Translate SHA-2 intermediate state for cross-endian peers

[yosuke-wolfssl]

Problem

wolfHSM supports a client and server on cores with different byte order: every
message header carries an endian marker and the server byte-swaps each field via
wh_Translate*. The SHA-2 wire structs declare the resume state as
uint8_t hash[32]/[64], and the translation helpers skipped it as "just a byte
array". But that array is a verbatim copy of wc_Sha256.digest /
wc_Sha512.digest, which wolfCrypt keeps as host-order word32/word64. A
cross-endian pair therefore exchanged byte-flipped chaining words: every
non-final update compressed from garbage and the digest was silently wrong — no
error, no crash. Final digests are unaffected (wolfCrypt emits canonical
big-endian at finalize), so only multi-message streams broke, and same-endian
pairs never saw it. SHA-3 was already correct: whMessageCrypto_Sha3State is
uint64_t s[25], swapped per word.

Addressed by Fenrir 4041.

Fix (src/wh_message_crypto.c)

New _TranslateSha2State() swaps the eight chaining words, going through a local
word via memcpy (no alignment or aliasing hazard, safe when src == dest).

The response direction is ambiguous — hash[] holds host-order state on an
update but a canonical digest on the last block, and the struct has no
isLastBlock — so the caller now states which it is. The existing response
symbols remain as wrappers passing 0; no public signature changed.

Translator	stateWordSize
...Sha256Request, ...Sha256DmaRequest	4, unconditional
...Sha512Request, ...Sha512DmaRequest	8, unconditional
...Sha2Response_ex, ...Sha2DmaResponse_ex (new)	from caller; server passes req.isLastBlock ? 0 : 4/8

src/wh_client_crypto.c is untouched: only the server translates, so the
client's copy defines the wire format. Same-endian wire bytes are identical to
before, so there is no cross-version interop break. Closes 4041.

Tests

New test-refactor/misc/wh_test_message_crypto.c — the translate layer had no
coverage at all. A loopback test cannot observe peers that disagree on byte
order, so it drives the helpers directly with a foreign-endian magic and checks
per-word swapping, byte-for-byte identity under a native magic, involution,
in-place translation, and that a finalized digest is left alone. It covers the
Keccak state too, which validates the test's own swap detector against
already-correct code.

Verification

• test-refactor: 38 passed / 0 failed of 63; DMA=1 42 passed; NOCRYPTO=1 12
  passed. Legacy test/ suite clean.
• Clean under -std=c90 -Werror -Wall -Wextra.
• Negative control: reducing the swap to a plain memcpy fails the new test
  (rc=-1).

[Copilot]

Pull request overview

This PR fixes mixed-endian client/server interoperability for multi-message SHA-2 hashing by correctly translating the intermediate chaining state (previously treated as an opaque byte array) while preserving the canonical byte order of finalized digests.

Changes:

• Add _TranslateSha2State() and new wh_MessageCrypto_TranslateSha2Response_ex() / wh_MessageCrypto_TranslateSha2DmaResponse_ex() so callers can specify whether hash[] is intermediate state (swap per word) or a finalized digest (no swap).
• Update server SHA-2 handlers to pass stateWordSize based on req.isLastBlock so only non-final responses have their chaining words swapped.
• Add a new direct-translation unit test covering SHA-2 (32/64-bit words), in-place translation, involution, and SHA-3 Keccak state translation; update draft docs accordingly.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
wolfhsm/wh_message_crypto.h	Adds _ex translator APIs documenting caller-provided stateWordSize.
src/wh_message_crypto.c	Implements SHA-2 state per-word swapping and wraps legacy response translators as digest-only.
src/wh_server_crypto.c	Uses _ex response translators with stateWordSize keyed off isLastBlock.
test-refactor/wh_test_list.c	Registers the new translation-focused test in the misc suite.
test-refactor/misc/wh_test_message_crypto.c	New tests for SHA-2/SHA-3 translation behavior, including foreign-endian and in-place cases.
docs/draft/async-crypto.md	Documents the non-opaque nature and endian rules for resumeState.hash and response hashes.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #468

Scan targets checked: wolfhsm-core-bugs, wolfhsm-crypto-bugs, wolfhsm-src

No new issues found in the changed files. ✅

[AlexLanzano]

Small nit. Looks good otherwise

[AlexLanzano]

We probably don't need to mention SHA3 here

[yosuke-wolfssl]

You are correct, I fixed the comment

[AlexLanzano]

@bigbrett over to you