pseudorandom generator
Let be a deterministic polynomial-time function
from to with stretch function , so that if has length then has length . Then let be the distribution
on strings of length defined by the output of on a randomly selected string of length selected by the uniform distribution
.
Then we say is pseudorandom generator if is pseudorandom.
In effect, translates a random input of length to a pseudorandom output of length . Assuming , this expands a random sequence (and can be applied multiple times, since can be replaced by the distribution of ).