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Important Notice

SafetyNet Attestation is now deprecated. New and existing developers should use the Play Integrity API instead.

This repository will remain for reference, but will not receive any updates in the future.

C# Server SafetyNet Samples

This sample demonstrates how to verify the response received from the SafetyNet service in C#.

It shows how to extract the compatibility check response from the JWS message, validate its SSL certificate chain, hostname and signature.

This check can be done completely offline (See OfflineVerify.cs) or by using the Android Verification API to verify the content and signature of the response (see OnlineVerifycs). This REST API requires you to register at the Google Developers console and register for an API key. Detailed steps are available [in the documentation] under Validating the response with Google APIs.

Note that this sample only provides a basic overview over the verification process and does not cover all possibilities. For example,it is reccomended to always verify the nonce in the request as well. This sample also does not show the app-to-server communication.

For more details, see the guide at https://developer.android.com/training/safetynet/index.html#verify-compat-check .

Next: Verify the response

This sample only demonstrates verification of the server response. The next step is to verify that the attestation response matches the request by verifying their contents, including the package name, digest, timestamp and nonce.

This step is crucial. If you do not verify the response and request, you may be vulnerable to a replay attack, in which an attacker can replay an old attestation response from a different device or app.

Pre-requisites

  • A C# compiler.

Getting Started

This sample was tested with Visual Studio 2015 and 2017, but should work with .NET core or mono.

To build this project using Visual Studio 2015 or 2017, simply open SafetyNetVerify.csproj and external dependencies should resolve automatically from NuGet.

You can modify Program.cs and set attestationStatementString to the value returned by getJwsResult() on the client device to attest a hardcoded value.

Online verification is available for test purposes only. To use it, define a compilation symbol called ONLINE_VERIFICATION, and online verification will be used. Note that online verification should not be used on production environments.

Additionally, online verification requires an API key for the Android Verification API. Follow the steps in the documentation under "Validating the response with Google APIs" and add the API key into the ApiKey field at the top of OnlineVerify.cs.

For different versions of Visual Studio, .NET core or mono, you may need to manually build the source. The required dependencies are stated in project.json.

Running the Samples

  • Build and run the Android component of this sample.
  • Retrieve a signed statement from the Android app and copy it to your machine. (You can use the "Share Result" option.)
  • Build this server component and provide the signed statement as input, either as a command line argument, or by hardcoding it into attestationStatementString in Program.cs.

Support

If you've found an error in this sample, please file an issue: https://github.com/googlesamples/android-SafetyNetSample

Patches are encouraged, and may be submitted by forking this project and submitting a pull request through GitHub. Please see CONTRIBUTING.md for more details.

License

Copyright 2017 Google Inc.

Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to you under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.