Definition 1 on Page 7 of “An Efficient System for Non-transferable Anonymous Credentials with Optional Anonymity Revocation” by Camenisch and Lysyanskaya, uses the term “simulator” in defining the security of a cryptographic credential system, which I'm finding a little confusing.
In particular, the sentence says:
CSS is secure if there exists a simulator S (ideal-world adversary [defined above as a probabilistic polynomial time machine]) such that the following holds: […]
What does “simulator” in a cryptographic credential system's definition of security?
Also, what does it mean for a probabilistic machine to be "interactive"?