1.代码及代码讲解。
代码编写工具：VsCode
（1）socket嗅探器
首先第一个脚本是最简单的原始socket嗅探器，它只会读一个数据包，然后直接退出：
import socketimport os#host to listen onHOST = ''
#这里输入自己的IP地址
def main(): #create raw socket, bin to public interface if os.name == 'nt': socket_protocol = socket.IPPROTO_IP else: socket_protocol = socket.IPPROTO_ICMP sniffer = socket.socket(socket.AF_INET,socket.SOCK_RAW.socket_protocol) sniffer.bind((HOST,0)) #include the IP header in the capture sniffer.setsockopt(socket.IPPROTO_IP,socket.IP_HDRINCL,1) if os.name =='nt': sniffer.ioctl(socket.SIO_RCVALL,socket.RCVALL_ON) #read one packet print(sniffer.recvfrom(65565)) if os.name == 'nt': sniffer.ioctl(socket.SIO_RCVALL,socket.RCVALL_OFF)if __name__ == '__main__': main()
注意：这里Windows和Linux的区别是，前者允许我们嗅探任何协议的所有流入数据，而后者强制我们指定一个协议来嗅探，这里指定的是ICMP。
上面这只是一个非常简单的嗅探器，那我们将对它的功能进行进一步的拓展。
（2）ip解码器
import ipaddressimport os import socketimport structimport sys#定义了一个Python结构，把数据包的前20个字节映射到IP头对象中。展示目前的通信协议和通信双方的IP地址class IP: def __init__(self, buff=None): header = struct.unpack('<BHHHBBH4s4s', buff) self.ver = header[0] >> 4 self.ihl = header[0] & 0xF self.tos = header[1] self.len = header[2] self.id = header[3] self.offset = header[4] self.ttl = header[5] self.protocol = header[6] self.sum = header[7] self.src = header[8] self.dst = header[9] # human readable IP addresses #使用新打造的IP头结构，将抓包逻辑改成持续抓包和解析 self.src_address = ipaddress.ip_address(self.src) self.dst_address = ipaddress.ip_address(self.dst) # map protocol constants to their names self.protocol_map = {1: "ICMP", 6: "TCP", 17: "UDP"} try: self.protocol = self.protocol_map[self.protocol_num] except Exception as e: print('%s No protocol for %s' % (e, self.protocol_num)) self.protocol = str(self.protocol_num) def sniff(host): # should look familiar from previous example if os.name == 'nt': socket_protocol = socket.IPPROTO_IP else: socket_protocol = socket.IPPROTO_ICMP sniffer = socket.socket(socket.AF_INET,socket.SOCK_RAW,socket_protocol) sniffer.bind((host,0)) sniffer.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) if os.name == 'nt': sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) try: while True: # read a packet #将前20字节转换成IP头对象 raw_buffere = sniffer.recvfrom(65535)[0] # create an IP header from the first 20 bytes ip_header = IP(raw_buffere[0:20]) # print the detected protocol and hosts #打印抓取信息 print('Protocol: %s %s -> %s' % (ip_header.protocol, ip_header.src_address, ip_header.dst_address)) except KeyboardInterrupt: # if we're on Windows, turn off promiscuous mode if os.name == 'nt': sniffer.ioctl(socket.SIO_RCVALL,socket.RCVALL_OFF) sys.exit()if __name__ == '__main': if len(sys.argv) == 2: host = sys.argv[1] else: host = '' sniffer(host)
在理解这一部分的内容之前，我们首先要了解一个python库。struct库：struct库提供了一些格式字符，用来定义二进制数据的结构。这个库在解码，密码学方面经常会用到。
注：在struct库里，不存在对应于nybble格式（即4个二进制位组成的数据块，也叫作nibble）的格式字符。
self.ver = header[0] >> 4
对于IP头的第一个字节，我们只想取高位nybble（整个字节里的第一个nybble）作为ver的值。取某字节高位nybble的常规方法是将其向右位移4位，相当于在该字节的开头填4个0，把其尾部的4位挤出去。这样我们就得到了原字节的第一个nybble。
self.ihl = header[0] & 0xF
我们想把低位nybble（或者说原字节的最后4个二进制位）填进hdrlen里，取某个字节低位nybble的常规方法是将其与数字0xF（00001111）进行按位与运算。它利用了0 AND 1 = 0的特性（0代表假，1代表真）。想要AND表达式为真，表达式两边都必须为真。所以这个操作相当于删除前4个二进制位，因为任何数AND 0都得0；它保持了最后4个二进制位不变，因为任何数AND 1还是原数字。
（3）解码ICMP
import ipaddressimport os import socketimport structimport sys#定义了一个Python结构，把数据包的前20个字节映射到IP头对象中。展示目前的通信协议和通信双方的IP地址class IP: def __init__(self, buff=None): header = struct.unpack('<BHHHBBH4s4s', buff) self.ver = header[0] >> 4 self.ihl = header[0] & 0xF self.tos = header[1] self.len = header[2] self.id = header[3] self.offset = header[4] self.ttl = header[5] self.protocol = header[6] self.sum = header[7] self.src = header[8] self.dst = header[9] # human readable IP addresses #使用新打造的IP头结构，将抓包逻辑改成持续抓包和解析 self.src_address = ipaddress.ip_address(self.src) self.dst_address = ipaddress.ip_address(self.dst) # map protocol constants to their names self.protocol_map = {1: "ICMP", 6: "TCP", 17: "UDP"} try: self.protocol = self.protocol_map[self.protocol_num] except Exception as e: print('%s No protocol for %s' % (e, self.protocol_num)) self.protocol = str(self.protocol_num)class ICMP: def __init__(self, buff): header = struct.unpack('<BBHHH', buff) self.type = header[0] self.code = header[1] self.sum = header[2] self.id = header[3] self.seq = header[4]def sniff(host): # should look familiar from previous example if os.name == 'nt': socket_protocol = socket.IPPROTO_IP else: socket_protocol = socket.IPPROTO_ICMP sniffer = socket.socket(socket.AF_INET,socket.SOCK_RAW,socket_protocol) sniffer.bind((host,0)) sniffer.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) if os.name == 'nt': sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) try: while True: # read a packet #将前20字节转换成IP头对象 raw_buffere = sniffer.recvfrom(65535)[0] # create an IP header from the first 20 bytes ip_header = IP(raw_buffere[0:20]) # if it's ICMP, we want it if ip_header.protocol == 'ICMP': print('Protocol: %s %s -> %s' % (ip_header.protocol,ip_header.src_address, ip_header.dst_address)) print(f'Version: {ip_header.ver}') print(f'Header Length; {ip_header.ihl} TTL: {ip_header.ttl}') # calculate where our ICMP packet starts offset = ip_header.ihl * 4 buf = raw_buffere[offset:offset + 8] # create our ICMP structure icmp_header = ICMP(buf) print('ICMP -> Yype: %s Code: %s\n' % (icmp_header.type, icmp_header.code)) except KeyboardInterrupt: if os.name == 'nt': sniffer.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) sys.exit() if __name__ == '__main': if len(sys.argv) == 2: host = sys.argv[1] else: host = '10.74.212.22' sniff(host)
这段代码在之前的IP结构下方又创建了一个ICMP结构。在负责接收数据包的主循环中，我们会判断接收到的数据包是否为ICMP数据包，然后计算出ICMP数据在原始数据包中的偏移，最后将数据按照ICMP结构进行解析。
（4）scanner.py
那前面我们已经完成了大部分工作，只剩下了一个任务——群发UDP数据包，并解析结果
importipaddress
importos
import socketimport structimport sysimport threadingimport time#subnet to targetSUBNET = '192.168.0.1/24'# magic string we'll check ICMP responses for
#添加的这点代码应该很好理解。我们定义了一个简单的字符串作为“签名”，用于确认收到的ICMP响应是否是由我们发送的UDP包所触发的
MESSAGE = 'PYTHONRULES!'#定义了一个Python结构，把数据包的前20个字节映射到IP头对象中。展示目前的通信协议和通信双方的IP地址class IP: def __init__(self, buff=None): header = struct.unpack('<BHHHBBH4s4s', buff) self.ver = header[0] >> 4 self.ihl = header[0] & 0xF self.tos = header[1] self.len = header[2] self.id = header[3] self.offset = header[4] self.ttl = header[5] self.protocol = header[6] self.sum = header[7] self.src = header[8] self.dst = header[9] # human readable IP addresses #使用新打造的IP头结构，将抓包逻辑改成持续抓包和解析 self.src_address = ipaddress.ip_address(self.src) self.dst_address = ipaddress.ip_address(self.dst) # map protocol constants to their names self.protocol_map = {1: "ICMP", 6: "TCP", 17: "UDP"} try: self.protocol = self.protocol_map[self.protocol_num] except Exception as e: print('%s No protocol for %s' % (e, self.protocol_num)) self.protocol = str(self.protocol_num)class ICMP: def __init__(self, buff): header = struct.unpack('<BBHHH', buff) self.type = header[0] self.code = header[1] self.sum = header[2] self.id = header[3] self.seq = header[4]def udp_sender(): with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sender: for ip in ipaddress.ip_network(SUBNET).hosts(): sender.sendto(bytes(MESSAGE, 'utf8'), (str(ip), 65212))class Scanner: def __init__(self, host): self.host = host if os.name == 'nt': socket_protocol = socket.IPPROTO_IP else: socket_protocol = socket.IPPROTO_ICMP self.socket = socket.socket(socket.AF_INET,socket.SOCK_RAW, socket_protocol) self.socket.bind((host, 0)) self.socket.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1) if os.name == 'nt': self.socket.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON) def sniff(self): hosts_up = set([f'{str(self.host)} *']) try: while True: # read a packet raw_buffer = self.socket.recvfrom(65535)[0] # create an IP header from the first 20 bytes ip_header = IP(raw_buffer[0:20]) # if it's ICMP, we went it if ip_header.protocol == "ICMP": offset = ip_header.ihl1 * 4 buf = raw_buffer[offset:offset + 8] icmp_header = ICMP(buf) if icmp_header.code == 3 and icmp_header.type == 3: if ipaddress.ip_address(ip_header.src_address) in ipaddress.IPv4Network(SUBNET): # make sure it has our magic message if raw_buffer[len(raw_buffer) - len(MESSAGE):] == bytes(MESSAGE, 'utf8'): tgt = str(ip_header.src_address) if tgt !=self.host and tgt not in hosts_up: hosts_up.add(str(ip_header.src_address)) print(f'Host Up: {tgt}') except KeyboardInterrupt: if os.name == 'nt': self.socket.ioctl(socket.SIO_RCVALL, socket.RCVALL_OFF) print('\nUser interrupted') if hosts_up: print(f'\n\nSummary: Hosts up on {SUBNET}') for host in sorted(hosts_up): print(f'{host}') print('') sys.exit()if __name__ == '__main': if len(sys.argv) == 2: host = sys.argv[1] else: host = '' s = Scanner(host) time.sleep(5) t = threading.Thread(target=udp_sender) t.start() s.sniff()
其中我们引入ipaddress库，这样就能对整个子网进行主机发现扫描。
sniff函数会嗅探网络上的数据，步骤跟之前的例子差不多，唯一的区别就是这次它会把在线的主机记录下来。接收到预期的ICMP消息时，我们首先检查这个响应是不是来自我们正在扫描的子网，然后检查ICMP消息里有没有我们自定义的签名。如果所有检查都通过了，就把发送这条ICMP消息的主机IP地址打印出来。如果使用Ctrl+C组合键中断扫描过程的话，程序就会关闭网卡混杂模式（如果是Windows平台），并且把迄今为止扫描出来的主机都打印到屏幕上。
那到这里我们的流量嗅探工具已经算编写完成了，希望大家有所收获。