Note: The notation from this problem is from Understanding Cryptography by Paar and Pelzl.We conduct a known-plaintext attack against an LFSR. Through trial and error we have determined that the number of states is m = 4.The plaintext given by01001000 = rgx1L2X3X4X5X6X7when encrypted by the LFSR produced the ciphertext10000011 = Y0Y1Y2Y3Y3Y5Y6Y7-What are the tap bits of the LFSR? Please enter your answer as unspaced binary digits (e.g. 0101 to represent p3 = 0, p2 = 1, P1 = 0, Po = 1).

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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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Note: The notation from this problem is from Understanding Cryptography by Paar and Pelzl. Consider the LFSR represented by the polynomial x4+x2+1x4+x2+1. What are the tap bits of the LFSR? Please enter your answer as unspaced binary digits (e.g. 010101 to represent p5=0,p4=1,p3=0,p2=1,p1=0,p0=1p5=0,p4=1,p3=0,p2=1,p1=0,p0=1).
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.
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.
The definition of a Shift Cipher can be expressed as follows:Def. Let x, y, k ∈ Z26 with the encryption operation as ek(x) ≡ x + k mod 26 and thedecryption operation as dk(y) ≡ y - k mod 26.Given the provided letter encoding, what would be the encoding of the plaintext word ATTACKafter applying a shift cipher with a k=17?
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 block ciphers, if we use AES for encryption, it does not matter whether the cipher is CBC-based or ECB-based (both will have equally strong results). true or false
Let E'(T,X) be a tweakable block cipher that has already been keyed. Given plaintext P = P1 || P2 || ... || Pn (ie, P is an n-block plaintext). Ci = E'(i, Pi) for i=1..nsum = P1 xor P2 xor ... xor Pntag = E'(0,sum) For simplicity let's say that E'(T,X) = ROTL(X,T+1) (ie, X rotated left T+1 bits. If the block cipher block size is 8 bits and you are encrypting the two byte plaintext 67 89, what ciphertext and tag would be created? Fill in each box as a two-digit hex value. C1____? C2____? tag____?
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”
A shortcoming of using an elliptic curve E(Fp) for cryptography is the fact that it takes two coordinates to specify a point in E(Fp). However, as discussed briefly at the end of Sect. 6.4.2, the second coordinate actually conveys very little additional information.(b) Alice and Bob decide to use the prime p = 1123 and the elliptic curveE : Y2 = X3 + 54X + 87.Bob sends Alice the x-coordinate x = 278 and the bit β = 0. What point is Bob trying to convey to Alice? What about if instead Bob had sent β = 1?
A Man-in-the-Middle attack on the Diffie-Hellman key exchange protocol may be effectively carried out if the adversary produces two public-private key pairs for the assault. Could the same assault be carried out with a single pair? Justify and describe the event in full.
Consider a large institution that has 16891 employees. How many keys are necessary to allow any pair of employees to securely communicate using a symmetric cipher? Suppose that we instead use an asymmetric cryptographic scheme. How many keys are required in this case?
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.

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