CTF show MISC base一条龙

题目地址：https://ctf.show 0x01

打开下载下来的文档，base64解码发现关键字 Rar!，然后保存下来解压得到steg.txt

0x02

打开steg.txt，发现为一堆base64，解码出来暂时没发现新的可利用信息，尝试base64隐写解密，脚本如下：

def get_base64_diff_value(s1, s2):
    base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
    res = 0
    for i in xrange(len(s2)):
        if s1[i] != s2[i]:
            return abs(base64chars.index(s1[i]) - base64chars.index(s2[i]))
    return res


def solve_stego():
    with open('1.txt', 'rb') as f:
        file_lines = f.readlines()
        bin_str = ''
        for line in file_lines:
            steg_line = line.replace('\n', '')
            norm_line = line.replace('\n', '').decode('base64').encode('base64').replace('\n', '')
            diff = get_base64_diff_value(steg_line, norm_line)
            print diff
            pads_num = steg_line.count('=')
            if diff:
                bin_str += bin(diff)[2:].zfill(pads_num * 2)
            else:
                bin_str += '0' * pads_num * 2
            print goflag(bin_str)


def goflag(bin_str):
    res_str = ''
    for i in xrange(0, len(bin_str), 8):
        res_str += chr(int(bin_str[i:i + 8], 2))
    return res_str


if __name__ == '__main__':
    solve_stego()
 

运行后结果为网站加提示

0x03

访问网站下载下来文件，看来这是要我们一直用base的各种类型解码了，尝试了一番以后（大概七八次）发现文件还是很大，算了，写个脚本。(说多了都是泪)

#author:羽
import base64
import base91
import base58
import py3base92
def hex_to_str(s):
        k=''
        for i in range(0,len(s),2):
                j = s[i]+s[i+1]
                k+=chr(int(j,16))
        print('16')
        return k

def ba32(s):
        s = base64.b32decode(s)
        s = bytes.decode(s)
        print('32')
        return s

def ba58(s):
        s = base58.b58decode(s)
        s = bytes.decode(s)
        print('58')
        return s

def ba64(s):
        s = base64.b64decode(s)
        s = bytes.decode(s)
        print('64')
        return s

def baa85(s):
        s = base64.a85decode(s)
        s = bytes.decode(s)
        print('a85')
        return s

def bab85(s):
        s = base64.b85decode(s)
        s = bytes.decode(s)
        print('b85')
        return s

def ba91(s):
        s = base91.decode(s)
        s = s.decode()
        print('91')
        return s

def ba92(s):
        s = py3base92.decode(s)
        print('91')
        return s

def start(s):
        for i in range(50):
                if len(s)