hkdf: unseal HmacImpl (#154)

Author: newpavlov

hkdf/CHANGELOG.md

@@ -4,13 +4,15 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## UNRELEASED
-### Breaking changes
+## 0.13.0 (unreleased)
+### Changed
 - Removed `std` crate feature ([#105])
 - Bump MSRV to 1.81 ([#105])
 - Bump `hmac` dependency to v0.13
+- Unseal `HmacImpl` trait ([#154])
 
 [#105]: https://github.com/RustCrypto/KDFs/pull/105
+[#154]: https://github.com/RustCrypto/KDFs/pull/154
 
 ## 0.12.3 (2022-02-17)
 ### Fixed

hkdf/src/sealed.rs hkdf/src/hmac_impl.rshkdf/src/sealed.rs renamed to hkdf/src/hmac_impl.rs

@@ -4,15 +4,21 @@ use hmac::digest::{
 };
 use hmac::{EagerHash, Hmac, SimpleHmac};
 
-pub trait Sealed<H: OutputSizeUser> {
+/// Trait representing a HMAC implementation.
+///
+/// Most users should use [`Hmac`] or [`SimpleHmac`].
+pub trait HmacImpl<H: OutputSizeUser>: Clone {
+    /// Create new HMAC state with the given key.
     fn new_from_slice(key: &[u8]) -> Self;
 
+    /// Update HMAC state.
     fn update(&mut self, data: &[u8]);
 
+    /// Finalize the HMAC state and get generated tag.
     fn finalize(self) -> Output<H>;
 }
 
-impl<H: EagerHash> Sealed<H> for Hmac<H> {
+impl<H: EagerHash> HmacImpl<H> for Hmac<H> {
     #[inline(always)]
     fn new_from_slice(key: &[u8]) -> Self {
         KeyInit::new_from_slice(key).expect("HMAC can take a key of any size")
@@ -24,15 +30,16 @@ impl<H: EagerHash> Sealed<H> for Hmac<H> {
     }
 
     #[inline(always)]
-    #[allow(deprecated)] // clone_from_slice
     fn finalize(self) -> Output<H> {
-        // Output<H> and Output<H::Core> are always equal to each other,
-        // but we can not prove it at type level
-        Output::<H>::clone_from_slice(&self.finalize_fixed())
+        Output::<H>::try_from(&self.finalize_fixed()[..])
+            .expect("Output<H> and Output<Hmac<H>> are always equal to each other")
     }
 }
 
-impl<H: Digest + BlockSizeUser + Clone> Sealed<H> for SimpleHmac<H> {
+impl<H> HmacImpl<H> for SimpleHmac<H>
+where
+    H: Digest + BlockSizeUser + Clone,
+{
     #[inline(always)]
     fn new_from_slice(key: &[u8]) -> Self {
         KeyInit::new_from_slice(key).expect("HMAC can take a key of any size")
@@ -44,10 +51,8 @@ impl<H: Digest + BlockSizeUser + Clone> Sealed<H> for SimpleHmac<H> {
     }
 
     #[inline(always)]
-    #[allow(deprecated)] // clone_from_slice
     fn finalize(self) -> Output<H> {
-        // Output<H> and Output<H::Core> are always equal to each other,
-        // but we can not prove it at type level
-        Output::<H>::clone_from_slice(&self.finalize_fixed())
+        Output::<H>::try_from(&self.finalize_fixed()[..])
+            .expect("Output<H> and Output<SimpleHmac<H>> are always equal to each other")
     }
 }

hkdf/src/lib.rs

@@ -18,9 +18,10 @@ use hmac::digest::{
 use hmac::{Hmac, SimpleHmac};
 
 mod errors;
-mod sealed;
+mod hmac_impl;
 
 pub use errors::{InvalidLength, InvalidPrkLength};
+pub use hmac_impl::HmacImpl;
 
 /// [`HkdfExtract`] variant which uses [`SimpleHmac`] for underlying HMAC
 /// implementation.
@@ -192,8 +193,3 @@ where
         f.write_str("> { ... }")
     }
 }
-
-/// Sealed trait implemented for [`Hmac`] and [`SimpleHmac`].
-pub trait HmacImpl<H: OutputSizeUser>: sealed::Sealed<H> + Clone {}
-
-impl<H: OutputSizeUser, T: sealed::Sealed<H> + Clone> HmacImpl<H> for T {}