# Helikopter

## Description

> Helikopter Helikopter! Or is it a mirror? What does `g?` do, In vim when given these characters? `hjpgs{ebg13_n6q5ro2}`

## GG?

I do not know what a Helikopter is, but I do vaguely know about vim, so let's start with that

I don't use vim myself so let's research about `g?`

{% embed url="<https://renenyffenegger.ch/notes/development/vim/commands/g>" %}

There are a few things of note:

* `g` scans lines, marks those that match a pattern, and runs a command on those lines
  * It may also take in a `range`
* There is nothing about `?`

This doesn't seem too fruitful, so let's try getting our hands dirty

## :q&#x20;

1. Open vim with `vim`
2. Struggle and panic as you try to figure out how to actually type in the new file&#x20;

   -> (I believe pressing the `i` key is what allows you to "insert", though I do not know if that's the correct command)
3. Insert the text `hjpgs{ebg13_n6q5ro2}` into the file
4. To call commands, press the `:` key and type in `g?` then `ENTER`

And... nothing happens?

Well except for the file seemingly deleting the text I painstakingly typed in. Also this error:

<figure><img src="/files/rUeza84kVmTioWhn47th" alt=""><figcaption></figcaption></figure>

Perhaps I should have tried learning vim as suggested by my university professors

### Mirror Mirror on the Wall...

Another line of thought surged regarding the reference to a mirror (I'm still avoiding the "Helikopter"), perhaps it has something to do with reversing?

I tried the text backwards. Nothing

I tried appending the reverse of the text to the end of the normal string, as though there is a "mirror" between them. Nothing

I tried a bunch of things, and to spare you the painful details, nothing seemed to work and I was at a lost

At least I learned how to exit vim

## Rotate Your Way of Thinking

Eventually, I did what I should have done at the start and noticed something peculiar about `hjpgs{ebg13_n6q5ro2}`

* It has open and closing curly braces `{}`
* There are 5 letters prior to the first bracket, similar to the format of the flags `uwctf{...}`
* Comparing the respective letters `u -> h`, `w -> j` etc. a certain pattern arises...

The letters `hjpgs` are precisely 13 characters away from `uwctf`

This is ROT 13

{% embed url="<https://rot13.com/>" %}

Equivalently write a quick Python function

```python
def rot13(word):
    m = ''

    # Iterate over each character in the word
    for ch in word:
        # Ignore if the character is a symbol or number
        if not ch.isalpha():
            m += ch
            continue

        # Convert the character to its numerical value ord(ch)
        # Since it's lowercase, subtract 97 to get its position in the alphabet
        # Add the offset 13
        # Mod 26 to account for wrap around
        # Add 97 back to get the lowercase letter
        # Convert back into a character with ch(num)
        m += chr((ord(ch) - 97 + 13) % 26 + 97)
    
    return m
```

It wasn't until later that I read the comment in this StackOverflow post which provided the answer

{% embed url="<https://stackoverflow.com/questions/45086981/what-are-the-vim-commands-that-start-with-g>" %}

```
g?             2  Rot13 encoding operator
```

Another thing I missed was that there was literally "13" in the flag

At least I learned how to exit vim

## Flag

`uwctf{rot13_a6d5eb2}`


---

# Agent Instructions: 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:

```
GET https://soyabeanboi.gitbook.io/bag-of-flags/2022/uw-ctf-s22/helikopter.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
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.