> For the complete documentation index, see [llms.txt](https://alham-rizvi.gitbook.io/alhamrizvi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alham-rizvi.gitbook.io/alhamrizvi/picoctf-writeups/picoctf/reverse-engineering/unpackme.md).

# unpackme

Another interesting challenge.

The first thing I did was **unpack the binary**, since it was packed with UPX. I used:

```
upx -d unpackme-upx
```

After unpacking, I opened the binary in **Ghidra** to analyze the code.

#### 🔍 Analysis

In the `main` function, I found a condition where the program asks:

```
What's my favorite number?
```

Then it checks if the input matches a specific value:

```c
if (local_44 == 0xb83cb)
```

So I converted this hexadecimal value to decimal:

```
0xb83cb = 754635
```

I ran the binary and entered the correct number:

```
./unpackme-upx
What's my favorite number? 754635
```

The program then decrypted and printed the flag:

```
picoCTF{up><_m3_f7w_5769b54e}


If you want, I can also make this more “pro CTF write-up style” or GitHub-ready 🔥
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://alham-rizvi.gitbook.io/alhamrizvi/picoctf-writeups/picoctf/reverse-engineering/unpackme.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.