. A fundamental cryptographic principle states that all messages must have redundancy. But we also know that redundancy helps an intruder tell if a guessed key is correct. Consider two forms of redundancy. First, the initial n bits of the plaintext contain a known pattern. Second, the final n bits of the message contain a hash over the message. From a security point of view, are these two equivalent? Discuss your answer.

. A fundamental cryptographic principle states that all messages must have redundancy. But we also know that redundancy helps an intruder tell if a guessed key is correct. Consider two forms of redundancy. First, the initial n bits of the plaintext contain a known pattern. Second, the final n bits of the message contain a hash over the message. From a security point of view, are these two equivalent? Discuss your answer.

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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2.(a) Consider the use of OTP. Let m be an arbitrary message to be encrypted and c be a given ciphertext in the ciphertext space. How many possible keys with which m can be mapped to c, i.e., f(m,k)=c? None 1 2 The size of the key space Depends on m (b) 3^(-n) is negligible. True or false? (c) n^(-100) is negligible. True or false?
Problems are on this Textbook: Stallings, W. (2019). Cryptography and Network Security (8/E). Pearson Publishing. ISBN: 978-0-13576-403-9 7.10 In discussing the CTR mode, it was mentioned that if any plaintext blocks that is encrypted data using a given counter value is known, then the output of the encryption function can be determined easily from the associated cipher text block. SHow the calculation.
1. (a) Suppose you are given an ElGamal encryption of an unknown plaintext M ∈G. Show how to construct a different ciphertext that also decrypts to the same M. (b) Suppose you are given two ElGamal encryptions, of unknown plaintexts M1,M2 ∈G. Show how to construct a ciphertext that decrypts to their product M1 ·M2
We have the following encryption scheme for message space . Gen will uniformly choose the key k from the key space . Enc(k, m) returns and Dec(k, c) returns . Is EAV secure (computationally indistinguishable)?
1. Suppose that we use a substitution cipher to encrypt an English word, from which we obtain the ciphertext is “AUXXME”. Which of the following words is possibly the plaintext? (Hint: In a substitution cipher, we replace each letter of the plaintext with another letter) A. greedy B. funny C. secret D. cheese 2. Which of the following statements are incorrect? A. Cryptographic systems tend to involve both an algorithm and a secret value. B. To secure systems, it is more efficient to update algorithms than updating keys. C. Often a scheme can be made more secure by making the key longer. D. We can always change the key length to better secure systems, no matter using which cryptographic algorithms. E. In a secret-key cryptosystem, secret keys can be used for both encryption and decryption. 3. Which of the following statements are incorrect about a cryptographical hash function? A. The input size can be arbitrary and the output size is fixed B. Given the input, the output should…
Alice and Bod have decided to use a symmetric encryption algorithm. They have someassumptions about their messages:- Messages only contain capital letters (i.e. A to Z)- The length of their shared key must be greater than or equal to the length of the plaintext- They assign each letter a number as follows: (A,0), (B,1), (C,2), (D,3),…, (Z,25)Their algorithm combines the key and the message using modular addition. The numerical valuesof corresponding message and key letters are added together, modulo 26. For example, if the plaintext is “HELLO” and the key is “SECRET” then the encrypted message is calculated as following:Since the length of the plaintext is 5, we just need the first 5 letters of the key (i.e. “SECRE”), thenfor each letter, we should add corresponding letters in both the plaintext and the key modulo 26.Plaintext: H (7) E (4) L (11) L (11) O (14)Key: S (18) E (4) C (2) R (17) E(4)Cipher: Z (25) I (8) N(13) C(2) S (18) a) Write a program in Python, C/C++ or JavaScript to…
1.Give the decryption of the following messages that have been encrypted with the key 4551. You should get readable messages. a. RTYAWJHVVJ b. WYFUMXYJGX c. VTRFS_NMPJEJPQNOSNX 2.Say you obtain a ciphertext of an English sentence encrypted with an unknown key using the same four-digit shift scheme as problems 8 and 9. For a brute-force attack, what is the maximum number of keys would you have to test?
We consider ElGamal cryptosystem with public prime p = 53 and generator g = 2. Let h = 16 be Bob’s public-key (his private key x is unknown, h = g^x ). Alice encrypted message m with Bob’s public key and sent the corresponding ciphertext to Bob: (C1 ,C2 ) = (15, 50). You intercepted this ciphertext. Can you break the encryption and recover the original message m? Hint: Both g and h are very small numbers, can you deduce private key x?
Alice and Bod have decided to use a symmetric encryption algorithm. They have some assumptions about their messages:- Messages only contain capital letters (i.e. A to Z)- The length of their shared key must be greater than or equal to the length of the plaintext- They assign each letter a number as follows: (A,0), (B,1), (C,2), (D,3),…, (Z,25)Their algorithm combines the key and the message using modular addition. The numerical values of corresponding message and key letters are added together, modulo 26. For example, if the plain text is “HELLO” and the key is “SECRET” then the encrypted message is calculated as following:Since the length of the plaintext is 5, we just need the first 5 letters of the key (i.e. “SECRE”), then for each letter, we should add corresponding letters in both the plaintext and the key modulo 26.Plaintext: H (7) E (4) L (11) L (11) O (14)Key: S (18) E (4) C (2) R (17) E(4)Cipher: Z (25) I (8) N(13) C(2) S (18) Write a program in Python, C/C++ or JavaScript to…
Consider a spy. The spy knows that messages m are encrypted to m′ using m′ ≡ mc mod 1189. Withoutknowing the factorization of 1189, explain how the spy could determine the decryption key d sothat m ≡ (m′)d mod 1189?
Problem #1Given below is a well-known cryptosystem called affine Caesar cipher, as well as someciphertext generated using the affine Caesar cipher.P = C = Z 26 = {0, 1, 2, ..., 25};K = {(a, b) Z26 Z26 | gcd(a, 26) = 1}y = E([a,b], x) = (ax + b) mod 26,x = D([a,b], y) = a-1 (y – b) mod 26,where x P, y C. Ciphertext sample:VPWOMFUWOFMYMHUNWBBWGCRVVPSFVPUTHUJWMCOMFUOVSVWOVWGSRSFSREOWOQMHKOBMHVPWOUFGHETVWMFOEOVUYVMMZCVGSFEMCCOUEMCHKFMQRUNIUMBRWFUSHSRIUZHSVMBWFNVPUOUGHUVKUEVMMVPUFEMCQWRRPSJUVHCREGHSGKUNVPUOEOVUY For this problem, please do the following:(a) provide an analysis detailing its strength/weakness;(b) attempt to uncover the plaintext associated with the ciphertext;(c) attempt to determine the secret key (a, b) used.
In the El Gamal cryptosystem, Alice and Bob use p = 17 and α = 3. Bobchooses his secret to be a = 6, so β = 15. Alice sends the ciphertext (r, t) = (7, 6). Determinethe plaintext m.