crypto: fix public PKCS8 export error

exportKeySpki() already rejects exporting a private key as 'spki'
with an InvalidAccessError, per the Web Crypto export key algorithm
steps for each of RSA, EC, CFRG, ML-DSA, and ML-KEM. exportKeyPkcs8()
was missing the symmetric check: exporting a public key as 'pkcs8'
fell through to the generic "Unable to export ... key using pkcs8
format" NotSupportedError instead of the spec-mandated
InvalidAccessError.

Add the same key-type check to exportKeyPkcs8(), mirroring
exportKeySpki(), and drop the now-redundant type guard around its
call site in exportKeySync(). This also fixes wrapKey(), which
delegates to the same export path.

Add test coverage for both subtle.exportKey('pkcs8', publicKey) and
subtle.wrapKey('pkcs8', publicKey, ...).

Signed-off-by: koreahghg <koreahghg@gmail.com>
PR-URL: #65609
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: koreahghg

lib/internal/crypto/webcrypto.js

@@ -530,45 +530,51 @@ function exportKeySpki(key) {
 }
 
 function exportKeyPkcs8(key) {
+  let exporter;
   switch (getCryptoKeyAlgorithm(key).name) {
     case 'RSASSA-PKCS1-v1_5':
       // Fall through
     case 'RSA-PSS':
       // Fall through
     case 'RSA-OAEP':
-      return require('internal/crypto/rsa')
-        .rsaExportKey(key, kWebCryptoKeyFormatPKCS8);
+      exporter = require('internal/crypto/rsa').rsaExportKey;
+      break;
     case 'ECDSA':
       // Fall through
     case 'ECDH':
-      return require('internal/crypto/ec')
-        .ecExportKey(key, kWebCryptoKeyFormatPKCS8);
+      exporter = require('internal/crypto/ec').ecExportKey;
+      break;
     case 'Ed25519':
       // Fall through
     case 'Ed448':
       // Fall through
     case 'X25519':
       // Fall through
     case 'X448':
-      return require('internal/crypto/cfrg')
-        .cfrgExportKey(key, kWebCryptoKeyFormatPKCS8);
+      exporter = require('internal/crypto/cfrg').cfrgExportKey;
+      break;
     case 'ML-DSA-44':
       // Fall through
     case 'ML-DSA-65':
       // Fall through
     case 'ML-DSA-87':
-      return require('internal/crypto/ml_dsa')
-        .mlDsaExportKey(key, kWebCryptoKeyFormatPKCS8);
+      exporter = require('internal/crypto/ml_dsa').mlDsaExportKey;
+      break;
     case 'ML-KEM-512':
       // Fall through
     case 'ML-KEM-768':
       // Fall through
     case 'ML-KEM-1024':
-      return require('internal/crypto/ml_kem')
-        .mlKemExportKey(key, kWebCryptoKeyFormatPKCS8);
+      exporter = require('internal/crypto/ml_kem').mlKemExportKey;
+      break;
     default:
       return undefined;
   }
+
+  if (getCryptoKeyType(key) !== 'private')
+    throw lazyDOMException('Key must be a private key', 'InvalidAccessError');
+
+  return exporter(key, kWebCryptoKeyFormatPKCS8);
 }
 
 function exportKeyRawPublic(key, format) {
@@ -777,9 +783,7 @@ function exportKeySync(format, key) {
       break;
     }
     case 'pkcs8': {
-      if (type === 'private') {
-        result = exportKeyPkcs8(key);
-      }
+      result = exportKeyPkcs8(key);
       break;
     }
     case 'jwk': {

test/parallel/test-webcrypto-export-import-ec.js

@@ -120,6 +120,12 @@ async function testImportSpki({ name, publicUsages }, namedCurve, extractable) {
     assert.strictEqual(
       Buffer.from(spki).toString('hex'),
       keyData[namedCurve].spki.toString('hex'));
+
+    await assert.rejects(
+      subtle.exportKey('pkcs8', key), {
+        message: 'Key must be a private key',
+        name: 'InvalidAccessError',
+      });
   } else {
     await assert.rejects(
       subtle.exportKey('spki', key), {

test/parallel/test-webcrypto-wrap-unwrap.js

@@ -567,6 +567,17 @@ async function testNonByteLengthWrapUnwrap({
       name: 'InvalidAccessError',
     });
 
+  // Symmetric case: exporting a public key as 'pkcs8' must also fail with
+  // InvalidAccessError, not the generic NotSupportedError.
+  await assert.rejects(
+    subtle.wrapKey('pkcs8', ecKey.publicKey, wrapKey, {
+      name: 'AES-GCM',
+      iv: new Uint8Array(12),
+    }), {
+      message: 'Key must be a private key',
+      name: 'InvalidAccessError',
+    });
+
   // --- unwrapKey validation tests ---
 
   const ciphertext = new Uint8Array(32); // Dummy ciphertext