Stream ciphers are algorithms that combine plaintext digits with a keystream produced by a pseudo-random generator to perform encryption or decryption.
In a stream cipher, each digit of the plaintext is encrypted one by one with the corresponding keystream digit to produce one digit of the ciphertext stream. More precisely, an initialization procedure determines the initial state of the generator from the secret key K and a public initialization vector IV. Then, for each digit s_i of the keystream, the internal state is updated by the function φ_i, and a filtering function f is applied.

STAP Lounge
The STAP Zoo currently collects information about the following list of STAP stream ciphers:
◊ Ciminion
◊ Elisabeth
◊ FLIP variants (FiLIP and FLIP)
◊ Hera
◊ Kreyvium
◊ Rasta variants (Dasta, Fasta, Masta, Pasta and Rasta)
◊ Rubato