Trivium

Trivium is a synchronous stream cipher designed to provide a flexible trade-off between speed and gate count in hardware, and reasonably efficient software implementation. Trivium was submitted to the Profile II (hardware) of the eSTREAM competition by its authors, Christophe De Cannière and Bart Preneel, and has been selected as part of the portfolio for low area hardware ciphers (Profile 2) by the eSTREAM project. It is not patented and has been specified as an International Standard under ISO/IEC 29192-3. It generates up to 264 bits of output from an 80-bit key and an 80-bit IV. It is the simplest eSTREAM entrant; while it shows remarkable resistance to cryptanalysis for its simplicity and performance, recent attacks leave the security margin looking rather slim. Description Trivium's 288-bit internal state consists of three shift registers of different lengths. At each round, a bit is shifted into each of the three shift registers using a non-linear combination of taps from that and one other register; one bit of output is produced. To initialize the cipher, the key and IV are written into two of the shift registers, with the remaining bits starting in a fixed pattern; the cipher state is then updated 4 × 288 = 1152 times, so that every bit of the internal state depends on every bit of the key and of the IV in a complex nonlinear way.