apk加固原理之dex加密

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apk加固原理之dex加密
原理其实不复杂，加固其实就是加密dex文件，防止dex专程jar 被阅读。后面才是热部署解密dex；
代码如下,注释有解释：
import android.os.Environment;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;import android.util.Log;import java.io.ByteArrayOutputStream;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;import java.util.zip.Adler32;public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        mergeDex();    }    private void mergeDex() {        File forceApk=new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/zzz/force.apk");        File unShellDex=new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/zzz/classes.dex");        File mergeDex = new File(Environment.getExternalStorageDirectory().getAbsolutePath()+"/zzz/merge.dex");        try {            byte[] apkBytes = encrpt(readFileBytes(forceApk));            byte[] dexBytes = readFileBytes(unShellDex);            int apkLen = apkBytes.length;            int dexLen = dexBytes.length;            int totalLen = apkLen+dexLen+4;            byte[] newBytes=new byte[totalLen];            System.arraycopy(dexBytes,0,newBytes,0,dexLen);            System.arraycopy(apkBytes,0,newBytes,dexLen,apkLen);            System.arraycopy(intToByte(apkLen),0,newBytes,totalLen-4,4);            fixFileSizeHeader(newBytes);            fixSHA1Header(newBytes);            fixCheckSumHeader(newBytes);            FileOutputStream fileOutputStream=new FileOutputStream(mergeDex);            fileOutputStream.write(newBytes);            fileOutputStream.flush();            fileOutputStream.close();        } catch (Exception e) {            Log.i("mytool", e.getMessage()+"");            e.printStackTrace();        }    }    /**     * 修改dex头，CheckSum 校验码     *     * @param dexBytes     */    private static void fixCheckSumHeader(byte[] dexBytes) {        Adler32 adler = new Adler32();        adler.update(dexBytes, 12, dexBytes.length - 12);// 从12到文件末尾计算校验码        long value = adler.getValue();        int va = (int) value;        byte[] newcs = intToByte(va);        // 高位在前，低位在前掉个个        byte[] recs = new byte[4];        for (int i = 0; i < 4; i++) {            recs[i] = newcs[newcs.length - 1 - i];            System.out.println(Integer.toHexString(newcs[i]));        }        System.arraycopy(recs, 0, dexBytes, 8, 4);// 效验码赋值（8-11）        System.out.println(Long.toHexString(value));        System.out.println();    }    /**     * 修改dex头 sha1值     *     * @param dexBytes     */    private static void fixSHA1Header(byte[] dexBytes)            throws NoSuchAlgorithmException {        MessageDigest md = MessageDigest.getInstance("SHA-1");        md.update(dexBytes, 32, dexBytes.length - 32);// 从32为到结束计算sha--1        byte[] newdt = md.digest();        System.arraycopy(newdt, 0, dexBytes, 12, 20);// 修改sha-1值（12-31）        // 输出sha-1值，可有可无        String hexstr = "";        for (int i = 0; i < newdt.length; i++) {            hexstr += Integer.toString((newdt[i] & 0xff) + 0x100, 16)                    .substring(1);        }        System.out.println(hexstr);    }    /**     * 修改dex头 file_size值     *     * @param dexBytes     */    private static void fixFileSizeHeader(byte[] dexBytes) {        // 新文件长度        byte[] newfs = intToByte(dexBytes.length);        System.out.println(Integer.toHexString(dexBytes.length));        byte[] refs = new byte[4];        // 高位在前，低位在前掉个个        for (int i = 0; i < 4; i++) {            refs[i] = newfs[newfs.length - 1 - i];            System.out.println(Integer.toHexString(newfs[i]));        }        System.arraycopy(refs, 0, dexBytes, 32, 4);// 修改（32-35）    }    /**     * int 转byte[]     */    public static byte[] intToByte(int number) {        byte[] b = new byte[4];        for (int i = 3; i >= 0; i--) {            b[i] = (byte) (number % 256);            number >>= 8;        }        return b;    }    /**     * 以二进制读出文件内容     *     * @param file     * @return     */    @SuppressWarnings("resource")    private static byte[] readFileBytes(File file) throws IOException {        byte[] arrayOfByte = new byte[1024];        ByteArrayOutputStream localByteArrayOutputStream = new ByteArrayOutputStream();        FileInputStream fis = new FileInputStream(file);        while (true) {            int i = fis.read(arrayOfByte);            if (i != -1) {                localByteArrayOutputStream.write(arrayOfByte, 0, i);            } else {                return localByteArrayOutputStream.toByteArray();            }        }    }    /**     * 直接返回数据，读者可以添加自己加密方法     */    private static byte[] encrpt(byte[] srcdata) {        for (int i = 0; i < srcdata.length; i++) {            srcdata[i] = (byte) (0xFF ^ srcdata[i]);        }        return srcdata;    }}
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