Re: Question on definition of semantic security: why "probability ensemble"?

Kristian Gjøsteen wrote:
Try an A' that always outputs 1.

A' that always outputs 1 will work when A also always outputs 1.
Algorithms A and A' have different quantifiers in the definition: "for
every A" and "there exists A' ". So, the choice of A' depends on the
choice of A.

Is it really more complex? Anyway, there can be many reasons for choosing
a more complex definition over a simpler definition.

(When I've used semantic security, I've used different, but equivalent,
definitions because those definitions make later proofs easier.)

I hope you are right. At least it is not just me who things that these
definitions might be equivalent :) Thanks.