JNI

JNI全称是Java Native Interface，一句话来说就是Java的本地接口，让Java代码可以C、C++语言进行互相调用，一些成熟的C、C++的类库，可以直接复用，一些加密、高性能要求的场景可以在Native层实现，提高反编译的难度

MD5加密

MD5加密，一般用于密码加密，一般也会加上特定的盐，而这个盐如果写在java代码上，因为是字符串常量，反编译直接就能得到，如果放在so库中，反编译的难度就会上升

配置NDK

• app模块的build.gradle文件中，配置ndk的版本，以及CMakeLists的位置

plugins {
    id 'com.android.application'
}

android {
    compileSdk 32

    ndkVersion '25.1.8937393'

    defaultConfig {
        applicationId "com.zh.nativeencrypt"
        minSdk 21
        targetSdk 32
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        externalNativeBuild {
            cmake {
                cppFlags ''
            }
        }
    }

    externalNativeBuild {
        cmake {
            path file('src/main/cpp/CMakeLists.txt')
            version '3.18.1'
        }
    }

    buildFeatures {
        viewBinding true
    }
}

MD5头文件

• 头文件，定义暴露的函数

#ifndef MD5_H
#define MD5_H

#include <string>
#include <fstream>

/* Type define */
typedef unsigned char byte;
typedef unsigned int uint32;

using std::string;
using std::ifstream;

/* MD5 declaration. */
class MD5 {
public:
    MD5();

    MD5(const void *input, size_t length);

    MD5(const string &str);

    MD5(ifstream &in);

    void update(const void *input, size_t length);

    void update(const string &str);

    void update(ifstream &in);

    byte *digest();

    string toString();

    void reset();

private:
    void update(const byte *input, size_t length);

    void final();

    void transform(const byte block[64]);

    void encode(const uint32 *input, byte *output, size_t length);

    void decode(const byte *input, uint32 *output, size_t length);

public:
    string bytesToHexString(byte *input, size_t length);

    /* class uncopyable */
    MD5(const MD5 &);

    MD5 &operator=(const MD5 &);

private:
    uint32 _state[4]; /* state (ABCD) */
    uint32 _count[2]; /* number of bits, modulo 2^64 (low-order word first) */
    byte _buffer[64]; /* input buffer */
    byte _digest[16]; /* message digest */
    bool _finished;   /* calculate finished ? */

    static const byte PADDING[64]; /* padding for calculate */
    static const char HEX[16];
    enum {
        BUFFER_SIZE = 1024
    };
};

#endif /*MD5_H*/

MD5.cpp文件

• cpp文件，C++实现头文件里面的函数

#include "MD5.h"

using namespace std;

/* Constants for MD5Transform routine. */
#define S11 7
#define S12 12
#define S13 17
#define S14 22
#define S21 5
#define S22 9
#define S23 14
#define S24 20
#define S31 4
#define S32 11
#define S33 16
#define S34 23
#define S41 6
#define S42 10
#define S43 15
#define S44 21


/* F, G, H and I are basic MD5 functions.
*/
#define F(x, y, z) (((x) & (y)) | ((~x) & (z)))
#define G(x, y, z) (((x) & (z)) | ((y) & (~z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))
#define I(x, y, z) ((y) ^ ((x) | (~z)))

/* ROTATE_LEFT rotates x left n bits.
*/
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))

/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
Rotation is separate from addition to prevent recomputation.
*/
#define FF(a, b, c, d, x, s, ac) { \
    (a) += F((b), (c), (d)) + (x)+ac; \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}
#define GG(a, b, c, d, x, s, ac) { \
    (a) += G((b), (c), (d)) + (x)+ac; \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}
#define HH(a, b, c, d, x, s, ac) { \
    (a) += H((b), (c), (d)) + (x)+ac; \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}
#define II(a, b, c, d, x, s, ac) { \
    (a) += I((b), (c), (d)) + (x)+ac; \
    (a) = ROTATE_LEFT((a), (s)); \
    (a) += (b); \
}


const byte MD5::PADDING[64] = {0x80};
const char MD5::HEX[16] = {
        '0', '1', '2', '3',
        '4', '5', '6', '7',
        '8', '9', 'a', 'b',
        'c', 'd', 'e', 'f'
};


/* Default construct. */
MD5::MD5() {
    reset();
}

/* Construct a MD5 object with a input buffer. */
MD5::MD5(const void *input, size_t length) {
    reset();
    update(input, length);
}

/* Construct a MD5 object with a string. */
MD5::MD5(const string &str) {
    reset();
    update(str);
}

/* Construct a MD5 object with a file. */
MD5::MD5(ifstream &in) {
    reset();
    update(in);
}

/* Return the message-digest */
byte *MD5::digest() {

    if (!_finished) {
        _finished = true;
        final();
    }
    return _digest;
}

/* Reset the calculate state */
void MD5::reset() {

    _finished = false;
    /* reset number of bits. */
    _count[0] = _count[1] = 0;
    /* Load magic initialization constants. */
    _state[0] = 0x67452301;
    _state[1] = 0xefcdab89;
    _state[2] = 0x98badcfe;
    _state[3] = 0x10325476;
}

/* Updating the context with a input buffer. */
void MD5::update(const void *input, size_t length) {
    update((const byte *) input, length);
}

/* Updating the context with a string. */
void MD5::update(const string &str) {
    update((const byte *) str.c_str(), str.length());
}

/* Updating the context with a file. */
void MD5::update(ifstream &in) {

    if (!in) {
        return;
    }

    std::streamsize length;
    char buffer[BUFFER_SIZE];
    while (!in.eof()) {
        in.read(buffer, BUFFER_SIZE);
        length = in.gcount();
        if (length > 0) {
            update(buffer, length);
        }
    }
    in.close();
}

/* MD5 block update operation. Continues an MD5 message-digest
operation, processing another message block, and updating the
context.
*/
void MD5::update(const byte *input, size_t length) {

    uint32 i, index, partLen;

    _finished = false;

    /* Compute number of bytes mod 64 */
    index = (uint32) ((_count[0] >> 3) & 0x3f);

    /* update number of bits */
    if ((_count[0] += ((uint32) length << 3)) < ((uint32) length << 3)) {
        ++_count[1];
    }
    _count[1] += ((uint32) length >> 29);

    partLen = 64 - index;

    /* transform as many times as possible. */
    if (length >= partLen) {

        memcpy(&_buffer[index], input, partLen);
        transform(_buffer);

        for (i = partLen; i + 63 < length; i += 64) {
            transform(&input[i]);
        }
        index = 0;

    } else {
        i = 0;
    }

    /* Buffer remaining input */
    memcpy(&_buffer[index], &input[i], length - i);
}

/* MD5 finalization. Ends an MD5 message-_digest operation, writing the
the message _digest and zeroizing the context.
*/
void MD5::final() {

    byte bits[8];
    uint32 oldState[4];
    uint32 oldCount[2];
    uint32 index, padLen;

    /* Save current state and count. */
    memcpy(oldState, _state, 16);
    memcpy(oldCount, _count, 8);

    /* Save number of bits */
    encode(_count, bits, 8);

    /* Pad out to 56 mod 64. */
    index = (uint32) ((_count[0] >> 3) & 0x3f);
    padLen = (index < 56) ? (56 - index) : (120 - index);
    update(PADDING, padLen);

    /* Append length (before padding) */
    update(bits, 8);

    /* Store state in digest */
    encode(_state, _digest, 16);

    /* Restore current state and count. */
    memcpy(_state, oldState, 16);
    memcpy(_count, oldCount, 8);
}

/* MD5 basic transformation. Transforms _state based on block. */
void MD5::transform(const byte block[64]) {

    uint32 a = _state[0], b = _state[1], c = _state[2], d = _state[3], x[16];

    decode(block, x, 64);

    /* Round 1 */
    FF(a, b, c, d, x[0], S11, 0xd76aa478); /* 1 */
    FF(d, a, b, c, x[1], S12, 0xe8c7b756); /* 2 */
    FF(c, d, a, b, x[2], S13, 0x242070db); /* 3 */
    FF(b, c, d, a, x[3], S14, 0xc1bdceee); /* 4 */
    FF(a, b, c, d, x[4], S11, 0xf57c0faf); /* 5 */
    FF(d, a, b, c, x[5], S12, 0x4787c62a); /* 6 */
    FF(c, d, a, b, x[6], S13, 0xa8304613); /* 7 */
    FF(b, c, d, a, x[7], S14, 0xfd469501); /* 8 */
    FF(a, b, c, d, x[8], S11, 0x698098d8); /* 9 */
    FF(d, a, b, c, x[9], S12, 0x8b44f7af); /* 10 */
    FF(c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
    FF(b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
    FF(a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
    FF(d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
    FF(c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
    FF(b, c, d, a, x[15], S14, 0x49b40821); /* 16 */

    /* Round 2 */
    GG(a, b, c, d, x[1], S21, 0xf61e2562); /* 17 */
    GG(d, a, b, c, x[6], S22, 0xc040b340); /* 18 */
    GG(c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
    GG(b, c, d, a, x[0], S24, 0xe9b6c7aa); /* 20 */
    GG(a, b, c, d, x[5], S21, 0xd62f105d); /* 21 */
    GG(d, a, b, c, x[10], S22, 0x2441453); /* 22 */
    GG(c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
    GG(b, c, d, a, x[4], S24, 0xe7d3fbc8); /* 24 */
    GG(a, b, c, d, x[9], S21, 0x21e1cde6); /* 25 */
    GG(d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
    GG(c, d, a, b, x[3], S23, 0xf4d50d87); /* 27 */
    GG(b, c, d, a, x[8], S24, 0x455a14ed); /* 28 */
    GG(a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
    GG(d, a, b, c, x[2], S22, 0xfcefa3f8); /* 30 */
    GG(c, d, a, b, x[7], S23, 0x676f02d9); /* 31 */
    GG(b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */

    /* Round 3 */
    HH(a, b, c, d, x[5], S31, 0xfffa3942); /* 33 */
    HH(d, a, b, c, x[8], S32, 0x8771f681); /* 34 */
    HH(c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
    HH(b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
    HH(a, b, c, d, x[1], S31, 0xa4beea44); /* 37 */
    HH(d, a, b, c, x[4], S32, 0x4bdecfa9); /* 38 */
    HH(c, d, a, b, x[7], S33, 0xf6bb4b60); /* 39 */
    HH(b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
    HH(a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
    HH(d, a, b, c, x[0], S32, 0xeaa127fa); /* 42 */
    HH(c, d, a, b, x[3], S33, 0xd4ef3085); /* 43 */
    HH(b, c, d, a, x[6], S34, 0x4881d05); /* 44 */
    HH(a, b, c, d, x[9], S31, 0xd9d4d039); /* 45 */
    HH(d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
    HH(c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
    HH(b, c, d, a, x[2], S34, 0xc4ac5665); /* 48 */

    /* Round 4 */
    II(a, b, c, d, x[0], S41, 0xf4292244); /* 49 */
    II(d, a, b, c, x[7], S42, 0x432aff97); /* 50 */
    II(c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
    II(b, c, d, a, x[5], S44, 0xfc93a039); /* 52 */
    II(a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
    II(d, a, b, c, x[3], S42, 0x8f0ccc92); /* 54 */
    II(c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
    II(b, c, d, a, x[1], S44, 0x85845dd1); /* 56 */
    II(a, b, c, d, x[8], S41, 0x6fa87e4f); /* 57 */
    II(d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
    II(c, d, a, b, x[6], S43, 0xa3014314); /* 59 */
    II(b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
    II(a, b, c, d, x[4], S41, 0xf7537e82); /* 61 */
    II(d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
    II(c, d, a, b, x[2], S43, 0x2ad7d2bb); /* 63 */
    II(b, c, d, a, x[9], S44, 0xeb86d391); /* 64 */

    _state[0] += a;
    _state[1] += b;
    _state[2] += c;
    _state[3] += d;
}

/* Encodes input (ulong) into output (byte). Assumes length is
a multiple of 4.
*/
void MD5::encode(const uint32 *input, byte *output, size_t length) {

    for (size_t i = 0, j = 0; j < length; ++i, j += 4) {
        output[j] = (byte) (input[i] & 0xff);
        output[j + 1] = (byte) ((input[i] >> 8) & 0xff);
        output[j + 2] = (byte) ((input[i] >> 16) & 0xff);
        output[j + 3] = (byte) ((input[i] >> 24) & 0xff);
    }
}

/* Decodes input (byte) into output (ulong). Assumes length is
a multiple of 4.
*/
void MD5::decode(const byte *input, uint32 *output, size_t length) {

    for (size_t i = 0, j = 0; j < length; ++i, j += 4) {
        output[i] = ((uint32) input[j]) | (((uint32) input[j + 1]) << 8) |
                    (((uint32) input[j + 2]) << 16) | (((uint32) input[j + 3]) << 24);
    }
}

/* Convert byte array to hex string. */
string MD5::bytesToHexString(byte *input, size_t length) {

    string str;
    str.reserve(length << 1);
    for (size_t i = 0; i < length; ++i) {
        int t = input[i];
        int a = t / 16;
        int b = t % 16;
        str.append(1, HEX[a]);
        str.append(1, HEX[b]);
    }
    return str;
}

/* Convert digest to string value */
string MD5::toString() {
    return bytesToHexString(digest(), 16);
}

CMakeLists.txt

• 编译配置脚本文件，在这里配置编译的相关配置
• 在add_library中，添加md5.cpp文件到编译文件中，这样才能编译到这个cpp文件

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.18.1)

# Declares and names the project.

project("nativeencrypt")

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.
        nativeencrypt

        # Sets the library as a shared library.
        SHARED

        # Provides a relative path to your source file(s).
        native-lib.cpp
        md5.cpp)

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
        log-lib

        # Specifies the name of the NDK library that
        # you want CMake to locate.
        log)

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
        nativeencrypt

        # Links the target library to the log library
        # included in the NDK.
        ${log-lib})

JNI的java类

• 创建一个java类，用来定义C++和Java桥接调用的方法

public class NativeEncrypt {
    static {
        System.loadLibrary("nativeencrypt");
    }

    /**
     * MD5加密
     */
    public static native String md5(String input);
}

native-lib.cpp

• JNI层函数的cpp文件，要和java层的桥接文件中的函数相对应
• 要注意java层的字符串，要转换成C的字符串，才能给cpp使用，而cpp进行MD5加密后的字符串，也要转换为java的字符串，才能返回给Android端

#include <jni.h>
#include <string>
#include <iostream>
#include <android/log.h>
#include "md5.h"

using namespace std;

extern "C"
JNIEXPORT jstring JNICALL
Java_com_zh_nativeencrypt_NativeEncrypt_md5(JNIEnv *env, jclass clazz, jstring input) {
    const char *c_input = env->GetStringUTFChars(input, nullptr);

    //需要加盐，则更换盐，放开这2行
    //char *k = "!1@$%2t5&";
    //std::string const &cc = std::string(c_input) + std::string(k);

    std::string const &cc = std::string(c_input);
    char const *c = cc.c_str();

    MD5 md5_input;
    md5_input.update(c);
    string result = md5_input.bytesToHexString(md5_input.digest(), 16);

    //看需求，要大写，则这里放开，实现转大写
    //transform(result.begin(), result.end(), result.begin(), ::toupper);

    return env->NewStringUTF(result.c_str());
}

Java层调用

public class MainActivity extends AppCompatActivity {
    private ActivityMainBinding mBinding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mBinding = ActivityMainBinding.inflate(getLayoutInflater());
        setContentView(mBinding.getRoot());
        //MD5加密
        mBinding.sampleText.setText(NativeEncrypt.md5("123"));
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        mBinding = null;
    }
}

签名校验

为了防止App被反编译后，又被重新打包，则可以在Native层做签名校验，通过C++中反射调用Java层获取应用签名的方法，获取到签名后，校验MD5值，如果不一致，就是被篡改了，直接让so库初始化失败，抛出异常，直接让闪退

修改native-lib.cpp文件，增加cpp层的校验代码

#include <jni.h>
#include <string>
#include <iostream>
//导入MD5的头文件
#include "md5.h"
//导入Log的头文件
#include <android/log.h>

//宏定义，定义Log的Tag
#define LOG_TAG "JNI"
//宏定义，打印方法名太长，定义一个短的
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__)
#define LOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)

using namespace std;

/**
 * 将byte数组转换成16进制字符串
 */
void ByteToHexStr(const unsigned char *byte_arr, char *char_result, const int length) {
    short i;
    unsigned char highByte, lowByte;

    for (i = 0; i < length; i++) {
        highByte = byte_arr[i] >> 4;
        lowByte = byte_arr[i] & 0x0f;

        highByte += 0x30;

        if (highByte > 0x39) {
            char_result[i * 2] = highByte + 0x07;
        } else {
            char_result[i * 2] = highByte;
        }

        lowByte += 0x30;
        if (lowByte > 0x39) {
            char_result[i * 2 + 1] = lowByte + 0x07;
        } else {
            char_result[i * 2 + 1] = lowByte;
        }
    }
}

/**
 * 把一个jstring转换成一个c语言的char* 类型
 */
char *JString2CStr(JNIEnv *env, jstring jstr) {
    jclass clazz = (*env).FindClass("java/lang/String");
    jstring charset = (*env).NewStringUTF("GB2312");
    jmethodID mid = (*env).GetMethodID(clazz, "getBytes", "(Ljava/lang/String;)[B");
    jbyteArray jBtyeArr = (jbyteArray) (*env).CallObjectMethod(jstr, mid, charset);
    jsize arrLength = (*env).GetArrayLength(jBtyeArr);
    jbyte *jByteArrPointer = (*env).GetByteArrayElements(jBtyeArr, JNI_FALSE);

    char *cCharPointer = nullptr;
    if (arrLength > 0) {
        cCharPointer = (char *) malloc(arrLength + 1); //"\0"
        memcpy(cCharPointer, jByteArrPointer, arrLength);
        cCharPointer[arrLength] = 0;
    }
    (*env).ReleaseByteArrayElements(jBtyeArr, jByteArrPointer, 0);
    return cCharPointer;
}

/**
 * java的字节数组，转MD5，返回java的字符串
 */
jstring ToMd5(JNIEnv *env, jbyteArray source) {
    // MessageDigest类
    jclass classMessageDigest = env->FindClass("java/security/MessageDigest");
    // MessageDigest.getInstance()静态方法
    jmethodID midGetInstance = env->GetStaticMethodID(classMessageDigest, "getInstance",
                                                      "(Ljava/lang/String;)Ljava/security/MessageDigest;");
    // MessageDigest object
    jobject objMessageDigest = env->CallStaticObjectMethod(classMessageDigest, midGetInstance,
                                                           env->NewStringUTF("md5"));

    // update方法，这个函数的返回值是void，写V
    jmethodID midUpdate = env->GetMethodID(classMessageDigest, "update", "([B)V");
    env->CallVoidMethod(objMessageDigest, midUpdate, source);

    // digest方法
    jmethodID midDigest = env->GetMethodID(classMessageDigest, "digest", "()[B");
    jbyteArray objArraySign = (jbyteArray) env->CallObjectMethod(objMessageDigest, midDigest);

    jsize intArrayLength = env->GetArrayLength(objArraySign);
    jbyte *byte_array_elements = env->GetByteArrayElements(objArraySign, nullptr);
    size_t length = (size_t) intArrayLength * 2 + 1;
    char *char_result = (char *) malloc(length);
    memset(char_result, 0, length);

    // 将byte数组转换成16进制字符串，发现这里不用强转，jbyte和unsigned char应该字节数是一样的
    ByteToHexStr((unsigned char *) byte_array_elements, char_result, intArrayLength);
    // 在末尾补\0
    *(char_result + intArrayLength * 2) = '\0';

    jstring stringResult = env->NewStringUTF(char_result);
    // release
    env->ReleaseByteArrayElements(objArraySign, byte_array_elements, JNI_ABORT);
    // 释放指针使用free
    free(char_result);

    return stringResult;
}

jstring loadSignature(JNIEnv *env, jobject context) {
    // 获取Context类
    jclass contextClass = env->GetObjectClass(context);
    LOGI("获取Context类");
    // 得到getPackageManager方法的ID
    jmethodID getPkgManagerMethodId = env->GetMethodID(contextClass, "getPackageManager",
                                                       "()Landroid/content/pm/PackageManager;");
    LOGI("得到getPackageManager方法的ID");
    // PackageManager
    jobject pm = env->CallObjectMethod(context, getPkgManagerMethodId);
    LOGI("PackageManager");
    // 得到应用的包名
    jmethodID pkgNameMethodId = env->GetMethodID(contextClass, "getPackageName",
                                                 "()Ljava/lang/String;");
    jstring pkgName = (jstring) env->CallObjectMethod(context, pkgNameMethodId);
    LOGI("get pkg name: %s", JString2CStr(env, pkgName));
    // 获得PackageManager类
    jclass cls = env->GetObjectClass(pm);
    // 得到getPackageInfo方法的ID
    jmethodID mid = env->GetMethodID(cls, "getPackageInfo",
                                     "(Ljava/lang/String;I)Landroid/content/pm/PackageInfo;");
    // 获得应用包的信息
    jobject packageInfo = env->CallObjectMethod(pm, mid, pkgName, 0x40); //GET_SIGNATURES = 64;
    // 获得PackageInfo 类
    cls = env->GetObjectClass(packageInfo);
    // 获得签名数组属性的ID
    jfieldID fid = env->GetFieldID(cls, "signatures", "[Landroid/content/pm/Signature;");
    // 得到签名数组
    jobjectArray signatures = (jobjectArray) env->GetObjectField(packageInfo, fid);
    // 得到签名
    jobject signature = env->GetObjectArrayElement(signatures, 0);
    // 获得Signature类
    cls = env->GetObjectClass(signature);
    // 得到toCharsString方法的ID
    mid = env->GetMethodID(cls, "toByteArray", "()[B");
    // 返回当前应用签名信息
    jbyteArray signatureByteArray = (jbyteArray) env->CallObjectMethod(signature, mid);
    return ToMd5(env, signatureByteArray);
}

JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void *reserved) {
    JNIEnv *evn;
    if (vm->GetEnv((void **) (&evn), JNI_VERSION_1_6) != JNI_OK) {
        return -1;
    }
    //包名的.，要换成/
    jclass appClass = evn->FindClass("com/zh/nativeencrypt/SigningContextProvider");
    jmethodID getAppContextMethod = evn->GetStaticMethodID(appClass, "getAppContext",
                                                           "()Landroid/content/Context;");
    //获取APplication定义的context实例
    jobject appContext = evn->CallStaticObjectMethod(appClass, getAppContextMethod);
    // 获取应用当前的签名信息
    jstring signature = loadSignature(evn, appContext);
    // 期待的签名信息
    jstring keystoreSigature = evn->NewStringUTF("BDB5AC29D4B1E7841AC5ADD3F8BA3833");
    const char *keystroreMD5 = evn->GetStringUTFChars(keystoreSigature, nullptr);
    const char *releaseMD5 = evn->GetStringUTFChars(signature, nullptr);
    //比较两个签名信息是否相等
    int result = strcmp(keystroreMD5, releaseMD5);
    //LOGI("strcmp releaseMD5 %s", releaseMD5);
    LOGI("strcmp %d", result);

    //这里记得释放内存
    evn->ReleaseStringUTFChars(signature, releaseMD5);
    evn->ReleaseStringUTFChars(keystoreSigature, keystroreMD5);

    //得到的签名一样，验证通过
    if (result == 0) {
        return JNI_VERSION_1_6;
    }
    return -1;
}

提供Java类，给JNI层反射获取Context

• 当前，你也可以提供另外的类，Context可以从其他地方获取，我这里为了方便，提供了一个ContextProvider，让Context尽早的赋值

/**
 * 签名校验时，JNI会反射调用该类的方法，所以需要提供Context实例
 */
public class SigningContextProvider extends ContentProvider {
    @SuppressLint("StaticFieldLeak")
    private static Context sContext;

    /**
     * 获取Context实例
     */
    public static Context getAppContext() {
        return sContext;
    }

    @Override
    public boolean onCreate() {
        //保存Context实例
        sContext = getContext();
        return false;
    }

    @Nullable
    @Override
    public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
        return null;
    }

    @Nullable
    @Override
    public String getType(@NonNull Uri uri) {
        return null;
    }

    @Nullable
    @Override
    public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
        return null;
    }

    @Override
    public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }

    @Override
    public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
        return 0;
    }
}

• 注册ContentProvider

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="com.zh.nativeencrypt">

    <application
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.NativeEncrypt"
        tools:targetApi="31">

        <provider
            android:name=".SigningContextProvider"
            android:authorities="signingContextProvider"
            android:exported="false" />
    </application>
</manifest>

签名配置

• app的build.gradle文件中，配置打包key和密码，以及相关配置

android {
    //省略其他配置...

    signingConfigs {
        debug {
            storeFile file('../key')
            storePassword '123456'
            keyAlias 'key'
            keyPassword '123456'
        }

        release {
            storeFile file('../key')
            storePassword '123456'
            keyAlias 'key'
            keyPassword '123456'
        }
    }

    buildTypes {
        debug {
            minifyEnabled false
            signingConfig signingConfigs.debug
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }

        release {
            minifyEnabled true
            signingConfig signingConfigs.release
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    //省略其他配置...
}