Android Overview

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The Android Open Source Project is a secure mobile operating system featuring strong app sandboxing, Verified Boot (AVB), and a robust permission control system.

Our Advice¶

Choosing an Android Distribution¶

When you buy an Android phone, the default operating system comes bundled with apps and functionality that are not part of the Android Open Source Project. Many of these apps—even apps like the dialer which provide basic system functionality—require invasive integrations with Google Play Services, which in turn asks for privileges to access your files, contacts storage, call logs, SMS messages, location, camera, microphone, and numerous other things on your device in order for those basic system apps and many other apps to function in the first place. Frameworks like Google Play Services increase the attack surface of your device and are the source of various privacy concerns with Android.

This problem could be solved by using a custom Android distribution that does not come with such invasive integration. Unfortunately, many custom Android distributions often violate the Android security model by not supporting critical security features such as AVB, rollback protection, firmware updates, and so on. Some distributions also ship userdebug builds which expose root via ADB and require more permissive SELinux policies to accommodate debugging features, resulting in a further increased attack surface and weakened security model.

Ideally, when choosing a custom Android distribution, you should make sure that it upholds the Android security model. At the very least, the distribution should have production builds, support for AVB, rollback protection, timely firmware and operating system updates, and SELinux in enforcing mode. All of our recommended Android distributions satisfy these criteria.

Our Android System Recommendations

Avoid Rooting¶

Rooting Android phones can decrease security significantly as it weakens the complete Android security model. This can decrease privacy should there be an exploit that is assisted by the decreased security. Common rooting methods involve directly tampering with the boot partition, making it impossible to perform successful Verified Boot. Apps that require root will also modify the system partition, meaning that Verified Boot would have to remain disabled. Having root exposed directly in the user interface also increases the attack surface of your device and may assist in privilege escalation vulnerabilities and SELinux policy bypasses.

Content blockers which modify the hosts file (AdAway) and firewalls (AFWall+) which require root access persistently are dangerous and should not be used. They are also not the correct way to solve their intended purposes. For content blocking, we suggest encrypted DNS or content blocking functionality provided by a VPN instead. TrackerControl and AdAway in non-root mode will take up the VPN slot (by using a local loopback VPN), preventing you from using privacy enhancing services such as Orbot or a real VPN provider.

AFWall+ works based on the packet filtering approach and may be bypassable in some situations.

We do not believe that the security sacrifices made by rooting a phone are worth the questionable privacy benefits of those apps.

Install Updates¶

It's important to not use an end-of-life version of Android. Newer versions of Android receive not only security updates for the operating system but also important privacy enhancing updates too.

For example, prior to Android 10 any apps with the READ_PHONE_STATE permission could access sensitive and unique serial numbers of your phone such as IMEI, MEID, or your SIM card's IMSI; whereas now they must be system apps to do so. System apps are only provided by the OEM or Android distribution.

You can avoid giving many apps permission to access your media with Android's built-in sharing features. Many applications allow you to "share" a file with them for media upload.

For example, if you want to post a picture to Discord you can open your file manager or gallery and share that picture with the Discord app, instead of granting Discord full access to your media and photos.

Security Protections¶

Verified Boot¶

Verified Boot is an important part of the Android security model. It provides protection against evil maid attacks, malware persistence, and ensures security updates cannot be downgraded with rollback protection.

Android 10 and above has moved away from full-disk encryption to more flexible file-based encryption. Your data is encrypted using unique encryption keys, and the operating system files are left unencrypted.

Verified Boot ensures the integrity of the operating system files, thereby preventing an adversary with physical access from tampering or installing malware on the device. In the unlikely case that malware is able to exploit other parts of the system and gain higher privileged access, Verified Boot will prevent and revert changes to the system partition upon rebooting the device.

Unfortunately, OEMs are only obliged to support Verified Boot on their stock Android distribution. Only a few OEMs such as Google support custom AVB key enrollment on their devices. Additionally, some AOSP derivatives such as LineageOS or /e/ OS do not support Verified Boot even on hardware with Verified Boot support for third-party operating systems. We recommend that you check for support before purchasing a new device. AOSP derivatives which do not support Verified Boot are not recommended.

Many OEMs also have broken implementation of Verified Boot that you have to be aware of beyond their marketing. For example, the Fairphone 3 and 4 are not secure by default, as the stock bootloader trusts the public AVB signing key. This breaks verified boot on a stock Fairphone device, as the system will boot alternative Android operating systems (such as /e/) without any warning about custom operating system usage.

Firmware Updates¶

Firmware updates are critical for maintaining security and without them your device cannot be secure. OEMs have support agreements with their partners to provide the closed-source components for a limited support period. These are detailed in the monthly Android Security Bulletins.

As the components of the phone, such as the processor and radio technologies rely on closed-source components, the updates must be provided by the respective manufacturers. Therefore, it is important that you purchase a device within an active support cycle. Qualcomm and Samsung support their devices for 4 years, while cheaper products often have shorter support cycles. With the introduction of the Pixel 6, Google now makes their own SoC, and they will provide a minimum of 5 years of support. With the introduction of the Pixel 8 series, Google increased that support window to 7 years.

EOL devices which are no longer supported by the SoC manufacturer cannot receive firmware updates from OEM vendors or after market Android distributors. This means that security issues with those devices will remain unfixed.

Fairphone, for example, markets their Fairphone 4 device as receiving 6 years of support. However, the SoC (Qualcomm Snapdragon 750G on the Fairphone 4) has a considerably shorter EOL date. This means that firmware security updates from Qualcomm for the Fairphone 4 will end in September 2023, regardless of whether Fairphone continues to release software security updates.

Android Permissions¶

Permissions on Android grant you control over what apps are allowed to access. Google regularly makes improvements on the permission system in each successive version. All apps you install are strictly sandboxed, therefore, there is no need to install any antivirus apps.

A smartphone with the latest version of Android will always be more secure than an old smartphone with an antivirus that you have paid for. It's better not to pay for antivirus software and to save money to buy a new smartphone such as a Google Pixel.

Android 10:

Scoped Storage gives you more control over your files and can limit what can access external storage. Apps can have a specific directory in external storage as well as the ability to store specific types of media there.
Tighter access on device location by introducing the ACCESS_BACKGROUND_LOCATION permission. This prevents apps from accessing the location when running in the background without express permission from the user.

Android 11:

One-time permissions which allows you to grant a permission to an app just once.
Auto-reset permissions, which resets runtime permissions that were granted when the app was opened.
Granular permissions for accessing phone number related features.

Android 12:

A permission to grant only the approximate location.
Auto-reset of hibernated apps.
Data access auditing which makes it easier to determine what part of an app is performing a specific type of data access.

Android 13:

A permission for nearby Wi-Fi access. The MAC addresses of nearby Wi-Fi access points were a popular way for apps to track a user's location.
More granular media permissions, meaning you can grant access to images, videos or audio files only.
Background use of sensors now requires the BODY_SENSORS permission.

An app may request a permission for a specific feature it has. For example, any app that can scan QR codes will require the camera permission. Some apps can request more permissions than they need.

Exodus can be useful when comparing apps that have similar purposes. If an app requires a lot of permissions and has a lot of advertising and analytics this is probably a bad sign. We recommend looking at the individual trackers and reading their descriptions rather than simply counting the total and assuming all items listed are equal.

Warning

If an app is mostly a web-based service, the tracking may occur on the server side. Facebook shows "no trackers" but certainly does track users' interests and behavior across the site. Apps may evade detection by not using standard code libraries produced by the advertising industry, though this is unlikely.

Note

Privacy-friendly apps such as Bitwarden may show some trackers such as Google Firebase Analytics. This library includes Firebase Cloud Messaging which can provide push notifications in apps. This is the case with Bitwarden. That doesn't mean that Bitwarden is using all of the analytics features that are provided by Google Firebase Analytics.

Privacy Features¶

User Profiles¶

Multiple user profiles can be found in Settings → System → Multiple users and are the simplest way to isolate in Android.

With user profiles, you can impose restrictions on a specific profile, such as: making calls, using SMS, or installing apps on the device. Each profile is encrypted using its own encryption key and cannot access the data of any other profiles. Even the device owner cannot view the data of other profiles without knowing their password. Multiple user profiles are a more secure method of isolation.

Work Profile¶

Work Profiles are another way to isolate individual apps and may be more convenient than separate user profiles.

A device controller app such as Shelter is required to create a Work Profile without an enterprise MDM, unless you're using a custom Android OS which includes one.

The work profile is dependent on a device controller to function. Features such as File Shuttle and contact search blocking or any kind of isolation features must be implemented by the controller. You must also fully trust the device controller app, as it has full access to your data inside the work profile.

This method is generally less secure than a secondary user profile; however, it does allow you the convenience of running apps in both the work and personal profiles simultaneously.

VPN Killswitch¶

Android 7 and above supports a VPN kill switch, and it is available without the need to install third-party apps. This feature can prevent leaks if the VPN is disconnected. It can be found in Settings → Network & internet → VPN → → Block connections without VPN.

Global Toggles¶

Modern Android devices have global toggles for disabling Bluetooth and location services. Android 12 introduced toggles for the camera and microphone. When not in use, we recommend disabling these features. Apps cannot use disabled features (even if granted individual permissions) until re-enabled.

Google Services¶

If you are using a device with Google services—whether with the stock operating system or an operating system that safely sandboxes Google Play Services like GrapheneOS—there are a number of additional changes you can make to improve your privacy. We still recommend avoiding Google services entirely, or limiting Google Play services to a specific user/work profile by combining a device controller like Shelter with GrapheneOS's Sandboxed Google Play.

Advanced Protection Program¶

If you have a Google account we suggest enrolling in the Advanced Protection Program. It is available at no cost to anyone with two or more hardware security keys with FIDO support.

The Advanced Protection Program provides enhanced threat monitoring and enables:

Stricter two-factor authentication; e.g. that FIDO must be used and disallows the use of SMS OTPs, TOTP and OAuth
Only Google and verified third-party apps can access account data
Scanning of incoming emails on Gmail accounts for phishing attempts
Stricter safe browser scanning with Google Chrome
Stricter recovery process for accounts with lost credentials

If you use non-sandboxed Google Play Services (common on stock operating systems), the Advanced Protection Program also comes with additional benefits such as:

Not allowing app installation outside the Google Play Store, the OS vendor's app store, or via adb
Mandatory automatic device scanning with Play Protect
Warning you about unverified applications

Google Play System Updates¶

In the past, Android security updates had to be shipped by the operating system vendor. Android has become more modular beginning with Android 10, and Google can push security updates for some system components via the privileged Play Services.

If you have an EOL device shipped with Android 10 or above and are unable to run any of our recommended operating systems on your device, you are likely going to be better off sticking with your OEM Android installation (as opposed to an operating system not listed here such as LineageOS or /e/ OS). This will allow you to receive some security fixes from Google, while not violating the Android security model by using an insecure Android derivative and increasing your attack surface. We would still recommend upgrading to a supported device as soon as possible.

Advertising ID¶

All devices with Google Play Services installed automatically generate an advertising ID used for targeted advertising. Disable this feature to limit the data collected about you.

On Android distributions with Sandboxed Google Play, go to Settings → Apps → Sandboxed Google Play → Google Settings → Ads, and select Delete advertising ID.

On Android distributions with privileged Google Play Services (such as stock OSes), the setting may be in one of several locations. Check

Settings → Google → Ads
Settings → Privacy → Ads

You will either be given the option to delete your advertising ID or to Opt out of interest-based ads (this varies between OEM distributions of Android). If presented with the option to delete the advertising ID, that is preferred. If not, then make sure to opt out and reset your advertising ID.

SafetyNet and Play Integrity API¶

SafetyNet and the Play Integrity APIs are generally used for banking apps. Many banking apps will work fine in GrapheneOS with sandboxed Play services, however some non-financial apps have their own crude anti-tampering mechanisms which might fail. GrapheneOS passes the basicIntegrity check, but not the certification check ctsProfileMatch. Devices with Android 8 or later have hardware attestation support which cannot be bypassed without leaked keys or serious vulnerabilities.

As for Google Wallet, we don't recommend this due to their privacy policy, which states you must opt out if you don't want your credit rating and personal information shared with affiliate marketing services.

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