wp_mlx_kmgmt: derive the classical public point when duplicating

[yosuke-wolfssl]

Problem

wp_mlx_dup() duplicates the public half first, then imports the classical
private key with wc_ecc_import_private_key_ex(..., pub=NULL, ...). That path
sets key->type = ECC_PRIVATEKEY_ONLY, so every later wc_ecc_export_x963()
returns ECC_PRIVATEONLY_E while dst->hasPub stays 1.

EVP_PKEY_dup() copies with OSSL_KEYMGMT_SELECT_ALL — exactly this
combination. Duplicating a SecP256r1MLKEM768 or SecP384r1MLKEM1024 key pair
yields a key whose public half cannot be read: OSSL_PKEY_PARAM_PUB_KEY and
ENCODED_PUBLIC_KEY fail, wp_mlx_export() fails before its callback (taking
the private half down with it), and EVP_PKEY_eq() fails on a key pair
selection. X25519MLKEM768 is unaffected — wc_curve25519_import_private_ex()
never touches pubSet.

Failures are loud error returns; no memory-safety or key-material exposure.
libssl does not dup key-share keys, so TLS 1.3 hybrid key exchange is not on the
failing path.

Fix (src/wp_mlx_kmgmt.c)

Derive the public point after the private import, matching what
wp_mlx_load_keys() already does for the same hazard:

rc = wc_ecc_import_private_key_ex(cPrivBuf, len, NULL, 0,
    &dst->classical.ecc, src->data->curveId);
if (rc == 0) {
    rc = wc_ecc_make_pub(&dst->classical.ecc, NULL);
}

Closes f_11549.

Tests (test/test_mlkem.c)

test_mlx_dup — the hybrid groups had no dup coverage at all; test_mlkem_dup
exercises only the pure ML-KEM levels. For each of the three hybrid names it
dups the key, compares public key bytes against the original, encapsulates
against the duplicate, and decapsulates that ciphertext with both keys.

Verification

• Negative control: fails on SecP256r1MLKEM768 without the fix
  (Dup public key retrieval failed); X25519MLKEM768 passes.
• With the fix: all three groups pass; full unit suite 212/212, 0 failures.
• Build clean under -Werror (OpenSSL 3.6.0, wolfSSL master, --enable-mlkem).

[Copilot]

Pull request overview

This PR fixes hybrid ML-KEM + classical key duplication so that duplicated keypairs retain a usable classical public component (matching OpenSSL’s EVP_PKEY_dup() behavior) and adds unit coverage to prevent regressions.

Changes:

• Derive the ECC public point after importing an ECC private key during wp_mlx_dup() to avoid ending up with an ECC_PRIVATEKEY_ONLY state that breaks public export.
• Add a new hybrid-group duplication roundtrip test that validates public-key retrieval and encapsulate/decapsulate behavior across original and duplicated keys.
• Register the new test in the unit test declarations and test case list.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/wp_mlx_kmgmt.c	Ensures duplicated ECC hybrids derive a classical public point after private import so public export works.
test/test_mlkem.c	Adds test_mlx_dup covering EVP_PKEY_dup() for hybrid groups, including pub-key byte equality and KEM roundtrips.
test/unit.h	Declares the new test_mlx_dup unit test.
test/unit.c	Registers test_mlx_dup in the unit test table.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #472

Scan targets checked: wolfprovider-bugs, wolfprovider-src

Fenrir result: Approved ✅

No new issues found in the changed files.

Advisory only — this automated result does not count as a GitHub approval.