2023年6月27日发(作者：)

android_id⽣成原理android_id 的⽣成原理是由系统⽣成的随机数，并与应⽤ app 签名，经过 HmacSHA256 算法⽣成的；从 android 8 以后开始就是随机的了，每个应⽤获取到的简要步骤；下⾯是追踪代码：2423 public Setting generateSsaidLocked(PackageInfo callingPkg, int userId) {2424 // Read the user's key from the ssaid table.2425 Setting userKeySetting = getSettingLocked(SETTINGS_TYPE_SSAID, userId, SSAID_USER_KEY);2426 if (userKeySetting == null || ()2427 || ue() == null) {2428 // Lazy initialize and store the user key.2429 generateUserKeyLocked(userId);2430 userKeySetting = getSettingLocked(SETTINGS_TYPE_SSAID, userId, SSAID_USER_KEY);2431 if (userKeySetting == null || ()2432 || ue() == null) {2433 throw new IllegalStateException("User key not accessible");2434 }2435 }2436 final String userKey = ue();2437

2438 // Convert the user's key back to a byte array.2439 final byte[] keyBytes = xToByteArray(userKey);2440

2441 // Validate that the key is of expected length.2442 // Keys are currently 32 bytes, but were once 16 bytes during Android O development.2443 if (keyBytes == null || ( != 16 && != 32)) {2444 throw new IllegalStateException("User key invalid");2445 }2446

2447 final Mac m;2448 try {2449 m = tance("HmacSHA256");2450 (new SecretKeySpec(keyBytes, orithm()));2451 } catch (NoSuchAlgorithmException e) {2452 throw new IllegalStateException("HmacSHA256 is not available", e);2453 } catch (InvalidKeyException e) {2454 throw new IllegalStateException("Key is corrupted", e);2455 }2456

2457 // Mac each of the developer signatures.2458 for (int i = 0; i < ; i++) {2459 byte[] sig = ures[i].toByteArray();2460 (getLengthPrefix(sig), 0, 4);2461 (sig);2462 }2463

2464 // Convert result to a string for storage in settings table. Only want first 64 bits.2465 final String ssaid = tring(l()).substring(0, 16)2466 .toLowerCase();追踪看写⼊代码：2724 public Setting getSettingLocked(int type, int userId, String name) {2725 final int key = makeKey(type, userId);2726

2727 SettingsState settingsState = peekSettingsStateLocked(key);2728 if (settingsState == null) {2729 return null;2730 }2731

2732 // getSettingLocked will return non-null result2733 return tingLocked(name);2734 } 2734 }

2860 @Nullable2861 private SettingsState peekSettingsStateLocked(int key) {2862 SettingsState settingsState = (key);2863 if (settingsState != null) {2864 return settingsState;2865 }2866

2867 if (!ensureSettingsForUserLocked(getUserIdFromKey(key))) {2868 return null;2869 }2870 return (key);2871 }2585 private void ensureSettingsStateLocked(int key) {2586 if ((key) == null) {2587 final int maxBytesPerPackage = getMaxBytesPerPackageForType(getTypeFromKey(key));2588 SettingsState settingsState = new SettingsState(getContext(), mLock,2589 getSettingsFile(key), key, maxBytesPerPackage, per());2590 (key, settingsState);2591 }2592 }252 public SettingsState(Context context, Object lock, File file, int key,253 int maxBytesPerAppPackage, Looper looper) {254 // It is important that we use the same lock as the settings provider255 // to ensure multiple mutations on this state are atomicaly persisted256 // as the async persistence should be blocked while we make changes.257 mContext = context;258 mLock = lock;259 mStatePersistFile = file;260 mStatePersistTag = "settings-" + getTypeFromKey(key) + "-" + getUserIdFromKey(key);261 mKey = key;262 mHandler = new MyHandler(looper);263 if (maxBytesPerAppPackage == MAX_BYTES_PER_APP_PACKAGE_LIMITED) {264 mMaxBytesPerAppPackage = maxBytesPerAppPackage;265 mPackageToMemoryUsage = new ArrayMap<>();266 } else {267 mMaxBytesPerAppPackage = maxBytesPerAppPackage;268 mPackageToMemoryUsage = null;269 }270

271 mHistoricalOperations = _DEBUGGABLE272 ? new ArrayList<>(HISTORICAL_OPERATION_COUNT) : null;273

274 synchronized (mLock) {275 readStateSyncLocked();276 }277 }跳到创建成功时，获取代码337 // The settings provider must hold its lock when calling here.338 @GuardedBy("mLock")339 public Setting getSettingLocked(String name) {340 if (y(name)) {341 return mNullSetting;342 }343 Setting setting = (name);344 if (setting != null) {345 return new Setting(setting);346 }347 return mNullSetting;348 }157 @GuardedBy("mLock")157 @GuardedBy("mLock")158 private final ArrayMap mSettings = new ArrayMap<>();新 setting 元素来⾃于新的插⼊；384 // The settings provider must hold its lock when calling here.385 @GuardedBy("mLock")386 public boolean insertSettingLocked(String name, String value, String tag,387 boolean makeDefault, boolean forceNonSystemPackage, String packageName) {388 if (y(name)) {389 return false;390 }391

392 Setting oldState = (name);393 String oldValue = (oldState != null) ? : null;394 String oldDefaultValue = (oldState != null) ? tValue : null;395 Setting newState;396

397 if (oldState != null) {398 if (!(value, makeDefault, packageName, tag, forceNonSystemPackage)) {399 return false;400 }401 newState = oldState;402 } else {403 newState = new Setting(name, value, makeDefault, packageName, tag);404 (name, newState);3602 if (currentVersion == 136) {3603 // Version 136: Store legacy SSAID for all apps currently installed on the3604 // device as first step in migrating SSAID to be unique per application.3605

3606 final boolean isUpgrade;3607 try {3608 isUpgrade = ceUpgrading();3609 } catch (RemoteException e) {3610 throw new IllegalStateException("Package manager not available");3611 }3612 // Only retain legacy ssaid if the device is performing an OTA. After wiping3613 // user data or first boot on a new device should use new ssaid generation.3614 if (isUpgrade) {3615 // Retrieve the legacy ssaid from the secure settings table.3616 final Setting legacySsaidSetting = getSettingLocked(SETTINGS_TYPE_SECURE,3617 userId, D_ID);3618 if (legacySsaidSetting == null || ()3619 || ue() == null) {3620 throw new IllegalStateException("Legacy ssaid not accessible");3621 }3622 final String legacySsaid = ue();3623

3624 // Fill each uid with the legacy ssaid to be backwards compatible.3625 final List packages;3626 try {3627 packages = talledPackages(3628 _UNINSTALLED_PACKAGES,3629 userId).getList();3630 } catch (RemoteException e) {3631 throw new IllegalStateException("Package manager not available");3632 }3633

3634 final SettingsState ssaidSettings = getSsaidSettingsLocked(userId);3635 for (PackageInfo info : packages) {3636 // Check if the UID already has an entry in the table.3637 final String uid = ng();3638 final Setting ssaid = tingLocked(uid); // 这⾥呢？3639

3640 if (() || ue() == null) {3641 // Android Id doesn't exist for this package so create it.3642 SettingLocked(uid, legacySsaid, null, true,3643 eName);3644 if (DEBUG) {3645 Slog.d(LOG_TAG, "Keep the legacy ssaid for uid=" + uid);3645 Slog.d(LOG_TAG, "Keep the legacy ssaid for uid=" + uid);3646 }3647 }3648 }3649 }3650

3651 currentVersion = 137;这个插⼊代码？/android-10.0.0_r2/xref/frameworks/base/packages/SettingsProvider/src/com/android/providers/settings/#24003002 @GuardedBy("")3003 private void ensureSecureSettingAndroidIdSetLocked(SettingsState secureSettings) {3004 Setting value = tingLocked(D_ID);3005

3006 if (!()) {3007 return;3008 }3009

3010 final int userId = getUserIdFromKey();3011

3012 final UserInfo user;3013 final long identity = allingIdentity();3014 try {3015 user = rInfo(userId);3016 } finally {3017 eCallingIdentity(identity);3018 }3019 if (user == null) {3020 // Can happen due to races when deleting users - treat as benign.3021 return;3022 }3023

3024 String androidId = tring(new SecureRandom().nextLong()); // 这⾥就是了3025 SettingLocked(D_ID, androidId,3026 null, true, _PACKAGE_NAME);3027

3028 Slog.d(LOG_TAG, "Generated and saved new ANDROID_ID [" + androidId3029 + "] for user " + userId);3030

3031 // Write a drop box entry if it's a restricted profile3032 if (ricted()) {3033 DropBoxManager dbm = (DropBoxManager) getContext().getSystemService(3034 X_SERVICE);3035 if (dbm != null && nabled(DROPBOX_TAG_USERLOG)) {3036 t(DROPBOX_TAG_USERLOG, tTimeMillis()3037 + "," + DROPBOX_TAG_USERLOG + "," + androidId + "n");3038 }3039 }3040 }2400 private void generateUserKeyLocked(int userId) {2401 // Generate a random key for each user used for creating a new ssaid.2402 final byte[] keyBytes = new byte[32];2403 final SecureRandom rand = new SecureRandom();2404 tes(keyBytes);2405

2406 // Convert to string for storage in settings table.2407 final String userKey = tring(keyBytes);2408

2409 // Store the key in the ssaid table.2410 final SettingsState ssaidSettings = getSettingsLocked(SETTINGS_TYPE_SSAID, userId);2411 final boolean success = SettingLocked(SSAID_USER_KEY, userKey, null, //这个 userkey 就是 value2412 true, _PACKAGE_NAME);2413

2414 if (!success) {2415 throw new IllegalStateException("Ssaid settings not accessible");2415 throw new IllegalStateException("Ssaid settings not accessible");2416 }2417 }1417 // Retrieve the ssaid from the table if present.1418 final Setting ssaid = tingLocked(SETTINGS_TYPE_SSAID, owningUserId,1419 name);1420 // If the app is an Instant App use its stored SSAID instead of our own.1421 final String instantSsaid;1422 final long token = allingIdentity();1423 try {1424 instantSsaid = tantAppAndroidId(eName, // 这个就是 value ,怎么通过 intent 传递到的呢？1425 owningUserId);1426 } catch (RemoteException e) {1427 Slog.e(LOG_TAG, "Failed to get Instant App Android ID", e);1428 return null;1429 } finally {1430 eCallingIdentity(token);1431 }1432

1433 final SettingsState ssaidSettings = tingsLocked(1434 SETTINGS_TYPE_SSAID, owningUserId);1435

1436 if (instantSsaid != null) {1437 // Use the stored value if it is still valid.1438 if (ssaid != null && (ue())) {1439 return mascaradeSsaidSetting(ssaidSettings, ssaid);1440 }1441 // The value has changed, update the stored value.1442 final boolean success = SettingLocked(name, instantSsaid, null,1443 true, eName);1444 if (!success) {