NOTE: yanked because hash_to_curve was improperly implemented (#785)

• Move AVX-512 backend selection logic to a separate CFG flag that requires nightly
• Add Elligator2 hashing methods EdwardsPoint::hash_to_curve() and FieldElement::hash_to_field()
• Deprecate FieldElement::as_bytes in favor of FieldElement::to_bytes
• Remove deprecated FieldElement::as_bytes
• Add batch conversion function EdwardsPoint::to_montgomery_batch()
• Make VartimePrecomputedStraus::optional_mixed_multiscalar_mul() and VartimeRistrettoPrecomputation::vartime_mixed_multiscalar_mul() accept more points than static scalars

• Security: Fix timing leak in Scalar subtraction on u32, u64, fiat_u32, and fiat_u64 backends
• Fix assorted new warnings and lints from rustc and clippy

• Fix nightly SIMD build

• Mark constants::BASEPOINT_ORDER deprecated from pub API
• Add implementation for PrimeFieldBits, behind the group-bits feature flag.

• Add arbitrary integer multiplication with MontgomeryPoint::mul_bits_be
• Add implementations of the ff and group traits, behind the group feature flag
• Adapt to new types introduced in fiat-crypto 0.2 in fiat backend
• Fix no_std for fiat backend
• Mark Scalar::clamp_integer as #[must_use]
• Various documentation fixes

Breaking changes

• Update the MSRV from 1.41 to 1.60
• Provide SemVer policy
• Make digest an optional feature
• Make rand_core an optional feature
• Remove std feature flag
• Remove nightly feature flag
• Automatic serial backend selection between u32 and u64 over the default u32
• Backend simd is now automatically selected over serial when a supported CPU is detected
• Backend override is now via cfg(curve25519_dalek_backend) over additive features
• Provide override to select u32 or u64 backend via cfg(curve25519_dalek_bits)
• Replace methods Scalar::{zero, one} with constants Scalar::{ZERO, ONE}
• Deprecate EdwardsPoint::hash_from_bytes and rename it EdwardsPoint::nonspec_map_to_curve
• Require including a new trait, use curve25519_dalek::traits::BasepointTable whenever using EdwardsBasepointTable or RistrettoBasepointTable
• Scalar::from_canonical_bytes now returns CtOption
• Scalar::is_canonical now returns Choice
• Remove Scalar::from_bytes_clamped and Scalar::reduce
• Deprecate and feature-gate Scalar::from_bits behind legacy_compatibility

Other changes

• Add EdwardsPoint::{mul_base, mul_base_clamped}, MontgomeryPoint::{mul_base, mul_base_clamped}, and BasepointTable::mul_base_clamped
• Add precomputed-tables feature
• Update Maintenance Policies for SemVer
• Migrate documentation to docs.rs hosted
• Fix backend documentation generation
• Fix panic when Ristretto::double_and_compress_batch receives the identity point
• Remove byteorder dependency
• Update the criterion dependency to 0.4.0
• Include README.md into crate Documentation
• Update the rand_core dependency version and the rand dev-dependency version.
• Relax the zeroize dependency to ^1
• Update the edition from 2015 to 2021

3.x series

• Add support for getting the identity element for the Montgomery form of curve25519, which is useful in certain protocols for checking contributory behaviour in derivation of shared secrets.

• Revert a commit which mistakenly removed support for zeroize traits for some point types, as well as elligator2 support for Edwards points.

• Fix documentation builds on nightly due to syntax changes to #![cfg_attr(feature = "nightly", doc = include_str!("../README.md"))].

• Add support for the Elligator2 encoding for Edwards points.
• Add two optional formally-verified field arithmetic backends which use the Fiat Crypto project's Rust code, which is generated from proofs of functional correctness checked by the Coq theorem proving system.
• Add support for additional sizes of precomputed tables for basepoint scalar multiplication.
• Fix an unused import.
• Add support for using the zeroize traits with all point types. Note that points are not automatically zeroized on Drop, but that consumers of curve25519-dalek should call these methods manually when needed.

• Fix documentation builds on nightly due to syntax changes to #![cfg_attr(feature = "nightly", doc = include_str!("../README.md"))].

• Multiple documentation typo fixes.
• Fixes to make using alloc+no_std possible for stable Rust.

• Update the optional packed-simd dependency to rely on a newer, maintained version of the packed-simd-2 crate.

Breaking changes

• Update the digest dependency to 0.9. This requires a major version because the digest traits are part of the public API, but there are otherwise no changes to the API.

2.x series

• Fix documentation builds on nightly due to syntax changes to #![fg_attr(feature = "nightly", doc = include_str!("../README.md"))].

• Multiple documentation typo fixes.
• Fix alloc feature working with stable rust.

• Update the optional packed-simd dependency to rely on a newer, maintained version of the packed-simd-2 crate.

• Make Scalar::from_bits a const fn, allowing its use in const contexts.

The only significant change is the data model change to the serde feature; besides the rand_core version bump, there are no other user-visible changes.

Breaking changes

• Fix a data modeling error in the serde feature pointed out by Trevor Perrin which caused points and scalars to be serialized with length fields rather than as fixed-size 32-byte arrays. This is a breaking change, but it fixes compatibility with serde-json and ensures that the serde-bincode encoding matches the conventional encoding for X/Ed25519.
• Update rand_core to 0.5, allowing use with new rand versions.

Other changes

• Switch from clear_on_drop to zeroize (by Tony Arcieri).
• Require subtle = ^2.2.1 and remove the note advising nightly Rust, which is no longer required as of that version of subtle. See the subtle changelog for more details.
• Update README.md for 2.x series.
• Remove the build.rs hack which loaded the entire crate into its own build.rs to generate constants, and keep the constants in the source code.

1.x series

• Fixes to make using alloc+no_std possible for stable Rust.

• Update the optional packed-simd dependency to rely on a newer, maintained version of the packed-simd-2 crate.

• Specify a semver bound for clear_on_drop rather than an exact version, addressing an issue where changes to inline assembly in rustc prevented clear_on_drop from working without an update.

• Fix an issue identified by a Quarkslab audit (and Jack Grigg), where manually constructing unreduced Scalar values, as needed for X/Ed25519, and then performing scalar/scalar arithmetic could compute incorrect results.
• Switch to upstream Rust intrinsics for the IFMA backend now that they exist in Rust and don't need to be defined locally.
• Ensure that the NAF computation works correctly, even for parameters never used elsewhere in the codebase.
• Minor refactoring to EdwardsPoint decompression.
• Fix broken links in documentation.
• Fix compilation on nightly broken due to changes to the #[doc(include)] path root (not quite correctly done in 1.2.2).

• Fix a typo in an internal doc-comment.
• Add the "crypto" tag to crate metadata.
• Fix compilation on nightly broken due to changes to the #[doc(include)] path root.

• Fix a bug in bucket index calculations in the Pippenger multiscalar algorithm for very large input sizes.
• Add a more extensive randomized multiscalar multiplication consistency check to the test suite to prevent regressions.
• Ensure that multiscalar and NAF computations work correctly on extremal Scalar values constructed via from_bits.

• New multiscalar multiplication algorithm with better performance for large problem sizes. The backend algorithm is selected transparently using the size hints of the input iterators, so no changes are required for client crates to start using it.
• Equality of Edwards points is now checked in projective coordinates.
• Serde can now be used with no_std.

• Fix typos in documentation comments.
• Remove unnecessary Default bound on Scalar::from_hash.

• Reverts the change in 1.1.0 to allow owned and borrowed RNGs, which caused a breakage due to a subtle interaction with ownership rules. (The RngCore change is retained).

• Disabled KaTeX on docs.rs pending proper support upstream.

• Fixed an issue related to #[cfg(rustdoc)] which prevented documenting multiple backends.

• Adds support for precomputation for multiscalar multiplication.
• Restructures the internal source tree into serial and vector backends (no change to external API).
• Adds a new IFMA backend which sets speed records.
• The avx2_backend feature is now an alias for the simd_backend feature, which autoselects an appropriate vector backend (currently AVX2 or IFMA).
• Replaces the rand dependency with rand_core.
• Generalizes trait bounds on RistrettoPoint::random() and Scalar::random() to allow owned and borrowed RNGs and to allow RngCore instead of Rng.

• Adds ConstantTimeEq implementation for compressed points.

• Fixes a typo in the naming of variables in Ristretto formulas (no change to functionality).

• Depends on the stable 2.0 version of subtle instead of 2.0.0-pre.0.