An encryption scheme consists of the following data
- a plaintext space $\mathcal M$
- a ciphertext space $\mathcal C$
- a key space $\mathcal K$
- a key generating algorithm Gen
- encryption and decryption algorithms $\operatorname{Enc}_k$ and $\operatorname{Dec}_k$ for each key $k\in \mathcal K$
I would like some clarification on the following extract from Katz & Lindell:
More specifically, my question is: What does, say, $P(K=k)$ mean exactly? What is the domain and codomain of the random variable $K$? What is the set $\{K=k\}$? Also, what is the domain of Gen?