Nioh Savedata Decryption Tool

Abstract

1. Introduction

Nioh uses a fairly complex algorithm to encrypt and decrypt save files. The full algorithm involves six pairs of AES-128 keys and IVs which are derived from a 148 byte chunk of memory and contents of the decrypted save file header. The AES-128 cipher is used in CTR mode with a custom, non-invertible SBox.

This tool allows the decryption and encryption of Nioh(Steam) user and system save files. Some basic save file editing features such as the transfer of save files to other steam accounts are also provided. You can find the latest release version here.

Files are encrypted and decrypted by dragging them onto the exe or equivalently by passing the file path as the first argument when using the tool in the command line. Whether encryption or decryption is performed is automatically determined based on the first 4 bytes of the input file. Decrypted save files always start with 4E 49 4F 48.

2. Objective

Nioh user and system save file encryption/decryption tool

This project demonstrates how C can be applied to a real-world Cybersecurity & Ethical Hacking problem.

4. Technology Stack

5. System Requirements

General requirements for this technology stack — check the README for exact versions.

• Arduino IDE / PlatformIO or a C compiler (gcc)
• Target board where applicable
• Git (to clone the repository)

6. Installation & Setup

git clone https://github.com/pawREP/Nioh-Savedata-Decryption-Tool.git
cd Nioh-Savedata-Decryption-Tool

Full setup instructions are in the project README.

7. Future Enhancements

Suggested extensions you can add to make this your own project.

• Add logging and alert notifications (email / Telegram)
• Write a threat model document for the tool
• Package it with Docker for safe lab testing

8. Viva / Review Questions

Common questions examiners ask for projects in this domain.

1. Which threat or attack does this project defend against?
2. What detection or protection technique is used and what are its limits?
3. How are false positives and false negatives handled?
4. Which cryptographic algorithms or security standards are involved?
5. What legal and ethical rules apply when testing a tool like this?

9. Source Code & License

This project is developed by pawREP and published on GitHub under the MIT License. Please follow the license terms and credit the original author when you use or modify this code.