feat: integrate webcrypto-liner for legacy algorithm support in S/MIME handling

lib/smime/crypto-engine.ts

@@ -0,0 +1,76 @@
+/**
+ * Crypto engine backed by webcrypto-liner for legacy algorithm support.
+ *
+ * webcrypto-liner extends the native Web Crypto API with algorithms
+ * like DES-EDE3-CBC (3DES) that are commonly found in S/MIME messages
+ * and PKCS#12 files produced by legacy clients (Outlook, Thunderbird, etc.).
+ *
+ * Native Web Crypto calls are passed through to the real implementation;
+ * liner only intercepts algorithms that the browser doesn't natively support.
+ */
+
+import * as pkijs from 'pkijs';
+
+// webcrypto-liner exports a Crypto constructor at runtime that extends native
+// Web Crypto with legacy algorithms (3DES, etc.). Its type declarations only
+// expose the type alias, so we import the module dynamically and cast.
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+const liner = require('webcrypto-liner') as {
+  Crypto: { new (): Crypto };
+  setCrypto: (subtle: SubtleCrypto) => void;
+  nativeCrypto: Crypto | Record<string, never>;
+};
+
+let linerEngine: pkijs.CryptoEngine | null = null;
+let linerCryptoInstance: Crypto | null = null;
+
+function ensureLiner() {
+  if (!linerCryptoInstance) {
+    // In Node.js, webcrypto-liner can't auto-detect the native crypto
+    // (it looks for self.crypto which doesn't exist). Feed it manually
+    // so that native algorithms (RSA, AES, etc.) stay hardware-accelerated
+    // and only truly missing algorithms (3DES) use the software fallback.
+    if (
+      typeof liner.nativeCrypto?.getRandomValues !== 'function' &&
+      typeof globalThis.crypto?.subtle !== 'undefined'
+    ) {
+      liner.setCrypto(globalThis.crypto.subtle);
+    }
+    linerCryptoInstance = new liner.Crypto();
+  }
+  if (!linerEngine) {
+    linerEngine = new pkijs.CryptoEngine({
+      crypto: linerCryptoInstance,
+      subtle: linerCryptoInstance.subtle,
+      name: 'webcrypto-liner',
+    });
+  }
+}
+
+/** Get a PKI.js CryptoEngine with 3DES (and other legacy algorithm) support. */
+export function getLinerCryptoEngine(): pkijs.CryptoEngine {
+  ensureLiner();
+  return linerEngine!;
+}
+
+/**
+ * Run an async operation with the global PKI.js engine set to webcrypto-liner,
+ * then restore the previous engine afterwards.
+ *
+ * Required for operations that use the global engine internally
+ * (e.g. PFX.parseInternalValues for PKCS#12 import).
+ */
+export async function withLinerEngine<T>(fn: () => Promise<T>): Promise<T> {
+  ensureLiner();
+
+  // Save the current global engine so we can restore it
+  const prev = pkijs.getEngine();
+
+  pkijs.setEngine('webcrypto-liner', linerCryptoInstance!, linerEngine!);
+  try {
+    return await fn();
+  } finally {
+    // Restore the previous engine
+    pkijs.setEngine(prev.name, prev.crypto as unknown as pkijs.CryptoEngine);
+  }
+}

lib/smime/pkcs12-import.ts

@@ -6,6 +6,7 @@ import {
   classifyCapabilities,
 } from './certificate-utils';
 import type { SmimeKeyRecord, Pkcs12ImportResult } from './types';
+import { withLinerEngine } from './crypto-engine';
 
 const KDF_ITERATIONS = 600_000;
 const AES_KEY_LENGTH = 256;
@@ -39,9 +40,12 @@ export async function importPkcs12(
     // PKIjs handles MAC verification internally during parseInternalValues
   }
 
-  // Parse internal values
-  await pfx.parseInternalValues({
-    password: stringToAB(p12Passphrase),
+  // Use webcrypto-liner as the global engine for 3DES support.
+  // Many PKCS#12 files use pbeWithSHAAnd3-KeyTripleDES-CBC internally.
+  await withLinerEngine(async () => {
+    await pfx.parseInternalValues({
+      password: stringToAB(p12Passphrase),
+    });
   });
 
   // Extract certificates and private key from parsed PKCS#12
@@ -63,7 +67,9 @@ export async function importPkcs12(
     }
     return {};
   });
-  await authSafe.parseInternalValues({ safeContents: safeContentsParams });
+  await withLinerEngine(async () => {
+    await authSafe.parseInternalValues({ safeContents: safeContentsParams });
+  });
 
   for (const safeContent of authSafe.parsedValue.safeContents) {
     const sc = safeContent.value ?? safeContent.parsedValue;
@@ -115,8 +121,10 @@ export async function importPkcs12(
             privateKeyInfo = shroudedBag.parsedValue;
           } else {
             // Decrypt shrouded key bag to get private key info
-            await (shroudedBag as unknown as { parseInternalValues(params: { password: ArrayBuffer }): Promise<void> }).parseInternalValues({
-              password: stringToAB(p12Passphrase),
+            await withLinerEngine(async () => {
+              await (shroudedBag as unknown as { parseInternalValues(params: { password: ArrayBuffer }): Promise<void> }).parseInternalValues({
+                password: stringToAB(p12Passphrase),
+              });
             });
             if (shroudedBag.parsedValue) {
               privateKeyInfo = shroudedBag.parsedValue;

lib/smime/smime-decrypt.ts

@@ -8,6 +8,7 @@
 import * as pkijs from 'pkijs';
 import * as asn1js from 'asn1js';
 import type { SmimeKeyRecord } from './types';
+import { getLinerCryptoEngine } from './crypto-engine';
 
 export interface DecryptionInput {
   /** Raw CMS EnvelopedData bytes (DER) */
@@ -359,11 +360,8 @@ async function decryptWithKey(
   const certAsn1 = asn1js.fromBER(keyRecord.certificate);
   const cert = new pkijs.Certificate({ schema: certAsn1.result });
 
-  const cryptoEngine = new pkijs.CryptoEngine({
-    crypto: crypto,
-    subtle: crypto.subtle,
-    name: 'webcrypto',
-  });
+  // Use webcrypto-liner engine for legacy algorithm support (e.g. 3DES)
+  const cryptoEngine = getLinerCryptoEngine();
 
   const result = await envelopedData.decrypt(
     recipientIndex,