Challenge Overview
Initial Analysis
It’s very clear from the challenge itself that the CTF players should find the ASCII value of a hexadecimal unit.
Prerequisite
Little bit understanding about binary-hexadecimal system.
Procedure
Understanding Hexadecimal:
Hexadecimal is a base-16 number system that uses 16 symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. Each hexadecimal digit represents 4 bits of binary data.
Converting Hexadecimal to ASCII:
To convert a hexadecimal value to its ASCII , we need to convert each hexadecimal digit to its binary representation, group the binary digits into 8-bit chunks (1 byte), and then interpret each byte as an ASCII character.
Breaking Down the Hexadecimal Value 0x70:
a. Hexadecimal to Binary:
0X70 — Lets focus on the last 2 digits
To find the binary value of 7
The binary of 7 -0111
The binary of 0 -0000
Thus, 0x70 in binary is 01110000.
b.Binary to ASCII:
Now, we know the binary value of 0x70 , convert it into ASCII value by looking up in the ASCII table .
Link to the ASCII table — ASCII
The binary value 01110000 corresponds to the ASCII character ‘p’. Therefore, if a word starts with 0x70 in hexadecimal, it will start with the letter ‘p’ in ASCII. ( ASCII values are case-sensitive)
Flag for this challenge — picoCTF{p}
