BUUCTF [GKCTF 2021]签到 1

YueXuan

发布于 2025-08-18 20:34:22

18600

代码可运行

运行总次数：0

代码可运行

题目描述：

师傅们玩的开心~（flag由flag头包裹

密文：

下载附件，得到tmpshell.pcapng文件

解题思路：

1、打开流量文件，照常追踪TCP数据流，到第五个流中发现flag相关信息。

tcp.stream eq 5

将传输的数据复制下来，进行解密。

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

首先，由十六进制数据转为字符串。（字符串以“=”结尾，结合提示“cat+%2Ff14g%7Cbase64”，推测要使用Base64解码）

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

脚本如下：

# @Author：YueXuan
# @Date  ：2024/10/8 22:00

def split_into_hex_pairs(s):
    """将输入字符串切片成每两个字符一组的列表"""
    return [s[i:i+2] for i in range(0, len(s), 2)]

def convert_hex_to_int(hex_pairs):
    """将十六进制列表转换为十进制整数列表"""
    return [int(pair, 16) for pair in hex_pairs]

def adjust_for_ascii(int_values):
    """将整数列表中的值减去128以获取ASCII值"""
    return [value - 128 for value in int_values]

def convert_int_to_str(int_values):
    """将整数列表转换为字符串"""
    return ''.join(chr(value) for value in int_values)

def main(hex_string):
    """主函数，调用上述函数并打印结果"""
    print("字符串长度：%s" % len(hex_string))

    hex_pairs = split_into_hex_pairs(hex_string)
    print("hex列表：%s" % hex_pairs)

    int_values = convert_hex_to_int(hex_pairs)
    print("转化为十进制int列表：%s" % int_values)

    result_str = convert_int_to_str(int_values) # ascii_values
    print('最终答案：%s' % result_str)

if __name__ == '__main__':
    hex_str = '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'
    main(hex_str)

然后，进行Base64解码，得到逆序的数据。 Base64 在线解码、编码
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==QIhM0QDN0Q

2、在tmpshell.pcapng文件的其他流量上，也存在逆序的数据。例如：命令whoami，得到数据595852685a4331336433634b。经过解密，得到atad-www，逆序应为www-data

所以，将上面的数据进行按行逆序输出。文字倒序排列

cat flag | rev
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再进行Base64解密得到如下数据：

#######################################
#         2021-03-30 20:01:08         #
#######################################
--------------------------------------------------
窗口:*new 52 - Notepad++
时间:2021-03-30 20:01:13
[回车] 
--------------------------------------------------
窗口:*new 52 - Notepad++
时间:2021-03-30 20:01:13
[回车] [回车] [回车] ffllaagg{{}}WWeellcc))[删除] [删除] 00mmee__GGkkCC44FF__mm11ssiiCCCCCCCCCCCC!!

将flag的重复数据去除一半，得到flag。