benchmarks are run using [`criterion.rs`][criterion]: +//! +//! ```sh +//! cargo bench --no-default-features --features "std u32_backend" +//! cargo bench --no-default-features --features "std u64_backend" +//! # Uses avx2 or ifma only if compiled for an appropriate target. +//! export RUSTFLAGS="-C target_cpu=native" +//! cargo bench --no-default-features --features "std simd_backend" +//! ``` +//! +//! Performance is a secondary goal behind correctness, safety, and +//! clarity, but we aim to be competitive with other implementations. +//! +//! # FFI +//! +//! Unfortunately, we have no plans to add FFI to `curve25519-dalek` directly. The +//! reason is that we use Rust features to provide an API that maintains safety +//! invariants, which are not possible to maintain across an FFI boundary. For +//! instance, as described in the _Safety_ section above, invalid points are +//! impossible to construct, and this would not be the case if we exposed point +//! operations over FFI. +//! +//! However, `curve25519-dalek` is designed as a *mid-level* API, aimed at +//! implementing other, higher-level primitives. Instead of providing FFI at the +//! mid-level, our suggestion is to implement the higher-level primitive (a +//! signature, PAKE, ZKP, etc) in Rust, using `curve25519-dalek` as a dependency, +//! and have that crate provide a minimal, byte-buffer-oriented FFI specific to +//! that primitive. +//! +//! # Contributing +//! +//! Please see [CONTRIBUTING.md][contributing]. +//! +//! Patches and pull requests should be make against the `develop` +//! branch, **not** `master`. +//! +//! # About +//! +//! **SPOILER ALERT:** *The Twelfth Doctor's first encounter with the Daleks is in +//! his second full episode, "Into the Dalek". A beleaguered ship of the "Combined +//! Galactic Resistance" has discovered a broken Dalek that has turned "good", +//! desiring to kill all other Daleks. The Doctor, Clara and a team of soldiers +//! are miniaturized and enter the Dalek, which the Doctor names Rusty. They +//! repair the damage, but accidentally restore it to its original nature, causing +//! it to go on the rampage and alert the Dalek fleet to the whereabouts of the +//! rebel ship. However, the Doctor manages to return Rusty to its previous state +//! by linking his mind with the Dalek's: Rusty shares the Doctor's view of the +//! universe's beauty, but also his deep hatred of the Daleks. Rusty destroys the +//! other Daleks and departs the ship, determined to track down and bring an end +//! to the Dalek race.* +//! +//! `curve25519-dalek` is authored by Isis Agora Lovecruft and Henry de Valence. +//! +//! Portions of this library were originally a port of [Adam Langley's +//! Golang ed25519 library](https://!github.com/agl/ed25519), which was in +//! turn a port of the reference `ref10` implementation. Most of this code, +//! including the 32-bit field arithmetic, has since been rewritten. +//! +//! The fast `u32` and `u64` scalar arithmetic was implemented by Andrew Moon, and +//! the addition chain for scalar inversion was provided by Brian Smith. The +//! optimised batch inversion was contributed by Sean Bowe and Daira Hopwood. +//! +//! The `no_std` and `zeroize` support was contributed by Tony Arcieri. +//! +//! The formally verified backends, `fiat_u32_backend` and `fiat_u64_backend`, which +//! integrate with the Rust generated by the +//! [Fiat Crypto project](https://github.com/mit-plv/fiat-crypto) were contributed +//! by François Garillot. +//! +//! Thanks also to Ashley Hauck, Lucas Salibian, Manish Goregaokar, Jack Grigg, +//! Pratyush Mishra, Michael Rosenberg, and countless others for their +//! contributions. +//! +//! [ed25519-dalek]: https://github.com/dalek-cryptography/ed25519-dalek +//! [x25519-dalek]: https://github.com/dalek-cryptography/x25519-dalek +//! [contributing]: https://github.com/dalek-cryptography/curve25519-dalek/blob/master/CONTRIBUTING.md +//! [docs-external]: https://doc.dalek.rs/curve25519_dalek/ +//! [docs-internal]: https://doc-internal.dalek.rs/curve25519_dalek/ +//! [criterion]: https://github.com/japaric/criterion.rs +//! [parallel_doc]: https://doc-internal.dalek.rs/curve25519_dalek/backend/vector/avx2/index.html +//! [subtle_doc]: https://doc.dalek.rs/subtle/ //------------------------------------------------------------------------ // External dependencies: