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. Let Σ be an encryption scheme with CPA$ security. Let Σ' be the encryption scheme defined by: Σ'.Enc(k, m) = 00||Σ.Enc(k, m) The decryption algorithm in Σ' simply throws away the first two bits of the ciphertext and then calls E.Dec. (a) Does Σ' have CPA$ security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage). (b) Does Σ' have CPA security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage).

. Let Σ be an encryption scheme with CPA$ security. Let Σ' be the encryption scheme defined by: Σ'.Enc(k, m) = 00||Σ.Enc(k, m) The decryption algorithm in Σ' simply throws away the first two bits of the ciphertext and then calls E.Dec. (a) Does Σ' have CPA$ security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage). (b) Does Σ' have CPA security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage).

Database System Concepts
Database System Concepts
7th Edition
ISBN:9780078022159
Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan
Chapter1: Introduction
Section: Chapter Questions
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Cryptography 

7.2. Let Σ be an encryption scheme with CPA$ security. Let Σ' be the encryption scheme defined by: Σ'. Enc(k, m) = 00||Σ. Enc(k, m) The decryption algorithm in Σ' simply throws away the first two bits of the ciphertext and then calls E.Dec. (a) Does Σ' have CPA$ security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage). (b) Does Σ' have CPA security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage).
Transcribed Image Text:7.2. Let Σ be an encryption scheme with CPA$ security. Let Σ' be the encryption scheme defined by: Σ'. Enc(k, m) = 00||Σ. Enc(k, m) The decryption algorithm in Σ' simply throws away the first two bits of the ciphertext and then calls E.Dec. (a) Does Σ' have CPA$ security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage). (b) Does Σ' have CPA security? Prove or disprove (if disproving, show a distinguisher and calculate its advantage).
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