Yachay
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About me

I enjoy doing CTFs and cybersecurity in general, whether it’s reverse engineering, forensics, pentesting, or other areas. Over time, my interests have broadened to include issues of online privacy, anonymity, respect for personal data, and the use of free software. These topics are essential to me because they touch not only on technology, but also on fundamental ethical issues and our individual freedom in an increasingly digitized world. On this site, I present my projects and CTF reports.

December 14, 2025

Windows keylogger

The purpose of this project is to familiarize yourself with programming via the Windows API and how Windows services work. The project consists of two programs, svc.exe and winkey.exe. svc.exe works like the Windows command sc.exe. winkey.exe is a keylogger that records keystrokes using a low-level function and stores each keystroke in a file in C:\Windows\Temp. There is also an interesting feature in svc.exe: a remote shell. Install and start service ...

January 31, 2026

Windows PE Reverse Engineering – Crackme #1

Analysis of a 64-bit Windows PE executable, tracing back step by step from the entry point to understand how the program processes user input, using assembly language, the internal workings of PE sections, and deliberately discreet validation logic, revealing a simple but clever mechanism typical of small reverse engineering challenges. Windows PE Reverse Engineering – Crackme #1 Infos: Executable name: crack_me.exe Format: PE32+ Architecture: x86-64 Windows Sections: 3 sections Executable: Console Techniques/Concepts used RIP-relative addressing to access data without an absolute address Data stored directly in the .text section (inline data) Mapping table indexed via a bitwise mask (AND 0x7) Verification loop combining user input and an internal table I use PE-bear, which analyzes files in PE (Portable Executable) format. ...

December 13, 2025

Windows PE Reverse Engineering – Crackme #2

Step‑by‑step analysis of a 64‑bit Windows PE executable, focusing on entry point analysis, runtime initialization, stack frame inspection, and conditional branching to understand how user input is validated in a basic crackme challenge. Windows PE Reverse Engineering – Crackme #2 Infos: Executable name: 3outof6.exe Format: PE32+ Architecture: x86-64 Windows Sections: 19 sections Executable: Console Techniques/Concepts used RIP-relative addressing to access data without an absolute address DLL imports & IAT (Import Address Table) Environment dependency awareness CRT / Runtime initialization analysis CRT (C RunTime) all code automatically added by the compiler. RIP = address of the next instruction, used for relative addressing in x86‑64. ...

December 14, 2025
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