Symmetric Encryption

Symmetric encryption — also called secret-key or shared-key cryptography — uses a single key, known to all communicating parties, for both encrypting plaintext and decrypting ciphertext. It comes in two main flavours: block ciphers (AES, 3DES, Blowfish) that operate on fixed-size blocks, and stream ciphers (ChaCha20, Salsa20) that produce a keystream XORed with the plaintext. AES-128 and AES-256 in authenticated modes such as GCM or OCB are the modern standards, offering both speed (often hardware-accelerated via AES-NI) and security. The main weakness is key distribution: every pair of parties must share a secret, which is typically solved by combining symmetric encryption with asymmetric key exchange (e.g., Diffie–Hellman) inside protocols like TLS.