How Does Encryption Protect Data?

Encryption transforms plaintext (readable data) into ciphertext (unreadable scramble) using an algorithm and a cryptographic key. There are two main types. Symmetric encryption uses the same key to encrypt and decrypt (e.g. AES-256: extremely fast, used for disk encryption and HTTPS data transfer). Asymmetric (public-key) encryption uses a pair of keys: one public (shared freely for encrypting) and one private (kept secret for decrypting). RSA and elliptic-curve cryptography (ECC) are common asymmetric algorithms. In practice, most systems combine both: asymmetric encryption securely exchanges a symmetric key, which then handles the bulk data transfer. Without the correct key, brute-forcing modern encryption would take longer than the age of the universe.