# What happens if five messages are generated in IND-CPA security?

I am wondering why in IND-CPA security game, the adversary generates two random messages. What happens if for example 5 messages are generated? What would be the advantage for the adversary?

Now as for why the adversary has to identify the message under $2$ instead of $n$ options.
• Two allows for 1-bit plaintexts. Suppose you had a scheme that is secure for all messages of 2 bits and longer, picking $n>2$ and enforcing same-length and distinctness would mean you have no statement about 1-bit messages.
• Two is perfectly sufficient to express the meaning of the messages. This would be to decide the which message was "picked" with all messages but one (so exactly one for $n=2$) being "not picked".
• Two makes the adversary the strongest and thus also our security model. By default the adversary has a 50% chance of getting the answer right, with other numbers this would be $1/n$.