Group revamp (#261)

* Revamp `KeGroup` trait

* Update dependencies

* Fix `hash_to_scalar` using `OprfGroup` instead of `KeGroup`

* Relax constraints on associated types of `KeGroup`

* Improve `KeGroup` implementation on `Curve`

* Improve `KeyExchange` trait

* Fix new Clippy 1.59 warnings

src/serialization/mod.rs

@@ -12,7 +12,7 @@ use generic_array::typenum::{U0, U2};
 use generic_array::{ArrayLength, GenericArray};
 use hmac::Mac;
 
-use crate::errors::ProtocolError;
+use crate::errors::{InternalError, ProtocolError};
 
 // Corresponds to the I2OSP() function from RFC8017
 pub(crate) fn i2osp<L: ArrayLength<u8>>(
@@ -157,6 +157,20 @@ impl<T: Mac> MacExt for T {
     }
 }
 
+pub(crate) trait GenericArrayExt {
+    fn try_from_slice(slice: &[u8]) -> Result<&Self, InternalError>;
+}
+
+impl<L: ArrayLength<u8>> GenericArrayExt for GenericArray<u8, L> {
+    fn try_from_slice(slice: &[u8]) -> Result<&Self, InternalError> {
+        if slice.len() == L::USIZE {
+            Ok(Self::from_slice(slice))
+        } else {
+            Err(InternalError::InvalidByteSequence)
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests;