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import android.content.Context; | |
import android.content.pm.PackageInfo; | |
import android.content.pm.PackageManager; | |
import android.content.pm.PackageManager.NameNotFoundException; | |
import android.content.pm.Signature; | |
public class TamperCheck { | |
//we store the hash of the signture for a little more protection | |
private static final String APP_SIGNATURE = "1038C0E34658923C4192E61B16846"; | |
/** | |
* Query the signature for this application to detect whether it matches the | |
* signature of the real developer. If it doesn't the app must have been | |
* resigned, which indicates it may been tampered with. | |
* | |
* @param context | |
* @return true if the app's signature matches the expected signature. | |
* @throws NameNotFoundException | |
*/ | |
public boolean validateAppSignature(Context context) throws NameNotFoundException { | |
PackageInfo packageInfo = context.getPackageManager().getPackageInfo( | |
getPackageName(), PackageManager.GET_SIGNATURES); | |
//note sample just checks the first signature | |
for (Signature signature : packageInfo.signatures) { | |
// SHA1 the signature | |
String sha1 = getSHA1(signature.toByteArray()); | |
// check is matches hardcoded value | |
return APP_SIGNATURE.equals(sha1); | |
} | |
return false; | |
} | |
//computed the sha1 hash of the signature | |
public static String getSHA1(byte[] sig) { | |
MessageDigest digest = MessageDigest.getInstance("SHA1"); | |
digest.update(sig); | |
byte[] hashtext = digest.digest(); | |
return bytesToHex(hashtext); | |
} | |
//util method to convert byte array to hex string | |
public static String bytesToHex(byte[] bytes) { | |
final char[] hexArray = { '0', '1', '2', '3', '4', '5', '6', '7', '8', | |
'9', 'A', 'B', 'C', 'D', 'E', 'F' }; | |
char[] hexChars = new char[bytes.length * 2]; | |
int v; | |
for (int j = 0; j < bytes.length; j++) { | |
v = bytes[j] & 0xFF; | |
hexChars[j * 2] = hexArray[v >>> 4]; | |
hexChars[j * 2 + 1] = hexArray[v & 0x0F]; | |
} | |
return new String(hexChars); | |
} | |
} |
What if the attacker decompiles the code and remove the function of validation(even with proguarded) or modifies the actual key APP_SIGNATURE
What if the attacker decompiles the code and remove the function of validation(even with proguarded) or modifies the actual key APP_SIGNATURE
There's no silver bullet in security. There will be always a way to attack an app/system. We can just make it harder for them but not impossible to hack.
Thanks for answering @tentenponce. Totally agree. I've updated the comment on the gist for extra clarity.
Please note: This was created in 2013, not actively maintained and may not be compatible with the latest Android versions. It's not particularly difficult for an attacker to decompile an .apk, find this tamper check, replace the APP_SIGNATURE with theirs and rebuild (or use method hooking to return true from
validateAppSignature()
). It'll make the task of running the .apk unsigned or with edited code slightly more time-consuming and hopefully reduce the effectiveness of automated attacker. But it's not bulletproof.
Hey can you please tell me how to get "APP_SIGNATURE" for release build?
Hey can you please tell me how to get "APP_SIGNATURE" for release build?
this might help:
https://stackoverflow.com/questions/5578871/how-to-get-apk-signing-signature
it is very easy to bypass this check by hooking
hooking what?
probably not the best, but one solution is:
packageInfo = getPackageManager().getPackageInfo(getPackageName(),PackageManager.GET_SIGNING_CERTIFICATES); signatures = packageInfo.signingInfo.getApkContentsSigners(); MessageDigest md = MessageDigest.getInstance("SHA-1"); for (Signature signature : signatures) { md.update(signature.toByteArray()); sigHash = StringEncryption.SHA1(signature.toCharsString()); }