Simple Android signature check. 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 `vali…

SignatureCheck.java

/*
 * Copyright 2013 Scott Alexander-Bown
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
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);
	}
  
    
}

hooking what?

What license and copyright does your published code have?

What license and copyright does your published code have?

Added header Apache License, Version 2.0. Although, as previously stated, this is not actively maintained.