Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?

Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?

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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Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?
Consider a new colleague.Alice who joins BitTorrent but does not have any piecesShe can't become a top-four uploader for any of the other peers if she doesn't have any chunks to post.So, how will Alice receive her first bite?
Approximately how many bits of entropy does a password consisting of five random English words have?
Suppose we have a very short secret s (e.g., a single bit or even a Social Security number), and we wish to send someone else a message m now that will not reveals but that can be used later to verify that we did know s. Explain why m = MD5(s) or m = E(s) with RSA encryption would not be secure choices, and suggest a better choice.
Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?
Suppose Bob joins a BitTorrent torrent, but he does not want to upload any data to any other peers (so called free-riding). a. Bob claims that he can receive a complete copy of the file that is shared by the swarm. Is Bob's claim possible? Why or why not? b. Bob further claims that he can further make his "free-riding" more efficient by using a collection of multiple computers (with distinct IP addresses) in the computer lab in his department. How can he do that?
Consider a program that allows a surgeon in one city to assist in an operation on a patient in another city via an internet connection. Who might want to attack the program? What type of harm might they want to cause? What kind of vulnerabilities might they exploit to cause harm? Could those vulnerabilities also cause harm in the absence of an active, malicious, attacker?
Suppose we have the encoding that enables Carol to mount the cube root attack (see The Cube Root Problem). If Carol sends a message to Bob, supposedly signed by you, will there be anything suspicious and noticeable about the signed message, so that with very little additional computation Bob can detect the forgery? Is there anything Carol can do to make her messages less suspicious? Cuberoot problem: Let's say you pad on the right with random data. You chose that scheme so that there is a negligible probability that anything you sign will be smooth. However, if the public exponent is 3, this enables Carol to forge your signature on virtually any message she chooses! Let's say Carol wants your signature on some message. The message digest of that message is h. Carol pads h on the right with zeroes. She then computes its ordinary cube root and rounds up to an integer r. Now she has forged your signature, because re = r3 = (h padded on the right with a seemingly random number).
Suppose Alice and Bob store their RSA public keys in a file on a server. Theycommunicate regularly using authenticated and confidential messages. Eve wants to readthe messages but is unable to crack the RSA private keys of Alice and Bob. However, Eve canbreak into the server and alter the file containing Alice’s and Bob’s public keys.a. How should Eve alter that file so that she can read confidential messages sent fromBob to Alice?b. How might Alice and/or Bob detect Eve’s subversion of the public keys?
Suppose Alice has a public key with modulus 815153 and encryption exponent 91. Eve intercepts a ciphertext 766247from Bob that was encrypted using this key. She calculates 766247⋅941^91(mod815153)=143804 and asks Alice to decrypt this message as an authentication test. Alice responds with the decrypted message 167698 Find the plaintext without factoring Alice’s modulus.
Consider a very simple symmetric block encryption algorithm in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as C = (PK₁) K₁ where C = ciphertext, K = secret key, Ko = leftmost 64 bits of K, K₁ = rightmost 64 bits of K,+ = bitwise exclusive OR, and is addition mod 264. a. Show the decryption equation. That is, show the equation for P as a function of C, Ko, and K₁. b. Suppose and adversary has access to two sets of plaintexts and their correspond- ing ciphertexts and wishes to determine K. We have the two equations: C = (PK) K₁; C = (PK) K₁ First, derive an equation in one unknown (e.g., Ko). Is it possible to proceed fur- ther to solve for Ko?
Consider the following sequence of commands and messages: $ git clone git:cisc210/example Cloning into 'example'... remote: Counting objects: 19, done. remote: Compressing objects: 100 % (12/12), done. remote: Total 19 (delta 1), reused 0 (delta 0) Receiving objects: 100 % (19/19), done. Resolving deltas: 100 % (1/1), done. $ touch sky $ git add sky fatal: not a git repository (or any parent up to mount point /) Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set). Enter two commands that would make it so the 'git add' wouldn't fail. Note: don't actually execute the "git add" command, just two commands that would let it work. Feel free to try it out on cisc210.cis.udel.edu!