sha3: backport fix of customized cshake initialization (#836)

This PR is a backport of #834.

Author: newpavlov

Cargo.lock

@@ -5,6 +5,14 @@ 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).
 
+## 0.10.9 (UNRELEASED)
+### Fixed
+- Non-compliant initialization of cSHAKE when serialized length of function name and
+  customization string is a multiple of the block size ([#836], backport of [#834])
+
+[#834]: https://github.com/RustCrypto/hashes/pull/834
+[#836]: https://github.com/RustCrypto/hashes/pull/836
+
 ## 0.10.8 (2023-04-08)
 ### Fixed
 - Performance regression: now uses `p1600` fn ([#472])

sha3/CHANGELOG.md

@@ -9,7 +9,7 @@
 //! * `SHAKE128`, an extendable output function (XOF)
 //! * `SHAKE256`, an extendable output function (XOF)
 //! * `Keccak224`, `Keccak256`, `Keccak384`, `Keccak512` (NIST submission
-//!    without padding changes)
+//!   without padding changes)
 //!
 //! Additionally supports `TurboSHAKE`.
 //!
@@ -72,7 +72,7 @@ use core::fmt;
 #[cfg(feature = "oid")]
 use digest::const_oid::{AssociatedOid, ObjectIdentifier};
 use digest::{
-    block_buffer::Eager,
+    block_buffer::{Eager, LazyBuffer},
     consts::{U104, U136, U144, U168, U200, U28, U32, U48, U64, U72},
     core_api::{
         AlgorithmName, Block, BlockSizeUser, Buffer, BufferKindUser, CoreWrapper,

sha3/src/lib.rs

@@ -394,7 +394,7 @@ macro_rules! impl_cshake {
                     };
                 }
 
-                let mut buffer = Buffer::<Self>::default();
+                let mut buffer = LazyBuffer::<$rate>::default();
                 let mut b = [0u8; 9];
                 buffer.digest_blocks(left_encode($rate::to_u64(), &mut b), |blocks| {
                     for block in blocks {