picoCTF General Skills Guide

binhexa

Name: binhexa
Description: How well can you perfom basic binary operations? Start searching for the flag here nc titan.picoctf.net 50052
Author: Nana Ama Atombo-Sackey
Tags: Easy, General Skills, picoCTF 2024, shell, browser_webshell_solvable
Challenge from: picoCTF 2024

Theory

According to the description, to get the flag we have do some binary operations, which I think we can solve by just using python. So like this, using int to convert to integer number, then doing the operation, then converting it back to binary, but then remove the 0b at the beginning, it's just an identifier to know it's binary, so for example hexadecimal uses 0x. For example, this one is for adding two binary numbers:

    >>> print(bin(int('10101010', 2) + int('01010101', 2)))
    0b11111111

Solution

First, let's enter to the NetCat, and now we can use the python code to get the answer for each of these:

shukularuni-picoctf@webshell:~$ nc titan.picoctf.net 50052

Welcome to the Binary Challenge!"
Your task is to perform the unique operations in the given order and find the final result in hexadecimal that yields the flag.

Binary Number 1: 11011100
Binary Number 2: 00101001


Question 1/6:
Operation 1: '|'
Perform the operation on Binary Number 1&2.
Enter the binary result:

    >>> print(bin(int('11011100', 2) | int('00101001', 2)))
    0b11111101

Enter the binary result: 11111101
Correct!

Question 2/6:
Operation 2: '+'
Perform the operation on Binary Number 1&2.
Enter the binary result:

    >>> print(bin(int('11011100', 2) + int('00101001', 2)))
    0b100000101

100000101
Correct!

Question 3/6:
Operation 3: '<<'
Perform a left shift of Binary Number 1 by 1 bits.
Enter the binary result:

Now here comes the tricky part, it says to do a left shift with the number 1 by 1 bit, so only one of the numbers is involved not the number 2:

    >>> print(bin(int('11011100', 2) << 1))
    0b110111000

Enter the binary result: 110111000
Correct!

Question 4/6:
Operation 4: '*'
Perform the operation on Binary Number 1&2.
Enter the binary result:

    >>> print(bin(int('11011100', 2) * int('00101001', 2)))
    0b10001100111100

Enter the binary result: 10001100111100
Correct!

Question 5/6:
Operation 5: '>>'
Perform a right shift of Binary Number 2 by 1 bits .
Enter the binary result:

And this one is a right shift, BUT ON THE SECOND NUMBER, so the command is this:

    >>> print(bin(int('00101001', 2) >> 1))
    0b10100

Enter the binary result: 10100
Correct!

Question 6/6:
Operation 6: '&'
Perform the operation on Binary Number 1&2.
Enter the binary result:

    >>> print(bin(int('11011100', 2) & int('00101001', 2)))
    0b1000

Enter the binary result: 1000
Correct!

Enter the results of the last operation in hexadecimal:

Finally we have to get the last's operation result in hexadecimal, which is actually really easy, you just need to change the output from bin to hex, to make it convert to hexadecimal after the operation is done, also remember to remove the 0x from the beginning:

    >>> print(hex(int('11011100', 2) & int('00101001', 2)))
    0x8

Enter the results of the last operation in hexadecimal: 8

Correct answer!
The flag is: picoCTF{b1tw^3se_0p3eR@tI0n_su33essFuL_aeaf4b09}
^C

There we go! That's the flag.

I rated this level as "good"! :3