Thanks for your help in advance.

I'm using React Native and Node.js to deliver a product for my company.

I've setup the steps on the backend to retrieve a password, validate it and respond with a token. The only problem is - the password I use on the front end (mobile app) to be validated by the back end is hardcoded.

My question is:

How should I securely store this password on the mobile app so that it can not be sniffed out by a hacker and used to compromise the backend?

My research so far.

Embedded in strings.xml

Hidden in Source Code

Hidden in BuildConfigs

Using Proguard

Disguised/Encrypted Strings

Hidden in Native Libraries

http://rammic.github.io/2015/07/28/hiding-secrets-in-android-apps/

These methods are basically useless because hackers can easily circumnavigate these methods of protection.

https://github.com/oblador/react-native-keychain

Although this may obfuscate keys, these still have to be hardcoded. Making these kind of useless, unless I'm missing something.

I could use a .env file https://github.com/luggit/react-native-config

Again, I feel like the hacker can still view secret keys, even if they are saved in a .env

I want to be able to store keys in the app so that I can validate the user an allow them to access resources on the backend. However, I don't know what the best plan of action is to ensure user/business security.

What suggestions do you have to protect the world (react- native apps) from pesky hackers, when they're stealing keys and using them inappropriately?

1 Answers

1
Exadra37 On

Your Question

I've setup the steps on the backend to retrieve a password, validate it and respond with a token. The only problem is - the password I use on the front end (mobile app) to be validated by the back end is hardcoded.

My question is:

How should I securely store this password on the mobile app so that it can not be sniffed out by a hacker and used to compromise the backend?

The cruel truth is... you can't!!!

It seems that you already have done some extensive research on the subject, and in my opinion you mentioned one effective way of shipping your App with an embedded secret:

Hidden in Native Libraries

But as you also say:

These methods are basically useless because hackers can easily circumnavigate these methods of protection.

Some are useless and others make reverse engineer the secret from the mobile app a lot harder. As I wrote here, the approach of using the native interfaces to hide the secret will require expertise to reverse engineer it, but then if is hard to reverse engineer the binary you can always resort to a man in the middle (MitM) attack to steel the secret, as I show here for retrieving a secret that is hidden in the mobile app binary with the use of the native interfaces, JNI/NDK.

To protect your mobile app from a MitM you can employ Certificate Pinning:

Pinning is the process of associating a host with their expected X509 certificate or public key. Once a certificate or public key is known or seen for a host, the certificate or public key is associated or 'pinned' to the host. If more than one certificate or public key is acceptable, then the program holds a pinset (taking from Jon Larimer and Kenny Root Google I/O talk). In this case, the advertised identity must match one of the elements in the pinset.

You can read this series of react native articles that show you how to apply certificate pinning to protect the communication channel between your mobile app and the API server.

If you don't know yet certificcate pinning can also be bypassed by using tools like Frida or xPosed.

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.

xPosed

Xposed is a framework for modules that can change the behavior of the system and apps without touching any APKs. That's great because it means that modules can work for different versions and even ROMs without any changes (as long as the original code was not changed too much). It's also easy to undo.

So now you may be wondering how can I protect from certificate pinning bypass?

Well is not easy, but is possible, by using a mobile app attestation solution.

Before we go further on it, I would like to clarify first a common misconception among developers, regarding WHO and WHAT is accessing the API server.

The Difference Between WHO and WHAT is Accessing the API Server

To better understand the differences between the WHO and the WHAT are accessing an API server, let’s use this picture:

Man in the Middle Attack

The Intended Communication Channel represents the mobile app being used as you expected, by a legit user without any malicious intentions, using an untampered version of the mobile app, and communicating directly with the API server without being man in the middle attacked.

The actual channel may represent several different scenarios, like a legit user with malicious intentions that may be using a repackaged version of the mobile app, a hacker using the genuine version of the mobile app, while man in the middle attacking it, to understand how the communication between the mobile app and the API server is being done in order to be able to automate attacks against your API. Many other scenarios are possible, but we will not enumerate each one here.

I hope that by now you may already have a clue why the WHO and the WHAT are not the same, but if not it will become clear in a moment.

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.

OAUTH

Generally, OAuth provides to clients a "secure delegated access" to server resources on behalf of a resource owner. It specifies a process for resource owners to authorize third-party access to their server resources without sharing their credentials. Designed specifically to work with Hypertext Transfer Protocol (HTTP), OAuth essentially allows access tokens to be issued to third-party clients by an authorization server, with the approval of the resource owner. The third party then uses the access token to access the protected resources hosted by the resource server.

OpenID Connect

OpenID Connect 1.0 is a simple identity layer on top of the OAuth 2.0 protocol. It allows Clients to verify the identity of the End-User based on the authentication performed by an Authorization Server, as well as to obtain basic profile information about the End-User in an interoperable and REST-like manner.

While user authentication may let the API server know WHO is using the API, it cannot guarantee that the requests have originated from WHAT you expect, the original version of the mobile app.

Now we need a way to identify WHAT is calling the API server, and here things become more tricky than most developers may think. The WHAT is the thing making the request to the API server. Is it really a genuine instance of the mobile app, or is a bot, an automated script or an attacker manually poking around with the API server, using a tool like Postman?

For your surprise you may end up discovering that It can be one of the legit users using a repackaged version of the mobile app or an automated script that is trying to gamify and take advantage of the service provided by the application.

Well, to identify the WHAT, developers tend to resort to an API key that usually they hard-code in the code of their mobile app. Some developers go the extra mile and compute the key at run-time in the mobile app, thus it becomes a runtime secret as opposed to the former approach when a static secret is embedded in the code.

The above write-up was extracted from an article I wrote, entitled WHY DOES YOUR MOBILE APP NEED AN API KEY?, and that you can read in full here, that is the first article in a series of articles about API keys.

Mobile App Attestation

The use of a Mobile App Attestation solution will enable the API server to know WHAT is sending the requests, thus allowing to respond only to requests from a genuine mobile app while rejecting all other requests from unsafe sources.

The role of a Mobile App Attestation service is to guarantee at run-time that your mobile app was not tampered, is not running in a rooted device and is not being the target of a MitM attack. This is done by running a SDK in the background that will communicate with a service running in the cloud to attest the integrity of the mobile app and device is running on. The cloud service also verifies that the TLS certificate provided to the mobile app on the handshake with the API server is indeed the same in use by the original and genuine API server for the mobile app, not one from a MitM attack.

On successful attestation of the mobile app integrity a short time lived JWT token is issued and signed with a secret that only the API server and the Mobile App Attestation service in the cloud are aware. In the case of failure on the mobile app attestation the JWT token is signed with a secret that the API server does not know.

Now the App must sent with every API call the JWT token in the headers of the request. This will allow the API server to only serve requests when it can verify the signature and expiration time in the JWT token and refuse them when it fails the verification.

Once the secret used by the Mobile App Attestation service is not known by the mobile app, is not possible to reverse engineer it at run-time even when the App is tampered, running in a rooted device or communicating over a connection that is being the target of a Man in the Middle Attack.

So this solution works in a positive detection model without false positives, thus not blocking legit users while keeping the bad guys at bays.

What suggestions do you have to protect the world (react- native apps) from pesky hackers, when they're stealing keys and using them inappropriately?

I think you should relaly go with a mobile app attestation solution, that you can roll in your own if you have the expertise for it, or you can use a solution that already exists as a SAAS solution at Approov(I work here), that provides SDKs for several platforms, including iOS, Android, React Native and others. The integration will also need a small check in the API server code to verify the JWT token issued by the cloud service. This check is necessary for the API server to be able to decide what requests to serve and what ones to deny.

Summary

I want to be able to store keys in the app so that I can validate the user an allow them to access resources on the backend. However, I don't know what the best plan of action is to ensure user/business security.

Don't go down this route of storing keys in the mobile app, because as you already know, by your extensive research, they can be bypassed.

Instead use a mobile attestation solution in conjunction with OAUTH2 or OpenID connect, that you can bind with the mobile app attestation token. An example of this token binding can be found in this article for the check of the custom payload claim in the endpoint /forms.

Going the Extra Mile

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.