security(crypto): make content-encryption keys non-extractable by default (#1691)

src/services/crypto/__tests__/content-key.test.ts

@@ -0,0 +1,30 @@
+import { generateContentKey } from "../content-key";
+
+describe("Content Key Security - Non-extractable default (#1691)", () => {
+  it("should generate content-encryption keys as non-extractable by default", async () => {
+    const key = await generateContentKey();
+
+    expect(key).toBeDefined();
+    expect(key.extractable).toBe(false);
+    expect(key.usages).toEqual(expect.arrayContaining(["encrypt", "decrypt"]));
+  });
+
+  it("should fail when attempting to export a default non-extractable key", async () => {
+    const key = await generateContentKey();
+
+    // Exporting non-extractable key should reject in Web Crypto API
+    await expect(crypto.subtle.exportKey("raw", key)).rejects.toThrow();
+  });
+
+  it("should allow encrypt and decrypt operations with non-extractable key", async () => {
+    const key = await generateContentKey();
+    const iv = crypto.getRandomValues(new Uint8Array(12));
+    const data = new TextEncoder().encode("Hello, Stealth Mail!");
+
+    const encrypted = await crypto.subtle.encrypt({ name: "AES-GCM", iv }, key, data);
+
+    const decrypted = await crypto.subtle.decrypt({ name: "AES-GCM", iv }, key, encrypted);
+
+    expect(new TextDecoder().decode(decrypted)).toBe("Hello, Stealth Mail!");
+  });
+});

src/services/crypto/content-key.ts

@@ -0,0 +1,53 @@
+export interface ContentKeyOptions {
+  length?: 128 | 192 | 256;
+  /**
+   * Whether the key can be exported using exportKey.
+   * Defaults to false for security hardening (Issue #1691).
+   */
+  extractable?: boolean;
+  usages?: KeyUsage[];
+}
+
+/**
+ * Generates an AES-GCM content-encryption key.
+ * By default, keys are non-extractable (`extractable: false`).
+ */
+export async function generateContentKey(options: ContentKeyOptions = {}): Promise<CryptoKey> {
+  const {
+    length = 256,
+    extractable = false, // Enforce non-extractable by default
+    usages = ["encrypt", "decrypt"],
+  } = options;
+
+  return await crypto.subtle.generateKey(
+    {
+      name: "AES-GCM",
+      length,
+    },
+    extractable,
+    usages,
+  );
+}
+
+/**
+ * Seals content into an envelope by encrypting payload data with a non-extractable AES key
+ * and wrapping the content key for the intended recipient.
+ */
+export async function sealEnvelope(
+  payload: Uint8Array,
+  recipientPublicKey: CryptoKey,
+): Promise<{ encryptedData: ArrayBuffer; wrappedKey: ArrayBuffer; iv: Uint8Array }> {
+  // Generate non-extractable content key within the wrapping boundary
+  const contentKey = await generateContentKey({ extractable: false });
+  const iv = crypto.getRandomValues(new Uint8Array(12));
+
+  // Encrypt payload using non-extractable key
+  const encryptedData = await crypto.subtle.encrypt({ name: "AES-GCM", iv }, contentKey, payload);
+
+  // Wrap key within the boundary using Web Crypto wrapKey
+  const wrappedKey = await crypto.subtle.wrapKey("raw", contentKey, recipientPublicKey, {
+    name: "RSA-OAEP",
+  });
+
+  return { encryptedData, wrappedKey, iv };
+}