. 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

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

Problem 1PE

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Question 2: Encoding Cryptography is the study of trying to create secure information by obscuring the original message. One simple encryption method is to substitute letters from the original message with other letters. To make it harder to decrypt the hidden message, we may also remove clues such as the length of the words in the message and any punctuation or capitalization. Write a function encode that consumes a string message. The function produces a string which is encrypted according the following procedure: * Only the letters from the original message will be encrypted. Other characters such as spaces, punctuation, numeric digits, etc. are not included in the encrypted message at all. * The encrypted message will only contain uppercase letters. * Each letter will be replaced by the uppercase letter at the opposite end of the English alphabet. In other words, A or a will become Z, B or b will become Y, C or c will become X, ..., Z or z will become A. * The encrypted message…
Question 2: Encoding Cryptography is the study of trying to create secure information by obscuring the original message. One simple encryption method is to substitute letters from the original message with other letters. To make it harder to decrypt the hidden message, we may also remove clues such as the length of the words in the message and any punctuation or capitalization. Write a function encode that consumes a string message. The function produces a string which is encrypted according the following procedure: * Only the letters from the original message will be encrypted. Other characters such as spaces, punctuation, numeric digits, etc. are not included in the encrypted message at all. * The encrypted message will only contain uppercase letters. * Each letter will be replaced by the uppercase letter at the opposite end of the English alphabet. In other words, A or a will become Z, B or b will become Y, C or c will become X, ..., Z or z will become A. * The encrypted message…
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8. Prior to the discovery of any specific public-key schemes, such as RSA, an existence proof was developed whose purpose was to demonstrate that public-key encryption is possible in theory. Consider the functions f₁(x₁) = Z₁; f₂(x2, y2) = Z2; f(x3, y3) = Z3 where all values are integers with Function can be represented by a vector M1 of length N, in which the kth entry is the value of Similarly, and can be represented by matrices M2 and M3. The intent is to represent the encryption/decryption process by table lookups for tables with very large values of N. Such tables would be impractically huge but could, in principle, be constructed. The scheme works as follows: Construct M1 with a random permutation of all integers between 1 and N; that is, each integer appears exactly once in M1. Construct M2 so that each row contains a random permutation of the first N integers. Finally, fill in M3 to satisfy the following condition: fi(fe(fi(k),p),k) = p for all k, p with 1 ≤k, p≤N In words, 1.…
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