PicoCTF Writeup – mus1c

# Information:

CTF Name: PicoCTF

CTF Challenge: mus1c

Challenge Category: General Skills/Misc

Challenge Points: 300

picoCTF 2019

# Used Tools:

# Challenge Description:

I wrote you a song. Put it in the picoCTF{} flag format.

Hints: Do you think you can master rockstar?

# Writeup

In this challenge, we are provided with a text file with song lyrics. A weird thing if you ask me. Considering the hint “can you master rockstar?” I went online and wrote rockstar programming, and this link came up.

It seems that there is indeed a programming language called rockstar!! After reading a little about it, I decided to give it a go.

Step 1

I went to https://codewithrockstar.com/online I pasted the lyrics provided in the challenge and the output was the following:

114
114
114
111
99
107
110
114
110
48
49
49
51
114

We are presented with a sequence of numbers. After some thought I tested the theory that these numbers pointed to letters in ASCII.

Step 2

In this step I tried the theorythat these numbers pointed to letters in ASCII.

114  -> r
114  -> r
114  -> r
111  -> o
99   -> c
107  -> k
110  -> n
114  -> r
110  -> n
48   -> 0
49   -> 1
49   -> 1
51   -> 3
114  -> r

Which becomes: rrrocknrn0113r.

Extra step – manual interpretation of the code.

If you want to interpret the code manual we can do that.

Note: To learn rockstar I saw this video starting at this time and also this site.

Pico's a CTFFFFFFF                       -> Pico = 19
my mind is waitin                        -> my mind = 6
It's waitin                              -> It = 6

Put my mind of Pico into This            -> This = Pico * my mind = 114
my flag is not found                     -> Initializes my flag
put This into my flag                    -> my flag = This = 114
put my flag into Pico                    -> Pico = my flag = 114


shout Pico                               -> prints Pico = 114
shout Pico                               -> prints Pico = 114
shout Pico                               -> prints Pico = 114

My song's something                      -> My song = 9
put Pico into This                       -> This = Pico = 114

Knock This down, down, down              -> This - 3 = 111
put This into CTF                        -> CTF = This

shout CTF                                -> prints CTF = 111
my lyric is nothing                      -> my lyric = null
Put This without my song into my lyric   -> my lyrics = This - my song = 102
Knock my lyric down, down, down          -> my lyric - 3 = 99

shout my lyric                           -> print my lyric = 99

Put my lyric into This                   -> This = my lyric
Put my song with This into my lyric      -> my lyric = my song + This = 108
Knock my lyric down                      -> my lyric = 107

shout my lyric                           -> prints my lyric = 107

Build my lyric up, up ,up                -> my lyric + 3 = 110

shout my lyric                           -> prints my lyric = 110
shout Pico                               -> prints Pico = 114
shout It                                 -> prints = It = my lyric = 110

Pico CTF is fun                          -> Pico CTF = 3
security is important                    -> security = 9
Fun is fun                               -> Fun = 3
Put security with fun into Pico CTF      -> Pico CTF = 3 + 9 = 12
Build Fun up                             -> Fun + 1 = 4
shout fun times Pico CTF                 -> prints 4 * Pico CTF = 48
put fun times Pico CTF into my song      -> my song = 48

build it up                              -> my song + 1 = 49

shout it                                 -> prints my song = 49
shout it                                 -> prints my song = 49

build it up, up                          -> my song = 51
shout it                                 -> prints my song = 51
shout Pico                               -> prints Pico = 114

The flag is:

Show flag
picoCTF{rrrocknrn0113r}

Thank you very much for reading!

Cheers,

MRegra


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