encryption

Encryption is a method of transforming readable data, known as plaintext, into an unreadable form, called ciphertext, using an algorithm and a key. The intended result is to prevent unauthorized access to information while preserving its recoverability by someone with the correct key. Encryption protects data in transit, such as online communications, and data at rest, such as files stored on a device.

Two broad categories exist: symmetric encryption uses one key for both directions, while asymmetric encryption uses a public key for encryption and a private key for decryption. Common symmetric algorithms include AES and ChaCha20; common asymmetric ones include RSA and ECC. Many systems use authenticated encryption modes, such as AES-GCM, to provide both confidentiality and integrity. In practice, a hybrid approach is common: a public-key operation to establish a shared session key, then fast symmetric encryption for data transfer.

Key management and trust are central. Public key infrastructure (PKI) and digital certificates support key verification, while key rotation, secure storage, and access controls reduce risk. Encryption underpins TLS for web security, email security with S/MIME or PGP, and data-at-rest protections such as full-disk encryption.

Security considerations: weaknesses can stem from weak keys, poor randomness, implementation flaws, or misconfiguration. Attacks include brute-force, side-channel analyses, and quantum threats to certain algorithms. Research areas include post-quantum cryptography and formal verification of cryptographic protocols.

History: Classical ciphers gave way to modern cryptography in the 20th century, with public-key cryptography introduced in the 1970s by Diffie, Hellman, and Merkle, and practical RSA and ECC algorithms developed thereafter. Encryption is foundational for digital privacy and secure communications.