【移動安全技術】-Java呼叫C函式_JNI

前言

??課程內容：Jni、Ndk、so、Ida，

??使用Jni實作java程式呼叫其它開發語言的函式，

??環境：NDK，CMake，

??實驗：用java呼叫C函式，

AS配置C語言環境

??通過科學上網方式，下載安裝 NDK 和 Cmake，
位置：File -> Settings -> Appearance -> System Settings -> Android SDK，

??創建C++專案

??查看CMakeLists.txt檔案的內容：

??查看MainActivity.java，可以看到加載了native-lib庫，并且宣告了相關的native方法 stringFromJNI()：

??查看native-lib.cpp，可以看到stringFromJNI方法，作用是通過C++回傳一個string資料：

撰寫登錄app，使用C語言實作驗證功能

程式原始碼

??（1）MainActivity.java

package com.example.hellojni;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;

import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import androidx.appcompat.app.AppCompatActivity;
import android.text.InputType;


public class MainActivity extends AppCompatActivity {

    //final String  username = "xiaoshen";
    //final String  passwd = "nihaoya";
    final String right = "恭喜小沈通過驗證！";
    final String wrong = "驗證失敗，加油！";
    String input_username = "";
    String input_passwd = "";



    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final EditText et1 = (EditText) findViewById(R.id.input_username);
        final EditText et2 = (EditText) findViewById(R.id.password);


        Button mybutton_1 = (Button) findViewById(R.id.login_in);

        mybutton_1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 點擊按鈕彈出文本
                input_username = et1.getText().toString();
                input_passwd = et2.getText().toString();

                //Toast.makeText(MainActivity.this, "點擊成功", Toast.LENGTH_SHORT).show();

                Verify();

            }
        }
        );

        Button mybutton_2 = (Button) findViewById(R.id.login_out);

        mybutton_2.setOnClickListener(new View.OnClickListener() {
            @Override 
            public void onClick(View v) {
                // 點擊按鈕彈出文本
                //input_passwd = et2.getText().toString();
                Toast.makeText(MainActivity.this, "請進行登陸驗證", Toast.LENGTH_SHORT).show();
            }
        }
        );


    }
    public void Verify() {

        if (checkNameAndPasswd(input_username, input_passwd)==1) {

            Toast.makeText(MainActivity.this, right, Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(MainActivity.this, wrong, Toast.LENGTH_SHORT).show();
        }
    }



    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native int checkNameAndPasswd(String uname, String passwd);

}

??（2）string.xml

<resources>
    <string name="app_name">HelloJni</string>
    <string name="xitong">網路準入認證系統</string>
    <string name="username">小沈</string>
    <string name="passwd">加油！</string>
    <string name="in">登錄</string>
    <string name="out">注銷</string>
    <string name="input1">用戶名</string>
    <string name="input2">密碼</string>

</resources>

??（3）colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#008577</color>
    <color name="colorAccent">#D81B60</color>
    <color name="colorPrimaryDark">#00574B</color>
    <color name="blue">#ff00ff</color>
    <color name="red">#ff0000</color>

</resources>

??（4）activity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/textView4"


            android:text="@string/input1"
            android:layout_width="70dp"
            android:layout_height="52dp"
            android:textSize="20dp"

            android:layout_marginTop="285dp"
            android:layout_marginLeft="20dp"


            tools:text="@string/input1" />

        <EditText
            android:id="@+id/input_username"


            android:layout_width="300dp"
            android:layout_height="52dp"


            android:hint="@string/username"
            android:layout_marginTop="280dp"
            android:inputType="text" />


    </LinearLayout>

    <LinearLayout
        android:orientation="vertical"
        android:layout_width="match_parent"
        android:layout_height="match_parent">


        <TextView
            android:id="@+id/title"
            android:layout_width="260dp"
            android:layout_height="50dp"

            android:text="@string/xitong"
            android:layout_marginTop="200dp"

            android:layout_gravity="center"
            android:textSize="30sp"
            android:textColor="#000000"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal">

        <TextView
            android:id="@+id/in_pass"


            android:text="@string/input2"
            android:layout_width="70dp"
            android:layout_height="52dp"
            android:textSize="20dp"

            android:layout_marginTop="402dp"
            android:layout_marginLeft="20dp"


            tools:text="@string/input2" />



        <EditText
            android:id="@+id/password"
            android:layout_width="280dp"
            android:layout_height="52dp"


            android:ems="10"
            android:hint="@string/passwd"
            android:gravity="center_vertical"
            android:layout_marginTop="400dp"
            android:textSize="17sp"
            android:inputType="textPassword" />

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        tools:layout_editor_absoluteX="411dp">

        <Button
            android:id="@+id/login_in"
            android:layout_width="100dp"
            android:layout_height="50dp"
            android:layout_marginTop="480dp"
            android:layout_marginLeft="80dp"
            android:background="@color/blue"
            android:text="@string/in" />

        <Button
            android:id="@+id/login_out"
            android:layout_width="100dp"
            android:layout_height="50dp"
            android:layout_marginLeft="50dp"
            android:layout_marginTop="480dp"
            android:background="@color/red"
            android:text="@string/out" />
    </LinearLayout>



</androidx.constraintlayout.widget.ConstraintLayout>

??（5）C語言驗證程式native-lib.cpp

#include <jni.h>
#include <string>


extern "C" JNIEXPORT jint JNICALL
Java_com_example_hellojni_MainActivity_checkNameAndPasswd(
        JNIEnv* env,
        jobject thiz, jstring uname, jstring passwd) {

    // 獲取 uname 和 passwd
    //const char *real_uname = "xianshen233";
    //const char *real_passwd = "61happy";

    char real_uname[20] = "xiaoshen233";
    char real_passwd[20] = "61happy";


    // 接收變數：用戶名uname、口令passwd，賦值給指標unameC、passwdC，
    const char *unameC = (char *)(env->GetStringUTFChars(uname, JNI_FALSE));
    const char *passwdC = (char *)(env->GetStringUTFChars(passwd, JNI_FALSE));

    // 將接收的變數，分別賦值給對應的陣列，unameCC和passwdCC，
    int len_uname = strlen(unameC);
    int len_passwd = strlen(passwdC);

    char unameCC[len_uname];
    char passwdCC[len_passwd];
    strcpy(unameCC, unameC);
    strcpy(passwdCC, passwdC);

    // 對兩隊陣列進行驗證，strcmp()相等時回傳0，
    if((strcmp(real_uname, unameCC)==0) && (strcmp(real_passwd, passwdCC)==0)){
        return 1;
    }
    else{
        return 0;
    }
}

驗證

??輸入正確的用戶名、以及錯誤的口令，驗證失敗，

??輸入正確的用戶名、以及正確的口令，驗證成功！

??把專案打包成APK檔案：
工具列點擊“Build”，在下拉欄選擇“Generate Signed Bundle /APK”，在彈出的對話框中選擇APK，在彈框中任意填寫資訊，此處口令填寫為123456，Build Variants選擇release，勾選V2，點擊Finish完成，

逆向破解

??使用IDA對上一位同學的app進行破解，未成功，

參考

??《NDK開發-ReleaseStringUTFChars呼叫的坑》
https://segmentfault.com/a/1190000005859213

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