Stream Ciphers

Approaches

Cryptographically secure pseudo-random number generators (PRNG).

• Using linear feedback shift registers (LFSR).

• Using block ciphers.

• Other (families of functions, etc.).

Usually not self-synchronized.

Usually without uniform random access.

• No immediate setup of the generator’s state for a given plaintext/cryptogram offset.

Most Common Algorithms

• A5/1 (US, Europe), A5/2 (GSM).

• RC4 (802.11 WEP/TKIP, etc.).

• E0 (Bluetooth BR/EDR).

• SEAL (w/ uniform random access).