Fix EncryptedPrivateKeyInfo encode + decode (PBES2) across all key types

[yosuke-wolfssl]

Fix EncryptedPrivateKeyInfo encode + decode (PBES2) across all key types

Summary

wolfProvider's EncryptedPrivateKeyInfo (encrypted PKCS#8) support was
both weak and incomplete:

1. Encoder (finding f_4081): the EPKI encoders derived the key with
   MD5 / PBKDF1 / 1 iteration, encrypted the DER in place, and emitted it
   under the unencrypted -----BEGIN PRIVATE KEY----- label. The output was
   not a valid EncryptedPrivateKeyInfo and could not be decoded by OpenSSL or
   by wolfProvider itself.
2. Decoder: only RSA could decode a raw-DER encrypted PKCS#8; EC/DH/ECX/ML-DSA
   decoders did not handle encrypted input, so those keys failed to load in DER
   form (PEM happened to work via a different path).

This PR replaces the encode path with standards-compliant PBES2
(PBKDF2 + AES-CBC) and makes the decode path handle encrypted PKCS#8 for every
key type, routed through shared helpers.

Changes

Encoder (finding f_4081)

• New shared wp_encrypt_key_pkcs8() / _size() in wp_internal.c wrapping
  wc_EncryptPKCS8Key (PBKDF2 + AES-CBC, WP_PKCS12_ITERATIONS_DEFAULT).
• All EPKI encoders (RSA, EC, DH, ECX, ML-DSA) route through it; RSA's existing
  PrivateKeyInfo+cipher path unified onto the same helper.
• Fixed PEM label to PKCS8_ENC_PRIVATEKEY_TYPE (ENCRYPTED PRIVATE KEY) and
  fixed output sizing to use the real LENGTH_ONLY_E query (block-rounding
  under-sized the structure).
• Removed the weak wp_encrypt_key / wp_BufferKeyEncrypt / wp_EncryptedInfoGet
  helpers and their MD5 dependency.

Decoder

• New shared wp_decrypt_key_pkcs8() in wp_internal.c (detect PBES2 via the
  PBKDF2 OID, get passphrase, wc_DecryptPKCS8Key in place).
• RSA wp_rsa_decode_enc_pki refactored onto it (removed the RSA-local
  pbkdf2_oid table / wp_rsa_find_pbkdf2_oid).
• Added wp_*_decode_enc_pki fallbacks to EC/DH/ECX/ML-DSA: on plaintext-decode
  failure, decrypt then re-decode. No change to wp_dec_epki2pki.c.

Common

• Both helpers guarded on HAVE_PKCS8 && !NO_PWDBASED and fail closed rather
  than emit weak/plaintext output. This matches the pre-existing decode-side
  requirement (wc_DecryptPKCS8Key, also HAVE_PKCS8).
• Passphrase buffers use the WOLFSSL_SMALL_STACK pattern and wc_ForceZero.

Tests

New encrypted-PKCS#8 round-trip tests via a shared test_epki_encode_decode
helper, gated on WP_HAVE_EPKI_TEST (WOLFSSL_ENCRYPTED_KEYS && HAVE_PKCS8 && !NO_PWDBASED).

Key type	DER wp→OpenSSL	PEM wp→OpenSSL	DER wp→wp	PEM wp→wp
RSA	✅	✅	✅	✅
EC (P-256)	✅	✅	✅	✅
DH	✅	✅	✅	✅
ECX (Ed25519)	⏸	⏸	✅	✅
ML-DSA-44	—	—	✅	✅

wp→OpenSSL = stock OpenSSL decrypts wolfProvider's output (interop guarantee).
wp→wp = wolfProvider round-trips its own output.

Verification

• Non-PQC build + make test: green (RSA/EC/DH/ECX; ML-DSA guarded out).
• PQC build (OpenSSL 3.6 + wolfSSL ML-DSA) + make test: green (all 5 EPKI
  tests).
• ASan + UBSan: clean across all modified sources.

Known limitations / follow-ups (out of scope)

• ECX interop (⏸): X25519/Ed25519 plaintext PKCS#8 is block-aligned;
  wc_EncryptPKCS8Key_ex omits the PKCS#7 padding block for block-aligned input
  (asn.c), which OpenSSL rejects. Fix belongs in wolfSSL; ECX wp→OpenSSL
  interop is not asserted until it lands.
  On going: Fix PKCS#7 padding for block-aligned input in wc_EncryptPKCS8Key_ex wolfssl#10836
• ML-DSA interop (—): stock OpenSSL does not decode wolfProvider's ML-DSA
  EPKI — a separate ML-DSA/PQC-decode matter, independent of this change.
• Iteration count stays at WP_PKCS12_ITERATIONS_DEFAULT (2048) for parity with
  OpenSSL's default output; raising it is a separate decision.

[Copilot]

Pull request overview

This PR upgrades wolfProvider’s EncryptedPrivateKeyInfo (encrypted PKCS#8) handling to be standards-compliant PBES2 (PBKDF2 + AES-CBC) and extends encrypted-PKCS#8 decode support across all key types, with shared helpers and new round-trip tests.

Changes:

• Introduces shared PKCS#8 PBES2 encrypt/decrypt helpers (wp_encrypt_key_pkcs8*, wp_decrypt_key_pkcs8) and routes key-type encoders/decoders through them.
• Fixes EncryptedPrivateKeyInfo PEM labeling/output sizing and removes the prior weak/incorrect encryption path.
• Adds encrypted-PKCS#8 encode/decode round-trip tests across RSA/EC/DH/ECX/ML-DSA (with feature gating).

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/unit.h	Adds WP_HAVE_EPKI_TEST feature gate and new EPKI test declarations.
test/unit.c	Registers new EPKI test cases under feature gates.
test/test_rsa.c	Adds RSA EncryptedPrivateKeyInfo encode/decode interop and self-roundtrip test.
test/test_pkey.c	Adds shared test_epki_encode_decode() helper using OpenSSL encoder/decoder APIs.
test/test_mldsa.c	Adds ML-DSA EncryptedPrivateKeyInfo self round-trip test.
test/test_ecx.c	Adds ECX (Ed25519) EncryptedPrivateKeyInfo self round-trip test.
test/test_ecc.c	Adds ECC EncryptedPrivateKeyInfo interop + self round-trip test.
test/test_dh.c	Adds DH EncryptedPrivateKeyInfo interop + self round-trip test.
src/wp_rsa_kmgmt.c	Refactors RSA encrypted PKCS#8 encode/decode onto shared PBES2 helpers and fixes PEM type handling.
src/wp_mldsa_kmgmt.c	Adds encrypted-PKCS#8 decode fallback and PBES2 EncryptedPrivateKeyInfo encode path with separate ciphertext buffer.
src/wp_internal.c	Implements shared PBES2 PKCS#8 encrypt/size/decrypt helpers and PBKDF2-based detection.
src/wp_ecx_kmgmt.c	Adds encrypted-PKCS#8 decode fallback and PBES2 EncryptedPrivateKeyInfo encode path with separate ciphertext buffer.
src/wp_ecc_kmgmt.c	Adds encrypted-PKCS#8 decode fallback and PBES2 EncryptedPrivateKeyInfo encode path using shared helpers.
src/wp_dh_kmgmt.c	Adds encrypted-PKCS#8 decode fallback and PBES2 EncryptedPrivateKeyInfo encode path using shared helpers.
include/wolfprovider/internal.h	Updates internal API declarations to new shared PKCS#8 encrypt/decrypt helpers.

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[wolfSSL-Fenrir-bot]

Fenrir Automated Review — PR #426

Scan targets checked: wolfprovider-bugs, wolfprovider-src

Findings: 1
1 finding(s) posted as inline comments (see file-level comments below)

This review was generated automatically by Fenrir. Findings are non-blocking.

[yosuke-wolfssl]

PRM-master-job failure would be fixed with #425