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Lecture 13: Encryption Schemes (VI)

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Recap: CCA-security of encryption schemes

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message

tag

 

 

ciphertext

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Security proof

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Define “bad event” ValidQuery

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Real Game (copied from slide 5)

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Simulated game

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How to simulate decryption oracle

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Step 1: Remove decryption oracle, becomes (essentially) CPA-security

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Step 3: Add back decryption oracle, becomes Game CCA1

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Putting it together

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