Cryptography¶

Cryptography is the practice and study of techniques for secure communication in the presence of adversarial behavior.

Fundamental Concepts¶

Symmetric Encryption¶

Uses the same key for both encryption and decryption.

Common Algorithms: - AES (Advanced Encryption Standard) - DES/3DES - ChaCha20

Use Cases: - Bulk data encryption - Secure file storage - VPN tunnels

Asymmetric Encryption¶

Uses a pair of keys: a public key for encryption and a private key for decryption.

Common Algorithms: - RSA - ECC (Elliptic Curve Cryptography) - Diffie-Hellman

Use Cases: - Secure key exchange - Digital signatures - TLS/SSL certificates

Hash Functions¶

One-way functions that produce a fixed-size output from variable-size input.

Common Hash Functions: - SHA-256, SHA-3 - BLAKE2 - Argon2 (for passwords)

Properties: - Deterministic - Pre-image resistant - Collision resistant

Digital Signatures¶

Provide authenticity, integrity, and non-repudiation.

Process: 1. Hash the message 2. Encrypt the hash with private key 3. Recipient verifies with public key

Key Management¶

Best Practices¶

Generate keys using cryptographically secure random number generators
Store keys securely (HSMs, key vaults)
Implement key rotation policies
Use appropriate key lengths
Destroy keys securely when no longer needed

Public Key Infrastructure (PKI)¶

A framework for managing digital certificates and public-key encryption: - Certificate Authorities (CAs) - Registration Authorities (RAs) - Certificate Revocation Lists (CRLs) - OCSP (Online Certificate Status Protocol)