Formal definition PRNG I tried to look for a book that presents cryptographic concepts(specially PRNG) in a formal way but what I find is an intuitive approach. So my question is what is the formal definition of Psuedo-random-number-generator(PRNG) or function?
If we call $U_k$ the random variable uniformly distributed over bit strings of length $k$, then a function $g: \{0,1\}^k \to \{0,1\}^m$ is called pseudo-random generator if no feasible(poly-time if you want) algorithm can distinguish $g(U_k)$ and $U_m$ with non-negligible probability.

More formally let $U'_m = g(U_k)$ then the distinguishing advantage of any distinguisher efficient $D$ that we denote as $\Delta^D(U'_m, U_m) = Pr^{DU_m}[Z = 1] - Pr^{DU'_m}[Z = 1]$ is negligible.  

Here $Z$ is the output of the distinguisher, and negligible is any suitable notion of "really small"; same for efficient.