Cryptography

Goal Understand cryptographic hash functions: what they do, how they differ from encryption, why some are broken (MD5), and how to use SHA-256 for file integrity verification. Prerequisites: Week 1 (Cypherpunk Ideals & Threat Modeling) This is Part 1 of 3 - Covers hashing fundamentals and integrity verification. Introduction: Why Cryptography Matters Before we dive into algorithms, let’s understand what we’re building toward: Cryptography is mathematics applied to privacy. It transforms the abstract right to privacy into concrete protection through proofs, not promises. ...

Goal Master symmetric encryption with AES: understand encryption modes (and why ECB is broken), use OpenSSL for file encryption, and learn how Key Derivation Functions transform weak passwords into strong keys. Prerequisites: Week 2a (Hash Functions) This is Part 2 of 3 - Covers symmetric encryption and key derivation. 1. Symmetric Encryption: Shared Secrets What Is Symmetric Encryption? Symmetric encryption uses the same key for both encryption and decryption. Alice Bob | | | "Meet at midnight" + Key123 | |---------> AES Encrypt --------------> | | f8a3b2c1d4e5f6 (ciphertext) | | | | <-------- AES Decrypt <-------------- | | f8a3b2c1d4e5f6 + Key123 | | "Meet at midnight" (plaintext) | Key challenge: How do Alice and Bob agree on “Key123” without anyone else learning it? (Solved in Week 3 with asymmetric crypto) ...

Goal Understand entropy and randomness as the foundation of cryptographic security, learn binary encoding (Base64, hex), and combine everything into practical encrypted workflows with best practices. Prerequisites: Week 2b (Symmetric Encryption) This is Part 3 of 3 - Covers entropy, encoding, workflows, and best practices. 1. Entropy and Randomness: The Foundation of Security What Is Entropy? Entropy is a measure of unpredictability (randomness). In cryptography: High entropy = Truly random, unpredictable Low entropy = Patterns, predictable Why it matters: ...