Writeup CTF #1: Cyber Apocalypse HTB 2021

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This is no secret in this blog that I am a n0ob. But hey, at least I try :). Now, this is a blog post about a recent CTF that I enter with my seniors group which is Betapwners
 
[P.S: I deadass did not link y'all to my HTB profile in a blog doing exactly just that so my name in HTB is FINX]
 
                         
 
Figure 1: The Event Poster
 
 
Figure 2: My proof of joining the thing.. Sorry for not showing my real name although I did link this specific blog on LinkedIn though, currently I just don't felt comfortable enough to show my real name in a public space, hope you understand😔

I would summarize this CTF experience using this meme:

                                                 

To be completely honest, there are some challenges that I am really frustrated cannot get the flag such as the 1 star revere engineering questions like passphrase and authenticator also the bug report question. Oh, well at least there are writeups on these question for me to see the solution.

At least I contribute 1 flag for my team(real proud here). So, here are 2 challenges that I get in this CTF:

Nintendo Base 64

  • We get an output.txt that have this as the content:

0w eE5GbFdWW GhT V0d4VVYwZ G9 XV mx yWk ZOV 1JteD BaV WRH YW xa c1 NsWl dS M1 JQ WV d4 S2RHVkljRm Rp UjJoMlZrZH plRmRHV m5WaVJtUl hUVEZLZVZk V1VrZFpWMU pHVDFaV1Z tSkdXazlXYW twdl Yx Wm Fj bHBFVWxWTlZ Xdz BWa 2M xVT FSc 1d uTl hi R2h XWW taS 1dG VXh XbU ZTT VdS elYy cz FWM kY2VmtwV2 JU RX dZ ak Zr U0 ZOc2JGWmlS a3 BY V1 d0 YV lV MH hj RVpYYlVaVFRWW mF lV mt 3V lR GV 01 ER kh Zak 5rVj JFe VR Ya Fdha 3BIV mpGU 2NtR kdX bWx oT TB KW VYxW lNSM Wx XW kV kV mJ GWlRZ bXMxY2xWc 1V sZ FRiR1J5VjJ 0a1YySkdj RVpWVmxKV 1V GRTlQUT09

  • Safe to say that this is a base64 encoded. So, I just run Base64 decoder on Cyberchef untill it comes out the flag(it's 8 time) and got this as the flag → CHTB{3nc0d1ng_n0t_3qu4l_t0_3ncrypt10n}

PhaseStream 1

  • You'll got this string 2e313f2702184c5a0b1e321205550e03261b094d5c171f5601190 with the hint of repeating xor key using the flag format.
  • In former challenges, we know that the flag format is CHTB{}
  • So, we just run em' into XOR decoder in dcode.fr

[Given hint by team mate/senior. Afiq, thanks]

  • so, after we decode using the flag we just take the first four letter of the output (myke) in the key
  • Just bruteforce (myke) into relevent word to get the key → mykey
  • got flag → CHTB{u51ng_kn0wn_pl41nt3xt}

Conclusion:

 
 
Honestly, don't do what I do here. Better if you can code the cypher decoder otherwise you will end up wasting your time bruteforcing the cypher on a tool.

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