Added exponential padding to increase security.

README.md

@@ -43,6 +43,7 @@ One-time pads can be trivially encrypted and decrypted using pencil and paper, m
 ## Features
 
 - **Perfect Security**: Implements true one-time pad encryption with information-theoretic security
+- **Traffic Analysis Resistance**: Exponential bucketing with ISO/IEC 9797-1 Method 2 (Padmé) padding hides message lengths
 - **Text & File Encryption**: Supports both inline text and file encryption
 - **Multiple Output Formats**: Binary (.otp) and ASCII armored (.otp.asc) file formats
 - **Hardware RNG Support**: Direct entropy collection from TrueRNG USB devices with automatic detection
@@ -58,14 +59,14 @@ One-time pads can be trivially encrypted and decrypted using pencil and paper, m
 
 ### Download Pre-Built Binaries
 
-**[Download Current Linux x86](https://git.laantungir.net/laantungir/otp/releases/download/v0.3.47/otp-v0.3.47-linux-x86_64)**
+**[Download Current Linux x86](https://git.laantungir.net/laantungir/otp/releases/download/v0.3.48/otp-v0.3.48-linux-x86_64)**
 
-**[Download Current Raspberry Pi 64](https://git.laantungir.net/laantungir/otp/releases/download/v0.3.47/otp-v0.3.47-linux-arm64)**
+**[Download Current Raspberry Pi 64](https://git.laantungir.net/laantungir/otp/releases/download/v0.3.48/otp-v0.3.48-linux-arm64)**
 
 After downloading:
 ```bash
 # Rename for convenience, then make executable
-mv otp-v0.3.47-linux-x86_64 otp
+mv otp-v0.3.48-linux-x86_64 otp
 chmod +x otp
 
 # Run it
@@ -189,8 +190,23 @@ git tag v1.0.0    # Next build: v1.0.1
 - Custom 256-bit XOR checksum for pad identification (encrypted with pad data)
 - Read-only pad files to prevent accidental modification
 - State tracking to prevent pad reuse
+- **Message Length Hiding**: Exponential bucketing (256B, 512B, 1KB, 2KB, 4KB...) prevents traffic analysis
+- **ISO/IEC 9797-1 Method 2 Padding**: Standard-compliant Padmé padding with 0x80 marker
 - **Zero external crypto dependencies** - completely self-contained implementation
 
+### Message Padding
+
+All encrypted messages and files are automatically padded using exponential bucketing to resist traffic analysis attacks:
+
+- **Minimum size**: 256 bytes
+- **Bucket sizes**: 256B → 512B → 1KB → 2KB → 4KB → 8KB → ...
+- **Padding method**: ISO/IEC 9797-1 Method 2 (Padmé padding)
+  - Appends `0x80` byte after message
+  - Fills remaining space with `0x00` bytes
+  - Unambiguous padding removal during decryption
+
+**Example**: A 10-byte message is padded to 256 bytes, while a 300-byte message is padded to 512 bytes. This provides strong protection for small messages where length leakage matters most, with logarithmic overhead for larger messages.
+
 ## Project Structure
 
 ```
@@ -205,6 +221,7 @@ otp/
 │   ├── ui.c             # Interactive user interface and menu system
 │   ├── state.c          # Global state management (pads directory, preferences)
 │   ├── crypto.c         # Core cryptographic operations (XOR, base64)
+│   ├── padding.c        # Message padding (exponential bucketing, Padmé padding)
 │   ├── pads.c           # Pad management and file operations
 │   ├── entropy.c        # Entropy collection from various sources
 │   ├── trng.c           # Hardware RNG device detection and collection
@@ -217,6 +234,7 @@ otp/
 ├── pads/                # OTP pad storage directory (created at runtime)
 ├── files/               # Encrypted file storage (created at runtime)
 └── tests/               # Test scripts and utilities
+    └── test_padding.sh  # Padding implementation tests
 ```
 
 ## Architecture
@@ -227,6 +245,7 @@ The OTP cipher uses a modular architecture with clean separation of concerns:
 - **ui.c**: Interactive user interface, menus, and terminal management
 - **state.c**: Global state management (pads directory, terminal dimensions, preferences)
 - **crypto.c**: Core cryptographic operations (XOR encryption, base64 encoding)
+- **padding.c**: Message padding implementation (exponential bucketing, ISO/IEC 9797-1 Method 2)
 - **pads.c**: Pad file management, checksums, and state tracking
 - **entropy.c**: Entropy collection from keyboard, dice, files, and hardware RNG
 - **trng.c**: Hardware RNG device detection and entropy collection from USB devices