jellyCTF

Cult_classic_1 [343 pts]

Writeup author: lolmenow

Difficulty: easy

Provided files: 01.zip and 01_welcome.txt

Description:

We are not a cult" - Starknights (probably)

This challenge contains two flags:

    Submit the first flag to cult_classic_1
    Submit the second (final) flag to cult_classic_2

Flags for this challenge are case insensitive.

The zip file for the next stage is password protected, and the password is somewhere in the 01_welcome.txt file.

I heavily overthinked the first password, however it was just the starting letter of each sentence.

01_welcome.txt contents:

Pleased to meet you.

Recruitment: we are currently looking for highly intelligent individuals.

In order to do this, we have devised a test.

Nested in this text is the first key to a series of challenges.

Capture the final flag to prove your worth.

Excitedly awaiting the few who make it through to the end.

Sincerely,

Starknights (not a cult)

First password: PRINCESS

The password unlocks the zip file, and now we are presented with 02.txt:

Congratulations on passing stage 1.
TGkgYnJ4IGZkcSBnaGZyZ2ggd2tsdiwgYnJ4IGZkcSBrZHloIHdraCBxaGF3IG5oYjogRUxKUUhVRw==

This is base64 encoding due to the 2 equal signs at the end of the string, decoding this gives:

Li brx fdq ghfrgh wklv, brx fdq kdyh wkh qhaw nhb: ELJQHUG

If you see jumbled up text like this without much special characters, assume its some type of rotational cipher. In this case, it was a caeser cipher (caeser ciphers can easily be bruteforced)

Using dcode’s Caeser Cipher Bruteforce we get this output:

Second password: BIGNERD

Once unlocking the next stage, we get 03.txt

OWZ OEU, KFZKF E WOBO LBV PRVZ KSJFUUA YB JRU: KMRYCTWG{BNVW_ZV_KCYG_E_NDSU_AC}
LFZFDKE CFXS RUHVEHZ QY ASK RWMX, GEBH UPOF OVB BVJ CVFFFMJ SSIZBZJ: NPZHO

This time, it was not a ROT or caeser cipher. But instead, a vigenere cipher with the key “BIGNERD” (this was guessy to figure out, but vigenere is common)

Using Cyberchef’s vigenere decode, we get:

NOT BAD, HERES A FLAG FOR YOUR EFFORTS SO FAR: JELLYCTF{THIS_IS_JUST_A_WARM_UP}
HOWEVER YOUR JOURNEY IS NOT OVER, TAKE THIS KEY AND PROCEED FORWARD: ALIEN

And there is our flag! That key will be important for the second edition of this challenge.

Final flag: JELLYCTF{THIS_IS_JUST_A_WARM_UP}

sakouk.me

jellyCTF

Cult_classic_1 [343 pts]