Custom Block Cipher for Logistics

A graphical encryption system that implements a custom block cipher algorithm based on a Substitution-Permutation Network (SPN), specifically designed to secure package tracking codes in legacy logistics systems using string manipulations and bitwise operations.

---

Main Features

• Custom SPN Block Cipher: 32-round Substitution-Permutation Network over a 36-character alphabet (A-Z, 0-9) with 20-character fixed blocks.
• String-Only Implementation: Deliberately avoids lists and dynamic arrays, relying solely on strings, integers, and bitwise operations.
• Shannon's Principles in Practice: Implements Confusion (chained substitution with carry mechanism) and Diffusion (fixed bijection transposition) as core cryptographic foundations.
• Avalanche Effect Analysis: Built-in single-bit perturbation tests to verify cipher resilience and diffusion quality across rounds.
• Round-by-Round Reporting: Detailed trace of internal block states at rounds 1, 8, and 32, or exhaustive output for all 32 rounds.
• No External Dependencies: Uses only the Python standard library (tkinter for GUI), making it cross-platform with zero setup overhead.
• Mathematical Validation: Experimentally demonstrates resistance to differential and linear cryptanalysis with quantified probability metrics.

---

Execution and Development Guide

1. Clone the repository

git clone https://github.com/CamiloAT/block-cipher.git
cd block-cipher

2. Verify Python version

Ensure you have Python 3.6 or higher installed:

python --version

3. Run the application

No installation or dependency setup is required. Launch the GUI directly:

python block_cipher.py

Note: The application uses tkinter, which is included by default in most Python distributions. If tkinter is not available, install it via your system's package manager (e.g., sudo apt-get install python3-tk on Debian/Ubuntu).

4. Use the application

Enter a logistics tracking code (e.g., PKG2024ABCDEF1234) in the message field and select one of the available operations from the GUI buttons.

---

Project Structure

block-cipher/
├── block_cipher.py   ← Main application: SPN cipher algorithm + Tkinter GUI
├── README.md         ← Project documentation

---

Tech Stack

Layer	Technology
Language	Python 3.6+
GUI Framework	Tkinter (standard library)
GUI Components	tkinter.scrolledtext, tkinter.messagebox
System	sys (stdout redirection)
Dependencies	None (standard library only)

---

Authors

Name	GitHub
Diego Fernando Aguirre Tenjo	@elcokiin
Camilo Andres Arias Tenjo	@CamiloAT
Katlyn Jennelis Galvis Rodriguez	@Katlyng

Cryptography & Applied Security