Introduction to Algorithms
3rd Edition
ISBN: 9780262033848
Author: Thomas H. Cormen, Ronald L. Rivest, Charles E. Leiserson, Clifford Stein
Publisher: MIT Press
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Chapter 32.2, Problem 4E
Program Plan Intro
To prove that there is at most one chance in 1000 that
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Suppose we are using a method of encryption that does as much as possible to hide any patterns of a file, including symbol frequencies. And suppose we also want to compress the same file. In terms of the compression performance (the size of compressed file), is it better to compress the file before encrypting it, or encrypt the file before compressing it? Briefly explain the reason
b.What is the maximum amount of time that it would take a computer that can test keys per second to carry out a brute-force attack on a file encrypted using 256-bit AES? Give your answer in seconds and years, using scientific notation, correct to 2 significant figures. You may assume a year is seconds and you may use a calculator to help work out the answer.
Show all your working clearly in a way that will help your tutor understand how you arrived at your answer.
Let the input size of a block cipher be 16 bits and the block cipher is used in the electronic code book (ECB) mode of operation. Suppose we have the following plaintext where all blocks are encrypted using the same key:
(02 34 67 88 02 34 44 AB 67 88 B0 3F)hex
i) Give an example of a ciphertext if the above plaintext is encrypted using the said block cipher.
ii) Let say the encrypted important file is stored in this scheme and each data record has a size of 16 bits. The records are not related to one another. Is ECB mode still appropriate in this scenario? Please state your reason.
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- I want Examples on el gamal cipher i want 2 Examples like this Example of ElGamal encryption Alice chooses pA = 107, α A = 2, dA = 67, and she computes β A = 267 ≡ 94 (mod 107). Her public key is ( pA, α A, β A) = (2,67,94), and her private key is dA = 67. Bob wants to send the message "B" (66 in ASCII) to Alice. He chooses a random integer k = 45 and encrypts M = 66 as (r, t) = ( αA k , βA kM) ≡ (245, 944566) ≡ (28, 9) (mod 107). He sends the encrypted message (28, 9) to Alice. Alice receives the message ( r, t) = (28, 9), and using her private key dA = 67 she decrypts to tr−dA = 9⋅28−67 ≡ 9⋅28106−67 ≡ 9⋅43 ≡ 66 (mod 107)arrow_forwardSuppose we will use Advanced Encryption Standard (AES) to encrypt a block of plaintext and the known round key for round 7 is: B5 8D BA D2 31 2B F5 60 7F 8D 29 2F EA D2 73 21 What is the third word (i.e. the third 4 bytes) of the round key for round 8?arrow_forwardLet's suppose, for the sake of simplicity, that 581132 is the position of a file block on the disc. What are your views and reactions to the content presented?arrow_forward
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- Experimenting with AES-128 symmetric key cipher.using python PART 2: you will try to use "brute force" to decrypt an encrypted message, where you only have the first 96-bits of the 128-bit secret key (last 4 bytes of the secret key are missing!) The program should be called "findk", and should deal with two files that contain the encrypted text as a stream of bytes and the first 96-bits of the key, respectively. The program should print out on standard output the missing 4 bytes of the key in hexadecimal, the decrypted message and the time it took to find the correct key.o To test this part, here is the encrypted file (ciphertext2.dat), and the first 96-bits of the key (partial-key.dat) Hint: the original message starts with the word "Salam". Answer you provided .from Crypto.Cipher import AESdef revpad(s):"""This function is to remove padding.parameters:s:strstring to be reverse padded"""k = ord(s[-1])temp = 0 # temporary variable to check paddingfor i in range(1, k): # for loop to…arrow_forwardFor simplicity, let us assume that a file block is located at the address 581132 on the disc. What are your thoughts on this information?arrow_forwardA [answer] cipher is typically implemented by performing a AND mathematical operation at least two bytes at a time. A. stream B. DES C. key D. blockarrow_forward
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