Stream Cipher Concepts & PRNG

Stream ciphers generate a pseudorandom keystream from a key and encrypt byte by byte. In this lesson we understand how keystreams work and what makes a stream cipher secure.

KeyGen(K, Nonce) → keystream K1, K2, K3, ... Ci = Pi XOR Ki Pi = Ci XOR Ki Encryption and decryption are identical: XOR with the keystream. The keystream must be pseudorandom and never reused.