feat(keys): persist BIP-32 wallet material

src/lnurlcash/passwordWrap.ts

@@ -0,0 +1,63 @@
+// Password wraps protect serialized wallet secrets with authenticated AES-GCM.
+// PBKDF2 parameters and wire fields stay centralized so legacy linking-key and
+// v2 wallet-material records remain interoperable with their own readers.
+
+import {bytesToHex, hexToBytes, utf8ToBytes} from '@noble/hashes/utils.js'
+
+const PBKDF2_ITERATIONS = 210_000
+
+const deriveAesKeyFromPassword = (password: string, salt: Uint8Array): Promise<CryptoKey> =>
+  crypto.subtle
+    .importKey('raw', utf8ToBytes(password), 'PBKDF2', false, ['deriveKey'])
+    .then((baseKey) =>
+      crypto.subtle.deriveKey(
+        {
+          name: 'PBKDF2',
+          salt: new Uint8Array(salt),
+          iterations: PBKDF2_ITERATIONS,
+          hash: 'SHA-256',
+        },
+        baseKey,
+        {name: 'AES-GCM', length: 256},
+        false,
+        ['encrypt', 'decrypt'],
+      ),
+    )
+
+export type EncryptedSecretParts = {
+  readonly salt: string
+  readonly iv: string
+  readonly ciphertext: string
+}
+
+export const encryptSecretParts = async (
+  value: string,
+  password: string,
+): Promise<EncryptedSecretParts> => {
+  const salt = crypto.getRandomValues(new Uint8Array(16))
+  const iv = crypto.getRandomValues(new Uint8Array(12))
+  const aesKey = await deriveAesKeyFromPassword(password, salt)
+  const ciphertext = new Uint8Array(
+    await crypto.subtle.encrypt({name: 'AES-GCM', iv}, aesKey, utf8ToBytes(value)),
+  )
+  return {
+    salt: bytesToHex(salt),
+    iv: bytesToHex(iv),
+    ciphertext: bytesToHex(ciphertext),
+  }
+}
+
+export const decryptSecretParts = async (
+  parts: EncryptedSecretParts,
+  password: string,
+): Promise<string> => {
+  const salt = hexToBytes(parts.salt)
+  const iv = hexToBytes(parts.iv)
+  const aesKey = await deriveAesKeyFromPassword(password, salt)
+  const plaintext = await crypto.subtle.decrypt(
+    {name: 'AES-GCM', iv},
+    aesKey,
+    hexToBytes(parts.ciphertext),
+  )
+  return new TextDecoder().decode(plaintext)
+}