Key generator

For a key generator to be cryptographically secure, its output must have several properties: • Uncorrelated sequences – no sequence of any given length should be correlated to any other sequence of the algorithm's output • Long period – the sequence should not repeat for a very long time • Uniform distribution – the output bits should be uniformly distributed • Unpredictability – it should be computationally infeasible to predict future output given past output Key generators typically rely on sources of entropy to seed their algorithms, which may be hardware-based (such as electronic noise or timing variations) or software-based. ==Types==

Symmetric key generators Symmetric key generators produce a single shared key used for both encryption and decryption. These generators often use pseudorandom number generators (PRNGs) seeded with entropy from various sources. Modern standards such as NIST SP 800-90 specify approved random bit generators for this purpose. Keystream generators In stream ciphers, a keystream generator produces a continuous stream of pseudorandom bits that are combined with the plaintext using the XOR operation. The keystream generator takes a relatively short key (typically 80–256 bits) and an initialization vector (IV) and expands them into a much longer keystream. ==Examples==

Common key generator implementations include: • Linear-feedback shift registers (LFSRs) – widely used in hardware implementations due to their simplicity, though typically combined with non-linear functions to improve security • Trivium – an eSTREAM finalist stream cipher using three interconnected shift registers • Grain – a lightweight stream cipher using both linear and non-linear feedback shift registers • Solitaire (or Pontifex) cipher – a manual keystream generator using a deck of playing cards ==See also==