BUU [GKCTF 2021]签到

BUU [GKCTF 2021]签到

1.题目概述

2.解题过程

追踪HTTP流

在下面发现了一串可疑字符

Base16转base64

放到010里看看

复制下来，去转字符

好像不是，再回去找找其他的

又发现了这个

看来flag与Base64编码有关，那么怎么才能得到呢？

可以利用base16转成base64，然后base64又可以转成字符，就这么干

又找出来2个base16字符串

复制到010

但是第一个解出来啥都没有

再解解第二个

看来有戏，但是解了一下没出来什么东西，还提示编码有误

看了看才发现，他这个地方有点问题

正常的==应该在最后，把他逆序一下
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==QIhM0QDN0Q
#正常情况应该是XXX==这种，所以逆序一下试试，注意是每行逆序才能得到标准的XXX==

然后建一个脚本：

每行逆序

a='wIDIgACIgACIgAyIK0wIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMiCNoQD'
b='jMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjMyIjoQDjACIgACIgACIggDM6EDM6AjMgAzMtMDMtEjM'
c='t0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0iCNMyIjMyIjMyIjMyI'
d='6AjMgAzMtMDMtEjMwIjO0eZ62ep5K0wKrQWYwVGdv5EItAiM1Aydl5mK6M6jlfpqnrQDt0SLt0SL'
e='t0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLt0SLK0AIdZavo75mlvlCNMTM6EDM'
f='z0yMw0SMyAjM6Q7lpb7lmrQDrsCZhBXZ09mTg0CIyUDI3VmbqozoPW+lqeuCN0SLt0SLt0SLt0SL'
g='sxWZld1V913e7d2ZhFGbsZmZg0lp9iunbW+Wg0lp9iunbW+Wg0lp9iunbW+WK0wMxoTMwoDMyACM'
h='DN0QDN0QDlWazNXMx0Wbf9lRGRDNDN0ard0Rf9VZl1WbwADIdRampDKilvFIdRampDKilvVKpM2Y'
i='==QIhM0QDN0Q'
print(a[::-1])
print(b[::-1])
print(c[::-1])
print(d[::-1])
print(e[::-1])
print(f[::-1])
print(g[::-1])
print(h[::-1])
print(i[::-1])
#耐心一点，正确分行

逆序后再转一下看看

base64转字符

哇，终于出来了，去重一下

flag{Welc0me_GkC4F_m1siC!}

或者利用栅栏密码网站，调整一下{}的位置就好了

(注意，下划线_不要漏了)

这道签到题好难啊！！！

3.flag

flag{Welc0me_GkC4F_m1siC!}