What I want to know is can a signed apk be extracted and edited? And can the attacker again compress the apk and attack a victim?
I know that we can use proguard to obscure the code but some people said that the apk still can be extracted and modified through reverse engineering.
My main concern is I want to encrypt my java files because I have some authentication data in my java files.
Can anyone give me a bulletproof method to protect java files from being inaccessible.
Edit -
Found few old thread in stack but they never explained about signed apk and protect them from getting exploited.
Yes. Cryptographic signing is not encryption. Signing proves that whoever signed it knew a secret key. Assuming the key is kept secure, you can be sure that two files signed by the same key are from the same person. With some forms of signing with public and private keys, it can be used to prove the identity of the signer. This does not provide any protection against reading that data, although it does provide protection against a counterfeit copy of the app being claimed as the real thing (assuming the user pays attention to the signature).
There is no way to do what you want to do. In the end, an app has to be run by a processor or interpreter. That means it needs to be translated into instructions that the processor understands. If you want something to be secure, do not put it on a client device. There is no way to protect it if you're sending it to a device that needs to decrypt it and use it.
Any APK can be decompressed and have its sources read. You cannot, however, edit it and sign it without the signing key.
There is no way to encrypt your source files and everything inside of them is readable by anyone. Authentication data shouldn't be stored in an application if it is expected to be secret.
signed apks can easily be reverse engineered. You should never place authentication data in the source code. There is no bullet proof solution for this. However you can make it difficult for the attacker by encoding and not placing your critical data in obvious places.
You should use another way to use your authentication data, I've read something about building a binary and storing inside the lib directory as a .so file, I'm not sure how exactly it's the proccess because I didn't tried, but you can research another methods, storing private data on Java source it's not secure.
When I built an APK file using cordova build, it bundles all the HTML/JS/CSS3 static files into the APK file in simple plain/text format. This way anyone will be able to easily use this code and create copy of my app. Is there any way to encrypt these files?
There is no 100% foolproof way for this, I could think of a solution where you will need a web server running a script for authenticating and then providing the core Javascript or a URL for the same in response. And you could save it locally for future use.
To keep the access restricted to your application, you will have to get the app's package name and then only provide the response. This post should help you to get your package's name.
In addition, you could add some logic on your server as well as your Javascript where you will generate a random unique string based on the timespan and add it to authentication process' parameters. And obfuscating all of your packaged JS in the apk will make it difficult for anyone to get your whole logic.
I generate a small metadata file (2KB) from my app which needs to be unreadable if the user browse through file system. These files will not be transferred elsewhere through my app.
After prolong research I figured I have to use Symmetry encryption. But I am lost what type of algorithm and how to use key/salt. Efficiency of the algorithm is important because the file is updated on onPause method.
Should I declare it in code and use that for all users or should I generate new one for each user. If I go with second option, where do I store the key/salt for later use. Should I obfuscate the code?
Please advice.
Currently I have short listed these two. Are they secure enough for my requirement? How can I improve them?
http://www.codejava.net/coding/file-encryption-and-decryption-simple-example
String Encryption in Android
I had stumbled upon this simple question of what is the best way for me to open a database or use a service which is secured, in the sense, will work only when correct password is provided.
I have looked at SharedPreferences as a way of retrieving information,but i need to create an app which will store the password in the first case, which by itself means i need to write it on code somewhere or the other
Account Manager is yet another way i've considered.
Store the actual password in an AES encrypted format, in a file, or in an sqlite db. But that means the key will have to be in the code.
I would've thought that this is a fairly common problem that people face and i'm wondering how people solved it!
In my opinion you can encrypt your data using AES encryption. But the main problem is the key is not safe. APK can be decompiled. So there is a method to hide the key. Implantation is bit difficult. Use native coding (NDK). You can write your key in a C file and after compilation you get a .SO file. This file can be included in your project. Make a call from java to a C function and return the key. But another problem is the strings written in C is visible when you open the .SO file. So assign generate ascii code of your key and make a string using the ascii code in C.
I am developing an application that has SQLite database to store personal information that must be protected. What are some ways of protecting these personal data? An APK can easily be de-compiled completely, so how can we secure an APK? Additionally, how can a database of a mobile application be protected?
Basically, there are 5 methods to protect your APK being cracking/ reversing/ repackaging:
1. Isolate Java Program
The easiest way is to make users unable to access to the Java Class program. This is the most fundamental way, and it has a variety of specific ways to achieve this. For example, developers can place the key Java Class on the server, clients acquire services by access relevant interfaces of the server rather than access to the Class file directly. So there is no way for hackers to decompile Class files. Currently, there are more and more standards and protocols services provided through interfaces, such as HTTP, Web Service, RPC, etc. But there are lots of applications are not suitable for this protection. For example, Java programs in stand-alone programs are unable to isolate.
2. Encrypt Class Files
To prevent Class files from being decompiled directly, many developers will encrypt some key Class files, such as registration number, serial number management and other related classes. Before using these encrypted classes, the program needs to decrypt these classes first, then loading these classes into JVM. These classes can be decrypted by hardware, or software.
Developers often loading cryptographic classes through a customed ClassLoader class (Applet does not support customed ClassLoader because of security). Customed ClassLoader will find cryptographic classes first, then decrypt them. And finally loading the decrypted classes to JVM. Customed ClassLoader is a very important class in this protect method. Because it itself is not encrypted, it may be the first target of a hacker. If the relevant decryption key and algorithm have been overcome, then the encrypted classes can easily be decrypted.
3. Convert to Native Codes
Convert program to native codes is also an effective way to prevent decompilation. Because native codes are often difficult to be decompiled. Developers can convert the entire application to native codes, or they can also convert only key modules. If just convert key part of the modules, it will need JNI technology to call when Java programs are using these modules. It abandoned Java's cross-platform feature when using this mothod to protect Java programs. For different platforms, we need to maintain different versions of the native codes, which will increase software support and maintenance workload. But for some key modules, sometimes this solution is often necessary. In order to guarantee these native codes will not be modified or replaced, developers often need to digitally sign these codes. Before using these native codes, developers often need to authenticate these local codes to ensure that these codes have not changed by hackers. If the signature check is passed, then developers can call relevant JNI methods.
4. Code Obfuscation
Code obfuscation is to re-organize and process Class file, making the treated codes accomplish the same function (semantics) with the untreated codes. But the obfuscated codes are difficult to be decompiled, i.e., the decompiled codes are very difficult to understand, therefore decompile staffs are hard to understand the really semantics. Theoretically, if hackers have enough time, obfuscated codes may still be cracked. Even some people are developing de-obfuscate tool. But from the actual situation, since the diversified development of obfuscation, the mature of obfuscation theory, obfuscated Java codes can well prevent decompilation.
5. Online Encryption
APK Protect was an online encryption website for APK, but activity has apparently been discontinued since 2013 or so. It provided Java codes and C++ codes protection to achieve anti-debugging and decompile effects.
I originally suggested you use this last method for it could save you more time. Based on my experience, it was very simple to operate and it wouldn't take long time.
With Jellybean this has now become a possibility.
$ openssl enc -aes-128-cbc -K 000102030405060708090A0B0C0D0E0F
-iv 000102030405060708090A0B0C0D0E0F -in my-app.apk -out my-app-enc.apk
$ adb install --algo 'AES/CBC/PKCS5Padding' --key 000102030405060708090A0B0C0D0E0F
--iv 000102030405060708090A0B0C0D0E0F my-app-enc.apk
pkg: /data/local/tmp/my-app-enc.apk
Success
Please read the following blog post for further details
If this is secret information that must not fall into the hands of your users, you cannot secure it. It is fundamentally impossible to put information on a device (code or data), and have your application access it, but not allow someone with the device to have access to that information.
Encrypting the information is pointless from a security point of view, because your application has to contain whatever is needed to decrypt it in order to use it, and a sufficiently motivated attacker can always extract that and decrypt it on their own.
All you can do is make it more annoying and time consuming to get access to that information, which only helps if there's not really that much of a need to keep it secret. This is what using proguard to obfuscate your .apk file can do.
Have you considered sqlite encryption? See this thread - sqlite encryption for android
As for protecting your .apk, try obfuscating your code using proguard. See http://developer.android.com/guide/developing/tools/proguard.html
You can try 'Anti Decompiler(Android)Trial'
https://play.google.com/store/apps/details?id=com.tth.AntilDecompilerTrial
It makes something Proguard doesn't:
Hide all const values (string, character), you will never see clear text like "my key", "my val"... in your apk file
Obfuscate file name, which is referenced in AndroidManifest.xml
Add fake code to your source code. Event the powerful decompilers likes: dex2jar, jd-gui,... can't reverse exactly your apk file. Most of functions will show with comment 'Error'.
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After transforming, if you give someone your source project, it will be nearly impossible to read and understand.
This solution doesn't exclude Proguard, You can combine them together. (function, field Obfuscation of Proguard is better than Obfuscation features of this solution)
You may read my post at: http://www.androidpit.com/en/android/forum/thread/567093/An-Analysis-of-Android-APK-Protect-Shell-APKProtect. The APK added with protect shell of APK Protect is seems unable decompile. I mean, the encrypt method is very advanced. Even a master hacker need long time to crack it.
If it is the database that contains sensitive data you can encrypt the values of several columns or the full database like mentioned in the other answer and make sure that the password is not stored on the device but has to be entered by the user on accessing the data.
If there are pieces of code you need to protect there's really no good way of securing it. All you can for a limited amount of use-cases is to create a dependency to an online service and secure the server. But for a lot of applications this would not be an option.
First, make apk that can never be modified and used. I do it by temper detection from the server. I use root check emulator check. Then on the important activity, it checks root and emulator on every oncreate and on resume, deletes important data on onpause, Great. Now encrypt data and place license to server, use SSL server. It app can not be modified and run, everything is safe for ever. Well, how to avoid decompiler and online tamper detection. I do placing a huge code to generate some sample string from apk file, and compare it with an apk copy placed on the server. I have converted apk file to string. Just enjoy.