🔐 Cryptography Fundamentals – A Practical Guide

A hands-on journey through the core concepts, algorithms, and techniques of modern and classical cryptography. This repository blends theory with Python-based implementations — ideal for students, developers, and security enthusiasts.

📘 Contents 🧩 Chapter 1 – Cryptography Basics

Goals: Confidentiality, Integrity, Authentication, Non-repudiation

Symmetric vs. Asymmetric cryptography

🔡 Chapter 2 – Caesar Cipher

Theory and Python implementation

Brute-force and frequency analysis

🔤 Chapter 3 – Vigenère Cipher

Key-based substitution cipher

Kasiski examination and cracking methods

⚙️ Chapter 4 – One Time Pad (OTP)

XOR encryption and perfect secrecy

True vs. pseudo-random key generation

🧱 Chapter 5 – Data Encryption Standard (DES)

Step-by-step DES implementation

Linear and differential cryptanalysis

🧠 Chapter 6 – Advanced Encryption Standard (AES)

AES rounds, confusion & diffusion principles

🔑 Chapter 7 – Asymmetric Cryptosystems

Limitations of symmetric keys

Prime and random number roles

➗ Chapter 8 – Modular Arithmetic

Prime generation, factorization, and discrete logs

🤝 Chapter 9 – Diffie-Hellman Key Exchange

Secure key sharing and MITM vulnerability

🔒 Chapter 10 – RSA Algorithm

Public/private key encryption and factorization security

🔢 Chapter 11 – Advanced Modular Arithmetic

Euclidean & Extended Euclidean Algorithm (EGCD)

Modular inverses

🧮 Chapter 12 – Elliptic Curve Cryptography (ECC)

ECC theory and Python examples

Why ECC powers Bitcoin & modern crypto systems

🧾 Chapter 13 – Cryptographic Hashing

MD5, SHA families, and the Birthday paradox

💻 Tech Stack

Language: Python 🐍

Focus: Cryptography, Mathematics, Security

🙌 Author

Avantika Shrivastava

GitHub: https://github.com/avantika77