OTP Cipher - One Time Pad Implementation

A secure one-time pad (OTP) cipher implementation in C with automatic versioning system.

Features

• Perfect Security: Implements true one-time pad encryption with information-theoretic security
• Keyboard Entropy: Optional keyboard entropy collection for enhanced randomness
• Automatic Versioning: Built-in semantic versioning with automatic patch increment
• Multiple Build Options: Standard and static linking builds
• Cross-Platform: Works on Linux and other UNIX-like systems

Version Information

This project uses an automatic versioning system that:

• Automatically increments the patch version on each build
• Embeds build timestamp, git commit hash, and branch information
• Creates git tags for version tracking
• Generates version header files with detailed build metadata

Current version can be viewed with: ./otp --help or by running the interactive mode.

Building

Prerequisites

• GCC compiler
• OpenSSL development libraries (libssl-dev on Ubuntu/Debian)
• Git (for version tracking)
• Make

Build Commands

Use the included build script for automatic versioning:

# Standard build (default)
./build.sh build

# Static linking build
./build.sh static

# Clean build artifacts
./build.sh clean

# Generate version files only
./build.sh version

# Install to system
./build.sh install

# Remove from system
./build.sh uninstall

# Show usage
./build.sh help

Traditional Make

You can also use make directly (without automatic versioning):

make            # Standard build
make static     # Static linking
make clean      # Clean artifacts
make install    # Install to /usr/local/bin/
make uninstall  # Remove from system

Usage

Interactive Mode

./otp

Command Line Mode

# Generate a new pad
./otp generate 1GB

# Encrypt text (interactive input)
./otp encrypt <pad_hash_or_prefix>

# Decrypt message (interactive input)  
./otp decrypt <pad_hash_or_prefix>

# List available pads
./otp list

Version System Details

Automatic Version Increment

Every build automatically increments the patch version:

• v0.1.0 → v0.1.1 → v0.1.2, etc.
• Creates git tags for each version
• Embeds detailed build information

Manual Version Control

For major/minor releases, create tags manually:

# Feature release (minor bump)
git tag v0.2.0    # Next build: v0.2.1

# Breaking change (major bump)  
git tag v1.0.0    # Next build: v1.0.1

Version Information Available

• Version number (major.minor.patch)
• Git commit hash and branch
• Build date and time
• Full version display with metadata

Generated Files

The build system automatically generates:

• src/version.h - Version constants and macros
• src/version.c - Version API functions
• VERSION - Plain text version number

These files are excluded from git (.gitignore) and regenerated on each build.

Security Features

• Uses /dev/urandom for cryptographically secure random number generation
• Optional keyboard entropy mixing using HKDF (Hash-based Key Derivation Function)
• SHA-256 pad integrity verification
• Read-only pad files to prevent accidental modification
• State tracking to prevent pad reuse

File Structure

otp/
├── build.sh          # Build script with automatic versioning
├── Makefile         # Traditional make build system  
├── otp.c            # Main source code
├── README.md        # This file
├── .gitignore       # Git ignore rules
├── src/             # Generated version files (auto-created)
│   ├── version.h    # Version header (generated)
│   └── version.c    # Version implementation (generated)
├── pads/            # OTP pad storage directory (created at runtime)
└── VERSION          # Plain text version (generated)

Examples

Build and Version Tracking

$ ./build.sh build
[INFO] Incrementing version...
[INFO] Current version: v0.1.4  
[INFO] New version: v0.1.5
[SUCCESS] Created new version tag: v0.1.5
[SUCCESS] Build completed successfully

$ ./otp
=== OTP Cipher v0.1.5 ===

=== Main Menu ===
1. Generate new pad
2. Encrypt message
3. Decrypt message
4. List available pads
5. Show pad information
6. Exit

$ ./otp --help
OTP Cipher - One Time Pad Implementation v0.1.5
Built on 2025-08-10 at 08:17:47 from commit 9edfa5f on branch master
Usage:
  ./otp                              - Interactive mode
  ...

Version History

$ git tag --list
v0.1.0
v0.1.1  
v0.1.2
v0.1.3
v0.1.4
v0.1.5

License

This project includes automatic versioning system based on the Generic Automatic Version Increment System.

Contributing

When contributing:

1. The version will automatically increment on builds
2. For major features, consider manually creating minor version tags
3. Generated version files (src/version.*, VERSION) should not be committed