fix: support PHP encryption format for TOTP secrets

PHP uses base64(nonce+ciphertext+tag), TS was using hex:hex:hex.
decrypt() now auto-detects the format. encrypt() now outputs
PHP-compatible base64 format for cross-compatibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/encryption.ts

@@ -10,18 +10,20 @@ export function encrypt(plaintext: string): string {
   const iv = crypto.randomBytes(IV_LENGTH);
   const cipher = crypto.createCipheriv(ALGORITHM, key, iv);
 
-  let encrypted = cipher.update(plaintext, 'utf8', 'hex');
+  const encrypted = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()]);
-  encrypted += cipher.final('hex');
   const tag = cipher.getAuthTag();
 
-  return iv.toString('hex') + ':' + encrypted + ':' + tag.toString('hex');
+  // Use PHP-compatible format: base64(nonce + ciphertext + tag)
+  return Buffer.concat([iv, encrypted, tag]).toString('base64');
 }
 
 export function decrypt(ciphertext: string): string {
   const key = Buffer.from(config.totp.encryptionKey, 'hex');
-  const parts = ciphertext.split(':');
-  if (parts.length !== 3) throw new Error('Invalid ciphertext format');
 
+  // Detect format: PHP uses base64(nonce+ciphertext+tag), TS uses hex:hex:hex
+  const parts = ciphertext.split(':');
+  if (parts.length === 3) {
+    // TS format: iv:encrypted:tag (hex)
     const iv = Buffer.from(parts[0], 'hex');
     const encrypted = parts[1];
     const tag = Buffer.from(parts[2], 'hex');
@@ -32,4 +34,22 @@ export function decrypt(ciphertext: string): string {
     let decrypted = decipher.update(encrypted, 'hex', 'utf8');
     decrypted += decipher.final('utf8');
     return decrypted;
+  }
+
+  // PHP format: base64(nonce + ciphertext + tag)
+  const raw = Buffer.from(ciphertext, 'base64');
+  if (raw.length < IV_LENGTH + TAG_LENGTH + 1) {
+    throw new Error('Invalid ciphertext format');
+  }
+
+  const iv = raw.subarray(0, IV_LENGTH);
+  const tag = raw.subarray(raw.length - TAG_LENGTH);
+  const encrypted = raw.subarray(IV_LENGTH, raw.length - TAG_LENGTH);
+
+  const decipher = crypto.createDecipheriv(ALGORITHM, key, iv);
+  decipher.setAuthTag(tag);
+
+  let decrypted = decipher.update(encrypted);
+  const final = decipher.final();
+  return Buffer.concat([decrypted, final]).toString('utf8');
 }