編碼環境：android API 19+Android studio

功能：開啟應用呼叫os庫的init方法校驗app是否被篡改!
流程：
—>開啟應用
—>os庫中init方法
—>C層獲取應用簽名（md5/sha1）
—>和本地正常的簽名對比
—>匹配不成功直接在C中退出應用。

實現：

在java層，新建一個native方法如：

public static native void init();

在jni下面新建一個.c檔案，名字隨意如test.c,在該檔案中要實現獲取應用簽名，對比，退出應用。
這個地方的init方法可以使用動態註冊的方式避免又長又臭的方法名在C檔案中（如何動態註冊請移步：

void init(JNIEnv* env, jobject thiz){
    //獲取到Context
    jobject context= getApplication(env);
    jclass  activity = (*env)->GetObjectClass(env,context);
    // 得到 getPackageManager 方法的 ID
    jmethodID methodID_func = (*env)->GetMethodID(env,activity, "getPackageManager"
 
, "()Landroid/content/pm/PackageManager;");
    // 獲得PackageManager物件
    jobject packageManager = (*env)->CallObjectMethod(env,context,methodID_func);
    jclass packageManagerclass = (*env)->GetObjectClass(env,packageManager);
    //得到 getPackageName 方法的 ID
    jmethodID methodID_pack = (*env)->
 
GetMethodID(env,activity,"getPackageName", "()Ljava/lang/String;");
    //獲取包名
    jstring name_str = (jstring)((*env)->CallObjectMethod(env,context, methodID_pack));
    // 得到 getPackageInfo 方法的 ID
    jmethodID methodID_pm = (*env)->GetMethodID(env,packageManagerclass,"getPackageInfo", "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");
    // 獲得應用包的資訊
    jobject package_info = (*env)->CallObjectMethod(env,packageManager, methodID_pm, name_str, 64);
    // 獲得 PackageInfo 類
    jclass package_infoclass = (*env)->GetObjectClass(env,package_info);
    // 獲得簽名陣列屬性的 ID
    jfieldID fieldID_signatures = (*env)->GetFieldID(env,package_infoclass,"signatures", "[Landroid/content/pm/Signature;");
    // 得到簽名陣列，待修改
    jobject signatur = (*env)->GetObjectField(env,package_info, fieldID_signatures);
    jobjectArray  signatures = (jobjectArray)(signatur);
    // 得到簽名
    jobject signature = (*env)->GetObjectArrayElement(env,signatures, 0);
    // 獲得 Signature 類，待修改
    jclass signature_clazz = (*env)->GetObjectClass(env,signature);
    //---獲得簽名byte陣列
    jmethodID tobyte_methodId = (*env)->GetMethodID(env,signature_clazz, "toByteArray", "()[B");
    jbyteArray signature_byte = (jbyteArray) (*env)->CallObjectMethod(env,signature, tobyte_methodId);
    //把byte陣列轉成流
    jclass byte_array_input_class=(*env)->FindClass(env,"java/io/ByteArrayInputStream");
    jmethodID init_methodId=(*env)->GetMethodID(env,byte_array_input_class,"<init>","([B)V");
    jobject byte_array_input=(*env)->NewObject(env,byte_array_input_class,init_methodId,signature_byte);
    //例項化X.509
    jclass certificate_factory_class=(*env)->FindClass(env,"java/security/cert/CertificateFactory");
    jmethodID certificate_methodId=(*env)->GetStaticMethodID(env,certificate_factory_class,"getInstance","(Ljava/lang/String;)Ljava/security/cert/CertificateFactory;");
    jstring x_509_jstring=(*env)->NewStringUTF(env,"X.509");
    jobject cert_factory=(*env)->CallStaticObjectMethod(env,certificate_factory_class,certificate_methodId,x_509_jstring);
    //certFactory.generateCertificate(byteIn);
    jmethodID certificate_factory_methodId=(*env)->GetMethodID(env,certificate_factory_class,"generateCertificate",("(Ljava/io/InputStream;)Ljava/security/cert/Certificate;"));
    jobject x509_cert=(*env)->CallObjectMethod(env,cert_factory,certificate_factory_methodId,byte_array_input);

    jclass x509_cert_class=(*env)->GetObjectClass(env,x509_cert);
    jmethodID x509_cert_methodId=(*env)->GetMethodID(env,x509_cert_class,"getEncoded","()[B");
    jbyteArray cert_byte=(jbyteArray)(*env)->CallObjectMethod(env,x509_cert,x509_cert_methodId);

    //MessageDigest.getInstance("SHA1")
    jclass message_digest_class=(*env)->FindClass(env,"java/security/MessageDigest");
    jmethodID methodId=(*env)->GetStaticMethodID(env,message_digest_class,"getInstance","(Ljava/lang/String;)Ljava/security/MessageDigest;");
    //如果取SHA1則輸入SHA1
    //jstring sha1_jstring=(*env)->NewStringUTF(env,"SHA1");
    jstring sha1_jstring=(*env)->NewStringUTF(env,"MD5");
    jobject sha1_digest=(*env)->CallStaticObjectMethod(env,message_digest_class,methodId,sha1_jstring);
    //sha1.digest (certByte)
    methodId=(*env)->GetMethodID(env,message_digest_class,"digest","([B)[B");
    jbyteArray sha1_byte=(jbyteArray)(*env)->CallObjectMethod(env,sha1_digest,methodId,cert_byte);
    //toHexString
    jsize array_size=(*env)->GetArrayLength(env,sha1_byte);
    jbyte* sha1 =(*env)->GetByteArrayElements(env,sha1_byte,NULL);
    char hex_sha[array_size*2+1];
    int i;
    for (i = 0;i<array_size;++i) {
        hex_sha[2*i]=HexCode[((unsigned char)sha1[i])/16];
        hex_sha[2*i+1]=HexCode[((unsigned char)sha1[i])%16];
    }
    hex_sha[array_size*2]='\0';
    LOGV("sin-sha1:%s",hex_sha);
    const  char *sign=(*env)->GetStringUTFChars(env,signstr,NULL);
    if (strcmp(hex_sha,sha1final)!=0){
        LOGV("驗證不通過！");
        exitApplication(env,0);
    }else{
        LOGV("驗證通過！");
    }
}

獲取Context上下文方法：

jobject getApplication(JNIEnv *env) {
    jclass localClass = (*env)->FindClass(env,"android/app/ActivityThread");
    if (localClass!=NULL)
    {
        // LOGI("class have find");
        jmethodID getapplication = (*env)->GetStaticMethodID(env,localClass, "currentApplication", "()Landroid/app/Application;");
        if (getapplication!=NULL)
        {
            jobject application = (*env)->CallStaticObjectMethod(env,localClass, getapplication);
            return application;
        }
        return NULL;
    }
    return NULL;
}

直接退出應用方法:（直接尋找到java/lang/Systemz這個類）

void exitApplication(JNIEnv *env, jint flag){
    jclass temp_clazz = NULL;
    jmethodID mid_static_method;
    // 1、從classpath路徑下搜尋ClassMethod這個類，並返回該類的Class物件
    temp_clazz =(*env)->FindClass(env,"java/lang/System");
    mid_static_method = (*env)->GetStaticMethodID(env,temp_clazz,"exit","(I)V");
    (*env)->CallStaticVoidMethod(env,temp_clazz,mid_static_method,flag);
    (*env)->DeleteLocalRef(env,temp_clazz);
}

常量

const char HexCode[]={'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
const char *sha1final="3A0558B19DE14EEC82FFA3721CED4AA9";

以上程式碼即可實現在應用中直接呼叫init方法即可觸發校驗。