Update curve25519-dalek to 4.0.0-pre.5 (#301)

* Update `curve25519-dalek`

* Improve documentation

* Update `voprf` to 0.5.0-pre.1

src/key_exchange/group/curve25519.rs

@@ -49,7 +49,7 @@ impl KeGroup for Curve25519 {
         loop {
             let scalar = Scalar::random(rng);
 
-            if scalar != Scalar::zero() {
+            if scalar != Scalar::ZERO {
                 break scalar;
             }
         }
@@ -69,7 +69,7 @@ impl KeGroup for Curve25519 {
 
         let scalar = Scalar::from_bytes_mod_order_wide(&uniform_bytes.into());
 
-        if scalar == Scalar::zero() {
+        if scalar == Scalar::ZERO {
             Err(InternalError::HashToScalar)
         } else {
             Ok(scalar)
@@ -77,7 +77,7 @@ impl KeGroup for Curve25519 {
     }
 
     fn is_zero_scalar(scalar: Self::Sk) -> subtle::Choice {
-        scalar.ct_eq(&Scalar::zero())
+        scalar.ct_eq(&Scalar::ZERO)
     }
 
     fn public_key(sk: Self::Sk) -> Self::Pk {
@@ -96,8 +96,8 @@ impl KeGroup for Curve25519 {
         bytes
             .try_into()
             .ok()
-            .and_then(Scalar::from_canonical_bytes)
-            .filter(|scalar| scalar != &Scalar::zero())
+            .and_then(|bytes| Scalar::from_canonical_bytes(bytes).into())
+            .filter(|scalar| scalar != &Scalar::ZERO)
             .ok_or(InternalError::PointError)
     }
 }

src/key_exchange/group/ristretto255.rs

@@ -66,7 +66,7 @@ impl KeGroup for Ristretto255 {
                 }
             };
 
-            if scalar != Scalar::zero() {
+            if scalar != Scalar::ZERO {
                 break scalar;
             }
         }
@@ -84,7 +84,7 @@ impl KeGroup for Ristretto255 {
     }
 
     fn is_zero_scalar(scalar: Self::Sk) -> subtle::Choice {
-        scalar.ct_eq(&Scalar::zero())
+        scalar.ct_eq(&Scalar::ZERO)
     }
 
     fn public_key(sk: Self::Sk) -> Self::Pk {
@@ -103,8 +103,8 @@ impl KeGroup for Ristretto255 {
         bytes
             .try_into()
             .ok()
-            .and_then(Scalar::from_canonical_bytes)
-            .filter(|scalar| scalar != &Scalar::zero())
+            .and_then(|bytes| Scalar::from_canonical_bytes(bytes).into())
+            .filter(|scalar| scalar != &Scalar::ZERO)
             .ok_or(InternalError::PointError)
     }
 }

src/lib.rs

@@ -1097,23 +1097,12 @@
 //!
 //! - The `serde` feature, enabled by default, provides convenience functions for serializing and deserializing with [serde](https://serde.rs/).
 //!
-//! - The backend features are re-exported from [curve25519-dalek](https://doc.dalek.rs/curve25519_dalek/index.html#backends-and-features)
-//!   and allow for selecting the corresponding backend for the curve arithmetic
-//!   used. The `ristretto255-u64` feature is included as the default. Other
-//!   features are mapped as `ristretto255-u32`, `ristretto255-fiat-u64` and
-//!   `ristretto255-fiat-u32`. Any `ristretto255-*` backend feature will enable
-//!   the `ristretto255` feature, which can be used too, but keep in mind that
-//!   `curve25519-dalek` will fail to compile without a selected backend. This
-//!   enables the use of [`Ristretto255`] as a `KeGroup` and `OprfCs`.
+//! - The `ristretto255` feature enables using [`Ristretto255`] as a `KeGroup`
+//!   and `OprfCs`. To select a specific backend see the [curve25519-dalek]
+//!   documentation.
 //!
-//! - The `curve25519` feature is similar to the `ristretto255` feature and
-//!   requires to select a backend like `curve25519-u64`, other backends are the
-//!   same as in `ristretto255-*`. This enables [`Curve25519`] as a `KeGroup`.
-//!
-//! - The `ristretto255-simd` feature is re-exported from [curve25519-dalek](https://doc.dalek.rs/curve25519_dalek/index.html#backends-and-features)
-//!   and enables parallel formulas, using either AVX2 or AVX512-IFMA. This will
-//!   automatically enable the `ristretto255-u64` feature and requires Rust
-//!   nightly.
+//! - The `curve25519` feature enables [`Curve25519`] as a `KeGroup`. To select
+//!   a specific backend see the [curve25519-dalek] documentation.
 //!
 //! - The `p256` feature enables the use of [`p256::NistP256`] as a `KeGroup`
 //!   and a `OprfCs` for `CipherSuite`.
@@ -1121,10 +1110,13 @@
 //! - The `bench` feature is used only for running performance benchmarks for
 //!   this implementation.
 //!
+//! [curve25519-dalek]:
+//!     (https://docs.rs/curve25519-dalek/4.0.0-pre.5/curve25519_dalek/index.html#backends)
 //! [`p256::NistP256`]: https://docs.rs/p256/latest/p256/struct.NistP256.html
 
-#![cfg_attr(not(test), deny(unsafe_code))]
 #![no_std]
+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![cfg_attr(not(test), deny(unsafe_code))]
 #![warn(clippy::cargo, missing_docs)]
 #![cfg_attr(not(test), warn(unused_crate_dependencies))]
 #![allow(type_alias_bounds)]

src/tests/full_test.rs

@@ -122,7 +122,7 @@ static STR_PASSWORD: &str = "password";
 static STR_CREDENTIAL_IDENTIFIER: &str = "credential_identifier";
 
 // To regenerate these test vectors, run:
-// cargo test --features curve25519-u64 -- --nocapture generate_test_vectors
+// cargo test --features curve25519 -- --nocapture generate_test_vectors
 #[cfg(feature = "ristretto255")]
 static TEST_VECTOR_RISTRETTO255: &str = r#"
 {