Encryption

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 the public-key cryptography revolution and generate your first GPG keypair. This is the foundation for everything else in the course. Prerequisites: Week 2 (Cryptography Fundamentals) This is Part 1 of 4 - Covers history, concepts, and key generation. Introduction: The Public Key Revolution Week 2 taught you symmetric encryption - Alice and Bob share the same secret key. But how do they exchange that key securely? The problem: ...

Goal Master practical GPG operations: understanding your keyring, encrypting files for yourself and others, and creating digital signatures that prove authorship and integrity. Prerequisites: Week 3a (GPG Introduction & Key Generation) This is Part 2 of 4 - Covers keyring management, encryption operations, and signatures. 1. Understanding Your GPG Keyring List All Keys # List public keys gpg --list-keys # Output: pub rsa4096 2025-10-14 [SC] [expires: 2027-10-14] ABCD1234ABCD1234ABCD1234ABCD1234ABCD1234 uid [ultimate] Alice Cypherpunk <[email protected]> sub rsa4096 2025-10-14 [E] [expires: 2027-10-14] Key anatomy: ...

Goal Complete your GPG mastery with key lifecycle management (rotation, revocation, backup), practical email encryption, and understanding when to use modern alternatives like age for simpler use cases. Prerequisites: Week 3c (Key Distribution & Web of Trust) This is Part 4 of 4 - Covers key management, email encryption, and modern alternatives. 1. Key Management: Rotation, Revocation, and Backup Extending Key Expiration Your key expires in 2 years. Before expiration: ...