How to check android apk integrity/tampering at runtime

TamperUtils.java

package com.twinpeek.android.app;

import java.io.File;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;

import android.content.Context;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.Signature;
import android.os.Build;
import android.util.Log;

/**
 * Created by ChrisC on 20/06/17.
 */
public class TamperUtils {

    private TamperUtils() {
        //prevent instantiation
    }

    private static final String SIGNATURE = "Your apk signature";
    private static final String PLAY_STORE_APP_ID = "com.android.vending";
    public static final String TAG = TamperUtils.class.getSimpleName();

    //computed the sha1 hash of the signature
    public static String getSHA1(byte[] sig) throws NoSuchProviderException, NoSuchAlgorithmException {
        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);
    }


    /**
     * 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 PackageManager.NameNotFoundException
     */
    public static boolean isAppSignatureValid(Context context) {

        PackageInfo packageInfo = null;
        try {
            packageInfo = context.getPackageManager().getPackageInfo(
                    context.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 SIGNATURE.equals(sha1);
            }

        } catch (PackageManager.NameNotFoundException | NoSuchAlgorithmException | NoSuchProviderException e) {
            Log.e(TAG, e.getMessage(), e);
        }
        return false;
    }


    public static boolean isFromPlayStore(final Context context) {
        final String installer = context.getPackageManager()
                .getInstallerPackageName(context.getPackageName());
        return installer != null && installer.startsWith(PLAY_STORE_APP_ID);
    }


    public static boolean isDebuggable(Context context) {

        return (context.getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0;

    }


    public static boolean isEmulator() {
        return Build.FINGERPRINT.startsWith("generic")
                || Build.FINGERPRINT.startsWith("unknown")
                || Build.MODEL.contains("google_sdk")
                || Build.MODEL.contains("Emulator")
                || Build.MODEL.contains("Android SDK built for x86")
                || Build.MANUFACTURER.contains("Genymotion")
                || (Build.BRAND.startsWith("generic") && Build.DEVICE.startsWith("generic"))
                || "google_sdk".equals(Build.PRODUCT);
    }




    private static boolean findBinary(String binaryName) {
        boolean found = false;
        if (!found) {
            String[] places = { "/sbin/", "/system/bin/", "/system/xbin/",
                    "/data/local/xbin/", "/data/local/bin/",
                    "/system/sd/xbin/", "/system/bin/failsafe/", "/data/local/" };
            for (String where : places) {
                if (new File(where + binaryName).exists()) {
                    found = true;

                    break;
                }
            }
        }
        return found;
    }

    public static boolean isRooted() {
        return findBinary("su");
    }
}