Protect string constant against reverse-engineering

I have android application that has hard coded (static string constants) credentials (user/pass) for sending emails via SMTP.

The problem is that .dex file in .apk can be easily reverse-engineered and everybody can see my password.

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  • 8 Solutions collect form web for “Protect string constant against reverse-engineering”

    We can use “jni module” to keep ‘Sensitive Hardcoded Strings’ in the app. when we try to reverse engineer APK file we get lib folder and .so files in respective process-folders. which can not decrypt.

    I guess you can try a code obfuscator, but really that won’t make your password 100% secure and I don’t know how well it goes along with the android compiler. Why not use a secured web authentication , like that of Google?

    You can save your string obfuscated by AES.

    In Licensing Verification Library you can find AESObfuscator. In LVL it is used to obfuscate cached license info that is read instead of asking Android Market to find out application is licensed or not. LVL can be downloaded as component of SDK.

    1. Hashing is not possible since it is not two way.
    2. Any encryption such as AES, DES, blowfish, etch is not a viable solution as you have to include the decryption part within your app and that can be decompiled with a combination of apktool, dex2jar and JD (java decompiler) which is a very powerful combo while decompiling any apk.
    3. Even code obfuscators don’t do anything except make life a little more difficult for the decompiling guy, who’ll eventually get it anyways.

    The only way which I think would work to an extent would be to host the credentials on a server which only your application can access via a web-service call through a separate authentication of some kind – similar to FB’s hash key thing. If it works for them, it should work for us.

    I was looking into a similar problem and came across this useful thread:
    http://www.dreamincode.net/forums/topic/208159-protect-plain-string-from-decompilers/

    I’m not too familiar with Android development, but the same ideas should apply.

    If you do not have the means to do a web authorization you will need to include the third party decryption with you application.

    This is what you could try
    1) Write a standalone program only to create a password hash one time. (This program should not be a part of your app). Make a note of the hash that was generated.
    http://www.mindrot.org/projects/jBCrypt/

     // Hash a password for the first time.
        String hashed = BCrypt.hashpw(password, BCrypt.gensalt(12));
    

    2) Store this password hash as a String constant in you APK.

    3) Then every time you need to check the password, compare with the hashed password, using bcrypt.

    // Check that an unencrypted password matches one that has
    // previously been hashed
    if (BCrypt.checkpw(candidate, hashed))
        System.out.println("It matches");
    else
        System.out.println("It does not match");
    

    jBCrypt is a single java file and it can be directly included in your application. It is considered one of the strongest encryption algorithms for passwords.
    Even through the decryption algorithm is present in you APK, trying to break this is very time consuming details of which can be read in the article below.

    Read this article for details and security of bcrypt.
    http://codahale.com/how-to-safely-store-a-password/

    Again, use this only if you do not have the means to do web based authentication.

    Use some kind of trivial encryption or cipher that only you (and your code) understand. Reverse the string, store it as array of integers where you need to take the mod of 217 or something silly to find the real password.

    One way you can 100% secure you hard-coded string.
    Firstly don’t use pro-guard use allatori
    Link: http://www.allatori.com/

    And secondly don’t take you hard coded string in any variable just use that string like this:

    if(var=="abc"){}
    

    "abc" is exampled hard coded string.

    Allatori fully obfuscate all string that are used in code like above.

    Hope it will help for you.

    Android Babe is a Google Android Fan, All about Android Phones, Android Wear, Android Dev and Android Games Apps and so on.