JNI_Onload—c++

发表于 | 分类于 | 作者：ESE

要逆向，必须会正向编写。so文件混淆——jni_load()——c++

JNI_Onload编写

利用JNI_Onload()函数

check.java

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package com.example.ese.zjgsuctf;
public class check {
    static {
        System.loadLibrary("check");
    }
    public native static String check(String sstr);
}

check.cpp

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#include<iostream>
#include <string.h>
#include <jni.h>
#include <stdio.h>
#include <assert.h>
#include <android/log.h>
#include "com_example_ese_zjgsuctf1_check.h"
#define JNIREG_CLASS "com/example/ese/zjgsuctf1/check"//指定要注册的类
struct Node{
	int data;
	Node *Pnext;
};
int enc_flag[]={52,67,41,1,31,85,44,87,46,89,19,111,55,0,46,91,31,69,112,73,20};
Node *ceateList(char *str){
	int len=0;
	Node *pHead = (Node *)malloc(sizeof(Node));
	Node *pTail = pHead;
	pTail->Pnext = NULL;
	if(pHead == NULL)
	{
		exit(-1);
	}
    while(str[len] != '\0')
    {
        len++ ;
    }
	pTail->data = len;
	for(int i=0;i<len;i++)
	{
		Node *pNew = (Node *)malloc(sizeof(Node));
		if(pNew == NULL)
		{
			exit(-1);
		}
		if(i%2==0)
		{
			pNew->data = str[i]^0x30;
		}else
		{
			pNew->data = str[i]^0x40;
		}
		pNew->Pnext = NULL;
		pTail->Pnext = pNew;
		pTail = pNew;
	}
	return pHead;
}
Node *insert(Node *lst,int pos,int data)
{
	int i=0;
    Node *pTmp = lst;
	while(i<pos&&lst!=NULL)
	{
		lst=lst->Pnext;
		i++;
	}
	Node *pNew = (Node *)malloc(sizeof(Node));
	if(pNew == NULL)
	{
		exit(-1);
	}
	pNew->data = data;
	pNew->Pnext = lst->Pnext;
	lst->Pnext = pNew;
	return pTmp;
}
Node *deletet(Node *lst,int pos,int data)
{
	int i=0;
    Node *pTmp = lst;
	if(lst==NULL)
	{
		return lst;
	}
	while(i<pos&&lst!=NULL)
	{
		lst=lst->Pnext;
		i++;
	}
	Node *pNew = (Node *)malloc(sizeof(Node));
	if(pNew == NULL)
	{
		exit(-1);
	}
	pNew = lst->Pnext->Pnext;
	lst->Pnext = pNew;
	return pTmp;
}
int select(Node *lst,int pos)
{
	int i=0;
	if(lst==NULL)
	{
		return 0;
	}
	while(i<pos&&lst!=NULL)
	{
		lst=lst->Pnext;
		i++;
	}
	return lst->data;
}
Node *reverseList(Node *lst){
	if(lst==NULL || lst->Pnext == NULL)
	{
		return lst;
	}
	Node *pTmp = reverseList(lst->Pnext);
	lst->Pnext->Pnext=lst;
	lst->Pnext = NULL;
	return pTmp;
}
int displayList(Node *lst)
{
	int i=0;
	Node *tmp = lst;
	while(tmp != NULL)
	{
		if(tmp->data!=enc_flag[i])
		{
			return 0;
		}
		i++;
		tmp = tmp->Pnext;
	}
	return 1;
}
int crypt(char *str)
{
	//string str = "y0u_kn0w_Single_1ist";
	Node *list1 = ceateList(str);
	list1 = reverseList(list1);
	if(displayList(list1))
	{
		return 1;
	}
	return 0;
}
//JNI
__attribute__((section (".mytext")))jstring esecheck( JNIEnv* env,jobject thiz,jstring str1)
{
    //LOGV("This is esecheck()");
            char* str = (char*)env->GetStringUTFChars(str1, NULL);
            if(str == NULL) {
                return NULL;
            }
            int key = crypt(str);
            char* tmpstr = "succeeded";
            if(key)
            {
                    jstring rtstr = env->NewStringUTF(tmpstr);
                    return rtstr;
            }else{
                    tmpstr = "failed!!";
                    jstring rtstr = env->NewStringUTF(tmpstr);
                    return rtstr;
            }
}
     /**
     * Table of methods associated with a single class.
     */
static JNINativeMethod gMethods[] = {//绑定，注意，V,Z签名的返回值不能有分号“;”
    { "check", "(Ljava/lang/String;)Ljava/lang/String;", (void*)esecheck},
};
     /*
     * Register several native methods for one class.
     */
     static int registerNativeMethods(JNIEnv* env, const char* className,
             JNINativeMethod* gMethods, int numMethods)
     {
        jclass clazz;
        clazz = env->FindClass( className);
        if (clazz == NULL) {
            return JNI_FALSE;
        }
        if (env->RegisterNatives(clazz, gMethods, numMethods) < 0) {
            return JNI_FALSE;
        }
        return JNI_TRUE;
     }
     /*
     * Register native methods for all classes we know about.
     */
     static int registerNatives(JNIEnv* env)
     {
        if (!registerNativeMethods(env,JNIREG_CLASS, gMethods,
                                      sizeof(gMethods) / sizeof(gMethods[0])))
            return JNI_FALSE;
        return JNI_TRUE;
     }
     /*
     * Set some test stuff up.
     *
     * Returns the JNI version on success, -1 on failure.
     */
jint JNI_OnLoad(JavaVM* vm, void* reserved)
     {
        JNIEnv* env = NULL;
        jint result = -1;
        if (vm->GetEnv((void**) &env, JNI_VERSION_1_4) != JNI_OK) {
                return result;
         }
        assert(env != NULL);
        if (!registerNatives(env)) {//注册
            return -1;
        }
        /* success -- return valid version number */
        result = JNI_VERSION_1_4;
        return result;
     }

Application.mk

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APP_ABI := armeabi-v7a
APP_STL:=stlport_static

Android

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LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := check
LOCAL_SRC_FILES := check.cpp
include $(BUILD_SHARED_LIBRARY)
LOCAL_CFLAGS := -fvisibility=hidden    #隐藏符号表

调用

在app目录下的build.gradle中添加

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android {
       ......
    sourceSets {
        main() {
            jniLibs.srcDirs = ['src/main/libs']
            jni.srcDirs = [] //屏蔽掉默认的jni编译生成过程
        }
    }
}

这时一个简单的输入结构:

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activity_main.xml
{
    .....
    <EditText
        android:id="@+id/input_flag"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="80dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="100dp"
        android:ems="10"
        android:inputType="textPersonName"
        android:hint="input your flag"
        app:layout_constraintBottom_toTopOf="@+id/button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:ignore="UnknownId" />
    <Button
        android:id="@+id/input_ok"
        android:layout_width="102dp"
        android:layout_height="45dp"
        android:layout_marginBottom="276dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:text="确认"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.458"
        app:layout_constraintStart_toStartOf="parent"
        tools:ignore="MissingConstraints" />
}

MainActivity结构

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import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final EditText sstr = (EditText) findViewById(R.id.input_flag);
        final Button ok = (Button) findViewById(R.id.input_ok);
        ok.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String st = sstr.getText().toString().trim();
                String res = check.Check(st);
                Toast.makeText(MainActivity.this, res, Toast.LENGTH_SHORT).show();
            }
        });
    }
}

运行就可以得到调用native方法的apk了。

优点

1.源码改动少，只需要添加JNI_Onload函数
2.无需加解密so，就可以实现混淆so中的JNI函数
3.后续可以添加so加解密，使破解难度更大

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