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Simple Android signature check. It's not bullet proof but does increase the difficulty of backdooring the app
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", "BC");
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);
}
}
@nildeka

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nildeka commented Nov 24, 2016

This is very useful. I have some query regarding signing key verification. What if the attacker decompiles the code and remove the function of validation(even with proguarded) or modifies the actual key APP_SIGNATURE

@Tindi

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Tindi commented Apr 11, 2017

What does it mean if it return false? I keep getting false

@doridori

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doridori commented Sep 19, 2017

Lint now will warn on PackageManager.GET_SIGNATURES due to the vuln spoken about here. SO suggests dont have to worry about this from 4.4. Personally I am only allowing one signature to be present. Who uses cert chains (on android) anyway!

@doridori

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doridori commented Sep 19, 2017

For paranoia purposes, may be better to use SHA-256 also? SO

Interesting as may want to just use default security provider (no BC dependency in code snippit)

@Omar1123

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Omar1123 commented Oct 2, 2017

A SHA1 is used because it is the algorithm with which the certificates are encrypted, you can see it as a standard even though there are examples of collisions with SHA1

@AswathiRevathi

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AswathiRevathi commented Apr 16, 2018

can i get a complete example on anti tamering
?

@DimaKoz

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DimaKoz commented Jun 24, 2018

@AswathiRevathi sure. The source code of native signature check can be found here: https://github.com/DimaKoz/stunning-signature

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