SCSC2026 Quals - unsolpable solpable - General Skills Writeup

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1 minute

SCSC2026 Quals - unsolpable solpable - General Skills Writeup

2026-02-17

Writeup

CTF

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Security

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General Skills

Category: General Skills

Server: nc 43.128.69.211 10002

Flag: scsc26{bin4ry_s34rch_like_an_OctoPath_Traveler}

Challenge Description#

Guess 30 secret numbers (range 1-1000) with only 10 attempts each.

Analysis#

With 10 attempts to find a number in range 1-1000, we need binary search. Since 2^10 = 1024 > 1000, binary search guarantees finding any number within 10 guesses.

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$ nc 43.128.69.211 10002
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Rockwell ada angka 1 - 1000, ayo tebak angka yang rockwell pikirkan ya!
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Kamu punya 10 kali kesempatan untuk menebak angka rockwell
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Tebakanmu: 500
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tebakanmu kekecilan!
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Sisa tebakan: 9
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Tebakanmu:

Server responses (Indonesian):

"tebakanmu kekecilan!" = your guess is too small
"tebakanmu kegedean!" = your guess is too big
"tebakanmu bener!" = your guess is correct

Solution#

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# !/usr/bin/env python3
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from pwn import *
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import time
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def main():
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    p = remote('43.128.69.211', 10002)
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    # Get banner
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    time.sleep(0.5)
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    p.recv(timeout=2)
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    print("[+] Connected!")
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    for round_num in range(30):
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        low, high = 1, 1000
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        for attempt in range(10):
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            mid = (low + high) // 2
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            p.sendline(str(mid).encode())
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            time.sleep(0.05)
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            response = p.recv(512, timeout=2).decode().lower()
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            if 'kekecilan' in response:  # too small
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                low = mid + 1
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            elif 'kegedean' in response:  # too big
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                high = mid - 1
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            elif 'bener' in response:  # correct!
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                print(f"[{round_num+1}/30] Found: {mid}")
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                break
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    # Get flag
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    print(p.recvall(timeout=3).decode())
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if __name__ == '__main__':
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    main()