1.4. Cryptography: The Language of Secrets

💡 First Principle: How do you keep a message secret across an open network? How do you prove it wasn't tampered with? Cryptography solves three fundamental problems in digital communication: keeping secrets (confidentiality), proving messages haven't been altered (integrity), and verifying who sent them (authentication/non-repudiation). Every cryptographic tool on the exam maps back to one or more of these problems.

Without cryptography, digital life would be impossible. Every online purchase, every login, every encrypted email, every VPN tunnel, every digital signature relies on mathematical algorithms that transform readable data into unreadable gibberish — and back again — using keys. The consequences of weak or absent cryptography are catastrophic: intercepted communications, forged documents, stolen credentials, broken trust.

Think of cryptography like a language that only authorized parties can understand. Encryption is speaking in code. Hashing is creating a unique fingerprint. Digital signatures are signing a document with invisible ink that only you can produce but anyone can verify. Each tool solves a different problem, and the exam expects you to match the right tool to the right problem.