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Lecture 7: Public Key Encryption 2 Public Key Encryption

Intuitively, semantic security promises that a PPT adversary does not learn any “new” information about a message m by looking at its ciphertext than what it already knew before (denoted as auxiliary information z). This is because adversary’s view (consisting of the ciphertext and z) can be efficiently simulated given only z and no other information on m. We now show that semantic security and IND-CPA security are, in fact, equivalent security notions.