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
ssh -p 53039 ctf-player@atlas.picoctf.net
Using the password 6dd28e9b. Accept the fingerprint
with yes, and ls once connected to begin. Remember,
in a shell, passwords are hidden!
SSH into the challenge based on the instructions in the description.
Welcome to the Binary Search Game!
I'm thinking of a number between 1 and 1000.
The first guess is going to always be 500 because it is the middle of 1 and 1000.
For each guess after 500 the known lower bound is taken and the known higher bound is taken and divided by two for the next guess.
Example Sequence:
Enter your guess: 500
Lower! Try again.
(1 + 500) / 2 = 250.5
Enter your guess: 251
Lower! Try again.
(1 + 250) / 2 = 125.5
Enter your guess: 125
Lower! Try again.
(1 + 125) / 2 = 63
Enter your guess: 63
Lower! Try again.
(1 + 63) / 2 = 32
Enter your guess: 32
Higher! Try again.
(32 + 63) / 2 = 47.5
Enter your guess: 47
Lower! Try again.
(32 + 47) / 2 = 39.5
Enter your guess: 39
Lower! Try again.
(32 + 39) / 2 = 35.5
Enter your guess: 36
Higher! Try again.
(36 + 39) / 2 = 37.5
Enter your guess: 38
Congratulations! You guessed the correct number: 38
Flag: picoCTF{g00d_gu355_de95...}