> For the complete documentation index, see [llms.txt](https://writeups.ayweth20.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://writeups.ayweth20.com/2021/dvctf-to-join-davincicode/reverse/code-pyn.md).

# Code Pyn

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**Category:** Reverse - **Points:** 34 - **Solves:** 20\
**Description:** I lost my pin code. Can you help me find it?

**Infos:**

> A .pyc file is provided (pyn.pyc)

**Solution:**\
To solve this challenge you need to find a solution to decrypt the .pyc file or to recover the program code.\
To do this I chose to develop a little python script (*bruteforcePYC.py*).\
The script recove the program structure and we can see what he is doing.\
For example the python script return this :

```
  8          24 LOAD_NAME                4 (len)
             26 LOAD_NAME                3 (pin)
             28 CALL_FUNCTION            1
             30 LOAD_CONST               5 (4)
```

This block indicate that the PIN is composed by 4 digits (*LOAD\_CONST (4)*)\
After theses lines indicate that we need to do a [XOR](https://xor.pw/#) between 5 and 3 :

```
60 LOAD_CONST               6 (5)
62 BINARY_XOR
64 LOAD_CONST               7 (3)
```

And it's the same for the 2 following PIN

```
86 LOAD_CONST               7 (3)
88 BINARY_XOR
90 LOAD_CONST               6 (5)
```

```
112 LOAD_CONST              10 (8)
114 BINARY_XOR
116 LOAD_CONST               8 (1)
```

So we have the 3 first digits (669) and the fourth need to be find manually.\
When we test the last digit, we found speedly that is 1.\
So we know the PIN code : 6691 and the FLAG is the PIN so...

<details>

<summary>🚩 FLAG</summary>

```
DVC{6691}
```

</details>