curve: implement ff and group traits (#562)

Originally authored by @str4d as #473
dalek-cryptography · Aug 27, 2023 · 4373695 · 4373695
1 parent 098658d
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diff --git a/curve25519-dalek/CHANGELOG.md b/curve25519-dalek/CHANGELOG.md
@@ -5,6 +5,10 @@ major series.
 
 ## 4.x series
 
+### Unreleased
+
+* Add implementations of the `ff` and `group` traits, behind the `group` feature flag.
+
 ### 4.0.0
 
 #### Breaking changes

diff --git a/curve25519-dalek/Cargo.toml b/curve25519-dalek/Cargo.toml
@@ -48,6 +48,7 @@ required-features = ["alloc", "rand_core"]
 
 [dependencies]
 cfg-if = "1"
+group = { version = "0.13", default-features = false, optional = true }
 rand_core = { version = "0.6.4", default-features = false, optional = true }
 digest = { version = "0.10", default-features = false, optional = true }
 subtle = { version = "2.3.0", default-features = false }
@@ -65,6 +66,7 @@ default = ["alloc", "precomputed-tables", "zeroize"]
 alloc = ["zeroize?/alloc"]
 precomputed-tables = []
 legacy_compatibility = []
+group = ["dep:group", "rand_core"]
 
 [target.'cfg(all(not(curve25519_dalek_backend = "fiat"), not(curve25519_dalek_backend = "serial"), target_arch = "x86_64"))'.dependencies]
 curve25519-dalek-derive = { version = "0.1", path = "../curve25519-dalek-derive" }
diff --git a/curve25519-dalek/README.md b/curve25519-dalek/README.md
@@ -49,6 +49,7 @@ curve25519-dalek = "4"
 | `digest`           |          | Enables `RistrettoPoint::{from_hash, hash_from_bytes}` and `Scalar::{from_hash, hash_from_bytes}`. This is an optional dependency whose version is not subject to SemVer. See [below](#public-api-semver-exemptions) for more details. |
 | `serde`            |          | Enables `serde` serialization/deserialization for all the point and scalar types. |
 | `legacy_compatibility`|       | Enables `Scalar::from_bits`, which allows the user to build unreduced scalars whose arithmetic is broken. Do not use this unless you know what you're doing. |
+| `group`            |          | Enables external `group` and `ff` crate traits |
 
 To disable the default features when using `curve25519-dalek` as a dependency,
 add `default-features = false` to the dependency in your `Cargo.toml`. To
@@ -190,9 +191,9 @@ From 4.x and on, MSRV changes will be accompanied by a minor version bump.
 Breaking changes to SemVer exempted components affecting the public API will be accompanied by
 _some_ version bump. Below are the specific policies:
 
-| Releases | Public API Component(s)               | Policy              |
-| :---     | :---                                  | :---                |
-| 4.x      | Dependencies `digest` and `rand_core` | Minor SemVer bump   |
+| Releases | Public API Component(s)                         | Policy              |
+| :---     | :---                                            | :---                |
+| 4.x      | Dependencies `group`, `digest` and `rand_core`  | Minor SemVer bump   |
 
 # Safety