Justas Masiulis
Software Engineer at Roblox
San Francisco, California, United States
Summary
🤩
Rockstar🎓
Top SchoolJustas Masiulis is a software engineer based in San Francisco with a decade of hands-on experience in Windows internals, kernel programming, and reverse engineering, primarily using C++. He has shipped low-level security and anti-tamper features at companies like Byfron and Nord Security and now applies that expertise at Roblox, bridging platform-level protections with product needs. An active open-source contributor, he maintains high-performance C++ projects such as xorstr (compile-time string encryption) and lazy_importer, and has improved the UI experience of the widely used x64dbg debugger. Comfortable across languages from x86-64 ASM to Rust and Go, he specializes in making reverse-engineering-unfriendly tooling while keeping cross-compiler compatibility and performance in mind. Colleagues describe him as a practical problem-solver who "solves life problems with templates," reflecting a knack for elegant, template-driven C++ design.
10 years of coding experience
1 year of employment as a software developer
Bachelor's degree, Computer Software Engineering, Bachelor's degree, Computer Software Engineering at Vilniaus universitetas / Vilnius University
English, Lithuanian, Russian
Github Skills (23)
c-language10
css10
ui-design10
obfuscation10
hash10
cpp10
reverse-engineering10
cprogramming-language10
encryption10
xor9
debug9
debugging9
template-engine9
templater9
windows9
Programming languages (7)
Github contributions (5)
JustasMasiulis/lazy_importer
Jan 2018 - Aug 2022
library for importing functions from dlls in a hidden, reverse engineer unfriendly way
Role in this project:
Back-end Developer
Back-end DeveloperContributions:5 reviews, 71 commits, 8 PRs in 4 years 7 months
Contributions summary:Justas is primarily responsible for developing a library for importing functions from DLLs in a reverse-engineering unfriendly manner, likely for game hacking or anti-reversing purposes. Their work focuses on implementing techniques to obfuscate and secure the import process. The contributions involve low-level C++ code, including PE file structure manipulation, hashing algorithms, and module/function lookup strategies.
hashingreverse-engineerpointerpe-analyzermalware
JustasMasiulis/xorstr
Mar 2018 - Nov 2021
heavily vectorized c++17 compile time string encryption.
Role in this project:Back-end Developer
Back-end DeveloperContributions:61 commits, 15 PRs, 38 pushes in 3 years 9 months
Contributions summary:Justas primarily focused on developing a compile-time string encryption library in C++. Their contributions included creating the core `xorstr.hpp` header file, implementing the string encryption logic using XOR operations, and optimizing the code for various compilers and platforms. The user also added inline macros and made improvements to ensure compatibility across different compiler versions. Overall, the user was responsible for the core functionality and optimization of this encryption library.
templatecppcompile-timestringvectorized
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