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?

Vim command: 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

1. Open vim with vim

2. Struggle and panic as you try to figure out how to actually type in the new file

   -> (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:

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

rot13.com

Equivalently write a quick Python function

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

What are the vim commands that start with g?Stack Overflow

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}