安卓逆向 -- 自吐算法（MD5和SHA）

一、主要框架，hook代码主要填写在try代码块里

package com.bucuo.a20210908;
import android.app.Application;
import android.content.Context;
import android.util.Log;
import de.robv.android.xposed.IXposedHookLoadPackage;
import de.robv.android.xposed.XposedBridge;
import de.robv.android.xposed.callbacks.XC_LoadPackage.LoadPackageParam;
import static de.robv.android.xposed.XposedHelpers.findAndHookMethod;
import de.robv.android.xposed.IXposedHookLoadPackage;
import de.robv.android.xposed.XC_MethodHook;
import de.robv.android.xposed.callbacks.XC_LoadPackage.LoadPackageParam;
public class hook implements IXposedHookLoadPackage {
    public void handleLoadPackage(final LoadPackageParam loadPackageParam) throws Throwable {
        Log.d("逆向有你", "hook成功");
        try{
        }catch (Exception e){
            e.printStackTrace();
        }
    }
    public String b2s(byte[] bt){
        StringBuffer sb=new StringBuffer();
        int i=0;
        while (i<bt.length){
            int k=bt[i];
            int j=k;
            if (k<0){
                j=k+256;
            }
            if (j<16){
                sb.append("0");
            }
            sb.append(Integer.toHexString(j));
            i+=1;
        }
        return sb.toString();
    }
}

二、MD5算法实现源码（SHA算法同理）

import java.security.MessageDigest;
String bs= "逆向有你a";
MessageDigest md=MessageDigest.getInstance("MD5");//我要用md5算法
md.update(bs.getBytes());//我要加密的数据
byte[] res = md.digest();//给我加密
System.out.println("MD5加密（字节）："+Arrays.toString(res));
System.out.println("MD5加密（字符串）："+bytes2HexString(res));
MessageDigest mdmd = MessageDigest.getInstance("MD5");
mdmd.update("逆向".getBytes(StandardCharsets.UTF_8));
mdmd.update("有你".getBytes(StandardCharsets.UTF_8));
byte[] mdmdres = mdmd.digest("a".getBytes(StandardCharsets.UTF_8));
System.out.println(bytes2HexString(mdmdres));

三、分析要hook的地方

1、hook的类就是导入的包，即“java.security.MessageDigest”

2、update可以使用多次（如果hook这里会无限循环）， digest只能使用一次（这里是hook点）

四、知道hook的类及方法名，开始编写代码

XposedBridge.hookAllMethods(XposedHelpers.findClass("java.security.MessageDigest", loadPackageParam.classLoader)
        , "digest",
        new XC_MethodHook() {
            @Override
            protected void afterHookedMethod(MethodHookParam param) throws Throwable {
                super.afterHookedMethod(param);
                Log.e("逆向有你", "Stack：", new Throwable("stack dump"));
                MessageDigest md = (MessageDigest) param.thisObject;//实例化
                String algorithm = md.getAlgorithm();//获取加密算法的名称
                if (param.args.length >= 1) {
                    byte[] params = (byte[]) param.args[0];
                    String data = new String(params);
                    String datahex = b2s(params);
                    String datab64 = Base64.encodeToString(params, 0);
                    Log.d("逆向有你",algorithm+"data:"+data);
                    Log.d("逆向有你",algorithm+"datahex:"+datahex);
                    Log.d("逆向有你",algorithm+"datab63:"+datab64);
                }
                byte[] res=(byte[])param.getResult();
                String reshex = b2s(res);
                String resb64 = Base64.encodeToString(res, 0);
                Log.d("逆向有你",algorithm+"resulthex:"+reshex);
                Log.d("逆向有你",algorithm+"resultb64:"+resb64);
                Log.d("逆向有你","========================================================================");
            }
        });

禁止非法，后果自负

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