CTF—MISC—USB键盘流量分析

题目

题目名称：键盘流量

题目类型：MISC

解题思路

题目下载解压发现是55.pcapng、miwen.txt两个文件

miwen.txt

miwen.txt内容为base64编码假flag，文件大小与实际内容不符，发现txt隐写了零宽字符
如何发现零宽字符，vim打开文件，如下图：

python脚本解密

python3 -m pip install zwsp-steg-py

#!/usr/bin/python
# -*- coding: utf-8 -*-
import zwsp_steg

decoded = zwsp_steg.decode('Z​​​​‎‍​​​​​‍​​​​​​‍‏​​​​​‏‎​​​​​‏​​​​​​‍‏‌​​​​‎‍‌​​​​‏‌‍​​​​‎‍‎​​​​‌‏‏​​​​‍‌‍​​​​‏‌‌​​​​‍​‍​​​​‏​‍​​​​‎​‏​​​​‎‎​​​​​‍‏‏​​​​‎‌‌​​​​‏​​​​​​‍​​​​​​‏‌‎​​​​‍​‌​​​​‍‎‎​​​​‍‎‍​​​​‏​‌​​​​‍‎‎​​​​‍‎‌​​​​‏‎‌​​​​‍‏‏​​​​‏‍‎​​​​‍​‎​​​​‎‌‏​​​​‍‌‌​​​​‌‎‎​​​​‎‍‎​​​​‏​​​​​​‏​‍​​​​‍‎‍​​​​‏‎​​​​​‍‏‏​​​​‍‌‍​​​​‎‍‍​​​​‍‏‏​​​​‎‌‎​​​​‎‌​​​​​‍‎‌​​​​‍‏​​​​​‏‎‍​​​​‎​‎​​​​‏‏‌​​​​‍​‏​​​​‎‌‌​​​​‏‎‍​​​​‎‌​​​​​‌‏‍​​​​‏​‌​​​​‏​​​​​​‎‌‍​​​​‍‏‍​​​​‏‎‏​​​​‏‏​​​​​‌‏‍​​​​‏​‌​​​​‏‏​​​​​‍​‎​​​​‏​​​​​​‏‎‍​​​​‏‎‎​​​​‏‏‍​​​​‍​‏​​​​‎‎​​​​​‍‏​​​​​‎‍‎​​​​‍​​​​​​‍‎‍​​​​‎​‎​​​​‍​‍​​​​‏​‎​​​​‏‌‏​​​​‏‌‏​​​​‍‏‏​​​​‏​‎​​​​‎‍‍​​​​‏​‍​​​​‌‏‏​​​​‎‌‌​​​​‍‍‌​​​​‍‍‌mxhZ3toYWhhfmZha2VmbGFnIX0=',zwsp_steg.MODE_FULL)
print (decoded)

output:
U2FsdGVkX19j4fOZJQd2l3DCeDBtJq5T8+XdfCsJ9WJSPBFuNy6QuP/edRHwx/ex5duvz6ZFX2CN4gmmJgWf1Q==

55.pcapng

打开pcap包，发现是usb的键盘流量，键盘流量的数据记录在Data中，需要把所有Data数据提取出来，进行十六进制键位转换得出数据包记录的键盘敲击内容
1、利用wireshark tshark.exe命令提取流量数据，详情如下：

tshark.exe -T json -r 55.pcapng > test.json
//用法 tshark.exe -T json -r 数据包名称 > 要导出的文件

导出的文件如下，键盘数据存储在usbhid.data中，将所有的usbhid.data值提取出来

2、利用python编写的脚本对提取出来的所有usbhid.data转化生成敲击内容,脚本原理

#!/usr/bin/env python
# -*- coding:utf-8 -*-

normalKeys = {"04":"a", "05":"b", "06":"c", "07":"d", "08":"e", "09":"f", "0a":"g", "0b":"h", "0c":"i", "0d":"j", "0e":"k", "0f":"l", "10":"m", "11":"n", "12":"o", "13":"p", "14":"q", "15":"r", "16":"s", "17":"t", "18":"u", "19":"v", "1a":"w", "1b":"x", "1c":"y", "1d":"z","1e":"1", "1f":"2", "20":"3", "21":"4", "22":"5", "23":"6","24":"7","25":"8","26":"9","27":"0","28":"<RET>","29":"<ESC>","2a":"<DEL>", "2b":"	","2c":"<SPACE>","2d":"-","2e":"=","2f":"[","30":"]","31":"\","32":"<NON>","33":";","34":"'","35":"<GA>","36":",","37":".","38":"/","39":"<CAP>","3a":"<F1>","3b":"<F2>", "3c":"<F3>","3d":"<F4>","3e":"<F5>","3f":"<F6>","40":"<F7>","41":"<F8>","42":"<F9>","43":"<F10>","44":"<F11>","45":"<F12>"}
shiftKeys = {"04":"A", "05":"B", "06":"C", "07":"D", "08":"E", "09":"F", "0a":"G", "0b":"H", "0c":"I", "0d":"J", "0e":"K", "0f":"L", "10":"M", "11":"N", "12":"O", "13":"P", "14":"Q", "15":"R", "16":"S", "17":"T", "18":"U", "19":"V", "1a":"W", "1b":"X", "1c":"Y", "1d":"Z","1e":"!", "1f":"@", "20":"#", "21":"$", "22":"%", "23":"^","24":"&","25":"*","26":"(","27":")","28":"<RET>","29":"<ESC>","2a":"<DEL>", "2b":"	","2c":"<SPACE>","2d":"_","2e":"+","2f":"{","30":"}","31":"|","32":"<NON>","33":""","34":":","35":"<GA>","36":"<","37":">","38":"?","39":"<CAP>","3a":"<F1>","3b":"<F2>", "3c":"<F3>","3d":"<F4>","3e":"<F5>","3f":"<F6>","40":"<F7>","41":"<F8>","42":"<F9>","43":"<F10>","44":"<F11>","45":"<F12>"}
output = []
keys = open('usbdata.txt')
for line in keys:
    try:
        if line[0]!='0' or (line[1]!='0' and line[1]!='2') or line[3]!='0' or line[4]!='0' or line[9]!='0' or line[10]!='0' or line[12]!='0' or line[13]!='0' or line[15]!='0' or line[16]!='0' or line[18]!='0' or line[19]!='0' or line[21]!='0' or line[22]!='0' or line[6:8]=="00":
             continue
        if line[6:8] in normalKeys.keys():
            output += [[normalKeys[line[6:8]]],[shiftKeys[line[6:8]]]][line[1]=='2']
        else:
            output += ['[unknown]']
    except:
        pass
keys.close()

flag=0
print("".join(output))
for i in range(len(output)):
    try:
        a=output.index('<DEL>')
        del output[a]
        del output[a-1]
    except:
        pass
for i in range(len(output)):
    try:
        if output[i]=="<CAP>":
            flag+=1
            output.pop(i)
            if flag==2:
                flag=0
        if flag!=0:
            output[i]=output[i].upper()
    except:
        pass
print ('output :' + "".join(output))

内容为

plk<DEL>eae<DEL>sey<DEL>fii<DEL>ndts<DEL>hery<DEL>ealy<DEL>keyd<DEL>words<DEL>
output :pleasefindtherealkeyword

解密

发现miwen是AES加密的密文，需要密钥进行解密
解密工具
用pleasefindtherealkeyword没有解密成功
用del删除的字节发现"keyisyyds"实际密钥为yyds，解出flag

tshark.exe使用参考