Understanding the IND-CPA Security of CTR and CBC Encryption Modes 🔐

Birthday attack on IND-CPA security of CTR$. Theorem showing CTR$ is IND-CPA secure assuming the underlying family of functions is PRF-secure, with bounds matching the birthday attack to show latter is best possible. Proof of theorem, using a game sequence. Fundamental Lemma of Game Playing. Applications of the Theorem.