A stream cipher is basically a cryptographically secure RNG. It takes a key (and sometimes an IV or nonce) and generates an endless stream of random bytes.
One popular way to make stream ciphers recently is to take a regular block cipher and just encrypting a counter with it.
Let’s say you have an encryption function E(k, x) that takes a key k and the plaintext block x, and returns the encrypted block.
An easy way to get a stream cipher out of a sponge function is as follows.
Tags: Cryptography