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.
Related
I was wondering what should be an ideal way for placing API keys, salts, or even private keys for encryption and ship them along with the APK. While doing research on this I saw a couple of methods widely used for placing some of these details:-
Place this info in gradle.properties - This is the simplest solution for placing these details but it is not secure at all. The information stored here can easily be extracted from the APK.
Store it in cpp - Create CPP files in the codebase where these details are placed and write JNIs to extract out these details when needed. This makes it harder for the attacker to extract out these details but it still is extractable
I read a couple of posts of which recommended using Keystore for securely storing this information but while seeing implementation at a couple of places I inferred that it usually stores values in runtime and I didn’t find any details on how to ship some salts or API keys along with the APK.
I wanted to know if there is any way for securely placing salts, API keys, etc along with the shipped APK. Or we can somehow use Keystore for this. Any help or suggestion will be really appreciated. Thank You!
Using this library You can easily secaure your api
https://github.com/MEiDIK/Cipher.so
Read Carefully there installation Process and still have any doubts or error i will help you
MD5 fingerprint of any app can be easily acquired using keytool. Then what is the most unique identifier an app has?
I am trying to build a client server app and I want a secure the communications.
My problem revolves around these two assumptions -
1) Someone can reverse engineer my app and understand how I interact with server webservices
2) My app can be simply uninstalled and replaced with malicious app with similar package name.
The system can easily compromised using these two loopholes.
My solution to these problems was transmitting MD5 signature of my app to the server. The MD5 signature will be conveyed to server before hand. MD5 signature is unique for every app, But there is big problem in this approach. MD5 signature of any apk can be generated using keytool. Anyone may pull my apk and generate MD5 and use it in the webservices communication.
What is the unique identifier of an android app?
Package name and MD5 fingerprint can be easily compromised!
Basically you want to be sure that you are talking to your client app at server end.
Verify Back-End Calls from Android. This link could be helpful as it gives high confidence for such a case. (HTTPS is must here)
As an additional step for #Maddy 's answer, you might think about tamper resistance/integrity protection techniques, that will make your app inoperable in case somebody tried to modify it. DexProtector (http://dexprotector.com) could be the solution here. The slides under the link also should be helpful.
N.B.
I am Licel's CEO, thus I am affiliated with DexProtector.
First question
1) My app can be simply uninstalled and replaced with malicious app with similar package name.
best approach is probably the use of ANDROID_ID
Try this link http://blog.vogella.com/2011/04/11/android-unique-identifier/
Check this also http://android-developers.blogspot.in/2011/03/identifying-app-installations.html
Solution for the second issue
2) Someone can reverse engineer my app and understand how I interact with server webservices
Use DexGuard, which can make reverse engineering even harder, like by encrypting strings
https://www.saikoa.com/dexguard
Proguard
“The ProGuard tool shrinks, optimizes, and obfuscates your code by removing unused code and renaming classes, fields, and methods with semantically obscure names. The result is a smaller sized .apk file that is more difficult to reverse engineer.”
When you create android project.
1. proguard.cfg file is automatically generated in the root directory of the project.
2. The default configuration file only covers general cases, so customize as per your needs.
Enable it
“Set the proguard.config property in the /project.properties file. The path can be an absolute path or a path relative to the project’s root.”
Case1: Just add proguard.config=proguard.cfg if the proguard.cfg is in projects root path.
Case2: Configure from other location [proguard.config=/path/to/proguard.cfg]
Remove the “#” (or uncomment) the proguard configuring statement in project.properties. Which will be in commented initially.
Customize it. try this link http://1belong2jesus.wordpress.com/
i believe this question is already asked but i am not satisfied with their answers and posting it again here.
can someone please tell me how to safeguard my android app assets from copy cats who want to build similar app?
As always there is a trade-off between convenience and security. The more secure you want your app the less convenient it will be for you to develop.
The source code is inherently insecure due to ease of decompiling especially with rooted phone. To protect your source code you can obfuscate and/or encrypt your code which will prevent decompiling. Not exactly sure what tools are available for Android, but I am sure it will complicate your build process. If you just obfuscate, decompiling may still be possible, but will be much more difficult and will likely require the person attempting to decompile your code to know and understand Bytecode if a strong level of obfuscation is used.
To protect your assets, I believe your only option is to use encryption. Again this will complicate the app and/or build process depending on where you implement.
Even if you use encryption to protect your assets, you must protect the encryption key within your source code. Obviously, it does not matter what encryption scheme you use if your encryption key is in plaintext in the source code then anybody can grab the key and your asset and decrypt. All this does is add one more small fence to jump over.
However, if you correctly protect the encryption key and use a good encryption algorithm you should have less to worry about. This is a fairly complicated process though, it is difficult to use a key for encryption within your code and not keep it in plaintext. Even if you don't keep it in plaintext within the code, at some point it must be in memory to perform decryption. So if somebody can attach a debugger or dump memory at the right time, it will compromise the key. Of course, this requires a much more skilled adversary.
Overall, you need to decide exactly who you are worried about stealing your assets. If you are worried about the average Joe copying them, then you should be ok. If you are worried about a professional hacker, script kiddie, etc. gaining access to them then you are probably out of luck.
can someone please tell me how to safeguard my android app assets from copy cats who want to build similar app?
Generally, you can't. If it's in the app, anyone who wants to can get to them.
You are welcome to roll your own encryption scheme, or use tools like DexGuard. However, since the decryption engine and key must be in the app itself, all these do is increase the level of effort required to get to your assets. Making it more difficult will reduce the odds that somebody grabs the assets out of your APK, but it does not prevent the possibility. And, of course, there are other ways to get at much of this stuff (e.g., screenshots and image editors, recording audio played back by the app).
You can secure assets folder contents by encrypt it using strong encryption algorithms and decrypt them at runtime. Copycats cannot easily decrypt and get assets folder contents by simply extract apk using zip tools.
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'.
=====
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.
I'm not familiar with the idea of signing files, and I can't find a satisfactory answer so far, so I think I'd better ask:
What I want to know is when signing a binary file (for Android), does the signing tool assign some sort of checksum to the file so that when a hacker changed something in the apk file, the program would refuse to start because the checksum doesn't match. Does this mechanism exist in Android's signing tool?
Well, I understand when a hacker has the binary, he can disable anything he wants, including the checksum check. But the question is: Does Android's signing tool provide this level or protection in the first place?
Thank you for reading, and answering!
The answers that say "no, they can't modify your apk" are only about halfway right: Yes, no one can modify your code and resign it with your key, meaning the malicious cracker can't make the modified app look like it actually came from you. But that doesn't mean they can't modify and run the APK after resigning it with a different key.
They could take your signed APK, modify its code, and resign it themselves with their own key; they couldn't issue that app as an update or anything like that, but the modified self-signed APK would normally be installable by any user, root or not.
EDIT: Worth crawling around xda-developers to see what people are doing in that respect (some semi-legitimate, like modifying and reissuing theme APKs; other much less so). Tools like android-apktool are particularly interesting.
Also see these SO questions:
Can I re-sign an .apk with a different certificate than what it came with?
is it even possible to modify .apk, by adding additional class to .dex and re-packing with modified manifest.xml?
Android binary signing is accomplished using the Jarsigner tool, part of the standard Java SDK. Signing a jar with this tool simply adds two files; one that contains the hashed values for each file within the jar/application (the signature or .sf file), and one that verifies the signature file and identifies the signing certificate (DSA file).
So checking the signature would, yes, necessarily involve checking whether the hashes of the binary file match the provided value, which would detect any changes to the binary. And yes, the Android documentation says that the system will not install or run an application without a valid signature.
So yes, you can assume that signing your file properly will prevent it from running after being altered.
Yes, the OS must check that the content of the binary actually matches up to the signature. It would be worthless otherwise - someone could just take a signature from a legitimate application and stick it on to any other binary.