网鼎杯CTF——朱雀组 (week 4)

What

用ida打开，大概看到的是一个go的逆向

看到是个置换表的base64，找一下明文

直接写一下脚本

#!/usr/bin/python
import base64
base_now="XYZFGHI2+/Jhi345jklmEnopuvwqrABCDKL6789abMNWcdefgstOPQRSTUVxyz01"
base_init="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="

clear="nRKKAHzMrQzaqQzKpPHClX=="
c=""
for i in range(len(clear)):
    b=base_now.find(clear[i])
    c+=base_init[b]
c=base64.b64decode(c)
print c

tree

一个数据结构的算法，类似与哈夫曼树的算法直接写exp了：

tree = {
    'y':'0000',
    'b':'00010',
    'q':'00011',
    'g':'0010',
    'f':'0011',
    'j':'010',
    'w':'01100',
    'p':'01101',
    'x':'011100',
    'd':'0111010',
    'i':'0111011',
    'k':'01111',
    's':'100',
    'z':'1010',
    'n':'1011',
    'c':'11000',
    't':'110010',
    'e':'110011',
    'h':'1101',
    'o':'11100',
    'l':'1110100',
    'u':'11101010',
    'r':'111010110',
    'a':'111111111',
    'm':'111011',
    'v':'1111'
}

a = 'zvzjyvosgnzkbjjjypjbjdvmsjjyvsjx'
flag=""

for i in a:
    flag += tree[i]
print (hex(int(flag,2)))