USB流量知识点小结
USB接口是目前最为通用的外设接口之一，通过监听该接口的流量，可以得到很多有意思的东西，例如键盘击键，鼠标移动与点击，存储设备的明文传输通信、USB无线网卡网络传输内容等。
前言
USB流量的捕获可以使用wireshark或usbpcap来进行，在ctf中通常会给出已经捕获好的流量包，而我们需要做的便是从流量包中还原捕获的数据。USB流量分为两大类：键盘流量和鼠标流量。下面会分别进行解析。
键盘流量
附件链接：https://pan.baidu.com/s/1aJ_EDTqpUJht7Mpybnw5zQ 提取码：zuqw
注：以下内容以附件中的题为例
USB协议的数据部分在Leftover Capture Data域中，用wireshark打开流量包
在蓝色部分可以看到这个区域，右键→应用为列，即可在上面显示出来这一列
键盘流量的数据长度为8个字节，其中有关击键的信息在第三字节（十六进制表示）
详细的击键信息对照表可参考：https://max.book118.com/html/2017/0407/99227972.shtm
用tshark命令可以提取对应的Leftover Capture Data域中数据：
tshark -r usb.pcap -T fields -e usb.capdata > usbdata.txt如果提取出来的数据有空行，可以将命令改为如下形式：
tshark -r usb.pcapng -T fields -e usb.capdata | sed '/^\s*$/d' > usbdata.txt提取出来的数据
提取出来的数据可能会带冒号，也可能不带（有可能和wireshark的版本相关），但是一般的脚本都会按照有冒号的数据来识别，有冒号时提取数据的[6:8]，无冒号时数据在[4:6]，可以用脚本来加上冒号
f=open('usbdata.txt','r')
fi=open('out.txt','w')
while 1:
a=f.readline().strip()
if a:
if len(a)==16: # 鼠标流量的话len改为8
out=''
for i in range(0,len(a),2):
if i+2 != len(a):
out+=a[i]+a[i+1]+":"
else:
out+=a[i]+a[i+1]
fi.write(out)
fi.write('\n')
else:
break
fi.close()
得到这样的数据，此时对应的第三字节，也就是[6:8]就代表了击键信息
提取出键盘流量后需要用脚本还原数据对应的信息，附上两个还原信息较为完整的脚本（python2）
normalKeys = {
"04":"a", "05":"b", "06":"c", "07":"d", "08":"e",
"09":"f", "0a":"g", "0b":"h", "0c":"i", "0d":"j",
"0e":"k", "0f":"l", "10":"m", "11":"n", "12":"o",
"13":"p", "14":"q", "15":"r", "16":"s", "17":"t",
"18":"u", "19":"v", "1a":"w", "1b":"x", "1c":"y",
"1d":"z","1e":"1", "1f":"2", "20":"3", "21":"4",
"22":"5", "23":"6","24":"7","25":"8","26":"9",
"27":"0","28":"<RET>","29":"<ESC>","2a":"<DEL>", "2b":"\t",
"2c":"<SPACE>","2d":"-","2e":"=","2f":"[","30":"]","31":"\\",
"32":"<NON>","33":";","34":"'","35":"<GA>","36":",","37":".",
"38":"/","39":"<CAP>","3a":"<F1>","3b":"<F2>", "3c":"<F3>","3d":"<F4>",
"3e":"<F5>","3f":"<F6>","40":"<F7>","41":"<F8>","42":"<F9>","43":"<F10>",
"44":"<F11>","45":"<F12>"}
shiftKeys = {
"04":"A", "05":"B", "06":"C", "07":"D", "08":"E",
"09":"F", "0a":"G", "0b":"H", "0c":"I", "0d":"J",
"0e":"K", "0f":"L", "10":"M", "11":"N", "12":"O",
"13":"P", "14":"Q", "15":"R", "16":"S", "17":"T",
"18":"U", "19":"V", "1a":"W", "1b":"X", "1c":"Y",
"1d":"Z","1e":"!", "1f":"@", "20":"#", "21":"$",
"22":"%", "23":"^","24":"&","25":"*","26":"(","27":")",
"28":"<RET>","29":"<ESC>","2a":"<DEL>", "2b":"\t","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('out.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))mappings = { 0x04:"A", 0x05:"B", 0x06:"C", 0x07:"D", 0x08:"E", 0x09:"F", 0x0A:"G", 0x0B:"H", 0x0C:"I", 0x0D:"J", 0x0E:"K", 0x0F:"L", 0x10:"M", 0x11:"N",0x12:"O", 0x13:"P", 0x14:"Q", 0x15:"R", 0x16:"S", 0x17:"T", 0x18:"U",0x19:"V", 0x1A:"W", 0x1B:"X", 0x1C:"Y", 0x1D:"Z", 0x1E:"1", 0x1F:"2", 0x20:"3", 0x21:"4", 0x22:"5", 0x23:"6", 0x24:"7", 0x25:"8", 0x26:"9", 0x27:"0", 0x28:"\n", 0x2a:"[DEL]", 0X2B:" ", 0x2C:" ", 0x2D:"-", 0x2E:"=", 0x2F:"[", 0x30:"]", 0x31:"\\", 0x32:"~", 0x33:";", 0x34:"'", 0x36:",", 0x37:"." }
nums = []
keys = open('out.txt')
for line in keys:
if line[0]!='0' or line[1]!='0' 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':
continue
nums.append(int(line[6:8],16))
keys.close()
output = ""
for n in nums:
if n == 0 :
continue
if n in mappings:
output += mappings[n]
else:
output += '[unknown]'
print 'output :\n' + output此题我用了第二个脚本，还原得到以下信息
将其中[DEL]对应的字符删去，得到
HELLO , I AM WRITING SOMETHING IMPORTANT .
BUT I DO NOT USE PINYIN
I AM OLD .
DDPEIYUJ,Q S GAVCLWBMPYG RUG STK B .
I FPI J ET K YYGY R GAAA LWBMR .
WQ SK C RCN GHDMP QKD YTD R RUUJ WT O PYG RUG STK RJUQ H FCU
Q YI J PYG RUG STK KWKW
OVER
ENJOY MY MISC .最后再用五笔输入下中间的看似乱码的字符串，就可以得到flag
ps：重要的不是五笔，而是借这道题来讲述有关键盘流量的提取和解密，不要过于纠结五笔……
鼠标流量
附件链接：https://pan.baidu.com/s/1lIDKVmnNkqhv4h3JNsx8Mg 提取码：a1tn
鼠标流量的提取方式和上述键盘流量的方式相同，但不同的是鼠标流量的数据长度为4字节
以附件中的流量包为例
删去提取出来的数据中长度不正确的数据（没有冒号可用上面提到过的脚本加上），得到
在鼠标流量数据中，第一字节代表按键，当取0x00时代表没有按键，取0x01时代表按左键，取0x02时代表按右键。第二个字节可以看成是一个signed byte类型，当这个值为正时，代表鼠标水平右移多少像素，为负时，代表水平左移多少像素。第三个字节与第二字节类似，代表垂直上下移动的偏移。（具体可见下面的代码）
nums = []
keys = open('out.txt','r')
f = open('xy.txt','w')
posx = 0
posy = 0
for line in keys:
if len(line) != 12 :
continue
x = int(line[3:5],16)
y = int(line[6:8],16)
if x > 127 :
x -= 256
if y > 127 :
y -= 256
posx += x
posy += y
btn_flag = int(line[0:2],16) # 1 for left , 2 for right , 0 for nothing
if btn_flag == 1 : # 1 代表左键
f.write(str(posx))
f.write(' ')
f.write(str(posy))
f.write('\n')
f.close()本题的flag信息藏在右键中，当脚本中btn_flag取2时可以得到一系列坐标
熟悉的坐标形式，用gnuplot转化成图像即可
看起来是颠倒的，导出后convert翻转一下即可
得到flag：XNUCA{USBPCAPGETEVERYTHING}
参考文章
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