4.4. Cryptography and Data Protection

Cryptography is the mathematical foundation of Linux security. You don't need to understand the mathematics — but you do need to know which algorithm to choose, which tool implements it, and what the operational implications are. The exam tests practical cryptographic decisions: which encryption to use at rest vs. in transit, which hash algorithm for integrity verification, and how to manage certificates.

💡 First Principle: Cryptography solves four problems: confidentiality (only authorized parties can read), integrity (data hasn't been tampered with), authentication (this is really who they say they are), and non-repudiation (they can't deny they sent it). Symmetric encryption (AES) provides confidentiality efficiently. Asymmetric encryption (RSA/ECC) solves key exchange. Hashing (SHA-256) provides integrity.

⚠️ Common Misconception: Encryption and hashing are not the same thing. Encryption is reversible — you can decrypt with the right key. Hashing is one-way — you cannot recover the original from the hash. Hashing verifies integrity; encryption ensures confidentiality.