Overview

This repository comprises of several projects written in assembly and C ranging from simple ones to quite complex.

DOS 💾

In order to get used to writing in assembly and don't feel overencumbered by the nuances and the security mechanisms of modern operating systems.

Drawing an animated frame

Difficulty: 🔫🔫🔫

This is just a one-evening program that for me to get acquainted with assembly. Nothing special - it draws an animated frame and inside of it you can convert numbers into several numeral base systems.

Interruption interception

Difficulty: 🔫🔫

Here I used the idea of intercepting system interruptions in order to implement the application that draws current contents of general-use registers.

Pair hacking

Difficulty: ⚔️

Huge thanks to vssense for being my opponent in this project and just being a good friend of mine, whom I could always rely on, in case I want to hear how stupid I am 🤡.

In pairs we had to write simple password-filling programs and then exchange only executables with each other. The idea was to understand how the opponent's program works using nothing but disassembled code. Then hacking began... Then our job was to do the following:

1. Find several wrong inputs (not the correct password), which however pass as correct. This can be achieved by overflowing the buffer that contains correct/user-entered password.
2. Write a key-gen with GUI that changes the executable so that any input passes as correct password.

Linux and NASM 💻

Here we step into the restraining modern world of Linux.

Printf

Difficulty: ⚔️

Simple implementation of C' printf() (see its documentation on cppreference) function, written in NASM, though lacking multiple options. My function's documentation:

;------------------------------------------------------------------------------
; Writes formatted output to stdout.
;
; Expects: [RBP + 16] = formatted string
;          [RBP + 24] = arg1
;          [RBP + 32] = arg2
;               ...
;
; Returns: RAX = number of successfully written characters or -1 if an error 
;                occurred.
; Changes: RAX, RBX, RCX, RDX, RDI, RSI, R8, R9, R10, R12
; Details: You can use either of these argument specifications
; 
;            Symb  Bytes            Description 
;          +------+-----+----------------------------------+
;          |  %c  |  1  |  ASCII character                 |
;          +------+-----+----------------------------------+
;          |  %s  |  8  |  null-terminated string          |
;          +------+-----+----------------------------------+
;          |  %d  |  4  |  decimal     integer (signed)    |
;          +------+-----+----------------------------------+
;          |  %u  |  4  |  decimal     integer (unsigned)  |
;          +------+-----+----------------------------------+
;          |  %x  |  4  |  hexadecimal integer (unsigned)  |
;          +------+-----+----------------------------------+
;          |  %o  |  4  |  octal       integer (unsigned)  |
;          +------+-----+----------------------------------+
;          |  %b  |  4  |  binary      integer (unsigned)  |
;          +------+-----+----------------------------------+
;           
;          To write symbol '%' you should pass '%%'.
;------------------------------------------------------------------------------
writeFormatted:
...

Even though it states that the function gets parameters only through stack, you can use this function from C/C++ code (the "callable" version is _writeFormatted())! This has been done by pushing first six parameters (rdi, rsi, rdx, rcx, r8, r9) into stack.

Mandelbrot set visualization using AVX2

Difficulty: ⚔️

Probably the most visually apealling project here. It's based on one unique set of complex numbers, which was defined by mathematician Benoit Mandelbrot and called Mandelbrot set. In order to boost the performance of computing colors of each pixel, AVX2 instructions have been used. With them, 8 pixels can be processed simultaneously!

Hash table optimization

Difficulty: ⚔️⚔️

See my full text on it.