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Google Online Security Blog: December 2018
Security Blog
The latest news and insights from Google on security and safety on the Internet
Android Pie à la mode: Security & Privacy
December 20, 2018
Posted by Vikrant Nanda and René Mayrhofer, Android Security & Privacy Team
[Cross-posted from the
Android Developers Blog
]
There is no better time to talk about Android dessert releases than the holidays because who doesn't love dessert? And what is one of our favorite desserts during the holiday season? Well, pie of course.
In all seriousness, pie is a great analogy because of how the various ingredients turn into multiple layers of goodness: right from the software crust on top to the hardware layer at the bottom. Read on for a summary of security and privacy features introduced in Android Pie this year.
Platform hardening
With Android Pie, we updated
File-Based Encryption
to support external storage media (such as, expandable storage cards). We also introduced support for
metadata encryption
where hardware support is present. With filesystem metadata encryption, a single key present at boot time encrypts whatever content is not encrypted by file-based encryption (such as, directory layouts, file sizes, permissions, and creation/modification times).
Android Pie also introduced a
BiometricPrompt API
that apps can use to provide biometric authentication dialogs (such as, fingerprint prompt) on a device in a modality-agnostic fashion. This functionality creates a standardized look, feel, and placement for the dialog. This kind of standardization gives users more confidence that they're authenticating against a trusted biometric credential checker.
New protections and test cases for the
Application Sandbox
help ensure all non-privileged apps targeting Android Pie (and all future releases of Android) run in stronger
SE
linux
sandboxes. By providing per-app cryptographic authentication to the sandbox, this protection improves app separation, prevents overriding safe defaults, and (most significantly) prevents apps from making their data widely accessible.
Anti-exploitation improvements
With Android Pie, we expanded our
compiler-based security mitigations
, which instrument runtime operations to fail safely when undefined behavior occurs.
Control Flow Integrity (CFI)
is a security mechanism that disallows changes to the original control flow graph of compiled code. In Android Pie, it has been enabled by default within the media frameworks and other security-critical components, such as for Near Field Communication (NFC) and Bluetooth protocols. We also implemented support for
CFI in the Android common kernel
, continuing our efforts to harden the kernel in previous Android releases.
Integer Overflow Sanitization
is a security technique used to mitigate memory corruption and information disclosure vulnerabilities caused by integer operations. We've expanded our use of Integer Overflow sanitizers by enabling their use in libraries where complex untrusted input is processed or where security vulnerabilities have been reported.
Continued investment in hardware-backed security
One of the highlights of Android Pie is
Android Protected Confirmation
, the first major mobile OS API that leverages a hardware-protected user interface (Trusted UI) to perform critical transactions completely outside the main mobile operating system. Developers can use this API to display a trusted UI prompt to the user, requesting approval via a physical protected input (such as, a button on the device). The resulting cryptographically signed statement allows the relying party to reaffirm that the user would like to complete a sensitive transaction through their app.
We also introduced support for a new Keystore type that provides stronger protection for private keys by leveraging tamper-resistant hardware with dedicated CPU, RAM, and flash memory.
StrongBox Keymaster
is an implementation of the Keymaster hardware abstraction layer (HAL) that resides in a hardware security module. This module is designed and required to have its own processor, secure storage, True Random Number Generator (TRNG), side-channel resistance, and tamper-resistant packaging.
Other Keystore features (as part of Keymaster 4) include Keyguard-bound keys, Secure Key Import, 3DES support, and version binding. Keyguard-bound keys enable use restriction so as to protect sensitive information. Secure Key Import facilitates secure key use while protecting key material from the application or operating system. You can read more about these features in our recent
blog post
as well as the accompanying
release notes
.
Enhancing user privacy
User privacy has been boosted with several
behavior changes
, such as limiting the access background apps have to the camera, microphone, and device sensors. New permission rules and permission groups have been created for phone calls, phone state, and Wi-Fi scans, as well as restrictions around information retrieved from Wi-Fi scans. We have also added associated
MAC address randomization
, so that a device can use a different network address when connecting to a Wi-Fi network.
On top of that, Android Pie added support for encrypting Android backups with the user's screen lock secret (that is, PIN, pattern, or password). By design, this means that
an attacker would not be able to access a user's backed-up application data
without specifically knowing their passcode. Auto backup for apps has been enhanced by providing developers a way to specify conditions under which their app's data is excluded from auto backup. For example, Android Pie introduces a new flag to determine whether a user's backup is client-side encrypted.
As part of a larger effort to move all web traffic away from cleartext (unencrypted HTTP) and towards being secured with TLS (HTTPS), we changed the defaults for Network Security Configuration to block all cleartext traffic. We're protecting users with
TLS by default
, unless you explicitly opt-in to cleartext for specific domains. Android Pie also adds built-in support for
DNS over TLS
, automatically upgrading DNS queries to TLS if a network's DNS server supports it. This protects information about IP addresses visited from being sniffed or intercepted on the network level.
We believe that the features described in this post advance the security and privacy posture of Android, but you don't have to take our word for it. Year after year our continued efforts are demonstrably resulting in better protection as evidenced by
increasing exploit difficulty
and
independent mobile security ratings
. Now go and enjoy some actual pie while we get back to preparing the next Android dessert release!
Making Android more secure requires a combination of hardening the platform and advancing anti-exploitation techniques.
Acknowledgements: This post leveraged contributions from Chad Brubaker, Janis Danisevskis, Giles Hogben, Troy Kensinger, Ivan Lozano, Vishwath Mohan, Frank Salim, Sami Tolvanen, Lilian Young, and Shawn Willden.
New Keystore features keep your slice of Android Pie a little safer
December 12, 2018
Posted by Lilian Young and Shawn Willden, Android Security; and Frank Salim, Google Pay
[Cross-posted from the
Android Developers Blog
]
New Android Pie Keystore Features
The Android
Keystore
provides application developers with a set of cryptographic tools that are designed to secure their users' data. Keystore moves the cryptographic primitives available in software libraries out of the Android OS and into secure hardware. Keys are protected and used only within the secure hardware to protect application secrets from various forms of attacks. Keystore gives applications the ability to specify restrictions on how and when the keys can be used.
Android Pie introduces new capabilities to Keystore. We will be discussing two of these new capabilities in this post. The first enables restrictions on key use so as to protect sensitive information. The second facilitates secure key use while protecting key material from the application or operating system.
Keyguard-bound keys
There are times when a mobile application receives data but doesn't need to immediately access it if the user is not currently using the device. Sensitive information sent to an application while the device screen is locked must remain secure until the user wants access to it. Android Pie addresses this by introducing keyguard-bound cryptographic keys. When the screen is locked, these keys can be used in encryption or verification operations, but are unavailable for decryption or signing. If the device is currently locked with a PIN, pattern, or password, any attempt to use these keys will result in an invalid operation. Keyguard-bound keys protect the user's data while the device is locked, and only available when the user needs it.
Keyguard binding and authentication binding both function in similar ways, except with one important difference. Keyguard binding ties the availability of keys directly to the screen lock state while authentication binding uses a constant timeout. With keyguard binding, the keys become unavailable as soon as the device is locked and are only made available again when the user unlocks the device.
It is worth noting that keyguard binding is enforced by the operating system, not the secure hardware. This is because the secure hardware has no way to know when the screen is locked. Hardware-enforced Android Keystore protection features like authentication binding, can be combined with keyguard binding for a higher level of security. Furthermore, since keyguard binding is an operating system feature, it's available to any device running Android Pie.
Keys for any algorithm supported by the device can be keyguard-bound. To generate or import a key as keyguard-bound, call
setUnlockedDeviceRequired(true)
on the
KeyGenParameterSpec
or
KeyProtection
builder object at key generation or import.
Secure Key Import
Secure Key Import is a new feature in Android Pie that allows applications to provision existing keys into Keystore in a more secure manner. The origin of the key, a remote server that could be sitting in an on-premise data center or in the cloud, encrypts the secure key using a public wrapping key from the user's device. The encrypted key in the
SecureKeyWrapper
format, which also contains a description of the ways the imported key is allowed to be used, can only be decrypted in the Keystore hardware belonging to the specific device that generated the wrapping key. Keys are encrypted in transit and remain opaque to the application and operating system, meaning they're only available inside the secure hardware into which they are imported.
Secure Key Import is useful in scenarios where an application intends to share a secret key with an Android device, but wants to prevent the key from being intercepted or from leaving the device. Google Pay uses Secure Key Import to provision some keys on Pixel 3 phones, to prevent the keys from being intercepted or extracted from memory. There are also a variety of enterprise use cases such as S/MIME encryption keys being recovered from a Certificate Authorities escrow so that the same key can be used to decrypt emails on multiple devices.
To take advantage of this feature, please review
this training article
. Please note that Secure Key Import is a secure hardware feature, and is therefore only available on select Android Pie devices. To find out if the device supports it, applications can generate a KeyPair with
PURPOSE_WRAP_KEY
.
Tackling ads abuse in apps and SDKs
December 7, 2018
Posted by Dave Kleidermacher, VP, Head of Security & Privacy - Android & Play
Providing users with safe and secure experiences, while helping developers build and grow quality app businesses, is our top priority at Google Play. And we’re
constantly working
to improve our protections.
Google Play has been working to minimize app install attribution fraud for several years. In 2017 Google Play made available the
Google Play Install Referrer API
, which allows ad attribution providers, publishers and advertisers to determine which referrer was responsible for sending the user to Google Play for a given app install. This API was specifically designed to be resistant to install attribution fraud and we strongly encourage attribution providers, advertisers and publishers to insist on this standard of proof when measuring app install ads. Users, developers, advertisers and ad networks all benefit from a transparent, fair system.
We also take reports of questionable activity very seriously. If an app violates our
Google Play Developer policies
, we take action. That’s why we began our own independent investigation after we received reports of apps on Google Play accused of conducting app install attribution abuse by falsely claiming credit for newly installed apps to collect the download bounty from that app’s developer.
We now have an update regarding our ongoing investigation:
On Monday, we removed two apps from the Play Store because our investigation discovered evidence of app install attribution abuse.
We also discovered evidence of app install attribution abuse in 3 ad network SDKs. We have asked the impacted developers to remove those SDKs from their apps. Because we believe most of these developers were not aware of the behavior from these third-party SDKs, we have given them a short grace period to take action.
Google Ads SDKs were not utilized for any of the abusive behaviors mentioned above.
Our investigation is ongoing and additional reviews of other apps and third party SDKs are still underway. If we find evidence of additional policy violations, we will take action.
We will continue to investigate and improve our capabilities to better detect and protect against abusive behavior and the malicious actors behind them.
ASPIRE to keep protecting billions of Android users
December 5, 2018
Posted by Billy Lau and René Mayrhofer, Android Security & Privacy Team
Customization is one of Android's greatest strengths. Android's open source nature has enabled thousands of device types that cover a variety of use cases. In addition to adding features to the Android Open Source Project, researchers, developers, service providers, and device and chipset manufacturers can make updates to improve Android security. Investing and engaging in academic research advances the state-of-the-art security techniques, contributes to science, and delivers cutting edge security and privacy features into the hands of end users. To foster more cooperative applied research between the
Android Security and Privacy team
and the wider academic and industrial community, we're launching ASPIRE (
A
ndroid
S
ecurity and
P
r
I
vacy
RE
search).
ASPIRE's goal is encouraging the development of new security and privacy technology that impacts the Android ecosystem in the next 2 to 5 years, but isn't planned for mainline Android development. This timeframe extends beyond the next annual Android release to allow adequate time to analyze, develop, and stabilize research into features before including in the platform. To collaborate with security researchers, we're hosting events and creating more channels to contribute research.
On October 25th 2018, we invited top security and privacy researchers from around the world to present at Android Security Local Research Day (ASLR-D). At this event, external researchers and Android Security and Privacy team members discussed current issues and strategies that impact the future direction of security research—for Android and the entire industry.
We can't always get everyone in the same room and good ideas come from everywhere. So we're inviting all academic researchers to help us protect billions of users. Research collaborations with Android should be as straightforward as collaborating with the research lab next door. To get involved you can:
Submit an Android security / privacy research idea or proposal to the
Google Faculty Research Awards (FRA)
program.
Apply for a
research internship
as a student pursuing an advanced degree.
Apply to become a
Visiting Researcher
at Google.
If you have any security or privacy questions that may help with your research, reach out to us.
Co-author publications with Android team members, outside the terms of FRA.
Collaborate with Android team members to make changes to the Android Open Source Project.
Let’s work together to make Android the most secure platform—now and in the future.
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