We introduce a new technique for constructing a family of universal hash functions.

This paper gives a survey on cryptographic hash functions. It gives an overview of all types of hash functions and reviews design principals and possible methods of attacks. It also focuses on keyed hash functions and provides the applications, requirements, and constructions of keyed hash functions.

: A number of keystream generators can be attacked by guessing the contents of one shift register and then checking to see whether this guess is consistent with the observed keystream. Where the target register is n bits long, this gives an attack of complexity 2 n\GammaO(1) . We present a further optimisation which appears to reduce the complexity to about 2 n=2 in many cases of practical interest. Introduction: Many stream cipher systems work by combining each successive bit of plaintext with a pseudo-random bit derived from a keystream generator, which will typically use a nonlinear function of one or more linear feedback shift register sequences to generate these pseudo-random bits. Examples are the multiplexer generator [1], the self-multiplexed generator [2], Geffe's generator [3] and the clock controlled or stop-and-go family of generators [4]. Such stream cipher algorithms are usually faster than block ciphers such as DES [5] and are often used in devices such as line encr...