为了完成计算机网络的实验，翻了一些博客，有的没源代码，有的记录不全。就很烦。所以自己写一篇吧。
首先我们通过wireshark看看FTP的登陆是怎么完成的。
（1）选一个当前在用的网络，我是WLAN
（2）选择TCP过滤器方便找到FTP的包（没有过滤FTP的，最多只能过滤出TCP）
（3）开始捕捉后我们就可以找到需要的包了。右键一个FTP包，点跟踪流，可以看到所有相关的包。
OK，现在我们已经知道FTP登陆的过程了。一个头部是USER的包，一个头部是PASS的包，以及头部是530表示登录失败（230代表成功）的包。三个包就足够让我们开一个暴力的beta程序了。
开始编程吧。我们首先要设置在程序中设置TCP过滤器。如下：
char packet_filter[] = "tcp";
//编译过滤器
if (pcap_compile(adhandle, &fcode, packet_filter, 1, netmask) <0)
{
fprintf(stderr, "\nUnable to compile the packet filter. Check the syntax.\n");
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}
//设置过滤器
if (pcap_setfilter(adhandle, &fcode)<0)
{
fprintf(stderr, "\nError setting the filter.\n");
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}然后在回调函数中，我们读取每个包信息部分（注意要跳过头部）的前四个字符，进行判断如下：
string com;//读取
for (int i = 0; i < 4; i++)
com += (char)pkt_data[head + i];
if (com == "USER")
{
string m_ip_message = get_request_m_ip_message(pkt_data);
string user;
ostringstream sout;
for (int i = head+5; pkt_data[i]!=13; i++)
{
sout << pkt_data[i];
}
user = sout.str();
ftp[m_ip_message][0] = user;
}
if (com == "PASS")
{
string m_ip_message = get_request_m_ip_message(pkt_data);
string pass;
ostringstream sout;
for (int i = head + 5; pkt_data[i] != 13; i++)
{
sout << pkt_data[i];
}
pass = sout.str();
ftp[m_ip_message][1] = pass;
}
if (com == "230 ")
{
string m_ip_message = get_response_m_ip_message(pkt_data);
ftp[m_ip_message][2] = "SUCCEED";
print(header, m_ip_message);
}
if (com == "530 ")
{
string m_ip_message = get_response_m_ip_message(pkt_data);
ftp[m_ip_message][2] = "FAILD";
print(header, m_ip_message);
}FTP是一个map<string,string[3]> 记录了以某两台电脑之间通讯的USER PASS以及访问状态。这样可以避免多个FTP同时访问造成错误。完成代码如下：
#include<iostream>
#include<sstream>
#include<string>
#include<map>
#include<fstream>
#include <pcap.h>
#pragma warning(disable:4996)
using namespace std;
map<string,string[3]> ftp;
bool flag;
ofstream out("mark.txt");
typedef struct mac_header
{
u_char dest_addr[6];
u_char src_addr[6];
u_char type[2];
} mac_header;
/* IPv4 首部 ,20字节*/
typedef struct ip_header {
u_char ver_ihl; // 版本 (4 bits) + 首部长度 (4 bits)
u_char tos; // 服务类型(Type of service)
u_short tlen; // 总长(Total length)
u_short identification; // 标识(Identification)
u_short flags_fo; // 标志位(Flags) (3 bits) + 段偏移量(Fragment offset) (13 bits)
u_char ttl; // 存活时间(Time to live)
u_char proto; // 协议(Protocol)
u_short crc; // 首部校验和(Header checksum)
u_char saddr[4]; // 源地址(Source address)
u_char daddr[4]; // 目的地址(Destination address)
u_int op_pad; // 选项与填充(Option + Padding)
}ip_header;
//TCP头部，总长度20字节
typedef struct tcp_header
{
u_short sport; //源端口号
u_short dport; //目的端口号
u_int th_seq; //序列号
u_int th_ack; //确认号
u_int th1 : 4; //tcp头部长度
u_int th_res : 4; //6位中的4位首部长度
u_int th_res2 : 2; //6位中的2位首部长度
u_char th_flags; //6位标志位
u_short th_win; //16位窗口大小
u_short th_sum; //16位tcp检验和
u_short th_urp; //16位紧急指针
}tcp_header;
/* 回调函数原型 */
void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data);
string get_request_m_ip_message(const u_char* pkt_data);
string get_response_m_ip_message(const u_char* pkt_data);
void print(const struct pcap_pkthdr *header, string m_ip_message);
int main()
{
flag = false;
pcap_if_t *alldevs;
pcap_if_t *d;
int inum;
int i = 0;
pcap_t *adhandle;
char errbuf[PCAP_ERRBUF_SIZE];
u_int netmask;
char packet_filter[] = "tcp";
struct bpf_program fcode;
/* 获得设备列表 */
if (pcap_findalldevs_ex(PCAP_SRC_IF_STRING, NULL, &alldevs, errbuf) == -1)
{
fprintf(stderr, "Error in pcap_findalldevs: %s\n", errbuf);
exit(1);
}
/* 打印列表 */
for (d = alldevs; d; d = d->next)
{
printf("%d. %s", ++i, d->name);
if (d->description)
printf(" (%s)\n", d->description);
else
printf(" (No description available)\n");
}
if (i == 0)
{
printf("\nNo interfaces found! Make sure WinPcap is installed.\n");
return -1;
}
printf("Enter the interface number (1-%d):", i);
scanf("%d", &inum);
if (inum < 1 || inum > i)
{
printf("\nInterface number out of range.\n");
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}
/* 跳转到已选设备 */
for (d = alldevs, i = 0; i< inum - 1; d = d->next, i++);
/* 打开适配器 */
if ((adhandle = pcap_open(d->name, // 设备名
65536, // 要捕捉的数据包的部分
// 65535保证能捕获到不同数据链路层上的每个数据包的全部内容
PCAP_OPENFLAG_PROMISCUOUS, // 混杂模式
1000, // 读取超时时间
NULL, // 远程机器验证
errbuf // 错误缓冲池
)) == NULL)
{
fprintf(stderr, "\nUnable to open the adapter. %s is not supported by WinPcap\n", d->name);
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}
/* 检查数据链路层，为了简单，我们只考虑以太网 */
if (pcap_datalink(adhandle) != DLT_EN10MB)
{
fprintf(stderr, "\nThis program works only on Ethernet networks.\n");
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}
if (d->addresses != NULL)
/* 获得接口第一个地址的掩码 */
netmask = ((struct sockaddr_in *)(d->addresses->netmask))->sin_addr.S_un.S_addr;
else
/* 如果接口没有地址，那么我们假设一个C类的掩码 */
netmask = 0xffffff;
//编译过滤器
if (pcap_compile(adhandle, &fcode, packet_filter, 1, netmask) <0)
{
fprintf(stderr, "\nUnable to compile the packet filter. Check the syntax.\n");
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}
//设置过滤器
if (pcap_setfilter(adhandle, &fcode)<0)
{
fprintf(stderr, "\nError setting the filter.\n");
/* 释放设备列表 */
pcap_freealldevs(alldevs);
return -1;
}
printf("\nlistening on %s...\n", d->description);
/* 释放设备列表 */
pcap_freealldevs(alldevs);
/* 开始捕捉 */
pcap_loop(adhandle, 0, packet_handler, NULL);
out.close();
return 0;
}
/* 回调函数，当收到每一个数据包时会被libpcap所调用 */
void packet_handler(u_char *param, const struct pcap_pkthdr *header, const u_char *pkt_data)
{
struct tm *ltime;
char timestr[16];
ip_header *ih;
tcp_header *uh;
u_int ip_len;
u_short sport, dport;
time_t local_tv_sec;
/* 将时间戳转换成可识别的格式 */
local_tv_sec = header->ts.tv_sec;
ltime = localtime(&local_tv_sec);
strftime(timestr, sizeof timestr, "%H:%M:%S", ltime);
int head = 54;//14位以太网头，20位ip头，20位tcp头
//选择出command为USER和PASS的包，当然这里就简单的以首字母来代表了，反正其他的
//command 没有以U和P开头的
string com;
for (int i = 0; i < 4; i++)
com += (char)pkt_data[head + i];
if (com == "USER")
{
string m_ip_message = get_request_m_ip_message(pkt_data);
string user;
ostringstream sout;
for (int i = head+5; pkt_data[i]!=13; i++)
{
sout << pkt_data[i];
}
user = sout.str();
ftp[m_ip_message][0] = user;
}
if (com == "PASS")
{
string m_ip_message = get_request_m_ip_message(pkt_data);
string pass;
ostringstream sout;
for (int i = head + 5; pkt_data[i] != 13; i++)
{
sout << pkt_data[i];
}
pass = sout.str();
ftp[m_ip_message][1] = pass;
}
if (com == "230 ")
{
string m_ip_message = get_response_m_ip_message(pkt_data);
ftp[m_ip_message][2] = "SUCCEED";
print(header, m_ip_message);
}
if (com == "530 ")
{
string m_ip_message = get_response_m_ip_message(pkt_data);
ftp[m_ip_message][2] = "FAILD";
print(header, m_ip_message);
}
/*if (flag == true)
{
cout << com;
for (int i = 0; i < 4; i++)
{
int a = com.c_str()[i];
cout << " " << a;
}
cout << endl;
}*/
}
string get_request_m_ip_message(const u_char* pkt_data)
{
mac_header *mh;
ip_header *ih;
string m_ip_message;
string str;//empty string
ostringstream sout;
int length = sizeof(mac_header) + sizeof(ip_header);
mh = (mac_header*)pkt_data;
ih = (ip_header*)(pkt_data + sizeof(mac_header));
for (int i = 0; i<5; i++)
sout << hex << (int)(mh->src_addr[i]) << "-";
sout << (int)(mh->src_addr[5]) << ",";
for (int i = 0; i<3; i++)
sout << dec << (int)(ih->saddr[i]) << ".";
sout << (int)(ih->saddr[3]) << ",";
for (int i = 0; i<5; i++)
sout << hex << (int)(mh->dest_addr[i]) << "-";
sout << (int)(mh->dest_addr[5]) << ",";
for (int i = 0; i < 3; i++)
sout << dec << (int)(ih->daddr[i]) << ".";
sout << (int)(ih->daddr[3]);
m_ip_message = sout.str();
return m_ip_message;
}
string get_response_m_ip_message(const u_char* pkt_data)
{
mac_header *mh;
ip_header *ih;
string m_ip_message;
string str;//empty string
ostringstream sout;
int length = sizeof(mac_header) + sizeof(ip_header);
mh = (mac_header*)pkt_data;
ih = (ip_header*)(pkt_data + sizeof(mac_header));
for (int i = 0; i<5; i++)
sout << hex << (int)(mh->dest_addr[i]) << "-";
sout << (int)(mh->dest_addr[5]) << ",";
for (int i = 0; i < 3; i++)
sout << dec << (int)(ih->daddr[i]) << ".";
sout << (int)(ih->daddr[3]) << ",";
for (int i = 0; i<5; i++)
sout << hex << (int)(mh->src_addr[i]) << "-";
sout << (int)(mh->src_addr[5]) << ",";
for (int i = 0; i<3; i++)
sout << dec << (int)(ih->saddr[i]) << ".";
sout << (int)(ih->saddr[3]);
m_ip_message = sout.str();
return m_ip_message;
}
void print(const struct pcap_pkthdr *header, string m_ip_message)
{
struct tm *ltime;
char timestr[16];
time_t local_tv_sec;
/* 将时间戳转化为可识别的格式 */
local_tv_sec = header->ts.tv_sec;
ltime = localtime(&local_tv_sec);
strftime(timestr, sizeof timestr, "%H:%M:%S", ltime);
/* 打印时间戳*/
cout << timestr << ",";
cout << m_ip_message << ",";
for (int i = 0; i < 2; i++)
cout << ftp[m_ip_message][i] << ",";
cout << ftp[m_ip_message][2] <<endl;
out << timestr << ",";
out << m_ip_message << ",";
for (int i = 0; i < 2; i++)
out << ftp[m_ip_message][i] << ",";
out << ftp[m_ip_message][2] << endl;
ftp.erase(m_ip_message);
}