数据包处理

stun协议去除

在处理语音和视频通话时，stun的协议头会影响wireshark对于协议的解析。比如dtls如果包裹在stun协议头下面，就无法解析出相应的dtls的握手过程，从而影响到相应的动作流程的判断。

现给出学习强国的stun去除首部脚本，脚本是借助python的kamene库来实现的

# -*- encoding: utf-8 -*-
# @File           : clip_stun.py
# @Description    : The Stun header affects wireshark parsing. So this script will help you to Remove stun headers
# @Time           : 2020/09/29 08:00:27
# @Author         : runope
# @version        : v1.0


# Need kamene library, pip3 install kamene
from kamene.all import *


# Only clip header of stun, which obtain attribute type of data
# Algorithm take advantage of data's attribute type of which Hexadecimal notation is 0x0013
# and The calculated length is verified
with PcapReader("audio.pcap") as pcap_reader:
    writers = PcapWriter("audio_clip_stun_header.pcap")

    for pkt in pcap_reader:
        if 'UDP' in pkt:
            # read Application layer data 
            if pkt.haslayer('Raw'):   
                Raw = bytes(pkt['Raw'])
                Raw_str = ''
                Raw_str = Raw_str.join(['%02X' % b for b in Raw])
                Raw_len = len(Raw_str)
                # Determine if there is any other protocol reuse
                if int(Raw_str[0], 16) >= 4:
                    # Throw out 4 bytes of Stun
                    remaining = Raw_str[8:]
                    pkt['Raw'] = bytes.fromhex(remaining)  
                    # Modify the LENGTH attribute of UDP's header
                    UDPtemp = bytes(pkt['UDP'])
                    UDPtemp2 = ''
                    UDPtemp2 = UDPtemp2.join(['%02X' % b for b in UDPtemp])
                    UDPtemp3 = bytearray(UDPtemp)
                    print((int(UDPtemp2[8:12], 16) - 4)) 
                    print((hex(int(UDPtemp2[8:12], 16) - 4))) 
                    j = bytearray(bytes.fromhex((hex(int(UDPtemp2[8:12], 16) - 4))[2:].zfill(4)))
                    UDPtemp3[4] = j[0]
                    print(j[0])
                    UDPtemp3[5] = j[1]
                    print(j[1])
                    pkt['UDP'] = bytes(UDPtemp3)
                    
                    # Modify the LENGTH attribute of IP's header
                    Iptemp = bytes(pkt['IP'])
                    Iptemp3 = bytearray(Iptemp)
                    Iptemp2 = ''
                    Iptemp2 = Iptemp2.join(['%02X' % b for b in Iptemp])  
                    print((int(Iptemp2[4:8], 16) - 4)) 
                    
                    k = bytearray(bytes.fromhex((hex(int(Iptemp2[4:8], 16) - 4))[2:].zfill(4)))
                    Iptemp3[2] = k[0]
                    Iptemp3[3] = k[1]
                    pkt['IP'] = bytes(Iptemp3)
                        
                    writers.write(pkt)   
                else:
                    # Determines whether there is a data attribute
                    start_index = Raw_str.find("0013")
                    # Extract the data for the data attribute
                    if start_index != -1:
                        remaining = Raw_str[start_index:]
                        remaining_length = int(remaining[4:8],16)
                        remaining = remaining[8:]
                        # 4-byte alignment, slove the error by padding
                        if len(remaining) // 8 == (remaining_length + 3) // 4:
                            pkt['Raw'] = bytes.fromhex(remaining[0:remaining_length*2])
                            sub_len = (Raw_len - remaining_length*2) // 2

                            # Modify the LENGTH attribute of UDP's header
                            UDPtemp = bytes(pkt['UDP'])
                            UDPtemp2 = bytearray(UDPtemp)
                            UDPtemp2[5] = UDPtemp2[5] - sub_len
                            UDPtemp3 = bytes(UDPtemp2)
                            pkt['UDP'] = UDPtemp3
                            
                            # Modify the LENGTH attribute of IP's header
                            Iptemp = bytes(pkt['IP'])
                            Iptemp2 = bytearray(Iptemp)
                            Iptemp2[3] = Iptemp2[3] - sub_len
                            Iptemp3 = bytes(Iptemp2)             
                            pkt['IP'] = Iptemp3
    
                            writers.write(pkt)  
        else:
           writers.write(pkt)      
    writers.flush()
    writers.close()

效果如下图：

去除首部前

去除首部后