soal

Want to play a game? As you use more of the shell, you might be interested in how they work! Binary search is a classic algorithm used to quickly find an item in a sorted list.
Can you find the flag? You’ll have 1000 possibilities and only 10 guesses.
Cyber security often has a huge amount of data to look through - from logs, vulnerability reports, and forensics.
Practicing the fundamentals manually might help you in the future when you have to write your own tools!
You can download the challenge files here:
challenge.zip

Additional details will be available after launching your challenge instance.

launch istance

ssh -p 64844 ctf-player@atlas.picoctf.net
Using the password 83dcefb7. Accept the fingerprint with yes, and ls once connected to begin. Remember, in a shell, passwords are hidden!

hint

• Have you ever played hot or cold? Binary search is a bit like that.
• You have a very limited number of guesses. Try larger jumps between numbers!
• The program will randomly choose a new number each time you connect. You can always try again, but you should start your binary search over from the beginning - try around 500. Can you think of why?

solve

wget https://artifacts.picoctf.net/c_atlas/4/challenge.zip
unzip challenge.zip

cd home/ctf-player/drop-in
cat guessing_game.sh
#            #!/bin/bash
#            # Generate a random number between 1 and 1000
#            target=$(( (RANDOM % 1000) + 1 ))

## disini bisa kita lihat bahwa ini adalah game tebak angka random
## yang dibatasi 10 kali (max_guest)

## disini saya langsung mencoba dengan memulai di angka 500 untuk mengetahui posisi mana yang pas
ssh -p 64844 ctf-player@atlas.picoctf.net
# ctf-player@atlas.picoctf.net's password:
# Welcome to the Binary Search Game!
# I'm thinking of a number between 1 and 1000.
Enter your guess: 500
# Lower! Try again.
Enter your guess: 250
# Lower! Try again.
Enter your guess: 125
# Higher! Try again.
Enter your guess: 175
# Higher! Try again.
Enter your guess: 200
# Lower! Try again.
Enter your guess: 185
# Higher! Try again.
Enter your guess: 190
# Lower! Try again.
Enter your guess: 187
# Congratulations! You guessed the correct number: 187
# Here's your flag: picoCTF{g00d_gu355_ee8225d0}
# Connection to atlas.picoctf.net closed.

flag

picoCTF{g00d_gu355_ee8225d0}