Security Games

used to model what an adversary can learn about a message from it's encryption. system is secure if cipher texts are indistinguishable

• I flip a coin and pick one of two messages and encrypt it.
• I give you the cipher text and you have to tell me which message picked.
• If you guess correctly, you win.
• If you guess incorrectly, I win.
• Just to make things interesting, I'll even let you pick the two messages.

If you guess randomly, you'll be right 50% of the time. Can you win more than 50% of the time?

winning >50% of the time = you can distinguish cipher texts (the system is leaking info)