转：Android开发：使用JNI读取应用签名

    博文转自http://www.tuicool.com/articles/UVjme2r,感谢博主的分享

    为了防止被反编译，打算把关键代码写到so里(比如加解密)，在so里加上判断APk包签名是否一致的代码，避免so被二次打包。其实用JNI读签名就是用了Java的反射机制。

    先看Java读取签名的方法:

try {
      PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 64);
      Signature sign = info.signatures[0];
      Log.i("test", "hashCode : " + sign.hashCode());
    } catch (NameNotFoundException e) {
      e.printStackTrace();
    }

    然后我们用JNI c语言实现,同样需要传递Context：

int getSignHashCode(JNIEnv *env, jobject context) {
  //Context的类
  jclass context_clazz = (*env)->GetObjectClass(env, context);
  // 得到 getPackageManager 方法的 ID
  jmethodID methodID_getPackageManager = (*env)->GetMethodID(env, context_clazz,
      "getPackageManager", "()Landroid/content/pm/PackageManager;");
 
  // 获得PackageManager对象
  jobject packageManager = (*env)->CallObjectMethod(env, context,
      methodID_getPackageManager);
//    // 获得 PackageManager 类
  jclass pm_clazz = (*env)->GetObjectClass(env, packageManager);
  // 得到 getPackageInfo 方法的 ID
  jmethodID methodID_pm = (*env)->GetMethodID(env, pm_clazz, "getPackageInfo",
      "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");
//
//    // 得到 getPackageName 方法的 ID
  jmethodID methodID_pack = (*env)->GetMethodID(env, context_clazz,
      "getPackageName", "()Ljava/lang/String;");
 
  // 获得当前应用的包名
  jstring application_package = (*env)->CallObjectMethod(env, context,
      methodID_pack);
  const char *str = (*env)->GetStringUTFChars(env, application_package, 0);
  __android_log_print(ANDROID_LOG_DEBUG, "JNI", "packageName: %s
", str);
 
  // 获得PackageInfo
  jobject packageInfo = (*env)->CallObjectMethod(env, packageManager,
      methodID_pm, application_package, 64);
 
  jclass packageinfo_clazz = (*env)->GetObjectClass(env, packageInfo);
  jfieldID fieldID_signatures = (*env)->GetFieldID(env, packageinfo_clazz,
      "signatures", "[Landroid/content/pm/Signature;");
  jobjectArray signature_arr = (jobjectArray)(*env)->GetObjectField(env,
      packageInfo, fieldID_signatures);
  //Signature数组中取出第一个元素
  jobject signature = (*env)->GetObjectArrayElement(env, signature_arr, 0);
  //读signature的hashcode
  jclass signature_clazz = (*env)->GetObjectClass(env, signature);
  jmethodID methodID_hashcode = (*env)->GetMethodID(env, signature_clazz,
      "hashCode", "()I");
  jint hashCode = (*env)->CallIntMethod(env, signature, methodID_hashcode);
  __android_log_print(ANDROID_LOG_DEBUG, "JNI", "hashcode: %d
", hashCode);
  return hashCode;
}

    第二个参数jobject不是JNI函数的默认参数，而是传入的Context实例。