Suppose that you have received the following encrypted message from your friend, ciphertext "ccbvrgu". He told you that the original message was first encrypted using the Caesar cipher with k=3 and then was re-encrypted using the Vigenere cipher with k= "old". Your task is to find the original message (i.e. plaintext). (5 Marks, show all steps in detail)

Suppose that you have received the following encrypted message from your friend, ciphertext "ccbvrgu". He told you that the original message was first encrypted using the Caesar cipher with k=3 and then was re-encrypted using the Vigenere cipher with k= "old". Your task is to find the original message (i.e. plaintext). (5 Marks, show all steps in detail)

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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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.
Suppose your RSA public key is PK: {n, e} = {13861, 37}. Your friend sends you a ciphertext C = 9908. But unfortunately you have forgotten your private key, now you have to crack it yourself.a) Write down a possible condition of factors p and q.p= q=b) What is your private key SK: {d}?d=c) What is the plaintext of your friend’s message?The plaintext M =d) Suppose the plaintext M is a 12-digit number consisting of a prefix “19” and 1234567890. What is the corresponding ciphertext? Since M is greater than n, you only need to encrypt four digits at a time. Ignore redundant zeros. e.g., 0001 = 1. The result should contain three integers.The ciphertext C0 =
A ciphertext has been generated with an affine cipher. The most frequent letter of the ciphertext is “F”, and the second most frequent letter of the ciphertext is “C”. Break this code by figuring out the key numbers. Hint: Based on the letter frequency, E is the most frequent letter and T is the second most frequent letter. Therefore, F should be the ciphertext of E and C should be the ciphertext of T.
An affine cipher has the form c = (am+b) mod n. Suppose m is an integer between 0 and 25, eachinteger representing a letter.(a) Let n = 26, a = 3, and b = 123. What is the ciphertext corresponding to the phrase THIS IS A CIPHERMESSAGE.(b) A requirement for a cipher is that every plaintext letter correspond to a different ciphertext letter. If either aand b is not relatively prime to n, does the affine cipher meet this property? Either prove it does or presenta counterexample.
Let Π = (Gen,Enc,Dec) be a private-key encryption scheme that has indistinguishable en- cryptions in the presence of an eavesdropper. Which of the following encryption schemes are also necessarily secure against an eavesdropper? If you think a scheme is secure, sketch a proof, if not, provide a counterexample. Here, for a bit string s, parity(s) is 1 if the number of 1’s in s is odd, and 0 otherwise. The || symbol stands for concatenation. So, for strings if x = 00 and y = 11, x||y = 0011. (a) Enc1k(m) = 0||Enck(m)(b) Enc2k(m) = Enck(m)||parity(m) (c) Enc3k(m) = Enck(m)||Enck(m)(d) Enc4k(m) = Enck(m)||Enck(m + 1). Here think of m as an integer. Please type answer note write by hend.
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?
In a public-key system using RSA, you intercept the ciphertext C=10, sent to a user whose public key is e=5, n=35. What is the plaintext M? In an RSA system, the public key of a given user is e=31, n=3599. What is the private key of this user? Hint: First use trial-and-error to determine p and q; then use the extended Euclidian algorithm to find the multiplicative inverse of 31 module φ(n).
In a substitution cipher, we “encrypt” (i.e., conceal in a reversible way) a message by replacing every letter with another letter. To do so, we use a key: in this case, a mapping of each of the letters of the alphabet to the letter it should correspond to when we encrypt it. To “decrypt” the message, the receiver of the message would need to know the key, so that they can reverse the process: translating the encrypt text (generally called ciphertext) back into the original message (generally called plaintext). A key, for example, might be the string NQXPOMAFTRHLZGECYJIUWSKDVB. This 26-character key means that A (the first letter of the alphabet) should be converted into N (the first character of the key), B (the second letter of the alphabet) should be converted into Q (the second character of the key), and so forth. A message like HELLO, then, would be encrypted as FOLLE, replacing each of the letters according to the mapping determined by the key. Let’s write a program called hw6.py…
Let k=( 4 1 3 2) be the encryption and key k = (2 4 3 1) be the decryption key used in a transposition cipher. Show all the steps to decrypt the following ciphertext using the keyed approach: “XYSEESRU”
The Lingala Language of Republic of Congo has 35 letters. Consider an Affine cipher, which encrypts each letter according to the rule: C=(p×k1+k2) mod 35. Here C, p, k1, and k2 are each members in the range 0 to 34, where C represents the ciphertext letter, p the plaintext letter, and k1 and k2 are constant keys. How many possible keys does this affine system have? Explain in details.
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…
Decrypt ciphertext (kx mod p = 7, ge mod p = 8). The ciphertext was created using Elgamal encryption over group Z*p with your public key (p=13, g=2, gd mod p=12) and your private key is d=6. What is the shared k value?_________ What is k-1 mod p?___________ What is the plaintext x?_________ Type each of your answers as an integer.