> 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/reverse.md).

# reverse

### Easy Method (Using `strings`)

First, we can quickly check the binary using:

```bash
strings binary
```

This reveals readable strings inside the binary, and we can directly spot the flag:

```
picoCTF{3lf_r3v3r5ing_succe55ful_fa9cb3b}
```

👉 So yes, the flag can be obtained easily using `strings`.

### Actual Reverse Engineering Method (GDB)

To properly understand the binary, I analyzed it using GDB.

#### Step 1: Find main

```bash
info functions
```

Then:

```bash
disas main
```

***

#### Step 2: Analyze main

Inside `main`, I found multiple `movabs` instructions loading large hex values:

```asm
movabs $0x7b4654436f636970,%rax
movabs $0x337633725f666c33,%rdx
movabs $0x75735f676e693572,%rax
movabs $0x6c75663535656363,%rdx
movabs $0x623362633961665f,%rax
```

These values are stored in memory and later used in:

```asm
call strcmp
```

👉 Meaning: The program compares user input with this hidden string.

***

#### Step 3: Convert Hex → ASCII

Since the system is **little endian**, we reverse the bytes and convert to ASCII.

Example:

```
0x7b4654436f636970 → picoCTF{
```

After converting all parts and combining them:

```
picoCTF{3lf_r3v3r5ing_succe55ful_fa9cb3b}
```

***

### 🎯 Final Flag

```
picoCTF{3lf_r3v3r5ing_succe55ful_fa9cb3b}
```

***

### 💡 Conclusion

* The flag was hardcoded inside the binary
* It could be extracted easily using `strings`
* But proper reversing involved:
  * Disassembling `main`
  * Identifying `strcmp`
  * Decoding hex values manually


---

# 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/reverse.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.