OTP Module Manager

Overview

This project implements an HMAC (Hash-based Message Authentication Code) algorithm using the Linux Kernel Crypto API.

It demonstrates how to:

• Implement a kernel module
• Register a device for user-space communication
• Use the Crypto API for cryptographic operations

This project is designed for kernel module development and should be compiled within a Linux kernel environment.

Features

• Uses HMAC-SHA1 to compute message authentication codes
• ...

Installation & Usage

Prerequisites

Ensure you have:

• A Linux system with kernel headers installed
• make and gcc for building kernel modules
• Root privileges for loading/unloading kernel modules

Makefile script

The Makefile contains the following targets:

• all - Builds the kernel module into an .ko file
• load - Builds and loads the kernel module
• unload - Unloads the kernel module
• reload - Unloads and loads the kernel module
• clean - Cleans the build directory
• info - Displays information about the kernel module
• log - Displays the kernel log
• logx - Displays the kernel log continuously
• help - Displays the Makefile help

Procedure

1. Clone the repository:

$ git clone https://github.com/NicolasReboule/OTPKernelModule.git

2. Go inside the module folder

$ cd OTPKernelModule/module

3. Run the make load command to build and load the kernel module:

$ make load

4. Check the kernel log for module information:

$ make log

5. Use the devices interfaces to interact with the module:

$ cat /dev/otp-hotp
$ 123456

6. Use the generatad otp to use the client

$ cd client
$ ./client 123456 upper bonjour
$ BONJOUR

Available commands

otp-hotp

• cat /dev/otp-hotp : Generate a hotp code

Using echo:

• update -a <algo> -s <secret> : Update the device's algorihm and secret
• info : Shows devices current algorihm and secret
• default : Shows usage

where:

• <algo> : SHA1 or SHA256
• <secret> : Any string

otp-totp

• cat /dev/otp-totp : Generate a totp code

Using echo:

• update -a <algo> -s <secret> -t : Update the device's algorihm and secret
• info : Shows devices current algorihm and secret
• default : Shows usage

where:

• <algo> : SHA1 or SHA256
• <secret> : Any string
• <timestep>: Number of seconds a TOTP code should be valid

otp-validator

• cat /dev/otp-validator : Returns last validation result

Using echo:

• <otp> : Validate an otp
• help : Shows usage

where:

• <otp> : OTP code generated by this module

Debugfs

With admin rights, you can use debugfs tu modify the list of hotp codes.

The list can be found at /sys/kernel/debug/otp_manager/otp_list

Usage

• cat /sys/kernel/debug/otp_manager/otp_list : Shows list of hotp codes

Using echo:

• add <code> : Adds code to hotp list
• delete <index> : Removes code at specified index from the list

where:

• <code> : Any number (less than 16 characters)
• <index> : Index number in the list

File Structure

.
├── crypto.c        # Main implementation of HMAC using Crypto API
├── Makefile        # Build script for compiling the module
├── module.c        # Kernel module initialization and cleanup
├── module.d/       # Directory for kernel module source files
│   └──  *          # Object files generated during compilation
├── ...             # ...
├── ...             # ...
└── README.md       # User Documentation

Authors

Fazanwolf - GitHub

Salocin - GitHub

Nekomay - GitHub

License

This project is licensed under the GPLv3 License - see the LICENSE file for details.

References

• Linux Kernel Crypto API Documentation