Is there any way to restrict post requests to my REST API only to requests coming from my own mobile app binary? This app will be distributed on Google Play and the Apple App Store so it should be implied that someone will have access to its binary and try to reverse engineer it.
I was thinking something involving the app signatures, since every published app must be signed somehow, but I can't figure out how to do it in a secure way. Maybe a combination of getting the app signature, plus time-based hashes, plus app-generated key pairs and the good old security though obscurity?
I'm looking for something as fail proof as possible. The reason why is because I need to deliver data to the app based on data gathered by the phone sensors, and if people can pose as my own app and send data to my api that wasn't processed by my own algorithms, it defeats its purpose.
I'm open to any effective solution, no matter how complicated. Tin foil hat solutions are greatly appreciated.
Any credentials that are stored in the app can be exposed by the user. In the case of Android, they can completely decompile your app and easily retrieve them.
If the connection to the server does not utilize SSL, they can be easily sniffed off the network.
Seriously, anybody who wants the credentials will get them, so don't worry about concealing them. In essence, you have a public API.
There are some pitfalls and it takes extra time to manage a public API.
Many public APIs still track by IP address and implement tarpits to simply slow down requests from any IP address that seems to be abusing the system. This way, legitimate users from the same IP address can still carry on, albeit slower.
You have to be willing to shut off an IP address or IP address range despite the fact that you may be blocking innocent and upstanding users at the same time as the abusers. If your application is free, it may give you more freedom since there is no expected level of service and no contract, but you may want to guard yourself with a legal agreement.
In general, if your service is popular enough that someone wants to attack it, that's usually a good sign, so don't worry about it too much early on, but do stay ahead of it. You don't want the reason for your app's failure to be because users got tired of waiting on a slow server.
Your other option is to have the users register, so you can block by credentials rather than IP address when you spot abuse.
Yes, It's public
This app will be distributed on Google Play and the Apple App Store so it should be implied that someone will have access to its binary and try to reverse engineer it.
From the moment its on the stores it's public, therefore anything sensitive on the app binary must be considered as potentially compromised.
The Difference Between WHO and WHAT is Accessing the API Server
Before I dive into your problem I would like to first clear a misconception about who and what is accessing an API server. I wrote a series of articles around API and Mobile security, and in the article Why Does Your Mobile App Need An Api Key? you can read in detail the difference between who and what is accessing your API server, but I will extract here the main takes from it:
The what is the thing making the request to the API server. Is it really a genuine instance of your mobile app, or is it a bot, an automated script or an attacker manually poking around your API server with a tool like Postman?
The who is the user of the mobile app that we can authenticate, authorize and identify in several ways, like using OpenID Connect or OAUTH2 flows.
Think about the who as the user your API server will be able to Authenticate and Authorize access to the data, and think about the what as the software making that request in behalf of the user.
So if you are not using user authentication in the app, then you are left with trying to attest what is doing the request.
Mobile Apps should be as much dumb as possible
The reason why is because I need to deliver data to the app based on data gathered by the phone sensors, and if people can pose as my own app and send data to my api that wasn't processed by my own algorithms, it defeats its purpose.
It sounds to me that you are saying that you have algorithms running on the phone to process data from the device sensors and then send them to the API server. If so then you should reconsider this approach and instead just collect the sensor values and send them to the API server and have it running the algorithm.
As I said anything inside your app binary is public, because as yourself said, it can be reverse engineered:
should be implied that someone will have access to its binary and try to reverse engineer it.
Keeping the algorithms in the backend will allow you to not reveal your business logic, and at same time you may reject requests with sensor readings that do not make sense(if is possible to do). This also brings you the benefit of not having to release a new version of the app each time you tweak the algorithm or fix a bug in it.
Runtime attacks
I was thinking something involving the app signatures, since every published app must be signed somehow, but I can't figure out how to do it in a secure way.
Anything you do at runtime to protect the request you are about to send to your API can be reverse engineered with tools like Frida:
Inject your own scripts into black box processes. Hook any function, spy on crypto APIs or trace private application code, no source code needed. Edit, hit save, and instantly see the results. All without compilation steps or program restarts.
Your Suggested Solutions
Security is all about layers of defense, thus you should add as many as you can afford and required by law(e.g GDPR in Europe), therefore any of your purposed solutions are one more layer the attacker needs to bypass, and depending on is skill-set and time is willing to spent on your mobile app it may prevent them to go any further, but in the end all of them can be bypassed.
Maybe a combination of getting the app signature, plus time-based hashes, plus app-generated key pairs and the good old security though obscurity?
Even when you use key pairs stored in the hardware trusted execution environment, all an attacker needs to do is to use an instrumentation framework to hook in the function of your code that uses the keys in order to extract or manipulate the parameters and return values of the function.
Android Hardware-backed Keystore
The availability of a trusted execution environment in a system on a chip (SoC) offers an opportunity for Android devices to provide hardware-backed, strong security services to the Android OS, to platform services, and even to third-party apps.
While it can be defeated I still recommend you to use it, because not all hackers have the skill set or are willing to spend the time on it, and I would recommend you to read this series of articles about Mobile API Security Techniques to learn about some complementary/similar techniques to the ones you described. This articles will teach you how API Keys, User Access Tokens, HMAC and TLS Pinning can be used to protect the API and how they can be bypassed.
Possible Better Solutions
Nowadays I see developers using Android SafetyNet to attest what is doing the request to the API server, but they fail to understand it's not intended to attest that the mobile app is what is doing the request, instead it's intended to attest the integrity of the device, and I go in more detail on my answer to the question Android equivalent of ios devicecheck. So should I use it? Yes you should, because it is one more layer of defense, that in this case tells you that your mobile app is not installed in a rooted device, unless SafetyNet has been bypassed.
Is there any way to restrict post requests to my REST API only to requests coming from my own mobile app binary?
You can allow the API server to have an high degree of confidence that is indeed accepting requests only from your genuine app binary by implementing the Mobile App Attestation concept, and I describe it in more detail on this answer I gave to the question How to secure an API REST for mobile app?, specially the sections Securing the API Server and A Possible Better Solution.
Do you want to go the Extra Mile?
In any response to a security question I always like to reference the excellent work from the OWASP foundation.
For APIS
OWASP API Security Top 10
The OWASP API Security Project seeks to provide value to software developers and security assessors by underscoring the potential risks in insecure APIs, and illustrating how these risks may be mitigated. In order to facilitate this goal, the OWASP API Security Project will create and maintain a Top 10 API Security Risks document, as well as a documentation portal for best practices when creating or assessing APIs.
For Mobile Apps
OWASP Mobile Security Project - Top 10 risks
The OWASP Mobile Security Project is a centralized resource intended to give developers and security teams the resources they need to build and maintain secure mobile applications. Through the project, our goal is to classify mobile security risks and provide developmental controls to reduce their impact or likelihood of exploitation.
OWASP - Mobile Security Testing Guide:
The Mobile Security Testing Guide (MSTG) is a comprehensive manual for mobile app security development, testing and reverse engineering.
No. You're publishing a service with a public interface and your app will presumably only communicate via this REST API. Anything that your app can send, anyone else can send also. This means that the only way to secure access would be to authenticate in some way, i.e. keep a secret. However, you are also publishing your apps. This means that any secret in your app is essentially being given out also. You can't have it both ways; you can't expect to both give out your secret and keep it secret.
Though this is an old post, I thought I should share the updates from Google in this regard.
You can actually ensure that your Android application is calling the API using the SafetyNet mobile attestation APIs. This adds a little overhead on the network calls and prevents your application from running in a rooted device.
I found nothing similar like SafetyNet for iOS. Hence in my case, I checked the device configuration first in my login API and took different measures for Android and iOS. In case of iOS, I decided to keep a shared secret key between the server and the application. As the iOS applications are a little bit difficult to reversed engineered, I think this extra key checking adds some protection.
Of course, in both cases, you need to communicate over HTTPS.
As the other answers and comments imply, you cant truly restrict API access to only your app but you can take different measures to reduce the attempts. I believe the best solution is to make requests to your API (from native code of course) with a custom header like "App-Version-Key" (this key will be decided at compile time) and make your server check for this key to decide if it should accept or reject. Also when using this method you SHOULD use HTTPS/SSL as this will reduce the risk of people seeing your key by viewing the request on the network.
Regarding Cordova/Phonegap apps, I will be creating a plugin to do the above mentioned method. I will update this comment when its complete.
there is nothing much you can do. cause when you let some one in they can call your APIs. the most you can do is as below:
since you want only and only your application (with a specific package name and signature) calls your APIs, you can get the signature key of your apk pragmatically and send is to sever in every API call and if thats ok you response to the request. (or you can have a token API that your app calls it every beginning of the app and then use that token for other APIs - though token must be invalidated after some hours of not working with)
then you need to proguard your code so no one sees what you are sending and how you encrypt them. if you do a good encrypt decompiling will be so hard to do.
even signature of apk can be mocked in some hard ways but its the best you can do.
Someone have looked at Firebase App Check ?
https://firebase.google.com/docs/app-check
Is there any way to restrict post requests to my REST API only to requests coming from my own mobile app binary?
I'm not sure if there is an absolute solution.
But, you can reduce unwanted requests.
Use an App Check:
The "Firebase App Check" can be used cross-platform (https://firebase.google.com/docs/app-check) - credit to #Xande-Rasta-Moura
iOS: https://developer.apple.com/documentation/devicecheck
Android: https://android-developers.googleblog.com/2013/01/verifying-back-end-calls-from-android.html
Use BasicAuth (for API requests)
Allow a user-agent header for mobile devices only (for API requests)
Use a robots.txt file to reduce bots
User-agent: *
Disallow: /
Let's suppose I have an Android application that needs to make some API call. I want to authenticate the deployed applications to that my API cannot be used by unauthorized clients.
I can put anything inside the application - HTTP headers that sign the requests, complete with nonces. However, if someone decompiles the application he will be able to replicate the method of authentication, like the algorithm for generating the signature and the shared secret. With Java and Android this is not unfeasible.
Is it possible to avoid? Probably not, but I wanted to be sure that cryptography has no solutions for me.
There is no solution to this problem. It is not possible for your server to know that it is talking to "your" client. The only thing you can reasonably authenticate is the user, not the application. It is also possible to reasonably authenticate certain secure hardware devices, but this is very expensive, and still does not ensure that your client is being used; it only demonstrates that the user has access to one of your secure hardware devices.
This has been discussed many times across SO. These posts discuss the issue and link to many more of these discussions:
Best practices for iOS applications security
Secure https encryption for iPhone app to webpage
While the posts above are framed in terms of iOS, the issue is universal.
When I am sending sms via j2me application, before message sent it appears question for can I use internet to sent message. Is it possible to exit this question to not appear?
This is happening because you Accessing HTTP & SMS API. For using such API you need to signed your Java ME Application. For Signed a the Java ME Application, you need to purchase Signing Certificate from VeriSign or Thawte Site by paying the Fees.
Plesae visit this link
For VeriSign's certificate, they costs 20K per certificate.
I think you can skip the prompt but your application must be signed. However, even if your application is signed, on some devices, the prompt will still appear once. This usually (or always) occurs on the session's first use of the Wireless Messaging API. This happens because the access to this API is set to something like "Ask first time."
If your app is signed, you can manually set the access to the wireless network settings to (something like) "Always allow." If it is set to (something like) this, the prompt will not appear.
For apps that are not signed, the option "Always allow" is not available. However, on most devices, the next best option is available: "Ask first time."
Well, the bad thing is, you are going to set it manually. The good thing, however, is that you are not going spend so much money just to set it to "Ask first time." :D
J2ME by the platform design have the drawbacks in which users of the applications are asked to select yes or no for any attempt to use any of the secure API's. Some devices gives this alerts in such a way which will make the end user to think if he should go ahead or stop it there. By digitally signing the application, one can reduce the alerts to levels depending on the device KVM implementation and the number of secure APIs in use.
In some device having Symbian OS Feature Pack 1, the prompts continue even if the code is signed.
This behavior of J2ME makes the applications less developer friendly and less user friendly. I think this is a wrong strategy and model adopted by SUN. There is some thing called Verified by Java in which you can get your application signed using a certificate which will make the application work seamlessly and without prompts in the end user device but unfortunately the process of getting that certification is expensive and not practical. The only advantage of J2ME platform is that it allows less chances of virus or malware code to be executed on the end user device. I think the trade off between security and ease of user use is not worked well and that is the reason we don't see very good apps in J2ME.
In contrast, Android for example, lets the user see all the permissions prior to installation of the app and the user is not bothered at run time when those secure API are used. That is the reason we see millions of apps there and not in J2ME. We can always say this approach had led to many malware types of applications in the end android user device but that is how it goes, people need to have smooth apps running and are happy with them.
we are using the native BlackBerry camera in our app, using the Invoke class to start the camera. We listen for an image being written to the filesystem, and when the user is finished with the camera, we call
Application.getApplication().requestForeground();
inside fileJournalChanged() to get back to our app.
This caused a problem with the camera lingering on the image taking on some devices, some of the time. If you want gory details you can see my post on the BB forums from a while back.
http://supportforums.blackberry.com/t5/Java-Development/restore-invoked-camera-after-deleting-an-image-from-the/m-p/511332
Suffice to say, I am still trying to fix this. Using EventInjector to inject an ESC key press works, however in this question
Getting Event Injector Permission
it is described as a security threat. However this is widely suggested as the way to close the camera and work around other issues. Has anyone had problems using this method to close the camera or to do anything else? Is there a better "best practices" method for closing the camera, as there apparently is in Android (I don't actually know, a senior developer here mentioned it)?
By "problems" I guess I really mean business rules types of problems... app getting blacklisted by an organization, slammed in the app store, etc?
Thanks in advance, this has been troubling me for a while.
I think the biggest problem you'll face is that using event injection requires special application permissions - ApplicationPermissions.PERMISSION_INPUT_SIMULATION to be exact. Since granting an application this permission basically allows it to simulate input events into ANY application at any time, it is considered quite dangerous because a badly-written or intentionally malicious application could do a lot of damage. Therefore many end-users and business do not allow applications that require this permission.
Just to be on the safe side, what's the best practice to ensure that only my application has access to my webservice, which is hosted on a public server? Should I implement I shared key or something?
My webservice is hosted on Googles App Engine and my Application runs on iPhones and iPads.
If you need further information, just ask.
Thanks,
Henrik
some sort of challenge/response authentication would be your best bet, but you could use something as simple as a key that's sent with every request. it might be quite easy for someone with a packet sniffer to reverse engineer that security though - i guess the amount of time you spend on it will relate to how much you really care :)
If you require your iphone app users to enter a loginid/password, then it is trivial to achieve what you want. But I assume you don't want that ..
Without that, there is no way to ensure you app has exclusive access to your web-services. People can always sniff HTTP traffic and spoof it. People can decompile/reverse-engineer your app to figure out the key/password.
See other discussions on StackOverflow - How to restrict access to my web service? and How can I create and use a web service in public but still restrict its use to only my app?
You could program your app to only serve requests that include your iPhone's unique identier - see StackOverflow question [Unique identifier for an iPhone app]. The id could still be sniffed, so depending on your needs, you may need methods to counter that.
Well, i had similar problem. What i realized, there is no 100% solution. What i did is, i used different approach. I have implemented OAuth and SSL, of course and than make algorithm for my web service to learn behavior of my app.
I try to put that algorithm in some kind of pattern, template, so it can be used in more scenarios. It's still in developing, so here is code of simple console app that will simulate that algorithm. Hope this can help:
https://github.com/vjeftovic/LearningRESTSimulation