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:

1 try {
2       PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 64);
3       Signature sign = info.signatures[0];
4       Log.i("test", "hashCode : " + sign.hashCode());
5     } catch (NameNotFoundException e) {
6       e.printStackTrace();
7     }

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然后我们用JNI c语言实现,同样需要传递Context：

 1 int getSignHashCode(JNIEnv *env, jobject context) {
 2   //Context的类
 3   jclass context_clazz = (*env)->GetObjectClass(env, context);
 4   // 得到 getPackageManager 方法的 ID
 5   jmethodID methodID_getPackageManager = (*env)->GetMethodID(env, context_clazz,
 6       "getPackageManager", "()Landroid/content/pm/PackageManager;");
 7  
 8   // 获得PackageManager对象
 9   jobject packageManager = (*env)->CallObjectMethod(env, context,
10       methodID_getPackageManager);
11 //    // 获得 PackageManager 类
12   jclass pm_clazz = (*env)->GetObjectClass(env, packageManager);
13   // 得到 getPackageInfo 方法的 ID
14   jmethodID methodID_pm = (*env)->GetMethodID(env, pm_clazz, "getPackageInfo",
15       "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");
16 //
17 //    // 得到 getPackageName 方法的 ID
18   jmethodID methodID_pack = (*env)->GetMethodID(env, context_clazz,
19       "getPackageName", "()Ljava/lang/String;");
20  
21   // 获得当前应用的包名
22   jstring application_package = (*env)->CallObjectMethod(env, context,
23       methodID_pack);
24   const char *str = (*env)->GetStringUTFChars(env, application_package, 0);
25   __android_log_print(ANDROID_LOG_DEBUG, "JNI", "packageName: %s
", str);
26  
27   // 获得PackageInfo
28   jobject packageInfo = (*env)->CallObjectMethod(env, packageManager,
29       methodID_pm, application_package, 64);
30  
31   jclass packageinfo_clazz = (*env)->GetObjectClass(env, packageInfo);
32   jfieldID fieldID_signatures = (*env)->GetFieldID(env, packageinfo_clazz,
33       "signatures", "[Landroid/content/pm/Signature;");
34   jobjectArray signature_arr = (jobjectArray)(*env)->GetObjectField(env,
35       packageInfo, fieldID_signatures);
36   //Signature数组中取出第一个元素
37   jobject signature = (*env)->GetObjectArrayElement(env, signature_arr, 0);
38   //读signature的hashcode
39   jclass signature_clazz = (*env)->GetObjectClass(env, signature);
40   jmethodID methodID_hashcode = (*env)->GetMethodID(env, signature_clazz,
41       "hashCode", "()I");
42   jint hashCode = (*env)->CallIntMethod(env, signature, methodID_hashcode);
43   __android_log_print(ANDROID_LOG_DEBUG, "JNI", "hashcode: %d
", hashCode);
44   return hashCode;
45 }

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