Tag Archives: app security

Evolving the App Defense Alliance

The App Defense Alliance (ADA), an industry-leading collaboration launched by Google in 2019 dedicated to ensuring the safety of the app ecosystem, is taking a major step forward. We are proud to announce that the App Defense Alliance is moving under the umbrella of the Linux Foundation, with Meta, Microsoft, and Google as founding steering members.

This strategic migration represents a pivotal moment in the Alliance’s journey, signifying a shared commitment by the members to strengthen app security and related standards across ecosystems. This evolution of the App Defense Alliance will enable us to foster more collaborative implementation of industry standards for app security.

Uniting for App Security

The digital landscape is continually evolving, and so are the threats to user security. With the ever-increasing complexity of mobile apps and the growing importance of data protection, now is the perfect time for this transition. The Linux Foundation is renowned for its dedication to fostering open-source projects that drive innovation, security, and sustainability. By combining forces with additional members under the Linux Foundation, we can adapt and respond more effectively to emerging challenges.

The commitment of the newly structured App Defense Alliance’s founding steering members – Meta, Microsoft, and Google – is pivotal in making this transition a reality. With a member community spanning an additional 16 General and Contributor Members, the Alliance will support industry-wide adoption of app security best practices and guidelines, as well as countermeasures against emerging security risks.

Continuing the Malware Mitigation Program

The App Defense Alliance was formed with the mission of reducing the risk of app-based malware and better protecting Android users. Malware defense remains an important focus for Google and Android, and we will continue to partner closely with the Malware Mitigation Program members – ESET, Lookout, McAfee, Trend Micro, Zimperium – on direct signal sharing. The migration of ADA under the Linux Foundation will enable broader threat intelligence sharing across leading ecosystem partners and researchers.

Looking Ahead and Connecting With the ADA

We invite you to stay connected with the newly structured App Defense Alliance under the Linux foundation umbrella. Join the conversation to help make apps more secure. Together with the steering committee, alliance partners, and the broader ecosystem, we look forward to building more secure and trustworthy app ecosystems.

Expanding the App Defense Alliance

The App Defense Alliance launched in 2019 with a mission to protect Android users from bad apps through shared intelligence and coordinated detection between alliance partners. Earlier this year, the App Defense Alliance expanded to include new initiatives outside of malware detection and is now the home for several industry-led collaborations including Malware Mitigation, MASA (Mobile App Security Assessment) & CASA (Cloud App Security Assessment). With a new dedicated landing page at appdefensealliance.dev, the ADA has an expanded mission to protect Android users by removing threats while improving app quality across the ecosystem. Let’s walk through some of the latest program updates from the past year, including the addition of new ADA members.

Malware Mitigation

Together, with the founding ADA members - Google, ESET, Lookout, and Zimperium, the alliance has been able to reduce the risk of app-based malware and better protect Android users. These partners have access to mobile apps as they are being submitted to the Google Play Store and scan thousands of apps daily, acting as another, vital set of eyes prior to an app going live on Play. Knowledge sharing and industry collaboration are important aspects in securing the world from attacks and that’s why we’re continuing to invest in the program.

New ADA Members

We’re excited to see the ADA expand with the additions of McAfee and Trend Micro. Both McAfee and Trend Micro are leaders in the antivirus space and we look forward to their contributions to the program.

Mobile App Security Assessment (MASA)

With consumers spending four to five hours per day in mobile apps, ensuring the safety of these services is more important than ever. According to Data.ai, the pandemic accelerated existing mobile habits - with app categories like finance growing 25% YoY and users spending over 100 billion hours in shopping apps.

That’s why the ADA introduced MASA (Mobile App Security Assessment), which allows developers to have their apps independently validated against the Mobile Application Security Verification Standard (MASVS standard) under the OWASP Mobile Application Security project. The project’s mission is to “Define the industry standard for mobile application security,” and has been used by both public and private sector organizations as a form of industry best practices when it comes to mobile application security. Developers can work directly with an ADA Authorized Lab to have their apps evaluated against a set of MASVS L1 requirements. Once successful, the app’s validation is listed in the recently launched App Validation Directory, which provides users a single place to view all app validations. The Directory also allows users to access more assessment details including validation date, test lab, and a report showing all test steps and requirements. The Directory will be updated over time with new features and search functionality to make it more user friendly.

The Google Play Store is the first commercial app store to recognize and display a badge for any app that has completed an independent security review through ADA MASA. The badge is displayed within an app’s respective Data Safety section.

This MASA program launched in beta earlier this year and is now available for all developers. We’ve seen strong early developer interest with leading apps across a diverse set of categories completing validation including Roblox, Uber, PayPal, Threema, Google Photos, YouTube and many more. On average, developers have completed validation within a month and resolved two outstanding issues identified by a security lab.

To learn more about the program and to help developers get started, there’s a Play Academy course dedicated to independent security review. Check out the interactive guidance on the Academy for App Success and get started today!

Cloud App Security Assessment (CASA)

As the industry continues to evolve and software connects more systems through complex cloud-to-cloud integrations, focusing on the security of cloud applications and their supporting infrastructure becomes increasingly critical. CASA (Cloud App Security Assessment) leverages the work set forth in OWASP’s Application Security Verification Standard ASVS to provide a consistent set of requirements to harden security for any application. The CASA framework provides multiple assurance levels in which low-risk cloud applications can be evaluated using either a self assessment or automated scan. For applications which present higher risk (such as a large user base, recent security breach, or processes highly sensitive data), an Authorized Lab may perform an assessment.

Further, the CASA accelerator provides developers with a workflow that minimizes the required checks depending on the developer's current valid certifications. The CASA checks have been mapped to 10 certifications and frameworks which eliminate redundant testing while lowering the cost of the assessment. Google is continuing to invest in this space with plans to use ASVS more proactively with the developer community next year.

It's been amazing to see the ADA grow this year and we are excited for the continued progress and expansion around the alliance’s mission.

Boost the security of your app with the nonce field of the Play Integrity API

Posted by Oscar Rodriguez, Developer Relations Engineer

illustration with a mobile device displaying a security shield with a check mark, flow chart imagery, and Android logo

With the recent launch of the Play Integrity API, more developers are now taking action to protect their games and apps from potentially risky and fraudulent interactions.

In addition to useful signals on the integrity of the app, the integrity of the device, and licensing information, the Play Integrity API features a simple, yet very useful feature called “nonce” that, when correctly used, can further strengthen the existing protections the Play Integrity API offers, as well as mitigate certain types of attacks, such as person-in-the-middle (PITM) tampering attacks, and replay attacks.

In this blog post, we will take a deeper look at what the nonce is, how it works, and how it can be used to further protect your app.

What is a nonce?

In cryptography and security engineering, a nonce (number once) is a number that is used only once in a secure communication. There are many applications for nonces, such as in authentication, encryption and hashing.

In the Play Integrity API, the nonce is an opaque base-64 encoded binary blob that you set before invoking the API integrity check, and it will be returned as-is inside the signed response of the API. Depending on how you create and validate the nonce, it is possible to leverage it to further strengthen the existing protections the Play Integrity API offers, as well as mitigate certain types of attacks, such as person-in-the-middle (PITM) tampering attacks, and replay attacks.

Apart from returning the nonce as-is in the signed response, the Play Integrity API doesn’t perform any processing of the actual nonce data, so as long as it is a valid base-64 value, you can set any arbitrary value. That said, in order to digitally sign the response, the nonce is sent to Google’s servers, so it is very important not to set the nonce to any type of personally identifiable information (PII), such as the user’s name, phone or email address.

Setting the nonce

After having set up your app to use the Play Integrity API, you set the nonce with the setNonce() method, or its appropriate variant, available in the Kotlin, Java, Unity, and Native versions of the API.


val nonce: String = ...

// Create an instance of a manager.
val integrityManager =

// Request the integrity token by providing a nonce.
val integrityTokenResponse: Task<IntegrityTokenResponse> =
             .setNonce(nonce) // Set the nonce


String nonce = ...

// Create an instance of a manager.
IntegrityManager integrityManager =

// Request the integrity token by providing a nonce.
Task<IntegrityTokenResponse> integrityTokenResponse =
            .setNonce(nonce) // Set the nonce


string nonce = ...

// Create an instance of a manager.
var integrityManager = new IntegrityManager();

// Request the integrity token by providing a nonce.
var tokenRequest = new IntegrityTokenRequest(nonce);
var requestIntegrityTokenOperation =


/// Create an IntegrityTokenRequest object.
const char* nonce = ...
IntegrityTokenRequest* request;
IntegrityTokenRequest_setNonce(request, nonce); // Set the nonce
IntegrityTokenResponse* response;
IntegrityErrorCode error_code =
        IntegrityManager_requestIntegrityToken(request, &response);

Verifying the nonce

The response of the Play Integrity API is returned in the form of a JSON Web Token (JWT), whose payload is a plain-text JSON text, in the following format:

  requestDetails: { ... }
  appIntegrity: { ... }
  deviceIntegrity: { ... }
  accountDetails: { ... }

The nonce can be found inside the requestDetails structure, which is formatted in the following manner:

requestDetails: {
  requestPackageName: "...",
  nonce: "...",
  timestampMillis: ...

The value of the nonce field should exactly match the one you previously passed to the API. Furthermore, since the nonce is inside the cryptographically signed response of the Play Integrity API, it is not feasible to alter its value after the response is received. It is by leveraging these properties that it is possible to use the nonce to further protect your app.

Protecting high-value operations

Let us consider the scenario in which a malicious user is interacting with an online game that reports the player score to the game server. In this case, the device is not compromised, but the user can view and modify the network data flow between the game and the server with the help of a proxy server or a VPN, so the malicious user can report a higher score, while the real score is much lower.

Simply calling the Play Integrity API is not sufficient to protect the app in this case: the device is not compromised, and the app is legitimate, so all the checks done by the Play Integrity API will pass.

However, it is possible to leverage the nonce of the Play Integrity API to protect this particular high-value operation of reporting the game score, by encoding the value of the operation inside the nonce. The implementation is as follows:

  1. The user initiates the high-value action.
  2. Your app prepares a message it wants to protect, for example, in JSON format.
  3. Your app calculates a cryptographic hash of the message it wants to protect. For example, with the SHA-256, or the SHA-3-256 hashing algorithms.
  4. Your app calls the Play Integrity API, and calls setNonce() to set the nonce field to the cryptographic hash calculated in the previous step.
  5. Your app sends both the message it wants to protect, and the signed result of the Play Integrity API to your server.
  6. Your app server verifies that the cryptographic hash of the message that it received matches the value of the nonce field in the signed result, and rejects any results that don't match.

The following sequence diagram illustrates these steps:

Implementation diagram for encoding the value of the operation inside the nonce. Steps outlined in the body of the blog.

As long as the original message to protect is sent along with the signed result, and both the server and client use the exact same mechanism for calculating the nonce, this offers a strong guarantee that the message has not been tampered with.

Notice that in this scenario, the security model works under the assumption that the attack is happening in the network, not the device or the app, so it is particularly important to also verify the device and app integrity signals that the Play Integrity API offers as well.

Preventing replay attacks

Let us consider another scenario in which a malicious user is trying to interact with a server-client app protected by the Play Integrity API, but wants to do so with a compromised device, in a way so the server doesn’t detect this.

To do so, the attacker first uses the app with a legitimate device, and gathers the signed response of the Play Integrity API. The attacker then uses the app with the compromised device, intercepts the Play Integrity API call, and instead of performing the integrity checks, it simply returns the previously recorded signed response.

Since the signed response has not been altered in any way, the digital signature will look okay, and the app server may be fooled into thinking it is communicating with a legitimate device. This is called a replay attack.

The first line of defense against such an attack is to verify the timestampMillis field in the signed response. This field contains the timestamp when the response was created, and can be useful in detecting suspiciously old responses, even when the digital signature is verified as authentic.

That said, it is also possible to leverage the nonce in the Play Integrity API, to assign a unique value to each response, and verifying that the response matches the previously set unique value. The implementation is as follows:

  1. The server creates a globally unique value in a way that malicious users cannot predict. For example, a cryptographically-secure random number 128 bits or larger.
  2. Your app calls the Play Integrity API, and sets the nonce field to the unique value received by your app server.
  3. Your app sends the signed result of the Play Integrity API to your server.
  4. Your server verifies that the nonce field in the signed result matches the unique value it previously generated, and rejects any results that don't match.

The following sequence diagram illustrates these steps:

Implementation diagram for assigning a unique value to each response, and verifying that the response matches the previously set unique value. Steps outlined in the body of the blog.

With this implementation, each time the server asks the app to call the Play Integrity API, it does so with a different globally unique value, so as long as this value cannot be predicted by the attacker, it is not possible to reuse a previous response, as the nonce won’t match the expected value.

Combining both protections

While the two mechanisms described above work in very different ways, if an app requires both protections at the same time, it is possible to combine them in a single Play Integrity API call, for example, by appending the results of both protections into a larger base-64 nonce. An implementation that combines both approaches is as follows:

  1. The user initiates the high-value action.
  2. Your app asks the server for a unique value to identify the request
  3. Your app server generates a globally unique value in a way that malicious users cannot predict. For example, you may use a cryptographically-secure random number generator to create such a value. We recommend creating values 128 bits or larger.
  4. Your app server sends the globally unique value to the app.
  5. Your app prepares a message it wants to protect, for example, in JSON format.
  6. Your app calculates a cryptographic hash of the message it wants to protect. For example, with the SHA-256, or the SHA-3-256 hashing algorithms.
  7. Your app creates a string by appending the unique value received from your app server, and the hash of the message it wants to protect.
  8. Your app calls the Play Integrity API, and calls setNonce() to set the nonce field to the string created in the previous step.
  9. Your app sends both the message it wants to protect, and the signed result of the Play Integrity API to your server.
  10. Your app server splits the value of the nonce field, and verifies that the cryptographic hash of the message, as well as the unique value it previously generated match to the expected values, and rejects any results that don't match.

The following sequence diagram illustrates these steps:

implementation diagram for combining both protections. Steps outlined in the body of the blog.

These are some examples of ways you can use the nonce to further protect your app against malicious users. If your app handles sensitive data, or is vulnerable against abuse, we hope you consider taking action to mitigate these threats with the help of the Play Integrity API.

To learn more about using the Play Integrity API and to get started, visit the documentation at g.co/play/integrityapi.

Introducing Security By Design

Integrating security into your app development lifecycle can save a lot of time, money, and risk. That’s why we’ve launched Security by Design on Google Play Academy to help developers identify, mitigate, and proactively protect against security threats.

The Android ecosystem, including Google Play, has many built-in security features that help protect developers and users. The course Introduction to app security best practices takes these protections one step further by helping you take advantage of additional security features to build into your app. For example, Jetpack Security helps developers properly encrypt their data at rest and provides only safe and well known algorithms for encrypting Files and SharedPreferences. The SafetyNet Attestation API is a solution to help identify potentially dangerous patterns in usage. There are several common design vulnerabilities that are important to look out for, including using shared or improper file storage, using insecure protocols, unprotected components such as Activities, and more. The course also provides methods to test your app in order to help you keep it safe after launch. Finally, you can set up a Vulnerability Disclosure Program (VDP) to engage security researchers to help.

In the next course, you can learn how to integrate security at every stage of the development process by adopting the Security Development Lifecycle (SDL). The SDL is an industry standard process and in this course you’ll learn the fundamentals of setting up a program, getting executive sponsorship and integration into your development lifecycle.

Threat modeling is part of the Security Development Lifecycle, and in this course you will learn to think like an attacker to identify, categorize, and address threats. By doing so early in the design phase of development, you can identify potential threats and start planning for how to mitigate them at a much lower cost and create a more secure product for your users.

Improving your app’s security is a never ending process. Sign up for the Security by Design module where in a few short courses, you will learn how to integrate security into your app development lifecycle, model potential threats, and app security best practices into your app, as well as avoid potential design pitfalls.

A New Standard for Mobile App Security

Posted by Eugene Liderman, Director, Android Security Strategy and Brooke Davis, Android Security & Privacy Partnerships

Mobile App Secruity image

With all of the challenges from this past year, users have become increasingly dependent on their mobile devices to create fitness routines, stay connected with loved ones, work remotely, and order things like groceries with ease. According to eMarketer, in 2020 users spent over three and a half hours per day using mobile apps. With so much time spent on mobile devices, ensuring the safety of mobile apps is more important than ever. Despite the importance of digital security, there isn’t a consistent industry standard for assessing mobile apps. Existing guidelines tend to be either too lightweight or too onerous for the average developer, and lack a compliance arm. That’s why we're excited to share ioXt’s announcement of a new Mobile Application Profile which provides a set of security and privacy requirements with defined acceptance criteria which developers can certify their apps against.

Over 20 industry stakeholders, including Google, Amazon, and a number of certified labs such as NCC Group and Dekra, as well as automated mobile app security testing vendors like NowSecure collaborated to develop this new security standard for mobile apps. We’ve seen early interest from Internet of Things (IoT) and virtual private network (VPN) developers, however the standard is appropriate for any cloud connected service such as social, messaging, fitness, or productivity apps.

The Internet of Secure Things Alliance (ioXt) manages a security compliance assessment program for connected devices. ioXt has over 300 members across various industries, including Google, Amazon, Facebook, T-Mobile, Comcast, Zigbee Alliance, Z-Wave Alliance, Legrand, Resideo, Schneider Electric, and many others. With so many companies involved, ioXt covers a wide range of device types, including smart lighting, smart speakers, and webcams, and since most smart devices are managed through apps, they have expanded coverage to include mobile apps with the launch of this profile.

The ioXt Mobile Application Profile provides a minimum set of commercial best practices for all cloud connected apps running on mobile devices. This security baseline helps mitigate against common threats and reduces the probability of significant vulnerabilities. The profile leverages existing standards and principles set forth by OWASP MASVS and the VPN Trust Initiative, and allows developers to differentiate security capabilities around cryptography, authentication, network security, and vulnerability disclosure program quality. The profile also provides a framework to evaluate app category specific requirements which may be applied based on the features contained in the app. For example, an IoT app only needs to certify under the Mobile Application profile, whereas a VPN app must comply with the Mobile Application profile, plus the VPN extension.

Certification allows developers to demonstrate product safety and we’re excited about the opportunity for this standard to push the industry forward. We observed that app developers were very quick to resolve any issues that were identified during their blackbox evaluations against this new standard, oftentimes with turnarounds in a matter of days. At launch, the following apps have been certified: Comcast, ExpressVPN, GreenMAX, Hubspace, McAfee Innovations, NordVPN, OpenVPN for Android, Private Internet Access, VPN Private, as well as the Google One app, including VPN by Google One.

We look forward to seeing adoption of the standard grow over time and for those app developers that are already investing in security best practices to be able to highlight their efforts. The standard also serves as a guiding light to inspire more developers to invest in mobile app security. If you are interested in learning more about the ioXt Alliance and how to get your app certified, visit https://compliance.ioxtalliance.org/sign-up and check out Android’s guidelines for building secure apps here.

Announcing the launch of the Android Partner Vulnerability Initiative

Posted by Kylie McRoberts, Program Manager and Alec Guertin, Security Engineer

Android graphic

Google’s Android Security & Privacy team has launched the Android Partner Vulnerability Initiative (APVI) to manage security issues specific to Android OEMs. The APVI is designed to drive remediation and provide transparency to users about issues we have discovered at Google that affect device models shipped by Android partners.

Another layer of security

Android incorporates industry-leading security features and every day we work with developers and device implementers to keep the Android platform and ecosystem safe. As part of that effort, we have a range of existing programs to enable security researchers to report security issues they have found. For example, you can report vulnerabilities in Android code via the Android Security Rewards Program (ASR), and vulnerabilities in popular third-party Android apps through the Google Play Security Rewards Program. Google releases ASR reports in Android Open Source Project (AOSP) based code through the Android Security Bulletins (ASB). These reports are issues that could impact all Android based devices. All Android partners must adopt ASB changes in order to declare the current month’s Android security patch level (SPL). But until recently, we didn’t have a clear way to process Google-discovered security issues outside of AOSP code that are unique to a much smaller set of specific Android OEMs. The APVI aims to close this gap, adding another layer of security for this targeted set of Android OEMs.

Improving Android OEM device security

The APVI covers Google-discovered issues that could potentially affect the security posture of an Android device or its user and is aligned to ISO/IEC 29147:2018 Information technology -- Security techniques -- Vulnerability disclosure recommendations. The initiative covers a wide range of issues impacting device code that is not serviced or maintained by Google (these are handled by the Android Security Bulletins).

Protecting Android users

The APVI has already processed a number of security issues, improving user protection against permissions bypasses, execution of code in the kernel, credential leaks and generation of unencrypted backups. Below are a few examples of what we’ve found, the impact and OEM remediation efforts.

Permission Bypass

In some versions of a third-party pre-installed over-the-air (OTA) update solution, a custom system service in the Android framework exposed privileged APIs directly to the OTA app. The service ran as the system user and did not require any permissions to access, instead checking for knowledge of a hardcoded password. The operations available varied across versions, but always allowed access to sensitive APIs, such as silently installing/uninstalling APKs, enabling/disabling apps and granting app permissions. This service appeared in the code base for many device builds across many OEMs, however it wasn’t always registered or exposed to apps. We’ve worked with impacted OEMs to make them aware of this security issue and provided guidance on how to remove or disable the affected code.

Credential Leak

A popular web browser pre-installed on many devices included a built-in password manager for sites visited by the user. The interface for this feature was exposed to WebView through JavaScript loaded in the context of each web page. A malicious site could have accessed the full contents of the user’s credential store. The credentials are encrypted at rest, but used a weak algorithm (DES) and a known, hardcoded key. This issue was reported to the developer and updates for the app were issued to users.

Overly-Privileged Apps

The checkUidPermission method in the PackageManagerService class was modified in the framework code for some devices to allow special permissions access to some apps. In one version, the method granted apps with the shared user ID com.google.uid.shared any permission they requested and apps signed with the same key as the com.google.android.gsf package any permission in their manifest. Another version of the modification allowed apps matching a list of package names and signatures to pass runtime permission checks even if the permission was not in their manifest. These issues have been fixed by the OEMs.

More information

Keep an eye out at https://bugs.chromium.org/p/apvi/ for future disclosures of Google-discovered security issues under this program, or find more information there on issues that have already been disclosed.

Acknowledgements: Scott Roberts, Shailesh Saini and Łukasz Siewierski, Android Security and Privacy Team