Take the tour ×  What's the standard way to express "$x$ knows
about $y$", or "$x$ has no knowledge of $y$" in cryptographic
notation?  Example (PRNG predictor):  $\exists f :
P(f(G(k)|_{0..n}) = G(k)|_{n+1}) \geq 0.5 + \epsilon$, for non
negligable $\epsilon$, where $f$ has no knowledge of $k$.
share|improve this question add comment  2 Answers  up vote 4
down vote accepted  The notation is "", i.e., the empty string.
$\;\;$ Since $k$ is not an input of $f$, $f$ has no knowledge of
$k$.  share|improve this answer So you're saying there's no such
notation? –  Polynomial May 25 '12 at 9:44 @Polynomial He's
saying that in your example such a notation is not necessary,
because it's implicit in the parameters of $f$. A function by
definition only knows what it sees in its parameters. – 
CodesInChaos May 25 '12 at 9:56 But your example is problematic,
since you did not restrict the cost of calculating $f$. If you
make no such restriction, you need entropy exceeding the output
size, i.e. a true RNG, and not a PRNG