Week 2b: Symmetric Encryption & Key Derivation
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) ...