> For the complete documentation index, see [llms.txt](https://docs.cooku222.kr/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cooku222.kr/security/web-hacking/dreamhack/dreamhack-amocafe.md).

# \[Dreamhack] amocafe

#### 문제 링크

<https://dreamhack.io/wargame/challenges/899>

#### 문제

<figure><img src="https://blog.kakaocdn.net/dna/mGbqH/btsEdJFYSJB/AAAAAAAAAAAAAAAAAAAAAMAFNXW8x4AH6ZZ1f0D8VucCZ6Dm3NiI9fhUPlOtudoq/img.jpg?credential=yqXZFxpELC7KVnFOS48ylbz2pIh7yKj8&#x26;expires=1782831599&#x26;allow_ip=&#x26;allow_referer=&#x26;signature=bXj8vZ%2FMoHHJRjGbdaKinTKvymM%3D" alt="" height="422" width="1022"><figcaption></figcaption></figure>

&#x20;

#### 풀이

<figure><img src="https://blog.kakaocdn.net/dna/brM9tc/btsEbBaMFNA/AAAAAAAAAAAAAAAAAAAAAOEPCr7Uo1lHD21QbtJ62fono7zk-M6-rX0dxroLlMbQ/img.jpg?credential=yqXZFxpELC7KVnFOS48ylbz2pIh7yKj8&#x26;expires=1782831599&#x26;allow_ip=&#x26;allow_referer=&#x26;signature=nW94Dvdb1UPfroDIesCOM26NBPU%3D" alt="" height="402" width="557"><figcaption></figcaption></figure>

웹에 접속하면 이런 화면이 펼쳐진다. 막막하므로 코드를 살펴본다.&#x20;

<figure><img src="https://blog.kakaocdn.net/dna/bc2x9T/btsEbA3ZIZs/AAAAAAAAAAAAAAAAAAAAAAg22pmJo55PdwiXV9kJPcPyJ1EkazBOthDesKWdsPMW/img.jpg?credential=yqXZFxpELC7KVnFOS48ylbz2pIh7yKj8&#x26;expires=1782831599&#x26;allow_ip=&#x26;allow_referer=&#x26;signature=Po1yiBpikvdvZ%2By%2BlUFlKJr4ZUs%3D" alt="" height="247" width="422"><figcaption></figcaption></figure>

일단 이 부분 코드부터 보면, 비트연산자가 쓰여서 16진수를 2진수로 바꿔서 생각을 할 수 있어야 하는 문제라는 것을 알 수 있다.\
코드를 파이썬으로 직접 짜는 방법도 있으나, 나는 여기서 직접 역연산을 하는 방법을 택했다.\
1\. 우선 사이트의 \_를 알려면 여기서 \~res & 0xf == 0x4 라는 것을 풀어야 하는데, 0xf, 0x4는 16진수로 쓰여있으므로 2진수로 바꾸면 \~res & 1111 == 0100\
res == 1011\
2\. 모두 16진수에서 2진수로 변환\
1 => 0001\
c => 1100\
3 => 0011\
0 => 0000\
f =>1111\
e =>1110\
이제 이걸 연달아서 입력해주면\
0001/1011/1100/1011/0011/1011/1100/1011/0000/1011/1011/1111/1111/1011/0011/1100\
\=> 0001101111001011001110111100101100001011101111111111101100111100\
여기서 끝나는게 아닌데, 윗부분 코드에

<figure><img src="https://blog.kakaocdn.net/dna/ewncKH/btsEf5VRF37/AAAAAAAAAAAAAAAAAAAAAObVObkxKrkdeJNQttVg2fga2hj61ZzTDk7LbGiqH6Sv/img.jpg?credential=yqXZFxpELC7KVnFOS48ylbz2pIh7yKj8&#x26;expires=1782831599&#x26;allow_ip=&#x26;allow_referer=&#x26;signature=cID51bRSjayF5cbjrQ75tX%2F9518%3D" alt="" height="128" width="331"><figcaption></figcaption></figure>

이런 부분이 있다. int형으로 변환을 시켜주라는 것이다. \
따라서 위에 입력된 2진수 값을 int형을 변환을 시켜주면(int형은 기본이 10진수이므로 쉽게 말하면 10진수로 변환을 시켜주는 것이다.)\
2002760202557848382 \
가 나온다.\
이를 프롬프트에 입력해주면

<figure><img src="https://blog.kakaocdn.net/dna/bnVQQu/btsEfuBrG0u/AAAAAAAAAAAAAAAAAAAAAAGFzMF8gCH1w22tb1b2vsubirQi7Cgio8E5y1gCtHrf/img.jpg?credential=yqXZFxpELC7KVnFOS48ylbz2pIh7yKj8&#x26;expires=1782831599&#x26;allow_ip=&#x26;allow_referer=&#x26;signature=p4oaB8JIQ8fogxLdH5RXeI3mZCw%3D" alt="" height="447" width="507"><figcaption></figcaption></figure>

<figure><img src="https://blog.kakaocdn.net/dna/bNaI2r/btsEdNIupeN/AAAAAAAAAAAAAAAAAAAAADN718s3GtrjzQj3R5LY-rePYFJfkrHp1EBHgHDOGTyp/img.png?credential=yqXZFxpELC7KVnFOS48ylbz2pIh7yKj8&#x26;expires=1782831599&#x26;allow_ip=&#x26;allow_referer=&#x26;signature=eu%2FZB1NsVBnHMkx0RR17v%2F7VgoU%3D" alt="" height="148" width="681"><figcaption></figcaption></figure>

플래그 값을 얻을 수 있다.


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