前言
网易云的Vip音乐下载下来,格式不是mp3/flac这种通用的音乐格式，而是经过加密的ncm文件。只有用网易云的音乐App才能够打开。于是想到可不可以把.ncm文件转换成mp3或者flac文件，上google查了一下，发现有不少人已经做了这件事，但没有发现C语言版本的，就想着写一个纯C语言版本的ncm转mp3/flac。
NCM文件结构
ncm文件的结构，网上有人解析出来了，分为下面几个部分
| 信息 | 大小 | 说明 |
|---|---|---|
| Magic Header | 10 bytes | 文件头 |
| Key Length | 4 bytes | AES128加密后的RC4密钥长度，字节是按小端排序。 |
| Key Data | Key Length | 用AES128加密后的RC4密钥。 1. 先按字节对0x64进行异或。 2. AES解密,去除填充部分。 3. 去除最前面’neteasecloudmusic’17个字节，得到RC4密钥。 |
| Music Info Length | 4 bytes | 音乐相关信息的长度，小端排序。 |
| Music Info Data | Music Info Length | Json格式音乐信息数据。1. 按字节对0x63进行异或。 2. 去除最前面22个字节。 3. Base64进行解码。 4. AES解密。 6. 去除前面6个字节得到Json数据。 |
| CRC | 4 bytes | 跳过 |
| Gap | 5 bytes | 跳过 |
| Image Size | 4 bytes | 图片的大小 |
| Image | Image Size | 图片数据 |
| Music Data | – | 1. RC4-KSA生成S盒。 2. 用S盒解密（自定义的解密方法)，不是RC4-PRGA解密。 |
两个AES对应密钥
unsigned char meta_key[] = { 0x23,0x31,0x34,0x6C,0x6A,0x6B,0x5F,0x21,0x5C,0x5D,0x26,0x30,0x55,0x3C,0x27,0x28 };
unsigned char core_key[] = { 0x68,0x7A,0x48,0x52,0x41,0x6D,0x73,0x6F,0x35,0x6B,0x49,0x6E,0x62,0x61,0x78,0x57 };
不得不佩服当初破解这个东西的人，不仅把文件结构摸得请清楚楚，还把密钥也搞到手，应该是个破解大神。有了上面的东西，剩下的就很简单了，按部就班来就行了。
一些算法准备
开始前我们需要把AES算法，BASE64算法,RC4算法和Json解析算法先写好。
除此之外还有一个编码问题，解析出来的ncm文件是用utf-8编码存储的，所以它在中文windows系统下汉字会出现乱码，因为中文windows系统采用的编码是GBK,两者不兼容，所以我们要写一个编码转换算法，将utf8格式字符串转位GBK的。Linux下不用转换，Linux本身就是用UTF-8的。
C语言没有这些库，都要自己来。
- AES用GitHub上的
tiny-AES-c - JSON用GitHub上的CJSON
cJSON - Base64和RC4算法比较简单我们自己写
unsigned char* base64_decode(unsigned char* code,int len,int * actLen){//根据base64表，以字符找到对应的十进制数据int table[] = { 0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,62,0,0,0, 63,52,53,54,55,56,57,58, 59,60,61,0,0,0,0,0,0,0,0, 1,2,3,4,5,6,7,8,9,10,11,12, 13,14,15,16,17,18,19,20,21, 22,23,24,25,0,0,0,0,0,0,26, 27,28,29,30,31,32,33,34,35, 36,37,38,39,40,41,42,43,44, 45,46,47,48,49,50,51};long str_len;unsigned char* res;int i, j;//计算解码后的字符串长度//判断编码后的字符串后是否有=if (strstr(code, "=="))str_len = len / 4 * 3 - 2;else if (strstr(code, "="))str_len = len / 4 * 3 - 1;elsestr_len = len / 4 * 3;*actLen = str_len;res = malloc(sizeof(unsigned char) * str_len + 1);res[str_len] = '\0';//以4个字符为一位进行解码for (i = 0, j = 0; i < len - 2; j += 3, i += 4){res[j] = ((unsigned char)table[code[i]]) <> 4); res[j + 1] = (((unsigned char)table[code[i + 1]]) <> 2); res[j + 2] = (((unsigned char)table[code[i + 2]]) << 6) | ((unsigned char)table[code[i + 3]]);}return res;}- RC4生成S盒
//用key生成S盒/** s: s盒* key: 密钥* len: 密钥长度*/void rc4Init(unsigned char* s, const unsigned char* key, int len) { int i = 0, j = 0;unsigned char T[256] = { 0 };for (i = 0; i < 256; i++){s[i] = i;T[i] = key[i % len];}for (i = 0; i < 256; i++) {j = (j + s[i] + T[i]) % 256;unsigned tmp = s[i];s[i]=s[j];s[j]=tmp;}}//针对NCM文件的解密//异或关系/** s: s盒* data: 要加密或者解密的数据* len: data的长度*/void rc4PRGA(unsigned char* s, unsigned char* data, int len) {int i = 0;int j = 0;int k = 0;int idx = 0;for (idx = 0; idx < len; idx++) {i = (idx + 1) % 256;j = (i + s[i]) % 256;k= (s[i] + s[j]) % 256;data[idx]^=s[k];//异或}}- Windows下utf8转GBK
#ifdef WIN32#include//返回转换好的字符串指针unsigned char* utf8ToGbk(unsigned char*src,int len){wchar_t* tmp = (wchar_t*)malloc(sizeof(wchar_t) * len+2);unsigned char* newSrc = (unsigned char*)malloc(sizeof(unsigned char) * len + 2);MultiByteToWideChar(CP_UTF8, 0, src, -1, tmp, len);WideCharToMultiByte(CP_ACP, 0, tmp, -1, newSrc, len+2, NULL,NULL);return newSrc;}#endifNCM文件解析
按照NCM文件结构一步一步读取数据来进行解析
//fileName:要转换的文件void readFileData(const char* fileName){FILE* f;f = fopen(fileName, "rb");if (!f){printf("No such file: %s\n", fileName);return;}unsigned char buf[16];int len=0;int i = 0;unsigned char meta_key[] = { 0x23,0x31,0x34,0x6C,0x6A,0x6B,0x5F,0x21,0x5C,0x5D,0x26,0x30,0x55,0x3C,0x27,0x28 };unsigned char core_key[] = { 0x68,0x7A,0x48,0x52,0x41,0x6D,0x73,0x6F,0x35,0x6B,0x49,0x6E,0x62,0x61,0x78,0x57 };fseek(f, 10, SEEK_CUR); //f从当前位置移动10个字节fread(buf, 1, 4, f);//读取rc4 key 的长度len = (buf[3] << 8 | buf[2]) << 16 | (buf[1] << 8 | buf[0]);unsigned char* rc4Key= (unsigned char*)malloc(sizeof(unsigned char) * len);fread(rc4Key, 1, len, f); //读取rc4数据//解密rc4密钥for (i = 0; i < len; i++){rc4Key[i] ^= 0x64;}struct AES_ctx ctx;AES_init_ctx(&ctx, core_key);//使用core_key密钥int packSize = len / 16;//采用的是AES-ECB加密方式，和Pkcs7padding填充for (i = 0; i < packSize; i++){AES_ECB_decrypt(&ctx, &rc4Key[i * 16]);}int pad = rc4Key[len - 1];//获取填充的长度rc4Key[len - pad] = '\0';//去除填充的部分，得到RC4密钥fread(buf, 1, 4, f);//读取Music Info 长度数据len = ((buf[3] << 8 | buf[2]) << 16) | (buf[1] << 8 | buf[0]);unsigned char* meta = (unsigned char*)malloc(sizeof(unsigned char) * len);fread(meta, 1, len, f); //读取Music Info数据//解析Music info信息for (i = 0; i < len; i++){meta[i] ^= 0x63;}int act = 0;unsigned char* data = base64_decode(&meta[22], len - 22, &act);//base64解码AES_init_ctx(&ctx, meta_key);//AES解密packSize = act / 16;for (i = 0; i < packSize; i++){AES_ECB_decrypt(&ctx, &data[i * 16]);}pad = data[act - 1];data[act - pad] = '\0';//去除填充部分unsigned char* newData = data;#ifdef WIN32newData = utf8ToGbk(data, strlen(data));#endifcJSON* cjson = cJSON_Parse(&newData[6]);//json解析，获取格式和名字等if (cjson == NULL){printf("cjson parse failed\n");return;}//printf("%s\n", cJSON_Print(cjson));//输出jsonfseek(f, 9, SEEK_CUR);//从当前位置跳过9个字节fread(buf, 1, 4, f);//读取图片大小len = (buf[3] << 8 | buf[2]) << 16 | (buf[1] <valuestring;cJSON* sub = cJSON_GetObjectItem(cjson, "artist");char*artist=cJSON_GetArrayItem(cJSON_GetArrayItem(sub, 0),0)->valuestring;char* format = cJSON_GetObjectItem(cjson, "format")->valuestring;char* saveFileName =(char*)malloc(strlen(musicName) + strlen(artist) + strlen(format)+5);sprintf(saveFileName, "%s - %s.%s", artist, musicName, format);FILE* fo=fopen(saveFileName, "wb");if (fo == NULL){printf("The fileName - '%s' is invalid in this system\n", saveFileName);}else{fwrite(musicData, 1, total, fo);fclose(fo);}#ifdef WIN32free(newData);#endiffree(data);free(meta);free(img);free(musicData);fclose(f);}- AES采用的是AES-ECB模式，pack7padding填充方式。即16个字节为一组，如果不够16个字节，那就缺几个字节就填充几个字节，每个字节的值都是缺少的字节数。所以获取最后一个字节的值就知道要填充了几个字节。
- RC4解密那里，不是按RC4的来的，虽说叫RC4，但只有生成S盒那里是一样的，其它的不是按RC4算法来的。
- 有些解析出来音乐的名字，系统是不支持的，比如带’/’的，在创建新文件写入时会失败。
- 以”結束バンド – ギターと孤独と蒼い惑星.ncm”为例看看它的json数据是怎么样的
{
“musicId”: 1991012773,
“musicName”: “ギターと孤独と蒼い惑星”,
“artist”: [[“結束バンド”, 54103171]],
“albumId”: 153542094,
“album”: “ギターと孤独と蒼い惑星”,
“albumPicDocId”: “109951167983448236”,
“albumPic”: “https://p4.music.126.net/rfstzrVK05hCPjU-4mzSFA==/109951167983448236.jpg”,
“bitrate”: 320000,
“mp3DocId”: “f481d20151f01d5d681d2768d753ad64”,
“duration”: 229015,
“mvId”: 0,
“alias”: [“TV动画《孤独摇滚！》插曲”],
“transNames”: [],
“format”: “mp3”,
“flag”: 4
}
可以根据需要自由提取需要的信息
完整代码
点击查看代码
/** date:2022-12-12* author: FL* purpose: ncm file to mp3*/#include #include #include #include "aes.h"#include "cJSON.h"#ifdef WIN32#include//返回转换好的字符串指针unsigned char* utf8ToGbk(unsigned char*src,int len){wchar_t* tmp = (wchar_t*)malloc(sizeof(wchar_t) * len+2);unsigned char* newSrc = (unsigned char*)malloc(sizeof(unsigned char) * len + 2);MultiByteToWideChar(CP_UTF8, 0, src, -1, tmp, len);//转为unicodeWideCharToMultiByte(CP_ACP, 0, tmp, -1, newSrc, len+2, NULL,NULL); //转gbkreturn newSrc;}#endifvoid swap(unsigned char* a, unsigned char* b){unsigned char t = *a;*a = *b;*b = t;}//用key生成S盒/** s: s盒* key: 密钥* len: 密钥长度*/void rc4Init(unsigned char* s, const unsigned char* key, int len){int i = 0, j = 0;unsigned char T[256] = { 0 };for (i = 0; i < 256; i++){s[i] = i;T[i] = key[i % len];}for (i = 0; i < 256; i++){j = (j + s[i] + T[i]) % 256;swap(s + i, s + j);}}//针对NCM文件的解密//异或关系/** s: s盒* data: 要加密或者解密的数据* len: data的长度*/void rc4PRGA(unsigned char* s, unsigned char* data, int len){int i = 0;int j = 0;int k = 0;int idx = 0;for (idx = 0; idx < len; idx++){i = (idx + 1) % 256;j = (i + s[i]) % 256;k = (s[i] + s[j]) % 256;data[idx] ^= s[k];//异或}}//base64 解码/** code: 要解码的数据*/unsigned char* base64_decode(unsigned char* code, int len, int* actLen){//根据base64表，以字符找到对应的十进制数据int table[] = { 0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,62,0,0,0, 63,52,53,54,55,56,57,58, 59,60,61,0,0,0,0,0,0,0,0, 1,2,3,4,5,6,7,8,9,10,11,12, 13,14,15,16,17,18,19,20,21, 22,23,24,25,0,0,0,0,0,0,26, 27,28,29,30,31,32,33,34,35, 36,37,38,39,40,41,42,43,44, 45,46,47,48,49,50,51};long str_len;unsigned char* res;int i, j;//计算解码后的字符串长度//判断编码后的字符串后是否有=if (strstr(code, "=="))str_len = len / 4 * 3 - 2;else if (strstr(code, "="))str_len = len / 4 * 3 - 1;elsestr_len = len / 4 * 3;*actLen = str_len;res = malloc(sizeof(unsigned char) * str_len + 1);res[str_len] = '\0';//以4个字符为一位进行解码for (i = 0, j = 0; i < len - 2; j += 3, i += 4){res[j] = ((unsigned char)table[code[i]]) <> 4); res[j + 1] = (((unsigned char)table[code[i + 1]]) <> 2);res[j + 2] = (((unsigned char)table[code[i + 2]]) << 6) | ((unsigned char)table[code[i + 3]]); }return res;}void readFileData(const char* fileName){FILE* f;f = fopen(fileName, "rb");if (!f){printf("No such file: %s\n", fileName);return;}unsigned char buf[16];int len=0;int i = 0;unsigned char meta_key[] = { 0x23,0x31,0x34,0x6C,0x6A,0x6B,0x5F,0x21,0x5C,0x5D,0x26,0x30,0x55,0x3C,0x27,0x28 };unsigned char core_key[] = { 0x68,0x7A,0x48,0x52,0x41,0x6D,0x73,0x6F,0x35,0x6B,0x49,0x6E,0x62,0x61,0x78,0x57 };fseek(f, 10, SEEK_CUR); //f从当前位置移动10个字节fread(buf, 1, 4, f);//读取rc4 key 的长度len = (buf[3] << 8 | buf[2]) << 16 | (buf[1] << 8 | buf[0]);unsigned char* rc4Key= (unsigned char*)malloc(sizeof(unsigned char) * len);fread(rc4Key, 1, len, f); //读取rc4数据//解密rc4密钥for (i = 0; i < len; i++){rc4Key[i] ^= 0x64;}struct AES_ctx ctx;AES_init_ctx(&ctx, core_key);//使用core_key密钥int packSize = len / 16;//采用的是AES-ECB加密方式，和Pkcs7padding填充for (i = 0; i < packSize; i++){AES_ECB_decrypt(&ctx, &rc4Key[i * 16]);}int pad = rc4Key[len - 1];//获取填充的长度rc4Key[len - pad] = '\0';//去除填充的部分，得到RC4密钥fread(buf, 1, 4, f);//读取Music Info 长度数据len = ((buf[3] << 8 | buf[2]) << 16) | (buf[1] << 8 | buf[0]);unsigned char* meta = (unsigned char*)malloc(sizeof(unsigned char) * len);fread(meta, 1, len, f); //读取Music Info数据//解析Music info信息for (i = 0; i < len; i++){meta[i] ^= 0x63;}int act = 0;unsigned char* data = base64_decode(&meta[22], len - 22, &act);//base64解码AES_init_ctx(&ctx, meta_key);//AES解密packSize = act / 16;for (i = 0; i < packSize; i++){AES_ECB_decrypt(&ctx, &data[i * 16]);}pad = data[act - 1];data[act - pad] = '\0';//去除填充部分unsigned char* newData = data;#ifdef WIN32newData = utf8ToGbk(data, strlen(data));#endifcJSON* cjson = cJSON_Parse(&newData[6]);//json解析，获取格式和名字等if (cjson == NULL){printf("cjson parse failed\n");return;}//printf("%s\n", cJSON_Print(cjson));//输出jsonfseek(f, 9, SEEK_CUR);//从当前位置跳过9个字节fread(buf, 1, 4, f);//读取图片大小len = (buf[3] << 8 | buf[2]) << 16 | (buf[1] <valuestring;cJSON* sub = cJSON_GetObjectItem(cjson, "artist");char*artist=cJSON_GetArrayItem(cJSON_GetArrayItem(sub, 0),0)->valuestring;char* format = cJSON_GetObjectItem(cjson, "format")->valuestring;char* saveFileName =(char*)malloc(strlen(musicName) + strlen(artist) + strlen(format)+5);sprintf(saveFileName, "%s - %s.%s", artist, musicName, format);FILE* fo=fopen(saveFileName, "wb");if (fo == NULL){printf("The fileName - '%s' is invalid in this system\n", saveFileName);}else{fwrite(musicData, 1, total, fo);fclose(fo);}#ifdef WIN32free(newData);#endiffree(data);free(meta);free(img);free(musicData);fclose(f);}int main(int argc,char**argv){readFileData("結束バンド - ギターと孤独と蒼い惑星.ncm");return 0;}GitHub项目
ncmToMp3
星期五女孩
博客园链接