Lesson 24: Intel-x86 Architecture Cover
Lesson Link:
https://cybertalents.com/learn/introduction-to-cybersecurity/lessons/24-intel-x86-architecture-cover
Introduction
In this lesson we will cover the basics of the Intel-x86 architecture. We will start by learning about the registers and how to use them. Then we will learn about the memory and how to access it. Finally, we will learn about the instructions and how to use them.
Challenge
Name:
bronze ASM
Description:
his Challenge will help you understand how to analyze simple assembly code.
the flag is the parameter of the function int he following format (“FLAG{0_%X_0}” % parmter)
Solution
In this challenge, we are given a .asm file. after reading the file, we will find the following code:
fx:
push rbp
mov rbp, rsp
mov DWORD PTR [rbp-4], edi
mov eax, DWORD PTR [rbp-4]
sal eax, 3
cmp eax, 5744
sete al
movzx eax, al
pop rbp
ret
So the function fx takes one parameter and, multiplies it by 8 (sal = shift arithmetic left, and 8 = 2^3), then compares it to 5744, if the result is equal to 5744, it returns 1, otherwise it returns 0.
So we need to find the parameter that makes the function return 1. So we need to solve the following equation:
8 * parameter = 5744
So the parameter is 718.
If we try to run the function with the parameter 718, like FLAG{0_718_0}, the flag will be incorrect.
Because the flag is in hex format, so we need to convert the parameter to hex, like FLAG{0_2CE_0}.
Flag
FLAG{0_2CE_0}