TJCTF 2018 Online CTF Competition Writeup

August 10, 2018 Script hunter

I solved some problems of TJCTF 2018 Online CTF COmpetition and this is TJCTF 2018 Online CTF Competition Writeup.Challenges are pretty easy and very helpful at same level.
TJCTF Challenges page

TJCTF 2018 Online CTF Competition Writeup

Task-Name: Cookie Monster
Category: WEB
Points: 10
Writeup:

Task-Name has suggested ,we need to do manipulation with Cookie.So i typed document.cookie in console and got the flag.Easy!!!
flag: tjctf{c00ki3s_over_h0rs3s}

Task-Name: Vinegar
Category: Cryptography
Points: 15
Writeup:

Task has given a txt file which is containing some keys and hashes.
file:-
key = Kkkkk kkkkKkkkkkkkkKkkkkkkkkKkk
flag = uucbx{simbjyaqyvzbzfdatshktkbde}
sha256 = 8304c5fa4186bbce7ac030d068fdd485040e65bf824ee70b0bdbac03862bec93

i decrypted sha256 hash at online websites and got this flag.
flag: tjctf{onevinaigrettesaladplease}

Task-Name: Central Savings Account
Category: Web
Points: 10
Writeup:

Directly go to source->main.js and scroll down to this function-

we have a md5 hash value – 698967f805dea9ea073d188d73ab7390 ,just decrypt it online and you will get your flag.
flag: avalon

Task-Name: Math Whiz
Category: Binary Exploitation
Points: 20
Writeup:

i just connected to nc problem1.tjctf.org 8001 through terminal and after looking at source code i decided to do buffer overflow.

flag: tjctf{d4n63r0u5_buff3r_0v3rfl0w5}

Task-Name: Validator
Category: Reverse Engineering
Points: 30
Writeup:

Task has given a executable program and we need to do reverse engineering on that.
i used radare2 and gdb both for disassembling the binary.
There is total three valid checking-

  1. Checking for whether input flag has given or not.
  2. Checking the input length and compare with original flag’s length
  3. Final Comparison between your input and original flag


set a breakpoint on address 0x0804858a> because here register eax is holding input length and we have to change its value with 43.

now we have string comparison with strcmp function.

What value contains in register $eax on this address? Go to address 0x080485ba for viewing register value then type x/s $eax
you will get your flag.

flag : tjctf{ju57_c4ll_m3_35r3v3r_60d_fr0m_n0w_0n}