Encryption - Symmetric Cryptography

Private Key

Alice and Bob share a key K the adversary does not know

Alice and Bob agree on cryptosystem and key

Bob encrypts plaintext using key, sends ciphertext to Alice

Alice decrypts ciphertext with same key and reads the message

Advantage: fast

Disadvantage: keys must be distributed secretly

Disadvantage: if key is compromised, all is lost

Disadvantage: number of needed keys is n²