Unpredictability

A PRG is unpredictable if for all bits i there does not exist and efficient algorithm A which can guess the i+1 bit of the PRG for non-negligible epsilon .

A PRG is unpredictable if it is NOT predictable

A PRG is predictable if there exists an efficient algorithm A - and there exists an i between 1 → (n-1) - such that if we give the algorithm A the first i bits out the output, it can predict the next bit, or bit i+1 with some probability greater than or equal to 1/2 + epsilon .

for random k from K; Pr[A(G(k))|(1…i) = G(k)|(i+1)] >= 1/2+ epsilon