# What is definition of adversary ? And what they do?

Currently I am writing my last assignment about secret sharing. But I don't get clearly about adversary. I know this seems so basic understanding in secret sharing. But I couldn't get references that clearly definite adversary. Moreover, what is passive attack and active attack ? What's the differences ?

Formally, an adversary is simply a (probabilistic) algorithm, which we usually assume to run in polynomial time in $n$, the security parameter. From a more intuitive point of view, an adversary is the model of an attacker on the real life, since every attacker follows an strategy that boils down to an algorithm.