Zufallsströme

Zufallsströme, often translated as "random streams" or "stochastic streams," is a concept primarily encountered in theoretical computer science and cryptography. It refers to a sequence of random bits that is computationally indistinguishable from a truly random sequence. This means that given a prefix of a Zufallsstrom, it is computationally infeasible for any probabilistic polynomial-time algorithm to predict the next bit with a probability significantly better than chance (i.e., 1/2).

The importance of Zufallsströme lies in their use as building blocks for various cryptographic primitives. They can be used to generate one-time pads, stream ciphers, and pseudo-random number generators (PRNGs). A key property is that if a sequence is a Zufallsstrom, then any computationally meaningful function of that sequence, such as applying a cryptographic hash function, will also result in a sequence that is computationally indistinguishable from random.

Constructing a true Zufallsstrom generator is a significant challenge. Often, they are built using pseudo-random number generators (PRNGs) that are designed to be cryptographically secure. These PRNGs typically take a short, secret seed value and expand it into a long sequence of bits that exhibit the properties of a Zufallsstrom. The security relies on the difficulty of predicting future outputs without knowing the initial seed or past outputs. The concept is foundational to modern cryptography, enabling secure communication and data protection.