编辑“︁计算机相关编码”︁（章节）

=== 例子 ===

题目描述参见 <code>ctf-challenge</code>中 [https://github.com/ctf-wiki/ctf-challenges/tree/master/misc/encode/computer/base64-stego misc 分类的 base64-stego 目录]中的 data.txt 文件。

使用脚本读取隐写信息。

<syntaxhighlight lang="python">import base64

def deStego(stegoFile):
    b64table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
    with open(stegoFile,'r') as stegoText:
        message = ""
        for line in stegoText:
            try:
                text = line[line.index("=") - 1:-1]
                message += "".join([ bin( 0 if i == '=' else b64table.find(i))[2:].zfill(6) for i in text])[2 if text.count('=') ==2 else 4:6]  
            except:
                pass
    return "".join([chr(int(message[i:i+8],2)) for i in range(0,len(message),8)])

print(deStego("text.txt"))</syntaxhighlight>
输出:

<pre>     flag{BASE64_i5_amaz1ng}</pre>
<!--
下面是原编辑者的代码，代码的小毛病在于查找隐写字符用`last = line[-3]`写死了，这种写法默认每行尾有一个'\n',而最后一行并非如此，因此左后一个字符显示错误。

一大串 Base64 密文，试试补 0 位的数据。

```python
# coding=utf-8
import base64
import re

result = []
with open('text.txt', 'r') as f:
    for line in f.readlines():
        if len(re.findall(r'=', line)) == 2:
            last = line[-4]
            if last.isupper():
                num = ord(last) - ord('A')
            elif last.islower():
                num = ord(last) - ord('a') + 26
            elif last.isdigit():
                num = int(last) + 52
            elif last == '+':
                num = 62
            elif last == '/':
                num = 63
            elem = '{0:06b}'.format(num)
            result.append(elem[2:])

        elif len(re.findall(r'=', line)) == 1:
            last = line[-3]
            if last.isupper():
                num = ord(last) - ord('A')
            elif last.islower():
                num = ord(last) - ord('a') + 26
            elif last.isdigit():
                num = int(last) + 52
            elif last == '+':
                num = 62
            elif last == '/':
                num = 63
            elem = '{0:06b}'.format(num)
            result.append(elem[4:])

flag_b = ''.join(result)
split = re.findall(r'.{8}', flag_b)
for i in split:
    print chr(int(i, 2)),
```

感觉像是程序有点毛病，不过还是能看出来 flag。

```
flag{BASE64_i5_amaz1ng~
```
-->

<span id="题目-1"></span>