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README.md
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README.md
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# OTP Cipher v2.0 - Enhanced One Time Pad Implementation
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A comprehensive and user-friendly One Time Pad (OTP) cryptographic system implemented in C for Linux, supporting massive pad sizes up to 10TB+ with both interactive and command-line interfaces.
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## New in Version 2.0 🚀
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- **Interactive Menu System** - User-friendly menu-driven interface
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- **Smart Size Parsing** - Supports K/KB/M/MB/G/GB/T/TB units
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- **Partial Hash Matching** - Use hash prefixes or pad numbers for selection
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- **Progress Indicators** - Real-time progress for large pad generation
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- **10TB+ Support** - Generate massive pads for external drives
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- **Enhanced Pad Management** - List, info, and usage statistics
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## Features
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- **Cryptographically secure** random pad generation using `/dev/urandom`
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- **ASCII armor format** similar to PGP for encrypted messages
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- **Integrity verification** using SHA-256 hashing of pad files
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- **State management** to prevent pad reuse
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- **Interactive text encryption/decryption**
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- **Hash-based file naming** for content verification
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- **Read-only pad protection** prevents accidental corruption
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## Dependencies
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- OpenSSL development libraries (`libssl-dev` on Ubuntu/Debian)
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- GCC compiler
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### Install dependencies on Ubuntu/Debian:
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```bash
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sudo apt update
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sudo apt install libssl-dev build-essential
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```
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## Building
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```bash
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make
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```
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This will create the `otp` executable.
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## Usage Modes
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### Interactive Mode (Recommended)
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Simply run the program without arguments:
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```bash
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./otp
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```
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This launches a menu-driven interface:
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```
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=== OTP Cipher Interactive Mode ===
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Version: OTP-CIPHER 2.0
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=== Main Menu ===
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1. Generate new pad
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2. Encrypt message
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3. Decrypt message
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4. List available pads
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5. Show pad information
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6. Exit
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```
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### Command Line Mode
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For automation and scripting:
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```bash
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./otp generate <size> # Generate new pad
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./otp encrypt <pad_hash_prefix> # Encrypt text
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./otp decrypt <pad_hash_prefix> # Decrypt message
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./otp list # List available pads
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```
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## Smart Size Parsing
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The system intelligently parses size specifications:
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```bash
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./otp generate 1024 # 1024 bytes
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./otp generate 5MB # 5 megabytes
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./otp generate 2GB # 2 gigabytes
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./otp generate 10TB # 10 terabytes
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./otp generate 1.5GB # 1.5 gigabytes (decimal supported)
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```
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**Supported units:** K, KB, M, MB, G, GB, T, TB (case insensitive)
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## Pad Selection
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Multiple convenient ways to select pads:
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1. **Full hash**: `./otp encrypt a1b2c3d4e5f6789012345678901234567890abcdef...`
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2. **Hash prefix**: `./otp encrypt a1b2c3d4`
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3. **Pad number**: `./otp encrypt 1` (from list output)
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## Example Workflows
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### Basic Usage
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```bash
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# Generate a 1GB pad
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./otp generate 1GB
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Generated pad: a1b2c3d4e5f6789...123456.pad (1.00 GB)
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Pad hash: a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456
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# List available pads
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./otp list
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Available pads:
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No. Hash (first 16 chars) Size Used
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--- ------------------- ---------- ----------
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1 a1b2c3d4e5f67890 1.00GB 0.0MB
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# Encrypt using hash prefix
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./otp encrypt a1b2
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Enter text to encrypt: Secret message
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-----BEGIN OTP MESSAGE-----
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Version: OTP-CIPHER 2.0
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Pad-Hash: a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456
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Pad-Offset: 0
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U2VjcmV0IG1lc3NhZ2U=
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-----END OTP MESSAGE-----
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```
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### Large Scale Usage
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```bash
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# Generate a 5TB pad for external drive
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./otp generate 5TB
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Progress: 100.0% (85.2 MB/s, ETA: 0s)
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Generated pad: f9e8d7c6b5a4932...654321.pad (5.00 TB)
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# Use pad number for quick selection
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./otp encrypt 1
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Enter text to encrypt: Classified information
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```
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### Interactive Mode Workflow
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```bash
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./otp
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# Select option 1 to generate
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# Enter size: 10GB
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# Select option 2 to encrypt
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# Choose pad from list
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# Enter your message
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```
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## Security Features
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### Perfect Forward Secrecy
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Each message uses a unique portion of the pad that is never reused, ensuring perfect forward secrecy.
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### Content-Based Integrity
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- **SHA-256 file naming**: Pad files named by their hash ensure content verification
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- **Integrity checking**: Embedded hashes detect pad corruption/tampering
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- **Read-only protection**: Pad files automatically set to read-only after creation
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### ASCII Armor Format
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Messages use a PGP-like ASCII armor format:
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```
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-----BEGIN OTP MESSAGE-----
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Version: OTP-CIPHER 2.0
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Pad-Hash: a1b2c3d4e5f6789012345678901234567890abcdef1234567890abcdef123456
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Pad-Offset: 0
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U2VjcmV0IG1lc3NhZ2U=
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-----END OTP MESSAGE-----
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```
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### State Management
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- **Automatic tracking**: Prevents pad reuse through state files
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- **Portable state**: State stored separately from immutable pad data
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- **Usage statistics**: Track pad consumption and remaining capacity
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## File Structure
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**Source Files:**
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- `otp.c` - Complete implementation (850+ lines)
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- `Makefile` - Build configuration
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- `README.md` - This documentation
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**Generated Files:**
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- `otp` - Compiled executable
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- `<hash>.pad` - Pad files (read-only, hash-named)
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- `<hash>.state` - State files (writable, tracks usage)
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## Advanced Features
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### Progress Indicators
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For large pads, see real-time generation progress:
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```
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Generating pad...
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Progress: 45.2% (78.5 MB/s, ETA: 125s)
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```
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### Pad Information
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Detailed statistics for each pad:
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```bash
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./otp list
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No. Hash (first 16 chars) Size Used
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--- ------------------- ---------- ----------
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1 a1b2c3d4e5f67890 5.00TB 2.1GB
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2 f9e8d7c6b5a49321 1.00GB 0.5GB
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```
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### Multiple Pad Management
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- List all available pads
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- Show detailed information per pad
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- Track usage across multiple pads
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- Quick selection by number or prefix
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## Performance
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### Size Limits
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- **Theoretical maximum**: 18 exabytes (uint64_t limit)
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- **Practical maximum**: Limited by available disk space
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- **Tested up to**: 10TB+ on modern systems
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- **Generation speed**: ~80-120 MB/s (system dependent)
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### Memory Efficiency
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- **Streaming operation**: Constant memory usage regardless of pad size
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- **64KB buffers**: Efficient I/O without excessive memory consumption
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- **Large file support**: Handles multi-terabyte pads efficiently
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## Security Notes
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⚠️ **Critical Security Requirements:**
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1. **Never reuse pad data** - Automatic prevention through state tracking
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2. **Secure pad distribution** - Use secure channels for pad sharing
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3. **Physical security** - Protect pad files like encryption keys
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4. **Verify integrity** - Always check pad hash verification during decryption
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5. **Secure systems** - Generate pads on trusted systems with good entropy
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## Installation
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### Local Installation
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```bash
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make install # Install to /usr/local/bin
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make uninstall # Remove from system
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```
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### Clean Up
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```bash
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make clean # Remove compiled files and generated pads
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```
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## Technical Specifications
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- **Entropy source**: `/dev/urandom` (cryptographically secure)
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- **Hash algorithm**: SHA-256 for integrity verification
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- **Encoding**: Base64 for ciphertext representation
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- **File format**: ASCII armor with embedded metadata
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- **Architecture**: Single C file, ~850 lines
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- **Dependencies**: OpenSSL libcrypto
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- **Platform**: Linux (easily portable)
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## Theory
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A One Time Pad is theoretically unbreakable when implemented correctly with:
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- **Perfect randomness**: Cryptographically secure entropy
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- **Key length**: Equal to or greater than message length
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- **Single use**: Each pad portion used exactly once
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- **Secure distribution**: Pads shared through secure channels
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This implementation satisfies all requirements for perfect cryptographic security while providing modern usability features for practical deployment.
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## Version History
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- **v2.0**: Interactive mode, smart parsing, 10TB+ support, enhanced UX
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- **v1.0**: Basic command-line implementation with hash-based naming
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